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JAERI-Conf95-014
JAERI-Conf—95-014
JP9602040
(' • - • • *
PROCEEDINGS OF THE IAEA/RCA WORKSHOP ON CALIBRATIONOF DOSIMETERS & SURVEY INSTRUMENTS FOR PHOTONS
November 28-December 2 ,1994 , Tokai, Japan
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June 1995
(Eds.) Hiroyuki MURAKAMI and Fumiaki TAKAHASHI
Japan Atomic Energy Research Institute
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This report is issued irregularly.
Inquiries about availability of the reports should be addressed to Information Division,
Department of Technical Information, Japan Atomic Energy Research Institute, Tokai-
mura, Naka-gun, lbaraki-ken 319-H, Japan.
© Japan Atomic Energy Research Institute, 1995
II * U -T )} W % )Tr
JAERI-Conf 95-014
Proceedings of the IAEA/RCA Workshop
on Calibration of Dosimeters & Survey Instruments for Photons
November 28 ~ December 2, 1994, Tokai,Japan
(Eds.) Hiroyuki MURAKAMI and Fumiaki TAKAHASHI
Department of Health Physics
Tokai Research Establishment
Japan Atomic Energy Research Institute
Tokai-mura, Naka-gun, Ibaraki-ken
(Received May 23,1995)
International Atomic Energy Agency (IAEA) has been conducting the Regional
Cooperative Agreement (RCA) for prevailing the nuclear-related techniques to
Asian and Pacific countries and supporting RCA ac t iv i t i e s technically and
economically. The RCA project for strengthening the radiation protection
infrastructure, which started in 1988 as one of the RCA act iv i t ies , has been
conducted with performing such programs as training courses, workshops, e t c . .
The present proceedings comprise of country reports which were presented at "
RCA Workshop on Calibration of Dosimeters and Survey Instruments for Photons"
held at Tokai Research Establishment, JAERI, November 28 - December 2, 199U, as
a program of RCA radiation protection project. In the workshop, various
subjects related to radiation protection dosimetry and practical calibration of
instruments were discussed. This workshop was also intended to put emphasis on
ICRU's new operational quantity and i t s concept and measurement. The country
reports presented by 15 participants from RCA member s ta tes revealed some
technical aspects on the adoption of the operational quantity. The workshop
successfully completed and provided with fruitful results on understanding
newest radiation protection dosimetry techniques and grasping future subjects.
The present proceedings will provide some useful information for engineers and
s c i e n t i s t s who are engaged in the ca l ibra t ion of radia t ion protection
instruments.
Keywords: Calibration, Dosimeter, Survey Instrument, Operational Quantity,
Standard, Radiation Protection Dosimetry.
JAERI-Conf 95-014
IAEA/RCAr(X)
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JAERI-Conf 95-014
Contents
1. Report on Radiation Protection Calibration Activities in Australia
N.J. Hargrave : AUSTRALIA - 1
2. Country Report
Mahfuza Begum : BANGLADESH 5
3. Present Status of Calibration System and Implementaion of the New
ICRU Operational Quantities in China
Zhang Qingli : CHINA 12
4. Calibration of Dosimeters and Survey Meters for Photons in India
Genasan Ramanathan : INDIA 16
5. Activities on Calibration of Radiation Protection Instruments
in Indonesia
Susetyo Trijoko : INDONESIA •• -—' 20
6. Quality Assurance of Reference Calibration Field
S.Mikami and T.Momose : JAPAN 26
7. Status of Radiation Protection Calibration Program in Korea
Bong-Hwan Kim : Rep. of KOREA 31
8. Calibration of Dosimeters and Survey Instruments for Photons
at the Malaysian Secondary Standard Dosimetry Laboratory
Abd. Aziz bin Mohd. Ramli : MALAYSIA 35
9. Calibration of Radiation Protection Instruments of the Mongolia
Dashyn Shadraabal : MONGOLIA HO
10. Radiation Protection Calibration Facilities at the National
Radiation Laboratory, New Zealand
B.J. Foote : NEW ZEALAND 42
11. Radiation Protection Calibration Activities in Pakistan
Syed Salman Ahmad : PAKISTAN 46
12. Calibration of Dosemeters and Survey Instruments for Photon
Arlean L. Alamares and Estrella S. Caseria : PHILIPPINES 53
13. Radiation Protection Calibration Activities
Nieva S. Otadoy-Lingatong : PHILIPPINES 57
14. SSDL for Radiation Protection of Thailand
Warapon Wanitsuksombut : THAILAND 62
JAERI-Conf 95-014
15. Current Radiation Protection Activities in Vietnam
Dang Thanh Luong : VIETNAM 69
Appendix 1 (Papers and/or Transparencies of Special Lectures) 73
1.1 Foundation on Gamma and X-ray Monitoring Instruments
Tamaki WATANABE 74
1.2 Computation of Dosimetric Quantities in External Radiation Protection
Yasuhiro YAMAGUCHI 96
1.3 Dissemination of Exposure Standard and the Irradiation Field on ICRU
Operational Quantities (A Suggestion of Practical Calibration)
Kentaro MINAMI and Hiroyuki MURAKAMI 109
1.4 Radiation Protection Quantities for External Monitoring and Work of
the ICRP/ICRU Joint Task Group
R.V. Griffith 118
1.5 The Australian Radiation Laboratory Intercomparison of Personal
Radiation Monitoring Services in the Asia/Pacific Region
N.J. HARGRAVE and J.G, YOUNG 140
Appendix 2
Summary of Answers to the Questionnaire on Calibration of Dosimeters
and Survey Instruments for Photons 144
Appendix. 3
Workshop Agenda and Participants' List 153
iv
JAERI-Conf 95-014
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ami (mmmz&nm$;£tz&Qm%mnn [OHP] ) : 73
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JAERI-Conf 95-014
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vi
JAERI-Conf 95-014
1. Report on Radiation Protection Calibration Activities in Australia.by
N J Hargrave, Australian Radiation Laboratory, Lower Plenty Road, Yallambie, 3085. .
INTRODUCTION
Australia is a federation of eight autonomous States or Territories. Each of these is responsible for many mattersincluding radiation safety within their borders. National matters are the responsibility of the FederalGovernment. The Australian Radiation Laboratory (ARL) is a part of the Federal Government Department ofHuman Services and Health and undertakes research and service activities related to radiation health. Workrelated to bodi ionising and non ionising radiation and regulatory matters is performed. Some of the researchactivities relate to radiation measurement standards, environmental radioactivity (e.g. radon in air, radioactivityin drinking water), effects of electro-magnetic fields on health (ELF), ultra violet radiation (UV) and laser safety,radiochemistry, medical applications of radiation (and doses to the population as a result), general health physics,thermoluminescent dosimetry (TLD) and electron spin resonance (ESR) dosimetry. The calibration of protectioninstruments are undertaken by the Ionising Radiation Standards Group within the Laboratory and by State HealthLaboratories.
NATIONAL RADIATION DOSIMETRY STANDARDS
For a measurement made in Australia to be legal it must be traceable as prescribed in the National MeasurementAct. In particular, Section 10 requires that the measurement be made in terms of Australian units ofmeasurement, traceable to the appropriate Australian standard.
The Australian standard of the quantity Exposure is maintained by ARL as an agent of the National MeasurementLaboratory (NML) of the Commonwealth Scientific and Industrial Research Organization, Division of AppliedPhysics. The Standard is an absolute primary stardard, maintained without reference to any other exposurestandard. It is maintained by means of free air and cavity ionisation chambers in which a sensitive volume isprecisely defined by design - the charge collected from the mass of air in this volume leads to a determinationof the unit of the quantity exposure (C.kg"1). The Laboratory also maintains working standards of absorbed dose.The primary standard for this quantity and for activity are maintained by the Australian Nuclear Science andTechnology Organisation (ANSTO) under similar agent arrangements. However the majority of protectioncalibrations are performed tracable to die exposure (or related air kerma) standard using transfer ionisationchambers.
The design of the free air chamber for low energy X-rays has been outlined elsewhere0-2). The free air chamberfor use between 50 kV and 300 kV was designed using published information™. For wCo and 137Cs gamma rays,ARL has a carbon cavity chamber similar to diat described by Boutillon and Niatel of BIPM'4', and an aluminiumcavity chamber based on die design of Kemp and Barber*5'. Factors to correct for various effects in diesechambers have been determined at ARL.
The national standard of Absorbed Dose is maintained using a graphite calorimeter which provides absolutemeasurements of die absorbed dose to carbon at wCo and 6, 18 and 25 MV linear accelerator (linac) photonqualities"17- !>. Absorbed dose to water is obtained using a transfer procedure. ARL maintains a secondarystandard therapy level dosemeter (Nuclear Enterprises NE2560/2561) which is calibrated against die nationalstandard of absorbed dose to both carbon and water at die ^Co quality1", and offers dosemeter calibrationsagainst diis working standard in graphite and water phantoms. ARL also has a Donien type calorimeter andanodier smaller portable microcalorimeter under development"0'. When completed diis will improve confidencein die present working standard dosemeter and will provide for calibrations at odier qualities, possibly includingl37Cs gamma rays, 300 kV X-rays (and higher up to 450 kV) and linac photon and electron beams from 5 to25 MV.
RECENT STANDARDS INTERCOMPARISONS
ARL regularly participates in interconiparisons of exposure standards, mostly at dose levels higher dian dioseusually applicable in radiation protection.
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JAERI-Conf 95-014
Section I of the Comite" Consultatif pour les Etalons de Mesures des Rayonnements Ionisants (CCEMRI(I)) hasrecommended diat national standards should be compared with those at BIPM at intervals not exceeding 10years"". The ARL exposure standard for medium energy X-rays was last compared with, the BIPM standard inApril 1988 when the wCo exposure standards were also compared"21. . •
ARL has participated in the IAEA postal thermoluminescent dosimetry (TLD) absorbed dose intercomparisonssince 1971"3). Results obtained by ARL are well within the 5% limits considered to indicate good agreement withdie IAEA.
ARL has participated in several indirect environmental level dosimetry intercomparisons conducted by dieEnvironmental Measurements Laboratory (EML) of the USA involving TLDs ( R l3). The results of theseintercomparisons have been within 5 % providing appropriate corrections are made for fading and transit doses.From time to time problems have been experienced due to the correction for fading and due to our transitexposures being higher than those for most other countries. Exposures are typically 15 to 75 mR over a threemonth period, the larger ones being laboratory exposures while the smaller ones are usually field exposures.The Laboratory recently undertook a joint project with the EML to better understand the fading. In addition in1982 the laboratory participated in an international protection level intercomparison which is outlined in the nextsection. The results were most satisfactory.
PROTECTION LEVEL CALIBRATION FACILITIES
ARL has calibration facilities at the protection level for X, gamma and beta radiations. These include theInternational Organization for Standardization (ISO) heavily filtered X-ray qualities"6'. At ARL the generatingpotential for these X-ray qualities is determined using a resistive divider in the high voltage generator oil-tank.The divider is checked by two external dividers with associated DVMs which are calibrated by the NMLtraceable to the Australian Standard Volt.
The laboratory possesses sealed radioactive sources of l37Cs, "Co, a 6Ra and M1Am - others having shorter half-lives are sometimes available. The exposure or absorbed dose produced by these sources is measured usingtransfer standard instruments traceable to the national exposure standard. The ion chambers used are producedby Nuclear Enterprises or Exradin.
ARL lias purchased a standard beta ray calibration system from the National Physical Laboratory ( NPL) of theUK. The system comprises ^Sr/^Y, ^ T l and ""Pm beta sources, together with beam flattening filters. It isused for survey meter calibrations.
Five large area sources (3 beta emitters and 2 alpha emitters) are also available for testing surface contaminationmeters. The sources are traceable to the Physikalisch-Techiusche Bundesanstalt (PTB) (Germany). There arenot many requests for these calibrations and there is ho overriding legal requirement for surface contaminationmonitors to be calibrated.
In recent years, with increasing State legislation and increasing use of ionising radiation in die community, thenumber of requests for protection level calibrations lias increased. In response to this demand each state has beensupplied widi a standard calibration facility, thus a regional system has been developed to disseminate theexposure standard"7*18). Equipment supplied by ARL lias been installed in all Australian capital cities (exceptDarwin, pending the availability of a suitable site) to enable State or Territory Health Departments to providetraceable calibrations.
Each facility includes a collimated source housing"6', an instrument support trolley and rails (Figure 3). A setof IJ7Cs sources is provided widi each facility (Table 3). A calibrated 100 ml ionisatiou chamber (Exradin modelA5) and electrometer (Keitliley model 35617) for use in X-ny beams are also supplied. The ability to performX-ray calibrations depends on access to suitable generators. One State has duplicated some of the ISO qualities.In addition to die facilities provided to them by die laboratory many of the State Health Laboratories have similaradditional sources. In most cases die accuracy of either their activity or their air kernia rates are not well knownin a manner traceable ir> the Australian standard.
The prototype facility was used in an international air kernia intercomparison"" involving fourteen major primarystandards laboratories. It was intended that each participant expose LiF TLDs to an air kerrna of 0.3 mGy at a
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JAERI-Conf 95-014
rate of 50 fiGy.h'1, and to 0.3 to 1.0 mGy at a freely chosen rate. The results obtained by ARL were within 1 %of die overall mean value. It is therefore reasonable to expect that the calibration facilities installed in the Statesare capable of similar results.
PRMS TRACEABILITY AND CALIBRATIONS
The laboratory uses a commercial (Teledyne) based fully automatic TLD personal monitoring system. Thecustom designed badge cases incorporate four filtered areas (an unfiltered area, 845 mg. cm"2 plastic, 0.25 mmCu + 2.8 mm Al and 2.7 mm Cu + 0.5 mm Al) and use a CaSO4-.Dy phosphor in a teflon matrix as thesensitive element. The dosemeters (TLD plus badge case) are calibrated by exposing them on a perspex blockphantom similar to the IAEA standard water phantom. They are used to assess the personal dose equivalent.They are exposed to a range of qualities covering the energy range from 10 kV up to MCo and referenced tostandards exposed to 2 mSv from "7Cs. Similar quality assurance standards are used throughout each batch ofapproximately 400 dosemeters assessed. Regular weekly tests of the automatic TLD readout machines areperformed to check their stability while second readouts are performed on the TLD cards to check the efficiencyof the readout system. The relationship between the various energy radiations and. the standards is re-evaluatedevery five years. The TLD cards are automatically read out in all four areas and the effective dose to which theyhave been exposed is derived using an algoritlim. The majority of monitors are issued for wearing over 4, 8 or12 week periods with most being for 12 weeks.
Other smaller services are operated in Australia by the Queensland Health Department, ANSTO and the WesternAustralian Health Department. The Laboratory, which monitors 25,000 of the 35,000 radiation workers inAustralia, is developing a data base on die cumulative doses of all radiation workers in Australia.
CALIBRATION FACILITIES FOR NEUTRONS.
A neutron calibration facility lias been established at the Laboratory in a room 8 m x l 0 m x 6 m ' A calibrationrail allows the source and die instrument to be calibrated to be located at the centre of die room. This resultsin minimum scatter. Exposures and measurements can be performed using the shadow cone method, the semi-empirical method where data is fitted to a universally accepted equation and by the polynomial method wheredata is fitted to an arbitrary polynomial.
A full set of 10 Bouner spheres ranging in diameter from 3 inches to 12 inches are available. These incorporatea 3He detector and a full set of shadow cones exist for them. In addition, two BFj detectors in 3 inch and 9 inchspheres which incorporate cadmium shields are also available. At present "'Am/Be sources are used, theabsolute emission strength of one of them has been determined using die NPL manganese sulphate bath. It isplanned to acquire a a 2Cf source in die near future. The facility has been designed so that the shadow conesand instruments can be moved in die x, y and z directions and rotated through 360 degrees. A Monte Carloneutron transport program (MCNP4A) is also used to support diese facilities.
CALIBRATION PROBLEMS AND EXPERIENCES
At one stage when calibrating a large volume chamber in terms of Dose Equivalent for one of die harder ISOqualities, problems were encountered due to non uniformity of the radiation field. This occurred when a 1 Lchamber was being compared to the 100 nil chamber which was used as die local reference instrument.
EMERGENCY PREPAREDNESS
The laboratory lias several sets of instruments wliich are kept in case diey are needed for emergency monitoring.These instruments include thick and tliin sodium iodide detectors, a range of GM and ionisation chamberinstruments. The calibration of these instruments is traceable to die protection calibration facilities outlinedabove.
USE OF THE ICRU NEW OPERATIONAL QUANTITIES
Use of these is recommended in Australia by the National Healdi and Medical Research Council for limitingoccupational exposure to ionising radiation. However, in terms of instrument calibration, unless specificallyrequested by a client, an instrument is usually calibrated in terms of die quantity and units in which it is scaled.
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JAERI-Conf 95-014
When the new operational quantities are required they are derived from the exposure standard by using theconversion coefficients recommeuded by die ICRU in its Report 47.
OTHER MATTERS RELATED TO CALIBRATION
From a regulatory viewpoint the Laboratory provides the secretariat and much input to the Radiation HealthAdvisory Committee (RHC), which is a committee of the National Health and Medical Research Council. TheRHC produces many "Codes of Practice" for matters related to radiation protection. While instrument calibrationis not specifically covered by die series, many useful matters related to radiation protection are covered.
REFERENCES.
(I) Hargrave, N.J., A Free Air Chamber for Measurement of X Ray Exposure below 50 kVp. AustralasianBulletin of Medical Physics and Biophysics (June 1967) p.24.
(Z) Hargrave, N.J., Frp-. Air Ionization Chamber for the Dosimetry of Low Energy X-rays. M.Sc. thesis,University of Mv-iUmrne (1971), unpublished.
(3) Vv-koff, H.O. and Attibc, F.H., Design of Free-air Ionization Chambers. National Bureau of StandardsL'.indbook 64 (1957).
(4) Buutillon, M. and Niatel M.-T., A Study of a Graphite Cavity Chamber for Absolute Measurement ofwCo t'^anaia Rays. Metrologia (1973) 9, 139-146.
(5) Kemp, L.A.W. and Barber, B., The Construction and Use of a Guarded-field Cavity IonizationChamber for the Measurement of Supervoltage Radiation. Physics in Medicine andBiology (1963) 8, 149-160.
(6) Urquhart, D.F., Johnson, E.P. and Badger, W.S., The Australian Commonwealdi Standard ofMeasurement for Absorbed Radiation Dose. Australian Atomic Energy Commission AAEC/E455(1978).
(7) Sherlock, S.L., Dosimetry Activities of the SSDL Lucas Heights.'Bureau International des Poids etMesures, CCEMRI(I)/88-16 (1988).
(8) Sherlock, S.L.., Private communication (1988).(9) Huntley, R.B., Interim Working Standard of Ionising Radiation Absorbed Dose for Cobalt-60 Gamma
Rays. Australian Radiation Laboratory Technical Report ARL/TR041 (1981) p.79.(10) Huntley, R.B., A Microcalorimeter as a Working Standard of Ionising Radiation Absorbed Dose.
M.App.Sc. thesis, Royal Melbourne Institute of Technology (1986), unpublished.(II) ComitS Consultatif pour les Etalons de Mesures des Rayonnements Ionisants, Section I (CCEMRI(I)),
Rapport au Comit6 International des Poids et Mesures (N.J. Hargrave - rapporteur) (1988).(12) Perroche, A-M. and Hargrave, N.J., Comparison of Air kerma Standards of ARL and BIPM for X-rays
(100 to 250 kV) and MCo Gamma Radiation, Bureau International des Poids et Mesures, Rapport BIPM-89/11 (1989).
(13) Eisenlohr, H.H. and Jayaraman, S., IAEA-WHO Cobalt-60 Teletherapy Dosimetry Service usingMailed LiF Dosenieters. A Survey of Results Obtained during 1970-75. Physics in Medicine andBiology (1977) 22, 18-28.
(14) de Planque, G. and Gessell, T.F., Environmental Measurements with Thermoluminescence Dosemeters- Trends and Issues, Radiation Protection Dosimetry (1986) 17, 193-200.
(15) Young, J.G., Hargrave, N.J. and Boas, J., Participation of the Australian Radiation Laboratory inInternational Interconiparisons of die Measurement of External Environmental Radiation UsingThermoluminescence Dosenieters, Australian Radiation Laboratory Technical Report ARL/TR091(1990).
(16) International Organization for Standardization, X and Gamma Reference Radiation for CalibratingDosenieters and Dose Ratemeters. International Standard ISO-4037-1979 (1979).
(17) Hargrave, N.J. and Allen, P.D., Australia-wide Calibration Facilities for Ionizing Radiation ProtectionMonitors. Radiation Protection Dosimetry (1989) 27, 157-162.
(18) Hargrave, NJ. and Allen, P.D., Calibration Facility for Radiation Protection Monitors in Australia -Technical Details aiid Instructions for Use. Australian Radiation Laboratory Technical ReportARL/TR088 (1989).
(19) Spanne, P., Carlsson, C.A. and Aim Carlsson, G., International Intercomparison of Standards for LowCollision Kemia Rates in Air by Means of Low Dose TLD Techniques. Radiation Protection Dosimetry(1984) 6, 261-264.
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JAERI-Conf 95-014
2. COUNTRY REPORT
IAEA/RCA WORKSHOP ON CALIBRATION OF DOSIMETERS AND SURVEYINSTRUMENTS FOR PHOTONS, NOVEMBER 28 - DECEMBER 2, 1994, TOKAI,
JAPAN
MAHFUZA BEGUMHEALTH PHYSICS DIVISIONATOMIC ENERGY CENTREDHAKA, BANGLADESH.
The application of radioisotopes and radiation sources in
research and development activities in medicine, food and
agriculture, industries, str-ilization of medical products and
appliances, etc. are rapidly increasing in Bangladesh. Bangladesh
Atomic Energy Commission (BAEC) has taken up a comprehensive
program in Nuclear Science and Technology including setting up a
3 MW TRIGA Mark-II Research Reactor and a 14 MeV neutron
generator at Atomic Energy research Establishment (AERE), Savar
one 3 MeV positive Van-de-graff Accelerator at Dhaka. It is also
expected to establish a Nuclear Power Reactor at Rooppur to meet
60increasing power demand in western zone of the country. Two Co
irradiation facilities, one in Dhaka and another at savar are
already under operation in the country including another one at
Mymensingh which is not working for the last five years• due to
some mechanical problems.
An isotope production laboratory has also been set up at
Savar where radioisotopes of short half-lives ( mTc, Sc and
131I) are being produced. Several Nuclear Medicine Centres at
different parts of the country have been working under the BAEC.
This paper is presented in IAEA/RCA Workshop on Calibration ofDosimeters and Survey Instruments for Photons, november 28 -December 2, 1994, Tokai, Japan.
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JAERI-Conf 95-014
A commercial irradiator ( Co) has been commissioned at
chittagong under a private sector. A good number of deep therapy
1 7 finand diagnostic X-ray machines, Cs and Co teletharapy units
are being constantly used in the country. Both in the private and
public sectors, radioisotopes and radiation sources are being
used in different industries mainly in non-destructive testings.
A significant amount of thorium nitrates are being used by some
private industries for gas mantle preparation.
From the above facts it is clear that the use of ionizing
radiation has significantly increased in Bangladesh. Therefore to
ensure the safety of the radiation workers and public at large it
has become essential to monitor area and personnel of nuclear and
radiation facilities more precisely and on regular basis. Various
kinds of radiation monitoring equipment, such as survey meters,
personel dosimeters and environmental monitors are being used at
nuclear and radiation facilities to monitor area and personnel
doses. Since these results are direct measurements and
essentially reflect back to assure the safety of the occupational
workers, members of the public at large and the facilities, the
radiation monitoring instruments should have the good operational
performance and the high reliability. For this reason, it is
necessary to calibrate and standardize periodically the
sensitivity of the instruments. To carry out the calibration of
the radiation monitoring instruments, a secondary standard
dosimetry laboraotory (SSDL) has been established at AERE, Savar
under the technical assistance of International Atomic Energy
Agency (IAEA), Vienna.
KxiBtine; SSDL Facilities:
- One multipurpose gamma calibrator OB-85.
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JAERI-Conf 95-014
- One panoramic gamma calibrator OB-34.
- One gamma calibrator OB-2.
- One nutron calibrator OB-26.
- One X-ray machine of 165 KV and 3 KW (Model HF 160C, series 2,
PANTAK Ltd.).
- Electrometers:
(1) Farmer dosimeter.
(2) Dosleader 2S10B
(3) NPL therapy level exposuremeter.
(4) Ionex type 2500/3.
- Ion chambers : 600 (cc); 0.6 (cc); 0.3 (cc).
3- One water phantom :30X30X22 cm
o
- One solid phantom : 22X20X15 cm
The detailed specifications of calibrators and probes/ion
chambers are shown in Table - 1 and 2 respectively.
Status of radiation protection calibration activities and
experiences of calibration:
A programme has been undertaken (by the SSDL, AERE, Savar)
in the begining of 1992 to calibrate and standardize perodically
the radiation measuring instruments available in the country.
Since then a good number of radiation measuring instruments have
been calibrated. It appears that the variation in calibration
factor varies to a maximum value of 22%.
After the implementation of "Nuclear safety and radiation
control regulations " (The Act have been passed in 1993 in the
Parliament of the govt. of the Peoples Republic of Bangladesh )
throughout the country, such calibration/standardization of the
radiation measuring instruments possesed by allied facilities
will be mandatory.
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JAERI-Conf 95-014
A study has been made (this study was made by SSDL,
INST, AERE Savar) to determine the energy dependant calibration
factors of several ion chambers using SSDL facilities at AERE,
Savar. In this study, one 600 cm thin window ion chamber (for
radiation protection purpose) and four different thimble ion
chambers having active volume of 0.6 cm (for therapy level dose
measurements) have been calibrated and standardized using
International Standard Organisation (I.S.O.) X-ray and Gamma
reference beams. The calibration factors in terms of air kerma
per unit charge (Gy/nc) of different ionization chambers have
been determined over the energy range 33 KeV to 118 KeV X-ray,
661.6 KeV (137Cs) and 1250 KeV (60Co) gamma energies.
The values of calibration factors show quite a variation not only
between different types but also in the same type of ionization
chambers.
An assessment of the variation in response with photon energy of
three different portable Geiger Muller counters used as survey
instruments such as PDR2, PDR3 and Berthold type LB1200 has been
made using the I.S.O. X-ray and Gamma reference beams for the
energy spectra: (a) 33 keV - 118 keV (Narrow Spectrum Series of
filtered X-ray), (b) 661.6 keV (Cs-137) and (c) 1252.9 keV (Co-
60). The variations in the energy response have been compared
with the performance requirement of International
Electrotechnical Commission (I.E.C.) recommendations for
evaluating the performance of the instruments. In compliance with
IEC recommendations it is found that the low energy (less than 60
KeV) responses of survey instruments PDR2 and PDR3 are poor but
their responses are excellent for the energy range from 100 KeV
to 1.25 MeV. The survey meter type LB1200 does not satisfy any of
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JAERI-Conf 95-014
the IEC photon requirements and not qualified for surveying an
unknown photon radiation field.
Regarding the intercomparison of personnel dosimeters,the
Health Physics Division of Atomic Energy Centre, Dhaka (Which
acts as the central laboratory to provide • personnel monitoring
services nationally) participated in the first phase of the
IAEA/RCA intercomparison of personnel dosimeters (1990-1992) and
this Division is interested to participate also in the 2nd phase
of the IAEA/RCA intercomparison of personal dosimeters and hopes
to introduce the ICRU new operational quantities in the country
in near future.
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JAERI-Conf 95-014
Table-1. Specifications of SSDL calibrators
Type of ! Type ofcalibrator J source
! Energy & ! Activity on | Half Life! photo fraction! 24.03.92 (GBq)! (years)
OB-85
137,Cs 0.662 MeV (Gamma)(85%)
60,Co
659.27 30
1.173 MeV(Gamma)(100%)1.332 MeV(Gamma)(100%)
19.48 5.27
OB-34/1
137Cs
60Co
0.662 MeV(Gamma)(85%)
(1) 6.53x10-3
(2) 65.38x10-3
(3) 653.85x10(4) 6.48x10 d
-3
1.173 MeV(Gamma)(100%)1.332 MeV (Gamma)(100%)
(1) 1.84x10-3
(2) 12.86x10(3) 0.184x10
-3
OB-2
OB-26/1
60Co 1.173 MeV (Gamma)(100%)1.332 MeV (Gamma)(100%)
NeutronEmmission Rate:
1-lxlO7 n/s
3.
183.
7
72
5.27
432
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JAERI-Conf 95-014
Table-2. List of ion chambers, probes,etc. of SSDL, AERE, Savar.
SI. Item withNo. Specifications.
Quantity Energy Response
2.
4.
5.
6.
7.
Ionization chamberType: 2561 3Volume: 0.325 cmPolarizing potential 200v.(N.E. Ltd., U.K.)
0.6 cc Ionization chamber(Guarded stem)Type: 2571, Volume:0.69 cmmaximum polarizingVoltage: +400 VDC(N.E. Ltd., U.K.)
0.6 cc Robust Ionizationchamber, Type: 2581,volume: 0.56 cm Maximumpolarizing voltage:+400VDC(N.E. Ltd., U.K.)
600 cc thin window 1Ionization chamber Type: ~2575, SI.No.278 Vol.2602cmWindow area: 100 cm .Maximumpolarizing voltage:±400VDC(N.E. Ltd., U.K.)
Portable X-ray dosemeter. 1Model: 3703(Vinten A.S., U.K.)
350 cc ionization chamber 2(N.E.T. Ltd.& DAP Ltd.,U.K.)
3.5 cc ionization chamber 1(DAP Ltd., U.K.)
Uniform within +1% from1.25 mm Al to 20 mm AlHVL
X & Gamma rays:50kV-300kVwithout protective buildupcagQ0.3 MV to 2MV,
id/Cs& Co with protectivebuildup cap.
X & Gamma rays:100KV-300KVwithout protective/buildupcap 0.3 MV to 2 MV, CsCo with protective/buiId
up cap. Electrons: 5MV-•35 MV in suitable photon.
It is assumed that theappropriate additionalwindow (if any) it fitted(i) Photons: Exposure inair X-rays, Generating Po-tential: 0.010 to 2.0 MV.Gamma-Rays, photon energy:0.008 to 1.5 MeV (ii)BetaParticles & Electrons:Betaparticles, Emax,electrons,energy: 0.15 to 2 MeV.
X & Gamma ray for lowest+5% on other system.
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JAERI-Conf 95-014
3. PRESENT STATUS OF CALIBRATION SYSTEM ANDIMPLEMENTATION OF THE NEW ICRU OPERATIONAL
QUANTITIES IN CHINA
( China Institute for Radiation Protection Taiyuan, Shanxi 030006)
Standard Dissemination SystemThere is a widely use of ionizing radiation in the fields of industry, agriculture,
medical science, energy production etc. The public have gradually been aware ofthe detriments of ionizing radiation. In the area of radiation protection and nuclearsafety, the accurate and reliable measurement of the quantities that refer to theradiation fields or the interaction effects between the radiation fields and theirradiated materials is the basis for the various radiation protection activities. As weknow, the adequate calibration (calibration standards, calibration facilities,calibration techniques) and proper use of radiation measuring instruments are thekey step of the measurement. Figl. shows the dissemination systems of radiationmeasuring standard in china.
primary standard
measuring Instrument
Y-ray irradiation apparatus
X-tay irradiation apparatus
primary standard Y-ray source
Secondary standard
measuring instrument
Y-ray irradiation apparatus
X-ray irradiation apparatus
secondary standard Y-ray source
practical standard
measuring instrument
practical irradiation
apparatus
National
dose labc
primary
dose labc
secondar
dose latx
workingdose lab
standard
ratory
standard
tatory
y standard
sratory
standard
oratory
Stale datum
primary standard
secondary standard
working standard
Figl. Metrological dissemination system of X (gamma)-raymeasuring standard in China
In China, national (primary) standards are maintained by the NationalInstitute of Metrology. The dissemination for the X(gamma)-ray measuringstandards is based on the exposure or air kerma. The secondary standards (whichincludes the standard reference radiation sources, standard reference instruments,
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JAERI-Conf 95-014
calibration phantoms and so on )in SSDLs or other main calibration services iscalibrated directly and periodically by the national (primary) standards. ICRU doseequivalent standards are established by exposure or air kerma multiplying byconversion coefficients suggested in ICRU Report 47. The calibration proceduresfollowed by us are consistent with the suggestions of International StandardOrganization.
Calibration FacilitiesFig2. illustrated a gamma ray calibration setup which includes a
multisource container with a conical ring-collimator and an appropriate angularaperture. For the calibration of dosimeters in the range of 30-300 kev, a series offiltered narrow or wide spectrum X-ray reference radiations are employed. Fig3.represents a typical X-ray machine and other relevant facilities for calibration inmost of standard dosimetry laboratories. There are also K-fiuorescence referenceradiations in some laboratories. The reference radiations used for calibration inmost of our standard laboratories include Gamma reference radiation sources andnarrow and wide spectrum series filtered X reference radiations which areaccordance with the ISO-4037. Additionally, there are other reference radiationssuch as gamma, beta-ray, neutron produced by other radionuclides, acceleratorsand reactors used in various laboratories for the calibration of various kinds ofinstrument, respectively. There are also several kinds of phantom used for thecalibration of individual dosimeters in the standard laboratories. They all suggestedby international organizations such as ISO. IAEA- ICRU. WHO. etc. we usuallycalibrate the dosimeters by the standard reference instrument method and in somecases by using the standard reference radiation source method.
Impact of New Operational QuantitiesFor a long time, we have devoted a great efforts to search the quantities that can
correctly and reasonably describe the detriments which are acquired by the peoplein the ionizing radiation fields. We adopted the exposure, air kerma, absorbed doseand effective dose equivalent for this purpose in the past
Fig2. Diagram of a gamma ray calibration facilities
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JAERI-Conf 95-014
Diaphragm MonitorDetector
Fig3. Diagram of X-ray calibration facilities
Since the issue of ICRU Report 39, the new operational quantities have beenintroduced, Ambient dose equivalent and directional dose equivalent for areamonitoring; individual dose equivalent, penetrating and superficial, for individualmonitoring, these quantities are measurable and comparable with dose-equivalentlimits and are considered to represent a good approximation for the radiationprotection purposes. In ICRU Report 47, a simplified concept, personal doseequivalent instead of individual dose equivalent, penetrating and superficial wasselected for individual monitoring. It is described as " the dose equivalent in softtissue below a specified point on the body at an appropriate depth ". In this report,ICRU also presents a detail discussion on the measurement of dose equivalent andrelevant calibration procedures and various sets of conversion coefficients betweenthe quantities involved in primary standardization (e.g. exposure, air kerma forphotons ) and the new operational quantities. In recent years, the acceptance andimplementation of the new operational quantities in world range have become themain purpose of many IAEA's activities. On the other hand, a great deals of paperconcentrate their concerns on the definition, implication, measurement of the newoperational quantities and the related calibration problems. Many people havedeveloped the various kinds of personal dosimeter and survey meter to fit the needfor the measurement of new operational quantities.
In China, although the new operational quantities have not been adopted bylaw as legal metrological quantities and units. But in practically, they have beenaccepted by the most workers in radiation protection areas, and gradually by theusers of the radiation measuring instrument The Bureau of Safety Protection &Health, China National Nuclear Corporation (CNNC) has conducted severalspecial meetings for experts to discuss the acceptance and implementation of newoperational quantities. The new operational quantities and their related problemsbecome a hot-point in many academic meetings in recent years. CIRP has holdseveral training courses on regionally and nationally, to help occupational radiationprotection workers to have correct understanding and to follow the propercalibration procedures in terms of the new operational quantities by theconsultation of specialists. In order to find the weakness and improperlyperformance of our dosimetry systems and to improve the calibration techniques,our SSDLs and some main dosimetry services not only take part in all of the IAEA/RCA intercomparison activities but also are the organizers or participants in some
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JAERI-Conf 95-014
of national intercomparison. In the IAEA/RCA programme, we got satisfactoryresults. Nevertheless, there are still some weakness and problems which were foundthrough the results of intercomparison and are expected to be eliminated in thefuture works.
Now, a well developing QA programme is emergence in China, Theconcepts of quality assurance in radiation monitoring have been introduced andsome authorities of QA programme have been established. In generally, the newoperational quantities for area monitoring and individual monitoring have beenwidely accepted and implemented in China, but there are still some problemsexisted in the performance of these quantities, such as the co-exist of different kindsof quantities and their units, due to the use of various radiation measuringinstruments (some of them were the products of several decades ago). In the most ofour dosimetry services, including SSDLs, the various calibration phantoms whichare closely connected with the new operational quantities, especially with thepersonal dose equivalent have been adopted, e.g. water cube, polyethylene slab,perspex slab, polyethylene sphere, etc. according to their financial and technicalabilities, respectively. In this case, the different sets of the conversion coefficientswhich link the primary quantities (exposure, air kerma) and the dose equivalenthave been used in practice. In other word, the lack of consistency in use of phantomand the conversion coefficients causes another major problem now. In somestandard laboratories, especially on the level of working (practical) standard, thereare great limits on the ranges of dose equivalent-rate and on the ranges of photonenergy.
Conclusion:There is a reliable metrological dissemination system of X(gamma)-ray
measuring standard in China and the new operational quantities have been acceptedinformally by well-trained dosimetric service personnel and will by the all of usersof radiation protection instruments. Meanwhile, there are still some problems in thedesign of dosimeter, the performance of standard dessemination and qualityassurance system, these problems will be improved in near future.
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JAERI-Conf 95-014
4. CALIBRATION OF DOSIMETERS AND SURVEY METERS FOR PHOTONS IN INDIA
INTRODUCTION :
The Radiation Standards Section of Bhabha Atomic ResearchCentre in India maintains the primary and secondary standards ofvarious parameters of radiation measurements. This is an apexlaboratory accredited by the National Coordination of Testing andCalibration facilities (NCTCF) programme of Government of India.The Radiation Standards Section (RSS) provides cal ibrat\=?tservices for various types of radiation protection survey metersand dosimeters used in nuclear installations as well as inIndustry, Medicine and research laboratories. This paper bringsout the status of calibration of dosimeters and survey meters forphotons in India including (i) The facilities available (ii) thetype,number and manufacturer of instruments for which thecalibration services are provided and (iii) Special problemsrelated to calibration.
I. FACILITIES AVAILABLE :
The photograph shows the layout of the calibration room andthe faci1ities.
The calibration facilities available include :
(i) Small radioactive sealed sources of Co-60, Cs-137,Ra-226 ofvarious strengths.
(ii) Collimated beams of CO-60, Cs-i37, l'r-192 h. Ara-241.
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JAERI-Conf 95-014
(iii)C0-60 teletherapy machine.
(iv) Optical benches for precise alignment of source and detector.
(v) Laser beam markers for the alignment.
(vi) A CC TV system for the read-out of instrument displays.
(vii)A large room measuring 10 meters x 10 meters x 10 meters tocreate near scatter-free conditions.
(viii)A panoramic exposure assembly for the precise delivery ofexposures to integrating type dosimeters such as TLDs andpocket dosimeters.
(x) Graphite cavity chamber with sensitive electronics used asreference gamma standard.
Panoramic exposure assembly : This set-up is useful for precisedelivery of exposures to integrating dosimeters such as TLDspocket dosimeters etc. The source is brought upto the irradiationposition by suction using a vacuum pump and the exposure durationis controlled by a crystal controlled timer. The exposureintervals can be preset from a few tens of seconds to severalthousand seconds. Number of detectors can be clamped on theperspex ring of radius 30 cm. A calibrated G.M.counter (Philips'18529) is also located on this detector positioning ring to checkthe precision of dose delivery. The system is remotely controlledand automatic.
Reference gamma standard for protection 1evel calibration : Acavity ion chamber has been designed and established to serve asthe reference standard for protection level calibration. It iscylindrical in shape and has a sensitive volume of 100.9 cc. andis madeof nuclear grade graphite Its sensitivity is 3.71 jiC/Gy(9x 10 ~ A/R/h) at STP and its response is constant to within+. 4% in the energy range 30 keV to 2 MeV. Its sensitivity asa function of photon energy has been calculated using Burlin'sgeneral cavity theory with suitable modification in the lowenergy region (hv <200 keV) and the results are experimentallyverified and validated. The sensitive electronics used with thisreference chamber is a veractor input electrometer amplifier. Thecurrent measurements are done using rate of charge method to anaccuracy better than +. 0.5% and this system is automatic.
II. INSTRUMENTS CALIBRATED :
Table.1. gives the details of the instruments (indigenouslydeveloped) calibrated. The RSS is maintaining calibration datarecords for more than 500 dosimeters and survey meters calibratedduring the last six years. Data on the repeat calibration donewith some of these instruments have shown the reproducibi1ity ofthe calibration factors within +10*.
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JAERI-Conf 95-014
Table 1. Types of dosiaeters and instruments calibrated
Instrument Type
A. Dosimeters
1. Film dosimeters
2. TL dasiseters
3. Quartz fibrepocket dosimeters
4. Electronic pocketdosimeters
B. SURVEY INSTRUMENTS
5. Beta Gauaa ExposureRate meter (GUN MONITOR)
6. Radiation SurveyMeter Model MR 12IC
7. Radiation SurveyMeter Model Minirad
8. Gamma Radiography surveymeter Model MR 4500
9. Wide Range Survey Meter
10.Samoa Area/ZoneMonitor
11.HR TO R RadiationMonitor
12.RAD MQN
13.INDRAM
14.SLIDIN8 ARM HIGH RAK6EMONITOR MODEL HRM 100A
Detector
Kodak Type 2 fila
•Ca So^'Dy
Ion charter
6.M. counter
Ion chaaber
G.M,counter
G.M.counter
G.M.counter
G.M.counter
G.M.counter
Plasticscintillator/P.M.tube
G.M.counter
G.M.counter
6.M.counter
Ranges
1 aRea to 1000 Ren
0.1 aRea to 1000 Rea
0 to 200 aR
0 to 1000 oft
0 to 50 sR/h to 0 to 5000 sR/h
0 to 0.2 aR/h to 0 to 20 aR/h
0 -to 5 aR/h to 0 to 5 R/h
0 to 5 oR/h to 0 to 50 R/h
0 to 10 aR/h to 0 to 100 R/h
0.1 to 100 (»R/h
0 to 10 (iR/h to 0 to 10 R/h
0 to 2 aR/h to 0 to 20 R/ht 0 to 200 aR
0 to 1000 BR/h & 0 to 10 R/h
0 to 50 oR/h to 0 to 1000 R/h
Manufacturer
BARC*
EARC
BARCPEA #ECIL a
ECILPEA
ECIL
PULSECHO $•
ECIL
BARC
EC1L.PEAPULSECHO
BARC
NUCLEONIX !
NUCLEONIX
BARC
* BHABHA ATOMIC RESEARCH CENTRE, TROHBAY/, BOMBAY-400
* PLA ELECTRO APPLIANCES LTD., BOMBAY.
i ELECTRONICS CORPORATION OF INDIA LTD.,HYDERABAD.
$ PULSECHO SYSTEMS LTD.,BOMBAY.
! NUCLEONIX SYSTEMS PVT.LTD..HYDERABAD.
085
- 1 8 -
JAERI-Conf 95-014
III. PROBLEMS AND EXPERIENCES OF CALIBRATION FOR ICRU'S NEWOPERATIONAL QUANTITIES:
Conversion factors required for the determination of AmbientDose equivalent from air kerraa at different x-ray beam qualitieshave been determined at RSS^using a water phantom. A Philips RT-250 therapy X-ray machine p'roducing moderately filtered X-raybeams under different kV filter combinations was used. A smallvolume tissue-equivalent(TE) chamber was used for measurements ofdose in phantom and air-kerma in air. The chamber was calibratedagainst a Nuclear Enterprises <NE) make graphite reference chamberfor different X-ray qualities, whose calibration factors wereknown to an accuracy of better than +3%. A veractor D.C.amplifierincorporating calibrated capacitors was used for chargemeasurements. A cuboid water phantom of dimensions 30 cm x 30 cm x30 cm with a waterproof perspsx tube of 1.9 mm wall thickness forpositioning TE chamber at the equivalent depth of 10 mm was used.Radiation field size used was 70 cm x 60 cm. The measurements madein- the cuboid water phantom were corrected for shape and non-tissue equivalence with correction factors evaluated using thedata from Physikal1sch-Technische Budesanstalt (PTB). Comparisonof the measured conversion factors with those obtained at PTB hasshown a good agreement between the two figures. The measured ADEconversion factors at different X-ray qualities are proposed to beused for routine calibrations. Studies are in progress to evaluateconversion factors for the determination of directional doseequivalent at effective energies from 25 keV to 50 keV.
Some of the problems & experiences of calibration are asfollows : a) Calibration of low energy and low exposure ratemeasuring instruments. b) Variation of background during thecalibration of environmental gamma monitors, c) Variation in theenergy response of instruments of the same type & model to lowenergy photons. d) Beam uniformity measurements for thecalibration of large number of dosimeters and instruments withlarge volume detectors using collimated photon beams. e>Traceability of calibration to National Standards Laboratory.
Efforts are on at the Radiation Standards Section to solve theabove listed problems.
REFERENCES :
1) Activities of Radiation Standards Section edited by A.Kannan,P.S. Rao, R.N.Sachdev, V.V.Shaha, D.Sharma and P. K.SrivastavaBARC Report No.BARC/1992/E/048.
2) Facility for calibration of Radiation survey meters in termsof Ambient Dose Equivalent Units, P.N.M.R.Vijayam and A.KannanBulletin of Radiation Protection, Vol.15 , No.l, January-march1992.
3) Calibration of environmental gamma radiation monitors,G.Ramanathan, P.S.Rao, S.C.Misra, and K.S.V.Nambi Proceedingsof Tenth National Symposium On Radiation Physics, Kalpakkam,Madras, 1993. pp. 194-197.
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JAERI-Conf 95-014
5. ACTIVITIES ON CALIBRATION OF RADIATION PROTECTION
INSTRUMENTS IN INDONESIA
Susetyo Tri joko
Centre for Standardization and Radiation Safety Research,
BATAN, Jakarta, Indonesia
INTRODUCTION
As the use of ionizing radiation emitted by radionuclides or
produced by modern machines in Indonesia has increased signifi-
cantly since the past two decades, demand for radiation protec-
tion measures has also grown up very rapidly. Ionizing radiation,
mainly alpha, beta, gamma, and netron is a unique one, because
until a certain amount it can not be seen or felt by any sensor
of human body. But unfortunately it always brings contemporary
issues which very easily spread around the world.
In the mind of Indonesian people at the moment, ionizing
radiation or sometime also called atomic radiation is always and
almost associated with atomic bomb, which could make disaster for
human living. Regarding the mentioned condition, Indonesian Gov-
ernment through the Act. No. 31/1964 has set up National Atomic
Energy Agency (BATAN) headed by a Director General who is respon-
sible directly to Presiden Republic of Indonesia. BATAN which has
responsibility in research & development, implementation, and
inspection of safe-use of ionizing radiation for peaceful pur-
poses, always put a great concern on radiation protection matter.
Since then the Centre for Standardization and Radiation Safety
Research (CSRSR) has been appointed to implement research and
services in the field of radiation safety, standardization,
dosimetry, radiation health, as well as the application of nucle-
ar technique in medicine.
In order to provide a national reference in term of radia-
tion dosimetry and calibration, by 1984 a Secondary Standard
Dosimetry Laboratory was completely set up in Jakarta through a
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JAERI-Conf 95-014
technical assistance project funded by IAEA. It is so called
SSDL Jakarta. Since that time SSDL Jakarta has been recognised as
a member of IAEA/WHO SSDLs Network. The laboratory is integrated
within the BATAN headquarter and run by the Centre for Standardi-
zation and Radiation Safety Research. Through Decree of Director
General BATAN No. 79/DJ/V/1984 the Centre has been appointed as
National Radiation Calibration Facility.
A further demand for accuracy and precision in radiation
dose measurement is always considered by the Centre in order to
always maintain and further establish the National Radiation
Calibration Facility. Since 1984, our laboratory has actively
been involved in international intercomparison of radiotherapy
dose conducted by IAEA using TLDs. The deviation of doses stated
by our laboratory are. always well within the acceptance limit
established by IAEA dosimetry laboratory. According to current
regulation in Indonesia the Secondary Standard must be calibrat-
ed in Primary Standard Dosimetry Laboratory at least once every
three year. Based on bilateral international-cooperative work,
the instrument so far is routinely calibrated in PSDL-ETL, Japan.
Radiation instruments used to determine radiation output in
air, e.g. exposure or kerma rate, must be calibrated against a
reference standard instrument. Decree of Director General BATAN
No. 78/DJ/V/1984 then further renewed by Decree No.
82/DJ/VI/1991, requests that all radiation protection instruments
used within the Republic of Indonesia must be calibrated at least
once a year or whenever something suspectious happens by Nation-
al Radiation' Calibration Laboratory or any Local Laboratory. In
addition to the National Radiation Calibration Facility at the
mean time we are going to set up a Local Calibration Facility for
radiation protection purposes in Yogyakarta.
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JAERI-Conf 95-014
AVAILABLE FACILITIES
In the case of photon calibration of radiation protection
instruments, the Centre has been facilitated with a number of
radiation sources and instruments which are routinely used for
calibration service and research. All equipments are well main-
tained in air conditioned room at a certain relative humidity.
Radi at ion Instruments
NPL Dosemeter type 2560 together with chamber detector of
0.325 cc type NE 2561 is currently employed as a Secondary Stan-
dard instrument on photon dosimetry for therapy level. In order
to establish standard exposures of photon beams used for cali-
brating radiation protection instruments, we use mainly two
dosemeters,
1. Digital Farmer Dosimeter NE 2570 connected to ionization
chamber detector of 600 cc NE 2575, and
2. Electrometer ALOKA connected to ionization chamber detector
of 400 cc, RIC-DRM.
Measurements are carried out free in air. Standard exposures
at various distances from source are tabulated. Values written in
the table are used as reference values by technicians when per-
forming calibration of radiation protection instrument, e.g.
survey instrument.
Radi at ion Sources
Our laboratory has been equiped with photon source machines
as follow.
1. Gamma calibrator, 08.2, Buchler
I t contains a collimated Co-60 source having original radia-
t ion act iv i ty of 100 mCi.
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JAERI-Conf 95-014
2. Gamma calibrator, OB.6, Buchler
It contains a collimated Cs-137 source having original radia-
tion activity of 1 Ci.
3. Gamma calibrator, OB.34, Buchler
It contains a number of panoramic sources of Co-60 and Cs-137.
(Co-60 : 3.7 MBq, 25.9 MBq, and 370 MBq;
Cs-137: 7.4 MBq, 74.0 MBq, 740 MBq, and 7.4 GBq).
4. Gamma calibrator, OB.85, Buchler
It has three radionuclides, Co-60 (37 GBq), Cs-137 (740 GBq),
and Ra-226 (1 mg), each housed in its home. When machine
operating, the source moves to a fixed position and a colli-
mated gamma beam comes out. This machine is also facilitated
with two lead absorbers that can be placed at just outside
collimating material. Using those absorbers we can make
variation of exposure rate at a certain distance. Exposure
rate for Co-60 at one meter distance from source without
absorber is around 550 mR/hr and for Cs-137 is around
5200 mR/hr.
5. X-ray machine MG-420, Philips.
This machine produces X-ray beams in the range from 10 kV
upto 420 kV. Originally it is used to facilitate calibration
of therapy level instruments, but it is also used for radia-
tion protection purposes.
CALIBRATION AND PERSONAL MONITORING SERVICES
In order to obtain correct reading, every radiation instru-
ment, such as surveymeter, for monitoring area or for other
radiation protection purposes must be calibrated routinely. At
the moment CSRSR is the only one that provides calibration
service -for all radiation instruments used in Indonesia. Cali-
bration of radiation protection instrument is carried out free in
air, in term of exposure rate. Each scale on the instrument is
calibrated at three different points, e.g. 30%, 50%, and 80% of
maximum reading and calibration factor is given for each corre-
sponding scale.
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JAERI-Conf 95-014
Demand for calibration of radiation protection instruments
has increased continuously from time to time. Requests for cali-
bration usually come from private or industrial companies, re-
search institutes, hospitals, and as well as military institu-
tions. The number of calibration services for the past five
years can be seen from table shown below.
Tabel 1. CALIBRATION SERVICES PERFORMED AT THE CENTRE
FROM 1989 - 1993
I I I| | Number of Instruments for Year |j Type of Calibration | 1
j 1 . Radiati
|2. Pocket
3. Contami
on Surveymeter
Dosimeter
nation Monitor
89/90
461
274
43
90/91
458
406
51
91/92
448
377
29
92/93
491
474
50
93/94
616
520i
69
J Total | 778 915 854 1015 1205 |i i i
In Indonesia we also have a number of fixed radiation moni-
tors, such as gate monitor, hand & foot monitor, and stack moni-
tor installed in several radiation laboratories. However we
still have problem in order to calibrate them in our laboratory.
CSRSR also provides personal monitoring service for radia-
tion workers who work in various industrial sectors, research
institutions, and private hospitals. More than 5,000 radiation
workers are covered by the personal monitoring serivice conducted
by CSRSR using Film and TLD personal monitoring badges. All
radiation workers under the National Atomic Energy Agency (BATAN)
are covered by a TLD service. The remaining industrial, research
and medical institutions are covered by a Film badge service. We
produce records of occupational dose received by workers wearing
Film badges on a monthly basis. On the other hand for workers
wearing TLD badges, we apply a three-monthly periode. In addition
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JAERI-Conf 95-014
to personal monitoring provided by CSRSR, personal monitoring
service for radiation workers in government hospitals are conr
ducted by Ministry of Health using Film badges only.
Calibration of personal dose monitoring is performed free
in air using gamma beam of Cs-137. To convert the exposure unit
to become air kerma unit we apply:
1 R = 2.58 x 10~4 C/kg and
W/e = 33.97 J/C.
and therefore the relationship between Exposure and Air Kerma
would be:
Ka (Gy) = 8.76 X 10~3 . X (R)
In order to obtain personal dose equivalent, Hp(10) in mSv
unit, we assume H'(10) equivalent with Hp(10) and therefore apply
a conversion coefficient, Hp(1O)/Ka^r, of 1.18 Sv/Gy with regard-
ing a correction for backscatter radiation. So far our Centre has
not provided personal dose monitoring in term of Hp(0.07) yet.
CONCLUSION
The task of the Centre for Standardization and Radiation
Safety Research coincidences with the 2nd IAEA/RCA personal
dosimetry programme. We definetely will support the proposed
programme that are going to be started by 1995. We would like to
be involved and to participate in the next personal dosimetry
intercomparison.
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JAERI-Conf 95-014
6. Quality assurance of reference calibration fieldProposal of Reference Dose Value Intercomparison using RPL Glass Dosemeter
S.MIKAMI, T.MOMOSEHealth and Safety Division,Tokai Works,Power Reactor and Nuclear Fuel Development Corporation4-33, Muramatsu,Tokai-mura, Naka-gun, Ibaraki,319-11, JAP AN
Abstract
The method for a reference dose value intercomparison of calibration fieldusing radiophotoluminescence (RPL) glass dosemeters was provided. Thismethod was applied to the intercomparison of the reference exposure value ofgamma irradiation fields among the 5 calibration facilities of Power Reactor andNuclear Fuel Development Corporation (PNC). The results showed a goodagreement by as much as 4% of deviation. These prove that reference exposurevalues of each calibration facility have been maintained in a good accuracy. Itwas shown also that the RPL glass dosemeters could be applied to a check ofexposure value of a calibration field. This method will be available for theintercomparison programme among the Regional Cooperative Agreement(RCA)member states.
Introduction
To assure a quality of dose evaluation for radiation protection, a calibrationof dosemeters and monitoring equipments is very important. The reference dosevalue of calibration fields should be evaluated by using a standard ionizationchamber which is calibrated on a traceability system to a primary standard.
National primary standards of radiation dose value have been established atthe Electro-Technical Laboratory (ETL) in Japan. Five sites in PNC (TokaiWorks, O-arai Engineering Center, Monju Construction Office, Fugen NuclearPower Station, and Ningyo Toge Works) have each calibration facility. Thereference dose of the calibration fields are measured by their standard ionizationchamber at each site. Tokai Works and Fugen Power Station request the ETL tocalibrate the standard ionization chambers (Victoreen 500 for detector, 550-3 forelectrometer). The standard ionization chambers of other 3 sites (O-arai, Monjuand Ningyo Toge Works) were calibrated at the calibration field of Tokai Works(Figure 1).
In 1992 the intercomparison for the reference exposure values of thecalibration fields was made with 5 calibration facilities by means of the ionization
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JAERI-Conf 95-014
chambers. And all results show a good agreement by as much as 3%.It was found that an intercomparison was a very effective method to check the
accuracy of irradiation. So it is desirable to carry out the same kind ofintercomparison periodically. However, the intercomparison using a standardionization chambers is not convenient, because an ionization chamber is verysensitive to mechanical shocks and humidity, and also this method needs muchman power and time. Then, the intercomparison of reference dose value usingRPL glass dosemeter was proposed.
Electro-Technical Laboratory
d monitoring (equipments
Figure 1. The traceability system of gamma calibration field in PNC
RPL glass dosemeter
The Toshiba Type SC-1 RPL glass dosemeters were used for the referencedose value intercomparison of the calibration fields because of its excellentcharacteristics. The dosemeters are readout by means of a pulsed UV laserexcitation. The structure and the external view of the dosemeter are shown inFigure 2 and Figure 3.
' glass detector
Figure 2. The structure of the dosemeter
27 -
JAERI-Conf 95-014
Figure 3.The external view of the dosimeter
The typical features of the RPL glass dosemeter are as follows. (1) Readingoutcan be done repeatedly. (2) Dispersion of sensitivity among the dosemeters issmall. (3) Fading is small. (4) Fluorescence come from predose is subtractedautomatically. (5) Dose imformation stored inside glass dosemeter can be erasedby annealing, etc.
In our experience, some special techniques.such as the sensitivity correctionfor each dosemeter, were also considered to get the good performance of dosemeasurements of RPL glass dosemeter.
The main characteristics of the RPL glass dosemeter are shown in Table 1.
Table 1. Characteristics of the RPL glass dosemeter
Item Condition Deviation
energy dependence 200keV to "Co <±5%
angular dependence direction of 0* ±30 ' < ± 1 %
'"Cs
dose rate response 20mR/h to lR/h < ± 1 %
deviation of readings 50mR< ±0.3%
Reference dose value intercomparison using RPL glass dosemeter
The convenient intercomparison method using RPL glass dosemeters wasprovided with the effort of Japan Atomic Energy Research Institute (JAERI). In1993 and 1994 the trial of intercomprison was made among 5 facilities of PNC.
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The sources used for the intercomparison are ""Co and "7Cs. The activities ofthe sources are from 1.85GBq to l . l lTBq for 137Cs and from 370MBq to3.7TBq for "Co. Table 2 shows the sources' data used for the intercomparison.
The JAERI Tokai Institute sent the dosemeters, which was already annealed toerase the predose of a dosemeter, to the participant facilities. Then theirradiations to the dosemeters were carried out at each facility. The distancesbetween source to dosemeter were 1 and 2 meters. In the intercomparison, 3pieces of glass dosemeters were used at one point. The dosemeters irradiated ateach facility were returned to JAERI with the data of the irradiated exposurevalue. After returning to JAERI, the dosemeters were read out. And themeasured values were compared to the reference exposure dose values of eachfacility using the following equation:
Exposure value - Measured valueDeviation(%) = x 100
Exposure value
Table 2.
Site
Tokai
O-arai
Monju
Fug en
Ningyo Toge
Gamma
nu elide
'"Cs
"Co
'"Cs
"Co
'"Cs
"Co
'"Cs
"Co
1J'Cs
"Co
sources used for
Source
activity
l.llTBq
3.7GBq
3.7GBq
l.llTBq
3.7GBq
3.7GBq
l.llTBq
7.4GBq
370MBq
740GBq
37GBq
2.59GBq
1.85GBq
the intercomparison
Distance
source to detecter
lm,2m
lm
lm
lm,2m
lm
lm
lm,2m
lm
lm
lm,2m
lm.2m
lm
lm
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JAERI-Conf 95-014
Result
The results of the intercomparison among 5 sites of PNC for .137Cs and "Cosources are shown in Table 3. The exposure value of each calibration facilityshowed the good agreement by as much as 2% of deviation, except 2 pointswhich differed by 3.7% and 2.7%. For these 2 points, investigations of a causewhy they differed more than 2 % are required.
Conclusion
It was found that reference exposure dose value of a calibration field couldbe checked easily and quickly by the intercomparison using RPL glass dosemeter.The total accuracy for the measurment of exposure dose value is 1.5%. Themethod using RPL glass dosemeters will be useful for the intercomprison amongthe RCA member states.
Table 3. Result of the reference exposure value check
Site
Tokai
O-arai
Monju
Fugen
Ningyo
Toge
Nu elide
' "Cs
60Co157Cs
60Co
'"Cs
60Co
'"Cs
60Co
'"Cs
"Co
Activity
l . l l T B q
3.7GBq
3.7GBq
l . l l T B q
3.7GBq
3.7GBq
l . H T B q
7.4GBq
370MBq
740GBq
37GBq
2.59GBq
1.85GBq
Distance
(m)1.0
2.0
1.0
1.0
1.0
2.0
1.0
1.0
1.0
2.0
1.0
1.0
1.0
2.0
1.0
2.0
1.0
1.0
Exposure"
(wRIh)8100
2025
25.43
15.62
6602
1638
28.5
45.2
9647
2344
65.89
9.86
4882
1220
654.8
163.1
21.15
22.50
Measured Valueof glass dosemeter
(mR/h)•8077
2025
25.64
15.71
6612
1577
28.25
45.3
9450
2317
66.16
10.05
4859
1205
661.9
164.4
21.72
22.32
Measured
Exposure
0.997
1.000
1.008
1.006
1.002
0.963
0.991
1.002
0.980
0.988
1.004
1.019
0.995
0.988
1.011
1.008
1.027
0.992
1) Reference Exposure (Jose value measuredby ioniaition chamber at each facility
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JAERI-Conf 95-014
7. STATUS OF RADIATION PROTECTION CALIBRATIONPROGRAM IN KOREA
BONG-HWAN KIMHEALTH PHYSICS DEPT.
KOREA ATOMIC ENERGY RESEARCH INSTITUTE
In Korea, radiation protection calibration program has been legally set under boththe Weights and Measures Act for the enforcement of the national standards ofradiation measurement and the Atomic Energy Act for the regulation of the radiationprotection.
According to these legal basis, there has been established a national network ofradiation protection calibration, in which the KRISSCKorea Research Institute ofStandards and Sciences) serves as a primary laboratory while both the KAERKKoreaAtomic Energy Research Institute) and the NIH (National Institute of Health) serveas secondary laboratories to maintain a national traceability to radiation standards.The" NIH was established at first by the IAEA through a technical aid project andbelongs to the IAEA/WHO network. That is a reason for NIH to concentrate hiscalibration work on dosimeters or survey instruments used in medical fields as manySSDLs in the IAEA/WHO network do. On the contary, KAERI calibrates mainlyradiation protection instruments and performs researches on the personal dosimetryfor the purpose of radiation protection purpose in the nuclear industry in Korea. So,even if it is not a rule, most of radiation protection instruments used in Korea havebeen mainly calibrated according to the general classification of nuclear industry andmedical field.
Besides the primary and secondary labs., self-regulating calibration laboratoriesas a tertiary lab. perform limited calibrations under the control and authorization ofthe primary laboratory. But their calibration activities are usually limited to some oftheir own instruments.
This paper briefly introduces some notes on the calibration activities in Korea,focusing mainly on the activities perfomed in the KAERI.
1. Dissemination of TraceabilityMost of standards on radiation dose or radioactivity come from the national
primary standard and finally are disseminated to radiation measurement devicesthrough the subordinated labs, in the scheme of national traceability system.
The basic transfer quantities for photon and beta are the exposure(R) and the airabsorbed dose(Gy). Photon sources(X-ray and gamma) of the KAERI are calibratedby using air equvalent plastic walled chambers, Shonka-Wyckoff type chambers, thatwere previously calibrated at the KRISS or foreign primary standard laboratory.
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These chambers are placed at a known calibration point and the exposure rate ismeasured. Although exposure is a quantity that is no longer supported by theInternational Commission on Radiation Unit and Measurement(ICRU), this is still usedin the calibration of photon measurement devices in Korea. When an exposure rate isdetermined at a distance it is then possible to substitute an instrument or dosimeterat the same point, and a known value of air kerma is delivered. Air kerma to doseequivalent conversion factors are then applied to compute the delivered doseequivalent to the dosimeters irradiated on the appropriate phantom.
Beta sources are not calibrated yet by tissue-equivalent plastic extrapolatonchamber and are used to irradiate dosimeters at fixed calibration point only under thecertification of PTB(primary lab. in Germany). It will be possible to calibrate somebeta sources using an extrapolation chamber for the measurement of ICRU tissuedose with the cooperation of the KRISS sooner or later.
Neutron source is calibrated at the NIST in terms of its total emission rate. Thecharacteristics such as neutron scattering etc. at the KAERI facility are beingstudied to calibrate several types of neutron measurements devices.
2. Facility and Instruments of KAERIThe radiation measurement and calibration calibration laboratory, which has been
reconstructed after moving to new building in the end of 1992, consists of fourirradiation rooms; gamma, X-ray, neutron, and low level gamma and beta irradiationroom. All is placed at underground level and so, environmental condition is properlymaintained by the independent air conditioning system of laboratory own to keep airtemperature and humidity constant.
Two kinds of gamma irradiators(OB-2 and OB-40, Buchler, Germany) are usedin gamma calibration and each has a Co~60 and three Cs-137 sources, respectively.
In case of X-rays, two generators are used to produce low and medium energybeam. In addition to these, another 320 kVp X-ray generator(MG-325, Phlips) will beinstalled in this year to replace old MG-320 system and then the old one be modifiedto produce flourescence X-ray beams.
Neutron irradiator(PTS-200, Atlan-tech., U.S.A.) can make two kinds of neutronspectra, a bare and a D2O moderated(30 cm Dia.) Cf-252 source. The Cf-252source(SR-CF-1273) was made by the ORNUOak Ridge National Laboratory) andcalibrated at the NIST, with the emission rate of 2.03 x 109 n/sec on 12 Feb., 1992.Beacuse of the limitation of geometrical configuration of irradiator and room capacity,special consideration on the correction for neutron scattering is necessary to producereference neutron field and so a series of experiment is currently going on.
Beta irradiation system is the BSS-1 (Buchler, Germany) and absorbed dose ofeach beta source at the calibration point was certified by the PTB, Germany.
Table 1. summarize the radiation fields provided at KAERI. Instruments shownin Table 2. are used in the measurement of each radiation source and regularly
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calibrated at the primary standard laboratory once a year.
3. Calibration of survey instruments and personal dosimetersAs mentioned above, exposure rate is still used in calibration of survey
instruments as a transfer quantity and most of these are irradiated in the field ofhigh energy gamma, such as Cs-137 and Co-60. If necessary, X-ray beams couldbe used to determine the energy response of surveymeters, but it would be not often.It will be necessary that the new operational quantity of the ICRU-39 be applied tocalibration of the area monitoring instruments to make monitoring results of radiationworkplace more realistic, compared with that of personal monitoring.
In 1992, the personal dosimetry performance evaluation and test program wasnewly acted by the ministrial ordinance in Korea. It was a personal dosimetryaccreditation program like as the NVLAP in U.S.A. and its implementation wasplanned in 1994. It is sure that KAERI be assigned as a performance testinglaboratory for the personal dosimetry accreditation program, in the consideration ofthe facilities and experience enough to carry out it.
In that program, test irradiation of personal dosimeters would be performedaccording to American National Standard Institute(ANSI) standard N13.ll andtherefore, KAERI have prepared the similar radiation fields as that, as well as somefields of International Standard Organization(ISO), especially for X-ray beams. Someprivate personal dosimetry processors already began to use the test irradiationservices of KAERI for the calibration of their personal dosimetry systems.
In order to keep abreast with the international advancement of personaldosimetry, KAERI have been also actively participated in the personal dosimetryintercomparision study since 1990 as follows;
.IAEA/RCA Intercomparision(JAERI, Phase I and II, 1990 ~ 1992)
.Asia/Pacific Regional Intercomparision (ARL, 1991)
.PDIS 16, 17, 18(ORNL, 1991 ~ 1993)
Nowadays, there are many kinds of foregin imported survey instruments andpersonal dosimeters being used in Korea to measure the radiation quantity, and theold and new unit are used together in the field of area monitoring. Therefore, thenecessity of developing calibration technique and adopting the ICRU operationalquantity especially for survey instruments are growing more, and more.
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Table 1. Radiation Fields Provided at KAERI
Radiation
Gamma.Cs-137.Co-60.
X-ray.low energy.mediumenergy
Beta.Pm-147.Tl-204
.Sr/Y-90.Sr/y-90
Neutron.Cf-252
-Bare-D2O
moderated
.Am-Be
Radioactivity
3.7, 185, 3700GBq3.7 GBq
75 kVp -10 mA320 kVp - 10 mA
518 MBq18.5 MBq74 MBq1.85 MBq
19 MBq(960mg)
111 MBq
Energy
662 keV1250 keV
10 ~ 48 keV37 ~ 167 keV
225 keV763 keV2820 keV2820 keV
2.02 MeV0.53 MeV
4.40 MeV
Dose range
0.3 ~ 310 mSv/h1.3 mSv/h
0.3 ~ 3000 mSv/h0.5 ~ 3000 mSv/h
3 mSv/h1 mSv/h
10.2 mSv/h282 mSv/h
19.3 mSv/h4.66 mSv/h
0.07 mSv/h
Remarks
OB-40, BuchlerOB-2, Buchler
HF-75, PantakMG-320, Philips
at 1.5 m
BSS-1, Buchlerat 20 cmat 30 cmat 30 cmat 30 cm
PTS-200,Atlan-Tech. '
at 1.0 mat 1.0 m
not used inirradiator
Table 2. KAERI owned secondary standard calibration instruments
Electrometer
lonex Dosemaster(IONEX 2590B)
Keithley 35617Programmable Dosimeter
Keithley 642 Electrometer
Chamber
0.3 cc NE 2536/335 cc NE 2530/1600 cc NE2575
3.6 cc, Shonka-Wyckoff A330 cc, " A4100 cc, " A5
0.55 cc, Spokas, A2, T2, M2
Extrapolation ChamberPTVV 30-360
Energy range
36 keV ~ 40 keV30 keV ~ Co-6030 keV ~ Co-60
30 keV ~ Co-60
BetaSoft X-ray(5 ~ 15 keV)
Uncertainty
<±3%
<±3%
notdetermined
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JAERI-Conf 95-014
8. CALIBRATION OF DOSIMETERS AND SURVEY INSTRUMENTS FOR PHOTONSAT THE MALAYSIAN SECONDARY STANDARD DOSIMETRY LABORATORY
1. Introduction
Calibration of an instrument is the determination of a calibration factor which is the quotient of thequantity to be measured and the instrument reading, obtained under well defined measuring conditions.This involves the comparison of a given instrument with a reference instrument or its irradiation in a fieldwhose properties are either defined through use of a standard source or one which has been fullyexplored with a reference instrument. Calibration of survey meter is to;
• ensure that the Instrument is working properly and functions reliably in the doserate rangespecified and within the whole energy range employed.
• estimate errors in the instrument readings or if possible, to improve overall accuracyof the measurement.
• establish a national network of traceability in radiation measurements.
The service is also used to establish an inventory of all survey meters available in the country. Theinformations are useful to assist user concerning the best available instruments for their requirementsand finally to inform them of any important design features of the equipment.
2. Status of Radiation Protection
In Malaysia, radiation protection is a legal requirement. The requirements are explained in theRadiation Protection (Basic Safety standards) Regulations 1988 which operates under the Atomic EnergyLicencing Act, 1984. For calibration of radiation measuring instruments, the following regulations arerelevant;
No. 50. (1) "The licensee shall ensure that all protective measures and devices meet therequirements of these regulations and that all instruments are in good workingcondition." and
No. 50. (2) 'The licensee shall ensure that inspection and testing of protective measures anddevices and measuring instruments are carried out periodically by a personacceptable to the appropriate authority."
Similarly, requirements for area and personnel monitoring are mentioned in greater detail in regulationno. 25 and 26 respectively. These regulations are enforced by the Atomic Energy Licensing Board(AELB), Ministry of Science, Technology and the Environment. The Malaysian Institute for NuclearTechnology Research (MINT) under the same ministry, through the Secondary Standard DosimetryLaboratory (SSDL) is given the task to provide the radiation protection services throughout the country.The SSDL is recognised as a national calibration centre and has been fully operational since 1985. Thelaboratory is also responsible to maintain national standard in ionising radiation measurements so as toprovide other dosimetry services including area and personal monitoring as well as high dose dosimetry.
3. Calibration Facilities
3.1. General Facilities
The calibration facilities, in general are similar to that of any member of the IAEA/WHO network ofSSDL's. The SSDL Malaysia became a member o1 the network since 1979 and was established, partlywith the aid of technical assistant from the IAEA under project no. MAL/003. The project was completedin 1987.
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JAERI-Conf 95-014
Calibration works are carried out in three irradiation rooms known as bunker 1, 2 and 3. Bunker 1 isequipped with a Philips constant potential X-ray machine model MG 320D and two metal ceramic tubesmodel MCN 321 and model MCN 161 with inherent filtration of 2.2 mmBe and 1.0 mmBe respectively.The first tube can be operated up to 320 kVp and the second, up to 160 kVp. Bunker 2 is equipped witha ^Co 3.5 kCi teletherapy unit model Aldorado 8, gamma irradiator model OB 85 and beta sourcesmodel BSS 1. Bunker 3 is equipped with low activity gamma sources for protection and environmentallevels model OB 2, model OB 6, model OB 34, model UPDK 1 and model UPDK 2. Filtered X-referenceradiations are prepared based on recommendations of the International Standard Organisation (ISO) asin its International Standard ISO 4037 (ISO, 1979), ISO 4037-1979/Addendum 1 (ISO, 1983) and ISO4037-1979/ Amendment 1-1983(E) (ISO, 1983). The specifications of filtered X-reference radiations andgamma sources are shown in table 1 and table 2 respectively.
Two kinds of phantom are available for the 'on phantom1 measurement conditions. One is a standardIAEA water phantom, size 30x30x30 cm.3 and the other is an anthropomorphic Alderson Randophantom. The former is normaly used to determine absorbed dose in water for radiotherapy calibrationwhile the later is normally used to estimate the entrance and organ dose to human body undergoingradiological examinations.The Rando phantom is devided into 35 slices, each of 2.5 cm. thick. Insidethe slices are large number of cylindrical holes which allow the positioning of TLD chips. Unused holescan be filled with tissue equivalent plugs.
3.2. Measuring Standards for Protection and Environmental Levels
A national standard dosimeter for the standardization of radiation measurements at protection andenvironmental levels is the Digital Current Integrator model NP2100 with three ionisation chambersmodel ND1001, model ND1000 and model LS10. The standard dosimeter is traceable to the AustrianResearch Centre (ARC), Austria with an accuracy of within ± 2%. A latest version of similar product,model DCI8500 with ionisation chamber model LS01 was purchased recently from the Physikalisch-Technische Werkstatten (PTW), Freiburg and will be delivered soon after calibration at the ARC. Forroutine applications, the following reference class instruments are used;
• Farmer dosimeter model NE2570A with ionisation chambers model NE2575 and modelNE2530, traceable to the National Radiological Protection Board and to the NuclearEnterprise Ltd., United Kingdom with an accuracy of within ± 5 %.
• Dosimentor PTW-IQ4 model 764 with ionisation chambers model M32002 and modelM23361, calibrated with reference to the national standard and accuracy is within * 5 %.
4. Calibration Experiences
4.1. Method of Calibration
For X-rays, survey meter is calibrated in air by using simultaneous irradiation technique. The ISO filteredX-reference radiation qualities namely narrow spectrum series are normally used for calibration.However, the wide spectrum series and low doserate series are also used for high or low doseratemeasurements respectively. Gamma survey meter is also calibrated in air by using a standard beamand the reading is compared with a pre-determined exposure (rate). Corrections for source decay andinverse square law are applied, if necessary. The standardization of a gamma source involved themeasurements of outputs at various distances and is performed at least once a year.
The exactness is verified at half scale deflection on every scales by using 137Cs sources. The next testis called scale linearity test and is performed to ensure that the instrument responses linearly withvarious doserates in its useful range. The test involves the measurement of exactness at three points i.e.
30%, 50% and 70% of full scale deflection on every scales. The scale of the instrument is so calledlinear if the exactness does not vary by more than the value specified by the manufacturer or within ±20%, whichever is lower.
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The response of an instrument depends on the energy of the radiation. The energy responsedependence test is done to verify the variation of instrument response to X or gamma radiation ofdifferent energies ranging from 29 keV to 1250 keV including to 137Cs and ^Co. This test is particularlyimportant for instruments used to monitor various radiation qualities.
The calibration certificate and calibration sticker which have the status of a legal document will only beissued to instrument that is confirmed to function satisfactorily. The certificate and sticker indicatevalidity period and the instrument to which it applies. The certificate is valid for one year starting from thedate when calibration was completed. It provides calibration factors to be multiplied to the instrumentreadings to convert them to the actual quantity being measured.
4.2. ICRU's New Operational Quantities
Since The International Commission on Radiation Units and Measurements (ICRU) published ICRUReport 33 (ICRU, 1980) entitled "Radiation Quantities and Units", a numbe.T of discussions have takenplace, especially in the field of quantities for use in radiation protection measurements. The results ofthese discussions have been published in ICRU Reports 39 (ICRU, 1985) and 43 (ICRU, 1988), whftreoperational quantities have been introduced for the specification of the dose equivalents forenvironmental and individual monitoring in the case of external radiation sources. The InternationalCommission on Radiological Protection (ICRP), in its 1990 recom-mendations (iCRP, 1991), hasintroduced radiation weighting factor, and two consequential new quantities, equivalent organ doses andeffective dose. The radiation weighting factors, applicable to the mean absorbed dose in a tissue ororgan, depend only on the type and energy of the radiation incident on the body in the case of externalirradiation. These new developements in this field led the ICRU through its committee on FundamentalQuantities and Units to revise ICRU Report 33. The Committee has concentrated their effort firsttowards the revision of part B of the report. As a result, a draft report has been published under thename of Committee Members in ICRU News, December 1991. Measurement of dose equivalent fromphotons and electrons and calibration procedures to be used for these measurements under simplifiedconditions on an appropriate phantom are explained in ICRU Report 47 (ICRU, 1992). However, due toproblems in understanding these new quantities especially to end users of the measuring instruments,these recommendations have not been adopted yet. The use of the ICRU operational quantities forcalibration of dosimeters and survey instruments will be introduced in the future.
4.3. Radiation Protection Services
For the first ten months of 1994, a total of 692 dosimeters and survey instruments belonging to 227private agencies were received for calibration. 50% of our clients are 50% dealing with gauging andelectronics business, 19.5% with industrial radiography, 7.6% with research activities and 5.5% withmedical practice. The remaining 17.4% are involved with amang industries, industrial radiationprocessing and suppliers. These different activities led to great variaties of radiation measuringinstruments being used in the country i.e. about 100 different products from 35 manufacturers.
Presently about 6,250 radiation workers are subject to individual monitoring of external radiation inMalaysia. The dosimeter can be obtained from one of two officially authorised personnel monitoringservices i.e. either MINT or the Department of Engineering Services, Ministry of Health. The former isresponsible for monitoring radiation workers from nonmedical fields while the later, for those frommedical fields. These two services are in the process of merging together to become a centralizeddosimetry service operated solely by MINT. At present, about 60% of radiation workers in Malaysia aremonitored by MINT by means of film dosimeter. PTW-Freiburg film badge type 8621 together with Agfa-Gevaert personnel monitoring film is issued by MINT to monitor the whole body exposure to beta, X andgamma radiations. Harshaw thermoluminescence dosimeter (TLD) type TLD-100 is used to monitor
partial body exposure with special emphasis on finger ring dosimeter. TLD's are also used for areamonitoring. Performance of calibration, personal and area monitoring services rendered by MINT since1985 to 1994 is shown in table 3.
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JAERI-Conf 95-014
Table 1: Calibration conditions of filtered X-reference radiations based on recommendations of theInternational Standard ISO 4037. The inherent filtration is 2.2 mmBe and FDD is 1 meter.
ISO Series
NARROWSPECTRUM
WIDESPECTRUM
LOWDOSERATE
EffectiveEnergy(keV)
304683
121175230
425479
108145188
27455884
110150192225
ConstantPotential(kVp)
4060
100150200250
6080
110150200250
355570
100125170210240
AdditionalFiltration (mm)Al Cu Sn Pb
4 0.2 - -4 0.62 - -4 5.04 - -4 - 2.5 -4 2.0 3.0 1.04 - 2.0 3.0
4 0.3 - -4 0.5 - -4 2.0 - -4 - 1.0 -4 - 2.0 -4 - 4.0 -
4 0.25 - -4 1.2 - -4 2.5 - -4 0.5 2.0 -4 1.0 4.0 -4 1.0 4.0 1.04 0.5 3.0 3.04 0.5 3.0 5.0
First HVL (mmCu)
Quoted Measured
0.09 0.0740.24 0.231.16 1.112.40 2.463.90 4.225.20 5.50
0.18 0.170.35 0.360.94 0.981.86 1.943.11 3.314.30 4.53
2.38* 1.68*0.25 0.210.48 0.431.28 1.132.14 2.003.67 3.454.91 4.675.89 5.40
H.C
0.950.970.970.980.990.99
0.970.930.920.930.980.99
0.950.980.960.960.991.001.000.97
* The unit is in mm Al
Table 2: Specifications of gamma sources of 241Am, 137Cs and Co at MINT.
Model
OB 34OB 34OB 85OB 85OB 85OB 85OB 2UPDK1OB 6UPDK2ALDORADO
Nuclide
137Cs60Co137Cs^Co22sRa241Am"'Co137Cs137Cs241Am'"Co
Activity Range
7.4-7400 MBq3.7-370 MBq740 GBq37GBq37 MBq11.1 GBq3.7 GBq11.5 GBq74 GBq11.1 GBq129.5 TBq
No. ofSource
43111111111
Covered doserate in mSv/hr
0.0002-2.480.0002-0.240.028-250.60.073-34.60.0005-0.0880.003-0.530.01-0.670.024-4.470.147-22.070.0059-0.14280-19310
SDD(m)
0.5-2.00.5-2.00.5-5.00.5-5.00.3-4.00.3-4.00.75-6.00.5-6.30.5-6.00.4-2.00.85-7.0
Field Size
An irrad.Ait irrad.25/50 cm.025/50 cm.010/40 cm.025/50 cm.014 cm.026 cm.026 cm.02n irrad.25-625 cm2
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JAERI-Conf 95-014
Table 3: Performance of calibration, personal and area monitoring services rendered by MINT since1985 to 1994.
Year
198519861987198819891990199119921993
1994**
CalibrationEquip.
121158352372493458597746 •713692
Cert.
93130265307392398509633616610
ServiceAgency
254286
120140147168193215227
PersonalFilm
20161157024000291003450035549366383873943308
MonitoringAgency
1284
126158190198227240259
TLD*
260235049509500
1072010330805496548901
_
(Equip. = equipments , Cert. = certificates)For personal and environmental monitoring
* Up to the month of October.
5. Conclusion
Radiation protection infrastructures are well established in Malaysia. The infrastructures include lawsand regulations regarding the use of ionising radiations, regulatory body to enforce the regulations, theradiation protection services and radiation protection training capability. The AELB is the regulatory bodyresponsible for licensing and enforcement of the law and regulation while MINT through its SSDL is toprovide radiation protection services throughout the country. The laboratory facilitates the properradiation calibration and verification of the instruments used for the measurement of radiation ensuringthe safe use of nuclear technology. The rapid growth in the application of nuclear technology is obviouslyto be welcomed but there must be someway of ensuring that the safety aspects really meet the requiredstandards.
- 3 9 -
JAERI-Conf 95-014
9. Calibration of radiation protection instrumentsof the Mongolia
At present, in our country more than 400 dosimeters of 10 types areused in various branches of the Health, Defence , Geology organizationsand research laboratories of radiation control and of University. For instance,10 dosimeters has been used in Health organizations, 6 - in Scientificresearch institutes, more than 320 - in branches of Defence , 12 - in Geologyand 8 - in laboratory of University and in radiation control laboratories.
However, the country hasn't the united laboratory for calibration ofradiation protection instruments. Only in the sphere of defence hasportable calibration laboratory for military and civil defence dosimeters.This laboratory is carry out calibration for instruments which has measuringrange 0.05 mR/h-200 R/h and is calibrate about 200-300 dosimetersper year. Now is planned to create the calibration laboratory for radiationprotection equipments and with this purpose is constructing new building.This laboratory will be similar to Russian calibration laboratory of radiationprotection equipments in the eighties (1980). According to economiccondition of the country some constraction work is delaying. But we hopeit can be solve next year.
- 4 0 -
JAERI-Conf 95-014
Dosimeters using in Radiation Protection1n Mo n go!la•
i11 4
'"Il-
3
i4
5
6
i
i
ii
7
8
9
{ l
M o d e l s
V l c t o r- e e n -47 0 A
Victoreen-47 1
VA-J-15A
Clinical'. 1 0 s 1 - r 2 7 0 1 2
FH-40F
PDR-102
103
PDM-101102, 152103
DRGZ-0 2
DP-5A
0 DP-63A
ProducedCountry
USA
USA
GDR
i5 DR
Germany
Japan
J a p a n
Russ lan
Russ lan
Russ lan
O.u -1 y
C
2
2
l set
4
C
u
221
5
150
170
Measurement ranges I
0, l-l 000 R/n, mR/h, rnK
0, 02-300 R/h, mR/h, mR
0, 02-300 R/h, mR/h, mR Ij
j
Different ranges
3rnSv/h-999mSv/h
i
00-1, 999 & 2, 00-19, 99rnSv/n j
0, 00-19, 99 & 2 0, 0-1999mSv/Ji I
0, 01-99, 99 pSv1-999 JASv0, 01-9 9, 9 9 rnSv
0, 1- 100 yiR/h
0, 1-1, 5 R/h, , 5-50 R/h
0,05 mR/h-200 R/h
R e m a r k ; i t e m s 9 & 1 0 o n l y u s i n g i n c i v i l d e f e n c e
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JAERI-Conf 95-014
10. Radiation protection calibration facilities at theNational Radiation Laboratory, New Zealand
B.J. Foote
National Radiation Laboratory, Christchurch, New Zealand
1. Introduction
The National Radiation Laboratory (NRL), serving under the Ministry of Health, provides
radiation protection services to the whole of New Zealand. Consequently it performs many functions
that are otherwise spread amongst several organisations in larger countries. It is the national
regulatory body for radiation protection. It writes and enforces codes of safe practice, and conducts
safety inspections of all workplaces using radiation. It provides a personal monitoring service for
radiation workers. It also maintains the national primary standards for x-ray exposure and Co air
kerma. These standards arc transferred to hospitals through a calibration service. The purpose of this
report is to outline the primary standards facilities at NRL. and to discuss the calibration of
dosemetcrs using these facilities.
2. X-ray standards
A single Pantak x-ray generator drives two exposure ranges covering beams from 10 to 300 kV.
The tube voltage has been calibrated using spectroscopy. The plant is controlled by a computer which
constantly monitors and adjusts the tube current and voltage to maintain a stable output. The
computer also performs quality control sequences and complete instrument calibration sequences.
The two free air ionisation standard chambers are of conventional design [1]. The correction
factors for the standard beams have been derived from measurements, analytic calculations and the
literature [2-4]. They will shortly be re-cvaluated using Monte Carlo simulation and measured
spectra.
The medium energy range consists of a Comet metal-ceramic medium energy tube. The thin
window of the tube (5 mm beryllium equivalent) allows a range of beams from 15 to 300 kV. The
instrument holder is mounted on two orthogonal sets of rails. One rail allows a choice of source to
detector distance between 50 and 600 cm. The other rail allows horizontal motion perpendicular to
the beam, enabling the exposure of up to three different devices, including the low or medium energy
chamber.
The low energy range has been specially designed to provide the short source to detector distance
and high dose rate usually measured with small volume low energy x-ray chambers. The tube is made
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JAERI-Conf 95-014
by AEG-Telefunken, with inherent filtration of 1 mm beryllium equivalent, and produces x-rays from
10 to 160 kV. The shutter, filters, monitor chamber and collimators are of very compact design and
allow a minimum range of 20 cm. •
A standard set of beams (combinations of kilovoltage and filtration) has been chosen to match the
kilovoltage of any therapy beam in New Zealand and to allow matching of the HVL by interpolation.
However NRL currently relies on hospital estimates of HVL. Often the hospital will use a graphite
cavity chamber for this purpose, giving a discrepancy of up to 25% in the HVL for particularly soft
beams.
The overall uncertainty of a dosemeter calibration directly against the x-ray standard is estimated
to be 0.3%.
3. Co standards
The Co standard is maintained with two graphite cavity chambers, one cylindrical with hemi-
spherical ends and a cavity volume of 6.5 cm , the other spherical with a volume of 10 cm . The
response of the chamber is converted to give £ a i r , the air kerma free in air, as required by the IAEA
high energy protocol [5]. The wall correction factors for this were first calculated using analytical
methods [6] and more recently using a Monte Carlo simulation [7]. This work is currently being
repeated using the codes EGS4 and ITS.
The overall uncertainty of a dosemeter calibration directly against the Co standard is estimated
to be 0.7%. This mainly arises from uncertainty in: stopping power ratio; mass energy absorption
ratio; determination of cavity volume.
4. NRL-ARL intercomparison
In 1989 an intercomparison was carried out between the primary standards for Co and four
medium energy x-ray beams at NRL and the Australian Radiation Laboratory. An NRL
NE2560/2561 dosemeter was calibrated at both centres and the result corrected according to the
response measured using a Sr check source. Over the five beams the agreement was within 0.4%.
5. Calibration of hospital doscmetcrs
Twice a year the NRL secondary standard dosemeters (Keithley 35617EBS electrometer; NE2571
0.6 cm chamber; PTW M23342 thin window chamber) are calibrated in each appropriate standard
beams. A change of more than 0.3% would be taken as an instrument instability, and this would be
investigated. A similar situation occurs for the Co beam.
- 4 3 -
JAERI-Conf 95-014
The NRL secondary standard is taken to each of the six radiation therapy centres once a year to
calibrate the dosemeters. Each centre has a dosemeter that serves as the local standard, but it is
normal to calibrate each instrument that is regularly used for absolute dose measurements as well.
For high energy dosimetry the standard for Afair is transferred to the hospital chamber by
simultaneous comparison at 5 cm depth in a perspex (PMMA) phantom, in a Co or 4 or 6 MV
photon beam. (The first is preferred but several hospitals have replaced their cobalt machines with 4
or 6 MV linear accelerators.) When the wall material of the hospital chamber differs from that of the
secondary standard, this is corrected for, using the formalism of the IAEA protocol.
For kilovoltage x-rays, the NRL secondary standard and the hospital dosemeter are compared in
each of the hospital beams. A large applicator is used to help give a uniform field and minimise the
scatter. The 0.6 cm chambers are exposed simultaneously in air which adds no mere than 0.1% to
the overall calibration uncertainty. The thin window chambers are exposed individually in air, which
may add as much as 0.5% to the overall calibration uncertainty if the beam output is drifting.
The exposure calibration factor for the NRL secondary standard, at the exact quality of the
hospital beam (kilovoltage and HVL), is obtained by interpolation of the factors from standard beams
at NRL of the same kilovoltage and at least three HVL points surrounding the hospital HVL.
6. Personal monitoring service
Personal monitoring in New Zealand is performed with film dosemeters. Two types of holder are
currently in use. The first contains plastic, aluminium and copper filters and is suitable for low to
medium energy photons. The other, an NRPB design, contains plastic, dural (aluminium alloy) and
tin/lead filters, and is suitable for electrons and high energy photons. The film is type 2, and is
manufactured by Eastman-Kodak.
The film dosemeters were originally used to measure absorbed dose in air. On 1 March 1994,
this was changed to H?(d), the personal dose equivalent at depth d introduced by the 1CRU [8].
While the ICRU proposes that the quantity be measured at d = 0.07, 3 and 10 mm, only d = 10 mm is
implemented at NRL. This is because the limit most likely to be exceeded in New Zealand is that for
effective dose, and tfp(10) is the best estimator of this. The next most likely limit to be exceeded is
that for eye dose, as estimated by HpO), but this differs little from H (10) in practice. Workers are
therefore advised to wear film doscmeters on their trunk, or on the collar if protective aprons are
worn.
Quality control of film processing is performed as follows. Every six months, when a stock of
films is delivered, films are placed under a tin/lead filter and exposed to a Co beam for various
times. The resulting relation between film density and Co dose allows the estimation of D3 , the
apparent dose of a film, defined as the dose required in the above configuration to produce equivalent
- 4 4 -
JAERI-Conf 95-014
darkening. At the same time, several control films are exposed in an x-ray beam, for a variety of
exposures. A set of control films (one from each exposure) is processed at once, and results are
compared with the density versus apparent dose relation. Each time a batch of used films is
processed, another set of control films is processed, and the results are compared with the initial set.
The curve of density versus apparent dose is corrected accordingly.
Type testing of film dosemeters was performed as follows. Film dosemeters were placed on the
front face of a PMMA half-cube phantom at a distance of 2 m from the medium energy x-ray source.
The front face of the phantom was angled at 30° with respect to the beam, since this is a realistic
average orientation when being worn by a radiation worker [R]. The films were exposed to beams in
the ISO narrow series, and the corresponding Ki]r was determined using the medium energy free air
chamber. The relative response D I Kiir was determined for each section of the film, as a function
of energy. With this information initially collected, it is possible to estimate H (10) from a used film
dosemeter. By taking ratios of apparent dose from the used film, a characteristic energy may be
estimated. Then from the apparent dose in a given section, the air kerma free in air may be estimated.
The conversion to dose equivalent is then performed according to the literature [10,11].
The uncertainty in the estimation of personal dose equivalent is estimated as 50%. This is
satisfactory, since the average annual dose received by radiation workers in New Zealand is 1-2 mSv.
References
[I] H.H. Wyckoff and F.H. Attix, Handbook 64, Natl Bureau of Standards, Washington DC (1957).
[2] R.H. Chapman and A.C. McEwan, Rep. NRL 1985/5, Natl Radiation Lab., Christchurch
(1985).
[3] A.C. McEwan, Rep. NRL 1981/3, Natl Radiation Lab., Christchurch (198.1).
[4] A.C. McEwan, Rep. NRL 1981/2, Natl Radiation Lab., Christchurch (1981).
[5] International Atomic Energy Agency, Technical Reports Series No. 277, IAEA, Vienna (1987).
[6} A.C. McEwan, Phys. Med. Biol. 25 (1980) 39.
[7] A.C. McEwan and V.G. Smyth, Rep. NRL 1983/7, Natl Radiation Lab., Christchurch (1983).
[8] International Commission on Radiation Units and Measurements, ICRU Rep. 47, Bethesda,
MD (1992).
[9] N. Adams, M.J. Heard and P.D. Holt, Rep. AERE-R4669, Atomic Energy Research
Establishment, Harwell (1965).
[10] B. Grosswendt, Rad. Prot. Dosim. 40 (1992), 169.
[II] W. Will, Rad. Prot. Dosim. 37 (1991) 79.
- 4 5 -
JAERI-Conf 95-014
11. Radiation Protection Calibration Activities inPakistan
1. INTRODUCTION
Calibration of radiation protection instruments is carried out in
a Secondary Standard Dosimetry Laboratory (SSDL). This laboratory(SSDL)
was established in Health Physics Division of Pakistan Institute of
Nuclear Science and Technology(PINSTECH) in 1981 with the main objective
to improve the accuracy in various field of applied dosimetry. In the
beigining the SSDL rendered only therapy dose level calibration services
to all the radiotherapy institutes in the country. Later on, in view of
the requirements of accuracy in radiation' protection dosimetry the
calibration of radiation protection instruments was also started in SSDL
in October 1991. During the period of about three years 92 different
types of radiation survey instruments received from various institutes
in the country were calibrated. The radiation dosimetry group health
physics division extends personal monitoring service to all the
radiation workers in the country. Film badge dosimeter is used at
country level and personal monitoring of the institute radiation workers
is done using thermoluminescent dosimetrs(TLDs). Pocket dosimetrs are
used by the worker in situations where the immediate- knowledge of the
radiation dose received by the workers is required. The avarage number
of personal dosimeters(Film badge and TLDs) issued to the radiation
workers every month amounts to be 2700 and 50 respectively.
The radiation protection survey instruments are brought to SSDL
for calibration by a representative of the organisation with prior
intimation to SSDL. After calibration the same are collected back by a
representative of the organisation concerned. A calibration certificate
- 4 6 -
JAERI-Conf 95-014
duly signed, by Head SSDL and counter signed by the Head of the division
containing all the details of calibration is issued with every survey
instrument.
At present calibration service is provided free of charge . However, in
future, some charges will be imposed on this'service.
2. INSTRUMENTATION AND FACILITIES
2.1 Protection Level Secondary Standard Dosimetry System
The protection level secondary standard dosimetry system available
with the laborarory consists of digital current integrator model NP-2000
as a measuring assembly, a spherical ionization chamber type LS-01 and a
cylindrical reference check source(Am-241, 14 mCi-1986) type SB-143. The
calibration of secondary standard ionisation chamber is traceable to
secondary standard of International Atomic Energy Agency(IAEA) Dosimetry
Laboratory and the credibility of the calibration factors of the
secondary standard ionisation chamber are further confirmed by comparing
it with IAEA travelling secondary standard from time to time. Farmer
dosimetry system consisting of measuring assembly, ionisation chambe4r
and a reference check source is also available as a back up system for
protection level dosimetry calibration.
Presently a Keithley Programmeable Electrometer connected with IBM
personal computer through a IEEE-488 interface and a spherical
ionisation chamber type LS-01 is being used for protection level
secondary standard dosimetry measurements. A computer programme in Basic
language has been developed which makes the routine protection level
dosimetry measurements procedure quite simple. The programme also
provides the possiblity of including more recent data required for
exposure computation and minimizes the chances of making errors in the
- 4 7 -
JAERI-Conf 95-014
final calculation of exposure or absorbed dose.
2.2 Irradiation Facilities
The gamma ray irradiation facilities consist of calibrators OB
34/1 and OB 85/1. The calibrator OB 34/1 is a panoramic irradiator and
contains seven sources of Cesium-137 and Cobalt-60 with different source
activities. The irradiation of personal dosimeters such as film badges,
TLDs are performed on this irradiator. The calibrator OB 85/1 contains
four sources i.e. Cs-137, Co-60, Ra-226 and Am-241. This calibrator
provides a collimated beam and the irradiation process is controlled by
a seprately available control desk.
The X-ray irradiation facility consists of a Philips MG-320 X-ray
machine, The generating potential of X-ray machine ranges from 32 kV to
320 kV. The tube current ranges from 3 mA to 30 mA. This X-ray machine
is also being used for therapy dose level calibration purposes.
2.3 Accessories
In addition to secondary standard dosimetry system and field
dosimetry system, some minor equipment such as precision aneriod
barometers are available for ambient pressure measurement. Ambient
temperature in bunkers is measured using mercury thermometer of 0.1 °C
minimum gratuation. The relative humidity is recorded using hygrometer.
For distance measurement a number of graduated steel rulers have
been installed at various places e.g. measuring carts, the side walls of
radiation bunkers etc. Telescopes, laser beams are also available to
help alignment of the detector in the central axis of the beam. The
small pieces of equipment include pocket alarm dosimeter with battery
charging unit, Victoreen mini-monitors, remote control filter changing
system and half value layer measurement device etc.
A Harshaw thermoluminescent dosimetry system consisting of model
- 4 8 -
JAERI-Conf 95-014
2000 B Picoammeter and model 2000 C TL Detector is also available for
postal dose intercomparison measurements.
3. CALIBRATION OF RADIATION SURVEY INSTRUMENTS
The calibration of survey instruments is carried out in SSDL by
irradiating them on known X and ganma radiation fields. The radiation
qualities offered for protection dose level calibration are presented in
table 1
Table i. Protection dose level calibration qualities
GeneratingPotential
(kV)
100
150
200
250
Cobalt-60
Cesium-137
5
2
1
1
.3
.1
.3
.3
AddedFilter(mm)
Cu
Pb+3.0 Cu+1
Pb+5.0 Cu+1
Pb+3.6 Cu+1
.2
.2
.2
Al
Al
Al
Half valueLayer
(mm)
1.14
2.45
4.05
5.20
Cu
Cu
Cu
Cu
EffectiveEnergy(k^V)
85.7
130.4
173.2
217.3
In routine, the calibration of the survey instrument is carried
out on Cobalt-60 and Cesium-137 radiation qualities. The calibration on
X-ray qualities is optional and is provided according to the requirement
of the user. About twenty different types of survey instruments are
presently in use in various establishments of the country. The number of
survey instruments calibrated yearly is shown in Fig. 1.
4. PROBLEMS AND EXPERIENCES OF CALIBRATION
Since October 1991, the calibration of protection level survey
instruments are being carried out in SSDL. On the basis of almost three
- 4 9 -
JAERI-Conf 95-014
years experience of running protection level calibration laboratory, it
is quite common that the users bring the survey instruments to SSDL in
faulty condition. Sometime it may be only due to batteries being
unserviceable. Minor repair such as unserviceable batteries etc. is done
at SSDL, however, it is not the responsiblity of the SSDL-" to repair the
surveymeter. SSDL,s would .need to be guided by international experts
keeping in view of the problems and quantum of work involved in the
repair of electronic equipment.
The overload test of the survey instrument is very important.
Every surveymeter must qualify this test at the time of calibration. The
procedure for the overload test is explained in the calibration
certificate.
The positioning of the detector in the central axis of the beam is
also very essential for the accurate calibration of surveymeter. The
effective center of the detector, particularly large volume surveymeter
should be marked on the detector. The reference check source should also
be available for a radiation survey instrument.
5.ICRD OPERATIONAL QOANTITES
In the field of plane parallel photon beam, the radiation doses at
depth 1 cm, 3 mm and 70 um from the spherical surface are standardized.
However, at present these monitoring quantities are not being evaluated
seperately. The significance of these operational quantities in
radiation protection cannot be overemphasised as regard the status of
developement of measuring instruments and the technique of calibration
are concerned. However, for routine practical radiation protection
dosimetry purposes where, the survey instruments of the order of an
accuracy +- 100 % are also used and the handling of these surveymeters
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JAERI-Conf 95-014
are also very crude, the concept of measuring practically the effective
dose equivalent HE does not appear to be suitable.
- 5 1 -
JAERI-Conf 95-014
c
E
CO
8CO
o
o
15O
L L
td
-O (D
- 5 2 -
JAERI-Conf 95-014
12. CALIBRATION OF DOSEMETERS ANDSURVEY INSTRUMENTS FOR PHOTON
by: Arlean L. Alamares and Estrella S. Caseria
I. Introduction:
The protection of radiation workers from the hazards ofionizing radiation has always been a primary concern of thePhilippine Nuclear Research Institute (PNRI), the country'sregulatory agency. The PNRI through its Radiation ProtectionUnit of the Nuclear Regulations Licensing and Safeguard Divisionprovides calibration services of nuclear instruments used byradiation workers from various institutions as part of itsradiation protection program.
Periodic calibration and standardization of radiation andprotection survey instruments are done to insure correct/validradiation readings. It is also a regulatory requirement forradiation workers to use only operable and pre-calibrated surveyinstruments in their work with radioactive materials.
II. The Calibration Facility
The PNRI maintains and operates a Secondary StandardDosimetry Laboratory (SSDL) which is available to provideperiodic calibration and standardization of radiation monitoringand protection survey instruments used by radiation workers inthe country. The SSDL also provides radiological hazards andperformance evaluation surveys of radiotherapy facilities,nuclear medicine centers, RI Laboratories and similar facilities.
The laboratory uses a Nuclear Enterprises IONEX 23 00, withNE 2303 30 cc ionization chamber as a standard measuringequipment for protection level photon dose, and NE 2560 NPLSecondary Therapy Level X-Ray Exposure Meter with NE 2561ionization chamber for therapy level.
For the calibration of survey instruments, standard sourcesof Cs-137 and Co-60 are used.
III. Calibration Procedure
A. For Survey Meters
The laboratory uses a fixed source-to-detector distancevariable-dose rate method. Upon receipt of survey meters,operational checks such as battery check, radiation response
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JAERI-Conf 95-014
and zero check are done.
In instruments with theoretical dose rate values of 400,200, 100, 80, 60, 40, 20, 10, 8, 6 mR/hr, the exposure distanceis computed using the inverse square law:
M l 2 = I2 d2 2
The survey meter is then exposed at computed distances andactual exposure dose rate readings are recorded. From thereadings taken, the Calibration Factor (C.F.) is computed.Acceptable limit ranges from 0.8 to 1.2. Survey instruments withC.F. not.within the acceptable limits are sent to the ElectronicUnits for further evaluation and repair.
C.F. = Theoretical_ReadinqObserved Value
The calibration frequency for survey meters is on anannually or quarterly (Once in three months) basis depending uponthe user's regulatory requirements.
B. For Pocket Dosimeters
Using the appropriate charging device, the dosimeter ischarged to zero. At a fixed distance from the standard source,the dosimeter is exposed at varying exposure times (15, 30minutes) . The dosimeter is arranged in such a way that thelongitudinal axis is perpendicular with the source axis.
The acceptable limit is from 0.70 to 1.30.
The calibration frequency for pocket dosimeters is on anannually or semi-annually basis also depending upon the user'sregulatory requirements.
IV. Clients Served
Calibration Services of PNRI caters to various institutionsin the country classified into medical (hospitals and individualphysicians), industrial, research, and commercial. Instrumentscalibrated includes survey meters and pocket dosimeters.Manufacturing brands of such intruments are as follows: forsurvey meters - Victoreen, Dosimeter, NDS Product, Anders,Eberline, Wallac, Nuclear Chicago and Nuclear Enterprise, forpocket dosimeter- Victoreen, Dosimeter, and PHY.
A summary of PNRI licencees and intruments calibrated areshown in Table 1 and Table 2 below
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JAERI-Conf 95-014
Table 1 Number of PNRI Licensees as of October 1994
Classification
Commercial
Hospital/Medical Facilities
Industrial Radiograpy
Medical Specialist(IndividualPhysicians)
Industry (Installed Gauges)
Research
Total
Number
36
62
28
10
109
27
272
Table 2 Number of Instruments Calibrated as of 1993
Instruments Calibrated 378
Institution Served 13 5
V. Personnel Dosimetry
The national film badge service of the PNRI, established in1963, provides monitoring services not only to PNRI employees andlicensees but also to medical facilities/users registered withthe (RHS) Radiation Health Service of the Department of Health.The standard AERE/RPS film badge is used by PNRI national filmservice for personnel monitoring. It is now envisioned by PNRIthat in the first quarter of 1995 the film badge monitoring willbe replaced over to TLD. Until such time, the film badge willremain as the single personnel dosemeter of choice in view ofeconomic reconsideration and relatively simple instrumentationused in dose estimation.
Exposure Dose Limits Of Radiation Workers
In accordance with the ALARA principle, the following levelsof exposure doses are promulgated and adapted by the PNRI.
1. Regulatory Limit - 4mSv/month
2. Reporting Limit - 2mSV/month
3. Operating Limit - lmSV/month
The regulatory limit of 4 mSv/month is based on ICRPrecommeendations computed from 50 .mSv/year at 2000 hours/year,rounded to the nearest whole number. The Reporting Limit of 2mSv/month is based on the PNRI Safety Committee recommendation of
• 5 5 -
JAERI-Conf 95-014
50% of the Regulatory Limit which, when exceeded, warrants anexamination of the situation to preclude unnecessary exposure inthe future. The Operating Limit of 1 mSv/month is based on theALARA priciple and shall be closely adhered to by radiationworkers in the course of normal work and is set at 25% of theRegulatory Limit by the PNRI Safety Committee.
Dose Distribution
The annual gamma dose equivalents distribution of a total of2145 workers monitored in 1993 are shown in Table 3.
: Dose Ranges
: < 2 mSv: < 5 mSv: < 10 mSv: < 20 mSv
< 40 mSv
Number of RadiationWorkers
20704020122
Percentage :% :
96.5 :: 1.87
0.98 :: 0.56: 0.09 :
VI. Application of ICRU Operational Quantities:
The radiation unit for personnel monitoring is now in Svunits while for area monitoring it is still in R and R/hr units.However PNRI is now in the process of implementing the new ICRUoperation unit for area monitoring of radiation fields.
VII. Problems Encountered/Recommendations
There is a need to upgrade the SSDL in terms of itsphysical structure, installation of additional equipment,standard sources, safety devices for the safety and convenienceof the personnel performing calibration and to efficiently caterto the increasing number of instruments submitted by clients.
The SSDL Staff needs further training and experience in thefield of dosimetry and maintenance and repair of instruments.
Financial support from the governmeent is urgently neededfor the upgrading of the building and in the acquisition ofadditional equipment and standard sources and for the maintenanceof the laboratory.
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JAERI-Conf 95-014
13. MJJ1A.TIG1N PROTECTION CALIBRATIONSecondary Standard Dosimetry Laboratery ofthe
Radiation Health Service, Department of HealthManila, Philippines
e a S. Otadoy-LingatongHealth Physicist IIRHS-SSDL
I. INTRODUCTION
The Philippines has been a member state of the Interna-tional Atomic Energy Agency/Werld Health Organization since1958. It has two (2) secondary standard dosirnetry laboratories,"both of v/hich are members of the IAEA./WHO Network of SSDLs.These twe(2) agencies, the Radiation Health Service ef theDepartment of Health and the Philippine Nuclear Research Ins-titute •of the Department of Science and Technolegy, signed amemorandum ©f agreement on December 15, 1989, delineatingresponsibilities t© avoid overlapping ef activities and tofurther ensure developmental work programs are complimentarywith one another.
The Radiation Health Service(formerly Radiation HealthOffice) was created on June 6, 1974 under P.D.48O, P.D. 1372and Executive Order No. 119 dated January 30, 1987. It ischarged with the responsibility of regulating the produc-tion, import, export and use of electrically-produced-radia-tion emitting apparatus, the energy of which does not reachthe thresheld required for the production of radioactivematerials, as well as non-ionieing radiation devices likemicrowave ovens, laser, etc.
II. THE RHS SECONDARY STANDARD DOSIMETRY LABORATORY
Under Presidential Decree No. 480, the Radiation HealthService is' charged with the responsibility to establish andmaintain a secondary standard dosimetry laboratory. The labo-ratory has two(2) rancor activities: calibration of therapylevel and protection level radiation detection and measuringinstruments and personnel monitoring service. Presently, itis staffed with three(3) health/medical physicists, tw© ofwhich are in charge of its electronics laboratory and one ofits personnel monitoring service. Due to limited manpower,calibration activities are carried out by all the SSDL staff.
The laboratory has two(2) standard measuring assemblieswhich are regularly calibrated in a primary laboratory oncein every three(3) years. The therapy level measuring assemblyconsist of a 0.325 cc Nuclear Enterprise NPI Secondary Stan-dard Model 2561 and the protection level measuring assembly
- 5 7 -
JAERI-Conf 95-014
consist of a 600 cc Nuclear Enterprise Ionex type Model 2575.The latest calibration was done at the Electrotechnical Labo-ratory, Japan on July 1994.
The laboratory calibrates survey raeters annually er as itmay deem necessaries following equipment performance check andrepair. The calibration facilities available are:
1. Philips Constant Potential X-ray machine: 53keV-i6ikeV
2. Theratron 80 Co-60 machine(therapy level)
3. Toshiba Go 60 machine(protection level)
4. Amersham Kedel 77302 Cs-137 calibrator
5. Dosimeter calibration source for pocket dosimeters
6. Assorted disc type gamma sealed sources for energycalibration of multichannel analyzer
III. CALIBRATION PROCEDURE
A.. SURVEY METER
In 1989, the laboratory's protection level standard wasmalfunctioning and requests for repair was never answered bythe mpnufacturer. The output of the radiation source was thendetermined using the formula
X/t = Ajx
d2
where X/t = exposure rateA = nominal activity of the radiation sourceG = specific gamma ray constant of the radionuclided = distance from radiation source to detector, 1 meter
The laboratory uses a. fixed-source-to-detector-distance-variable-attenuator method. The survey meters are subjectedto operational checks at the electronics laboratory beforecalibration which include leakp.ge check, zero /background checkand dessicant replacement.
The instrument is mounted in a source to detector distanceof oned) meter and exposed. The readings at different scalesare obtained and the experimental values of the exposure rateare computed as follows:
(X/t)£ = Instrument Reading x Kpt
where:(X/t)E = experimental value of exposure rate
Kpt = pressure-temperature correction factor
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The instrument calibration factor is computed using theformula
C.F. = (X/t)E(X/t)R
where C.F. = instrument calibration factor(X/t)E = experimental value of exposure rate
(X/t)R = reference value of exposure rate/output ofcalibration source
The acceptable limit is 0.8000 to 1.2000. Instruments withunacceptable calibration factors are sent to the .electronicslaboratory to further evaluation and repair. ICRU operatio-nal quantities are not yet applied in survey meter calibra-tion.
B. THERMOLUMIKiiSOEKCE DOSlriEIER
The RHS TLD badge uses LiF(Harshaw TLD 100) chips,measuring 3.175 mm x 3.175 mm x 0.889 mm and a holder madeof transparent colorless acrylic plastic measuring 4'.5 cm x3.0 cm x 0.4-5 cm with a.hole, 0.65 cm in diameter, 3.0 mmdeep, to accomodate oned) TLD element. No filtration isused except for the thin layers of paper and cellophane tapeused to protect the detector from dirt and contamination,moisture and white light. This personnel monitor is intendedto measure radiation doses from x and gamma photons witheffective energies ranging from 35 keV to 1.25 MeV for a two(2)-month monitoring period.
Calibration is done in-phpntom using Cs 137 source. Theirradiated chit>s are evaluated using Harshaw TLD System Model2000B"and 2000C The detector calibration factor is deter-mined individually using the formula
C.JF.= Dose equivalent delivered in mSv
TLD signal in nC
Conversion coefficients from Table 10 of ICRP Publication51 and from kxtzthe computation
IV. SPECIFIC PROBLEMS.
51 and from Appendix A of IGRU Report 47 are applied in;ion of calibration factors in units of mSv/nC
1. The constant potential x-ray machine cannot be fullyutilized yet due to lack of filters.
2. The protection standard electrometer is stillunrepaired due to lack of cooperation by the ins-trument manufacturer. Presently, the RHS-SSDL usesthe electrometer of the PNRI-SSDL during outputmeasurements.
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5. Manpower
4. The SSDL needs more training for its staff in thefields of dosimetry and instrument maintenance andrepsir.
5. Government support is needed for "building repairand acquisition of additional equipment for thempintenance of the laboratory's environmental con-ditions like humidity and temperature.
V. APPLICATION OF ICRU OPERATIONAL QUAM'iTlTiSS
The operational quantities are applied only in TLDcalibration. However, more technical information and skillsin this field is needed "by the laboratory staff for fullimplementation, that is in "both TLD and survey meter calibra-tion'.
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JAERI-Conf 95-014
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JAERI-Conf 95-014
14. SSDL FOR RADIATION PROTECTION OF THAILANDWarapon WANITSUKSOMBUT
Radiation Measurement Division
Office of Atomic Energy for Peace
THAILAND
Introduction
Thailand has adopted the Atomic Energy for peace since very
beginning of the age. The ATOMIC ENERGY FOR PEACE ACT, B.E. 2504
was enacted by the King in 1961. And Office of Atomic Energy for Peace was
established to serve as the secretariat of the Atomic Energy for Peace
Commission of Thailand. The responsibility of OAEP is taking charge and
control of the execution of this Act. The import to and export from the country of
radioactive materials has to file the request for license to OAEP. The owner
and user of radioactive materials are also licenced from OAEP. In the request
of possesion and utilization of these materials the licensee is asked to provide
safe handling and knowledge to their employee. It is therefore indicated in the
request form, the radiation measuring device and personnel radiation monitor.
As duty on controlling the safe utilization of radioactive material, the
office has asked IAEA for technical coorperation to establish SSDL for
calibrating radiation protection instrument!1]. The program started from 1981
and was completed in 1990. In the meantime, calibration is provided for
surveymeter and direct reading personnel dosimeter since 1986. The statistic
number of device receiving calibration per month is shown in Fig. 1. Personnel
monitoring of OAEP providing film and TLD are also calibrated from the SSDL.
The amount of personnel dosimeter calibration is 200 pieces anually.
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Categories of radiation utilization in Thailand
At beginning, radiation was known in medical use. Now the application
of radiation or nuclear technology is spread to all fields. Medical utilization still
may be the highest using field of radiation, but there are some other
challenged fields such as
1. Nucleonic gauging and control
1.1 level gauging
1.2 thickness gauging
1.3 moisture gauging
2. Nondestructive Testing
2.1 Radiography
2.2 Qualitative and quantitative analysis of trace element
3. Oil and coal logging
4. Radiation Technology
4.1 Sterilization of disposable medical device
4.2 Others
5. Research
Capability of SSDL
The laboratory is equiped with modestly sources and accessories. In
order to cover the necessary range of radiation and energy to calibrate the
radiation measuring device, the gamma, X-rays, beta and neutron source are
provided. List of radiation sources and their calibration range are shown in
Table 1. The standards used for calibration are transferred from primary
standard laboratories well known in the world. A set of ionization chamber
(Nuclear Enterprise IONEX TYPE 2500/3) has been calibrated from NPL of
United Kingdom, another set of ionization chamber (DCI 8500 of Austrian
Research Center) has been calibrated from the Primary Standard Laboratory
of Austria. The Beta Secondary Standard sources have been calibrated from
PTB of Germany. Furthermore the output of gamma and X-ray sources are
periodic rechecked by travelling standard ionization chamber of IAEA. The
results are found acceptable.
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Categories of radiation measuring device
The devices calibrated by SSDL can be grouped by their function into
three categories :
1. Surveymeter
2. Direct Reading pesonnel dosimeter
3. Area monitor
Almost all devices requested for calibration are surveymeters. The
instruments are used for initial evaluation of radiation safety. They must have
been calibrated at least once a year. Some company may request for
calibration twice a year or when they have been repaired. OAEP has
distributed cheap surveymeter made in the office name model 2105A, which
are now passed the calibration by SSDL. But the market is still open for the
imported one such as ALOKA, DOSIMETER, LUDLUM, VICTOREEN, etc.
From the records of calibration, there are 670 surveymeters from 834 devices
calibrated, and 468 out of 670 are the model 2105A. There may be some other
instrument have not been calibrated, because some user still do not know
SSDL.
The second group is active personnel dosimeter. It means pocket
ionization chamber, digital dosimerter, alarm, beeper, etc. The amout used and
that came to calibration are 160 pieces.
The last device mentioned is area monitor. Since there are not many
places required, there are only 3 sets calibrated.
Devices devote to each category of work
From the request for calibration, the devices can be group into their
utilized as shown in Fig. 2. The number of instruments used in radiography are
leading with 217 devices. Nucleonic gauging and control is the second with
171 devices. The third is research work with 126 devices. Oil and coal logging,
hospital, irradiator and other are following with 54,39, 27 and 32 devices
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respectively. Other 167 devices are not declared.
Expecting activity of SSDL in future
With increasing use of radioactive material, the work of radiation safety
must be improved. Together with the license authority, the SSDL must expand
its activity to assure the safe handling of radiation sources. The correct reading
of field instruments through calibration is one solution. The personnel
monitoring service must be controlled by other method. And the solution is to
organize in-land regularly intercomparison program^.
References
1. Radiation Protection Procedure, Safety Series No. 38. IAEA, Vienna, Austria,
1973
2. Basic Principles for Occupational Radiation Monitoring, Safety Series No.
84. IAEA, Vienna, Austria, 1987
3. Measurment of Dose Equivalents from External Photon and Electron
Radiations, ICRU Report 47. International Commission on Radiation Units and
Measurements, Maryland, U.S.A. 1992
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Table 1. list of radiation sources and calibration doserate
Radiation
Gamma
Gamma
Gamma
X-rays
33-118
Beta
Neutron
source
60 Co
137 Cs
60 Co
137 Cs
60 Co
137 Cs
keV
90 Sr
147 pm
204 Tl
241 Am-Be
Air Kerma
(mGy/H)
0.3-2.11
2.9 - 48
(|XGy/H)
16-267
287 • 4810
0.104-9.45
0.142 - 135
(JlGy/min)
170-350
(JLLGy/sec)
1.923-505.3
0.403
1.139
Dose Equivalent^)
(mSv/H)
0.34 - 2.45
3.5 - 58
(JlSv/H)
19-310
348 - 5820
0.12 - 10.96
0.17-163
(mSv/H)
11.93-33.18
(mSv/H)
0.13
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JAERI-Conf 95-014
device
i
Mar-86 Aug-87 Dec-88 May-90 Scp-91 Jan-93 Jun-94 Oct-i)5
Fig. 1 Average number of devices per month calibrated by SSDL
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devices
250
200 -
150 --
100 -•
50 -•
0 -f-
Fig . 2 Number of cfevices devoted to each work
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15. CURRENT RADIATION PROTECTION ACTIVITIES IN VIETNAMDang Thanh Luong
tludean, Sciutce*. cutd
Abstract:The paper presents the current radiation protection activities in Vietnam, particularly
personal radiation dosimetry. The dose calibration in term of new ICRU's operationalquality such as Hp(lO) for personal dose is discussed.
IntroductionWith increasing the application of ionizing radiation in the industry, medicine,
agriculture and research works. The attention has been paid more and more to RadiationProtection by Government. At present time the Ordinance on Radiation Control isprepared to submit the National Assembly for approving. Since 1985 two laboratories (In Dalat and Hanoi cities ) belonging to Vietnam National Atomic Energy Commissionhave played a role of central laboratories for carrying out personal radiation monitoringand calibrating radiation monitoring equipments for Southern and Northern parts ofVietnam, respectively. Before this moment some other laboratories had been carrying outthe personal radiation services for their own staff by the film badges and pocketdosimeters, but life time of these works was very short. Because the radiation protectionactivities are dealing with many different aspects, here only the personal radiationmonitoring and calibration have a speak.
1/ The Role of Centre of Radiation ProtectionCentre of Radiation Protection belonging to Institute for Nuclear Sciences and
Techniques of VINATON. The laboratories of the Centre have been accepted by GeneralDepartment for Standardization Metrology and Quality Control as Vietnam Laboratoryof Standard on radiation dosimetry and radioactivities with a nickname "I-VILAS-17".The responsibilities of the Centre are following:
- Researching and developing the radiation protection techniques, methods ofcalibration and measurements of ionizing radiation and radioactivities.
- Researcliing and application of environmental radiation- Application of nuclear techniques into medicine- Development and maintenance of radiomeasuring instruments- Testing and calibrating measuring instruments and samples and carrying out QA and
QC for radiotherapy and diagnostic radiology.The current activities of Centre are as follows:
- Determining radioactivity of natural radionuclides in samples- Determining radioactivity of artificial radionuclides ( Cs-137,Sr-9O... ) in
environmental samples (such as water, soil, food )- Determining radioactivity of Radon in the air and Ra in the water- Developing the methods of dose calibration and measurements
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- Calibrating instrumentsThe Laboratory of Radiation Dosimetry of the Centre is responsible for preparing a
standards for calibrating the radiation monitoring instruments and carrying out the qualitycontrol services for the radiotherapy and diagnostic facilities. The Laboratory is alsocarrying out the research works on developing TLD for personal and environmentalradiation dosimetry.2/ Calibration Facilities and Methods of Radiation Measuring
The main standard measuring equipments are following:Farmer Dosimeter System: 2570/1AIonizing Chambers :NE 2525 (600cc)
:NE2571 (0.6cc)Standard Sources : OB-6 Cs-137 20CiPhantom :IAEA water phantom 30x30x30 cm3
All equipments are calibrated against NPL calibrated secondary standard instrumentsand IAEA's standard instruments.
3/ Method of Determining Hp(10) &Hs(0.07)
The method of determining Hp(10)was reported in [1]. In the Fig. 1 thediagram of determining Hp(10) ispresented. This method is applied forVINATOM TLD cassettes made fromthe natural flourites hi Vietnam.
For determining Hp(10) it isnecessary to have two TL signals. Oneis under the filter and another one isfree of the filter. In this way theenergies of the incident radiation anddoses are simultaneously are estimated.TL signals are transmitted to PCcomputer and then Hp evaluationprocess will be started.
Fig. 1 Diagram for determining Hp( 10)by VINATOM TLD Cassettes
The conversion factors Cp = Hp(10)/ Kair calculated for IAEA's water phantomf 2 ] areapplied for determining Hp(10) in our cases. For selecting Cp the following calculationalgorithm based on data in [2] are used:
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From lOKeV to 80KeV Cp= - 0.78 + 0.078*E -5.610-* * E 2 (1)
From80KeV tol50KeV Cp= 1.3* EXP( - 0.011 * E ) +1.4 (2) .
From 150 KeV to 600KeV Cp= 0.89*EXP(-0.005 * E ) +1.2 (3)The energy E are evaluated via the ratio of TL signals without and with the filters
and Hp(10) = Kair * Cp (4)
In the fig.2 the results of the Hp(10) determination intercomparison calculated by twomethods : Computation and graphical are presented. It was found that accuracy of Hp(10)calculated by the computation method is better than one by graphical method, particularlyin low energy range.
ttf10) Detenrinad by Qjiijxieriaed IcQapNcarf Methods
Q Compulsion
IS Graphic
662
Fig. 2 Hp(10) calculated by computation andgraphical methods
The Hs(0.07) intercomparison results presented in fig.3 are calculated by followingalgorithm:
Hs(0.07) = Kair *Cs (5)The Cs were computerized by below approximated formulas:From 10 KeV to 40 KeV Cs = 0.906 -3.82510"4*E + 3.4210"4*E2 (6)From 40KeV to 70 KeV Cs = 6.7110"2 + 4.8110-**E - 3.4510"4* E2 (7)From 70 KeV to lOOKeV Cs = 1.86 -1.42 10"3 * E -2.510"6 * E2 (8)From lOOKeV to 200KeV Cs = 2.01 - 3.92 10"3* E + 5.410-6*E2 (9)From 200KeV to lOOOKeV Cs = 1.58 - 9.18 10"4 *E + 5.310"7* E2 (10)
4/ Calibrating Radiation monitoring equipments:at present time almost of equipments are calibrated in the different units such as
mJR/h. R/h. mRem/h. mSv/h. It depends on the units used in the measuring scale ofequipments. The new ICRU's operational qualities such as H*(d), H'(d,oc) are still notintroduced into a practice . One problem occurred hi the calibrating practices is that thereis a lack of low and medium energy reference radiation beams.
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Restitof Hp(lO) & Hs(0.07) htercomparison
l 3 Hi(0 07)
202 662
Enargy.Kev
Fig. 3 : Results of Intercompariscm onHp(10) and Hs(0.07) monitoring
5/Conclusion:The new ICRU's personal operational quantities such as Hp(10) and Hs(0.07)
have been used in our Institute. In near future the Harshaw 4000 and TLD cards will beused in the practice along with VINATOM -TLD cassettes for personal radiationmonitoring. The IAEA/ RCA program sponsored by Japan Government on RadiationDosimetry Intercomparison is very useful. Through these activities of IAEA/RCAprogram accuracy of dose measurements and calibration are rather improved.
References:
[1] Dang Thanh Luong, Pham Quang DienMethod of Measuring Hp(10) By VINATOM TLD CassettesIVth National Conference on The Physics , 5-8 Oct. 1993, Hanoi
[2] B. GrosswendtConversion Factor For The IAEA Cube Phantom For External Photon IrradiationRadiation Protection Dosimetry, Vol.29, No 3, pp. 177-182 (1989)
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APPENDIX 1
Papers and/or Transparencies of Special Lectures
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Special Lecture for IAK4/RCA Workshop on Calibration of Dosimeters and SurveyInstruments for Photons, held Nov. 28 - Dec. 2, 1994, Tokai, Japan
1 • 1 Foundation on gamma- and X-ray monitoring instruments
Tamaki WATANABEProfessor Emeritus, Nagoya University
1. Introduction
Gas filled counters and scintillation counters are the most useful detectors for measuringradiation dose. The gas filled counters, which are known as the ionization chamber, theproportional counter and the Geiger-Mueller counter, are the oldest and simplest detectorsfor nuclear radiations. The scintillation counter is originated in the famous measurement byprof. E.Rutherford that his eyes viewed the scintillations caused by the alpha particleimpinging on a zinc sulfide screen. However, it becomes a modern detector by applicationof a photomultiplier tube alternative to the eyes.
As the output from the ionization chamber is an extremely small current, variouselectometers were developed for measuring the ionization current. A linear amplifier witha shaping network is used to amplify the output pulse from detectors.
2. Gas filled counter
The ionizing radiation passing through the gas filled counter will produce positive ionsand free electrons in the gas. When the positive potential is applied to the anode, theelectrons will move towards the anode and the positive ions towards the cathode. The outputcharge from the counter per event are shown in Fig.2.1 for two different types of radiationand as a function of applied voltage. One is the passage of electron and the other is that ofalpha particle. In the region A, the applied voltage is low, then recombination occurs, so thatonly a part of ion pairs formed are collected. In the region B, the applied voltage issufficiently high so that the recombination is negligible. This is called the ionizationchamber region. In the region C, as the applied voltage is higher, an electron approaching;J.'-; anode gains sufficient energy between collisions with gas molecules and produces newion pairs. This is called the proportional region. The size of the signal from the counteris proportional to the number of ion pairs initially formed and the avalanche is in a limitedregion. In the region E, the avalanche spreads along the total region of the anode wire andeven a minimum ionizing particle will produce a very large signal. This is called theGeiger-Mueiler region. When the applied voltage is increased beyond the region E, spuriousuntriggered breakdown occurs.
3. Ionization chamber
There are two types of the configuration of ionization chamber as shown in Fig.3.1, that
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is, coaxial(or cylindrical) and parallel plate(or rectangular). With any design, a supportinginsulator must be provided between the two electrodes. The leakage current through theinsulator must be kept small. The guard ring as shown in Fig.3.2 is employed to reduce thecomponent of leakage current in the signal.
The measurement of absorbed dose using the ionization chamber bases upon the Bragg-Gray theory of cavity chamber. If the cavity in solid medium is small and filled with gas,the ratio of the energy loss of the secondary particles per unit mass of medium Em to that ofthe gas is equal to the ratio Sm of mass stopping power of the medium to that of the gas(Fig.3.3). Therefore Em is given by the following equation.
Where Jg is the number of ion pairs formed per unit mass of the gas and W is the averageenergy loss per ion pair formed in the gas.
The parallel plate ionization chamber which is used to the standardization of X-rayexposure in roentgen is illustrated in Fig.3.4. A narrow beam of X-ray passes throughbetween parallel plates. If the electric charge Q(coulomb) is obtained from the collectingelectrode, the exposure X(roentgen) is
Y_(?x3xl09,760 T >V P 273
where the expression in parentheses normalizes the density of the air under the conditions ofmeasurement, and V(cm3) is the restricted volume to collection of ions.
The quartz-fiber electroscope within the ionization chamber as illustrated in Fig.3.5 is oneof the simplest devices for measuring personal dose. Two types of electrometer coupled withionization chamber arc available. In the picoammeter as shown in Fig.3.7(a), the voltageacross the resistance Rs due to the ionization current is measured using an amplifier withnegative feedback circuit. An alternative electrometer is the vibrating reed electrometer,shown in Fig.3.8, which converts the signal from DC to AC at early stage and amplifies insubsequent stage. The electrometer picoammeter coupled with coaxial type ionizationchamber with air volume of several hundred cm3 is used as portable survey meter. A typicalenergy calibration curve of survey meter is shown in Fig.3.9.
4. Geigcr-Mueller counter
As the applied voltage is increased beyond the region D in Fig.2.1, a number of photonsemitted by dcexitation of the exited gas molecules release photoelectrons from the gas andthe cathode wall(Fig.4.1). The second avalanche develops near the anode wire. Theavalanches spread along the whole length of the anode wire by successive creation ofavalanches. The electrons are quickly collected, but more slowly moving positive ions forma positive ion sheath around the anode wire so that the electric field near the anode reducestoo low to create a new avalanche. The positive ion sheath slowly drifts to the cathode anda free electron emerges from the cathode surface when the positive ions are neutralized onthe cathode surface. The free electrons drift towards the anode and trigger anotheravalanche. The entire cycle is repeated and the Geiger counter generates a continuous outputof pulses. External quenching is to reduce the high voltage applied to the tube during a fixed
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time after each pulse. Internal quenching is accomplished by adding a second componentcalled the quench gas to the counting gas.
The building of the positive ion space charge cannot create the second Geiger dischargecaused by successively incident radiations. As the positive ions drift outward, the electricfield near the anode recovers to original value. During this time of the order of hundredmicroseconds, the tube is dead.
As the applied voltage increases from low voltage, pulses are first registered at thestarting voltage as shown in Fig.4.3. With increasing in voltage, count rate increases towardsthreshold value. Beyond the threshold voltage, no count rate increases and the curve showsa flat plateau. Length and slop of the plateau are 200V and less than 10%/100V,respectively for a typical Geiger tube.
The counting efficiencies of the Geiger tubes with the cathode made of various metalsare shown in Fig.4.4 as a function of gamma-ray energy. As the response of the Geiger tubefor gamma-rays comes to interactions with mainly cathode wall, the efficiency increases withatomic number of the wall material. The response to exposure and 1 cm dose equivalent fora commercially available GM survey meter are shown in Fig.4.5 for gamma-ray energy.
5. Scintillation counter
Schematic arrangement of the scintillation counter is illustrated in Fig.5.1. The photonsproduced in the scintillation crystal optically coupled with a photocathode of the photomulti-plicr tube liberate electrons from the photocathode. The electrons are accelerated bypotential difference between the photocathode and the first dynode and they impinge on thefirst dynode. A number of secondary electrons are released by the impact. The secondaryelectrons arc accelerated again by the potential difference between the first and the seconddynodc, where the number of electrons arc further multiplied. Most of photomultiplier rubeshave usually ten dynodes, therefore photons striking the photocathodc cause an avalanche ofelectron to hit the anode. The output charge per event from the anode is proportional to theenergy deposited by the primary radiation in the crystal.
Photodiodcs, which are recently developed, have advantages of low operating voltage andcompact size. However, the spectral response of a commercially available photodiode haslower sensitivity in a short wavelength range as plotted in Fig.5.2. Therefore the scintillationcrystal coupled with the photodiode is limited. CsI(Tl) and BGO, which have dominantemission spectra in longer wave length, arc usually used. Another demerit of the photodiodeis the absence of internal electric charge gain, so that a low noise amplifier with high gainmust be provided.
Various types of scintillation crystal arc used for radiation measurement. A Nal(Tl)crystal is the most versatile in all the phosphors for detection of gamma ray, while it has thedisadvantage that it is hygroscopic and must be sealed in an aluminum can.
A typical energy calibration curve of Nal(Tl) scintillation survey meter is shown inFig.5.3.
The low level environmental radiation monitoring system developed by S.Moriuchi1* canbe evaluated annual integrated dose less than 10u.Sv due to Ar-41 plume from a nuclearfacility. The system consists of a Nal(Tl) scintillation probe with a special concave radiationshield as shown in Fig.5.4 and separative measurement of spectral energy distribution.
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6. Circuit elements used to monitor6.1 Anode circuit
The anode circuit can be idealized as shown in Fig.6.1. The waveform of the voltagepulse produced at the anode of counter depends on the time constant of the anode circuit.The time constant is generally large compared with a period of time of charge output fromcounter. When the impulse with charge of Q is added to the circuit, the output of the circuitV, is given by the next equation and illustrated in Fig.6.2.
s 1
6.2 RC networkThe basic RC network as shown in Fig.6.3 may be introduced in an amplifier as parasitic
or wired circuit. When V, is added into the input of RC network, the output V2 from thenetwork is given by the following equation and by the plot in Fig.6.2.
6.3 Count rate meterThe count rate meter can be represented by the diode pump' circuit as shown in Fig.6.4.
The logic pulse deposits a small amount of charge on the capacitor Co. The charge iscontinuously discharged through the resistance Rg. When the rate of the pulse is constantand an equilibrium is established, the average voltage at the output of the circuit Vo is
where r is the average rate of the pulse supplied to the circuit.
The author would like to thank Dr.M.Yoshida for his kind help of making the manuscriptof the lecture including the figures.
Some of the figures arc reproduced from published reports and textbooks (see references).
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References
1) S.Moriuchi, et al.: J.Nucl.Sci.Tech., Vol.17, No.9, P.710 (1980)
[References for figures are below]
2) HAEnge: Introduction to Nuclear Physics, Addison-Wesley (1971)
3) W.E.Burcham: Nuclear Physics an Introduction; 2nd ed., Longman (1973)
4) G.F.Knoll: Radiation Detection and Measurement; 2nd ed., John Wiley & Sons (1989)
5) GJ.Hine and G.L.Brownell: Radiation Dosimetry, Academic Press (1956)
6) G.Murphy: Element of Nuclear Engineering, John Wiley & Sons (1961)
7) K.Minami: Isotope News, No.414 (1988) (in Japanese)
8) K.Minami: Isotope News, No.413 (1988) (in Japanese)
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Counter
izing particle
B c D aA p p l i e d v o l t a g e V
Fig.2.1 Caracteristics of gas filled counter 2)
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i—i
coaxi al p a r a l l e l p l a t e s
Fig.3.1 Configuration of ionization chambers3;
Outer insulator
Guard ring
Inner insulator
leakage current
Fig.3.2 Functioning of guard ring 4)
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Bragg-Gray theory of cavity chamber
Rn ~
= J 9 W
Fig.3.3 Bragg-Gray theory4'
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Shielded Box
>To Current Meter
y , Q x 3 x109 , 760 TV l p 273
X: Eeposure(roentogen)
Q: Collected charge(coulomb)
V: Volume(cm3)
Fig.3.4 Configuration of parallel plateionization chamber5)
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Window-
Transparent/ scale
Lenst - Lens
Movable loop
Fixedloop
Eyepiece
Fig.3.5 Cross-sectional view ofpocket dosimeter6)
CD
COo
exp
0
CDCOCoaCOCDcc
z J . U
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
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JAERI-Conf 95-014
1.3 Dissemination of Exposure Standard and the Irradiation Field
on ICRU Operational Quantities
(A Suggestion of Practical Calibration for Operational Quantities)
Kentaro MINAMI and Hiroyuki MURAKAMI
Department of Health Physics,
Japan Atomic Energy Research Institute
Tokai, Naka-gun, Ibaraki 319-11
JAPAN
1. Introduction
Calibration of radiation protection instruments is made by reference irradiation fields which are
traceable to the primary standard. The reference irradiation fields are necessary to be
characterized to the suitable objective quantity, e.g. ICRU operational quantity1)|2>l3) for radiation
protection instruments. For workplace monitoring, ambient dose equivalent and directional dose
equivalent are used as such operational quantities. On the other hand, personal dose equivalent
is used for- individual monitoring. These operational quantities should be produced at any
"traceable" irradiation facility and the certain values of the quantities should be delivered to
various types of instruments at the facility. Traceability is maintained with physical standard
quantity like "exposure" in most irradiation facilities, and then the method of irradiation being
conformed to the operational quantity concept is quite important as well as the selection of
conversion factors. In these point of view, this paper reviews how we can obtain the
irradiation field for ICRU operational quantity and also describes how we should perform the
calibration of radiation protection instruments.
2. Exposure standard dissemination
The terminal point of dissemination on radiation dose standard is common radiation protection
instruments which are used at the workplace, such as survey meters, personal dosimeters etc..
Radiation dose standard for photons is transferred by "exposure" from the primary standard
laboratory using a transfer instrument (Standard instrument;"ionization chamber having an air
equivalent wall" is mostly used) to the lower level reference irradiation laboratory ( calibration
laboratory ), e.g. secondary standard dosimetry laboratory (SSDL). Figure 14) shows an
example of standard transfer system in Japan. Figure 24) shows a schematic view of transfer
instrument irradiation which are commonly adopted in Japan. The irradiation must be made
as the exposure value would be the same values throughout the area covering the detector of
the instrument.
- 1 0 9 -
JAERI-Conf 95-014
In the standard transfer process, the overall accuracy is quite important. In Japan, secondary
standard is transferred from the primary standard a few percent in accuracy. For the lower
level standard, the accuracy tolerance level may become a little bit larger, but regulated by
Japan Industrial Standard not to be larger than the range of 4 to 6 %.
3. Calibration of survey instruments for ICRU sphere quantities
Operational quantities for workplace monitoring are ambient dose equivalent and directional
dose equivalent. These are both defined in the ICRU sphere. So, in Japan, we call these
"ICRU sphere quantity". The survey instruments are used in actual workplace without any
scattering material such as human body in case of individual monitoring. This means that the
above ICRU sphere quantities are both free-in-air quantity and thus the instruments should
be calibrated on free-in-air condition. Even a small passive type dosimeter such as thermo-
luminescent dosimeters, RPL glass dosimeter and film dosimeter can measure ICRU sphere
quantity, if it is calibrated and used in the free air space.
Irradiation of survey instruments is made as the same way as that of standard instruments as
shown in Fig.l but the reference dose quantity is different. Figure 35) shows examples of
response of ionization chamber as a function of physical quantity (exposure) and operational
quantity (ambient dose equivalent), which were obtained by single series of irradiation. Most
of the traditional ionization chamber would be manufactured as the response of which is well
conformed to exposure and then it is not good enough to ambient dose equivalent by itself.
In that case, suitable calibration factor would be used.
For free-in-air irradiation, the reading of instrument (I) is expressed using the values of
objective quantities (exposure:X; ambient dose equivalent:H"(d)) and each calibration factor (Kx,
K": where calibration factor is defined as reciprocal of response) as follows.
/ - JL , MMKx
If the instrument's reading scale has the same unit as of the objective quantity, the calibration
factor(K) is dimensionless, but when it is differed from the objective quantity, K has a certain
dimension. This procedure means that the any type of traditional "exposure-measuring
instruments" can also measure new operational quantity such as ambient dose equivalent with
using the suitable calibration factor. For H"(d) measurement, however, the instruments should
have the isotropic response, or characteristics independent from incident angle distribution.
Most survey instruments for penetrating radiations (photons, neutrons) have sphere or
cylindrical shape detectors, and then, such instruments can be regarded as sufficiently isotropic.
The instruments for directional dose equivalent H'(d,£2) should have the response which varies
with incident angle distribution (Q.) of radiations. A surface contamination survey meter with
- 1 1 0 -
JAERI-Conf 95-014
thin window is a typical example of such instruments when it is used as 0-ray survey meter
in free air space, but the response variation would not always agree with H"(d,Q) for all
irradiation conditions. The calibration of angular-dependent instruments is carried out for each
incident direction of radiations. Sometimes H'(d,8), where 8 is the plane angle between the
direction of radiations and the axis perpendicular to detector window, is used for expressing
how instrument's response meeis the variation of directional dose equivalent. Considering the
most situation of actual workplace survey for p-rays, the angular dependence of instruments
should be obtained for 9 values up to 60°.
4. Calibration of personal dosimeters for ICRU operational quantities
Individual monitoring is generally carried out with a small dosimeter attached on a human
body. In this situation, the dosimeter has a large scattering and shielding effect by the human
body. Therefore, the calibration of personal dosimeters must be complied with this irradiation
condition, and that is, when being irradiated, personal dosimeters must be attached on a
suitable phantom.
Operational quantity for individual monitoring is personal dose equivalent HP(d), which is
defined at the point inside human body. This definition of HP(d) is quite important for
calibration of personal dosimeter; the reference point of irradiation should not be on the
dosimeter but inside a phantom at the depth of d. In actual irradiation condition, if the
irradiation field is sufficiently uniform for all over the large space around the reference point
in the absence of phantom, the reference point can be moved in a small distance of d. This
means that the reference point can be set at the phantom surface when irradiation is uniform
between the points of surface and of d in depth from the surface. This condition would be
mostly satisfied for d=10 mm with the irradiation of penetrating radiations at 2 m irradiation
distance, and for d=0.07 mm with at least 10 cm distance irradiation of 0-rays. When the
reference point of irradiation is determined at the front surface of the phantom, the dosimeter
is considered to be merely a censor which gives us the information on irradiated radiations
including dose, and then the dosimeter size and the distance between dosimeter and phantom
surface would not affect for calibration procedure.
Figure 4 explains the relation between the dosimeter position (e.g. A,B,C) and the calibration
factor K; (i=A,B,C). Kj is expressed as follows using each dosimeter reading If,
Hp(d) Hid) Hid)
K f A K p * 1 (2)
Then, the same personal dose equivalent value should be obtained from every dosimeter's
reading using the equation HP(d) = Kj • Ij.
- I l l -
JAERI-Conf 95-014
Selection of conversion factor, or reference value of operational quantity, is another problem
for personal' dosimeter calibration. HP(d) has rare calculated data and then, the substitute dose
values for HP(d) is necessary. Since HP(d) has a large dependence to incident angle, H'(d) had
been regarded as a substitute dose quantity for calibration of personal dosimeters on HP(d)2).
Recently, ICRU3) recommended the dose equivalent at the depth of d inside the ICRU tissue
equivalent slab phantom (30x30x15 cm; hereafter, we call the quantity H^d)) as the reference
quantity for personal dosimeter calibration. And ICRU3) also recommended the PMMA slab
phantom of same size for actual calibration procedure, but a water filled slab phantom (same
size) would be finally adopted in the near future.
Irradiation procedure for personal dosimeter calibration is summarized as follows;
1) Measure the value of standard quantity (e.g. exposure) at a reference point without a
phantom and determine the H^d) value at the reference point using the conversion
factor. (Reference dosimetry; Irradiation distance should be 2 m or more for photons)
2) Set a suitable phantom as the center of front surface of the phantom is on the
reference point.
3) Put dosimeters on the phantom surface and irradiate them.
To confirm that the variation of dose rate during the irradiation would be negligible, reference
dosimetry should be done again after personal dosimeter irradiation is completed.
5. Conclusion
Calibration of radiation protection instruments for ICRU operational quantities can be
performed at any irradiation facility in which the traceability of dose standard to primary
standard is being well maintained. If the instruments and the conversion factors would be
common in all the irradiation facilities, quality of radiation protection measurements would
mostly depend on the reliability of technical calibration procedures for both standard transfer
and practical instrument calibration.
- 1 1 2 -
JAERI-Conf 95-014
References
1) International Commission on Radiation Units and Measurements;
ICRU Report No.39 (1985)
2) International Commission on Radiation Units and Measurements;
ICRU Report No.43 (1988)
3) International Commission on Radiation Units and Measurements;
ICRU Report No.47 (1992)
4) Japan Industrial Standard; JIS Z 4511 (1991) (In Japanese)
5) Yamashita,M. and Minami,K.; Radioisotopes, Vol.39, No.2 P.34-45 (1990)
(In Japanese)
- 1 1 3 -
JAERI-Conf 95-014
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- 1 1 6 -
JAERI-Conf 95-014
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- 1 1 7 -
JAERI-Conf 95-014
RCA REGIONAL WORKSHOP ONCALIBRATION OF DOSIMETERS AND SURVEY
INSTRUMENTS FOR PHOTONS
RADIATION PROTECTION QUANTITIES FOREXTERNAL MONITORING AND WORK OF
THE ICRP/ICRU JOINT TASK GROUP
Richard GriffithInternational Atomic Energy Agency
Occupational exposure:
All exposures of workers incurred in the course of theirwork with the exception of
exposures excluded from the Standards and exposuresfrom practices or
sources exempted by the Standards
- 1 1 8 -
JAERI-Conf 95-014
Calculated using Q(L)
and simple phantoms
(sphere or slab)
validated by
measurements
Primary physical quantities
Fluence, <j>(E, 0)
Kerma, K jj, Kn
Absorbed dose, D j , D n
ICRU Operational quantitiesAmbient dose equivalent, H (d)
Directional dose equivalent, H'(d, f?)
Personal dose equivalent, H p (d)
Related by type
test and calculation
Monitored quantities
Actual signals measured:
(device specific)
Compared by
measurement and
calculations using w R
and anthropomorphic
phantoms
Calculated using w R
and anthropomorphic
phantoms
ICRP Protection quantities
Effective dose, E
Organ equivalent dose, H j
Relationship of quantities for radiation protection purposes
Equivalent dose:
The absorbed dose in an organ or tissue multiplied by therelevant radiation weighting factor wR:
H T , R = DT / R
where DTR is the average absorbed dose in the organ ortissue T and wR is the radiation weighting factor forradiation R
When the radiation field is composed of radiations withdifferent values of wR, the equivalent dose is:
HT = I w R • DT<R
The unit of equivalent dose is J#kg , termed sievert (Sv)
- 1 1 9 -
JAERI-Conf 95-014
Effective dose:
A summation of the tissue equivalent doses, each
multiplied by the appropriate tissue weighting factor:
E = 1 wT • HT
T
where HT is the equivalent dose in tissue T and wT is thetissue weighting factor for tissue T
Effective dose:
From the definition of equivalent dose, it follows that:
E = I wT • I wR • DTR = I wR • I wT • DTR
T R 'R T
where wR is the radiation weighting factor for radiationR, and DTR the average absorbed dose in the organ ortissue T
The unit of effective dose is J*kg "1, termed sievert (Sv)
- 1 2 0 -
JAERI-Conf 95-014
Recommended Dose Limits1
ApplicationDose
Occupationallimit
Public
Effective dose
Annual equivalentdose in
the lens of the eyethe skinthe hands and feet
20 mSv per year,averaged overdefined periods of5 years
150 mSv500 mSv500 mSv
1 mSv ina year
15 mSv50 mSv
The limits apply to the sum of doses from external exposure and the 50-year committed dose (toage 70 years for children) from intakes in the same period (see paragraph 143 of ICRP 60)
Radiation weighting factor:
A factor by which the absorbed dose is multiplied in order to account for the relative healthhazard of different types of radiation. The values of radiation weighting factor used forradiation protection purposes are as follows:
Type and energy range of radiation Radiationweightingfactor wn
Photons, all energies 1
Electrons and muons, all energies1 1
Neutrons, energy < 10keV 510keVto 100 keV 10> 100keVto 2MeV 20> 2 MeVto 20MeV 10> 20 MeV 5
Protons, other than recoil protons, energy > 2 MeV 5
Alpha particles, fission fragments, heavy nuclei 20
Excluding Auger electrons emitted from nuclei to DNA, lor which special microdosimelric considerations are needed.
- 1 2 1 -
JAERI-Conf 95-014
Radiation weighting factor:
If calculation of the radiation weighting factor forneutrons requires a continuous function, the followingapproximation can be used:
where E is the neutron energy in MeV
Neutron radiation weighting factors
WR
30
25
20
15
10
ICRP Recommendation
ICRP Approximation
Energy - MeV1O"8 1O"7 10"6 10'5 10"4 1O"3 10"2 1O"1 1 10 100
- 1 2 2 -
JAERI-Conf 95-014
Radiation weighting factor
For radiation types and energies_not included in the table,WR can be taken to be equal to Q at 10 mm depth in theICRU sphere and can be obtained as follows:
where D is the absorbed dose, Q(L) is the quality factor interms of the unrestricted linear energy transfer L in water,specified in ICRP Publication No. 60, and DL is thedistribution of D in L.
1 for/.<10Q(L) = 0.32L-2.2 for10<Z.< 100
300A/L for/. > 100
where L is expressed in keV»//m"1
The ICRP/ICRU Joint Task Group is to provide:
• Fluence to effective dose calculations for a variety ofradiations and energies for reference man and 15 yearold, 5 year old, and 3 month old children
• Fluence to ambient dose equivalent, directional doseequivalent, individual dose equivalent (penetrating),and individual dose equivalent calculations(superficial)
• A detailed discussion of the relationship between thetwo sets of calculations
- 1 2 3 -
JAERI-Conf 95-014
Calculation of conversion coefficients for effective dose, E
1. Calculate DT for critical organs and tissues
2. Use WR to calculate HT
3. Joint Task Group determines single set of HT valuesfrom published data
4. Using proper tissue weighting convention, calculate E
The Joint Task Group is using:
E = 0.2[Htestes + Hovaries]/2 + 0.05HbreasUemaIe
+ Z WT[HtfinalB + HtffemaIe]/2
.s
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- 1 2 4 -
JAERI-Conf 95-014
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Photon dose conversion coefficients for Effective Dose
10 e
0.01 0.1 1.Energy - MeV
- 1 2 5 -
JAERI-Conf 95-014
Neutron dose conversion coefficients for Effective Dose
10
10
pSv cm
10
— — — ROT
Energy - MeV
Personal dose equivalent:
10'8 10"7 10"6 10"5 10"4 10"3 10"2 10"1 1 10 1 0 2 10 3
Hp(d) is defined for both strongly and weaklypenetrating radiations
HP(d) is the dose equivalent in soft tissue below aspecified point on the body at an appropriatedepth d
Depths of d = 10 mm for strongly penetratingradiation and d = 0.07 mm for weakly penetratingradiation are recommended
- 1 2 6 -
JAERI-Conf 95-014
Basic requirements for personal dosimeters
Provide a reliable measurement of the appropriatequantities,- i.e. Hp(0.07) and H (10)- for almost all practical situations- independent of type, energy and incident angle of the
radiation- and with a prescribed overall accuracy
Additional requirements important from a practical pointof view include- small size- appropriate shape- light weight- dosimeter identification
Photon dose conversion coefficients
""" ~~ Hci_u(10)
0.01 0.1 1.Energy - MeV
10.
- 1 2 7 -
JAERI-Conf 95-014
Neutron dose conversion coefficients
10
10
pSv
10
10"8 10"7 10'6 10"5 10 ' 4 10"3 10"2 10 ' 1 1 10 10 2 10 3
Energy - MeV
Hs)ab(cl) conversion coefficients for electrons
nSv cm'
0.01
0.001
d = 0.07 mm
d = 10 mm
0.1 10
Electron energy - MeV
- 1 2 8 -
JAERl-Conf 95-014
Type testing of dosimeters on a slab phantom
• Energy response
• Angular dependence
• 30 cm x 30 cm x 1 5 cm
• Conversion coefficients for ICRU tissue substitute
- Monoenergetic photons- ISO photon reference radiations
ICRU tissue substitute cannot be produced exactly
• 30 cm x 30 cm x 1 5 cm PMMA phantom may be used
® PMMA backscatter is similar to tissue photons
• ISO has also proposed a thin wall, water filled slab
• For neutrons water is preferred
• Dosimeter response should still be interpreted in termsof the tissue equivalent slab conversion coefficients
• This procedure effectively calibrates the dosimeterseven though they are irradiated on a PMMA slab
- 1 2 9 -
JAERI-Conf 95-014
The type testing procedure can be summarized using thefollowing example:
1. Choose the photon energy from the ISO referenceradiations
2. Set up the radiation beam and a monitor chamber
3. The monitor chamber, phantom and dosimeters mustbe completely enveloped by the beam at a distance ofat least 2 m
4. Measure air kerma (Ka) at the position to be occupiedby the front surface of the phantom, but without theslab present, for a given indication on the monitorchamber
Dosimeter type testing example (Cont.):
5. Multiply the air kerma by the appropriate conversioncoefficient (C)
6. Dose equivalent is then given by (Ka»C) for a monitorindication of D
7. Each unit on the monitor chamber thus corresponds toa dose equivalent of (Ka*C) / D
8. Place the slab phantom and dosimeter(s) with the beamincident on the dosimeters at angle a" and the centerof the phantom front face on the beam axis at theposition at which the air kerma was measured in step 4
- 1 3 0 -
JAERI-Conf 95-014
Dosimeter type testing example (Cont.)
9. Choose the dose equivalent (H) to be delivered to thedosimeters
10. Irradiate the phantom until the monitor chamberindicates the desired value of (H»D) / (Ka»C).
11 . Process the dosimeters and compare their readingswith the conventional true dose equivalent, H
Calibration of dosimeters in terms of HS|ab (d) [Hp(d)]
Dosimeter forI measurement of Ka
beam axis
Dosimeter onbearruaxis
^J DosimeteDosimeters offbeam axis
- 1 3 1 -
JAERI-Conf 95-014
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Photon conversion coefficients for ISO reference radiations
Mean
EnergykeV
9.8817.423.1
• 25.230.933486583
100118161205248662
1250
a = 0°
0.4490.7780.8791.151.221.681.891.871.801.721.571.481.421.211.15
Hp(10,
a = 20°
0.4200.7570.8611.131.201.641.861.851.781.711.551.471.421.211.15
a = 40°
0.3420.6780.782i.041.101.531.741.741.691.631.491.421.381.201.15
a = 60°
0.1840.4840.5830.8300.891.261.461.481.451.411.341.301.271.201.15
Hp(0.07,a)/K.
a = 0 °
0.9511.011.091.121.251.291.571.721.711.671.611.491.421.371.211.15
a = 20°
0.9461.011.081.121.241.281.561.711.711.651.601.491.421.381.211.15
a =40°
0.9411.001.081.111.221.261.521.661.661.621.581.481.411.371.221.16
a =60°
0.9190.9871.061.091.171.231.421.541.561.531.50
,1.43;1.391.361.231.20
- 1 3 2 -
JAERI-Conf 95-014
Angular dependence of Hs|ab(0.07) for photons
1.8
1.6
Sv/Gy1.4 =•
1.2 =•
1.0 '-
0.8 r
0.60.01
Photon energy - MeV
Angular dependence of Hsjab(10) for photons
2.0
Sv/Gy
0.01 0.1
Photon energy - MeV
- 1 3 3 -
JAERI-Conf 95-014
Angular dependence of Hslab(1O) for neutrons
1000 c
pSv cm
"8 10"7 10"6 10"5 10"4 10"3 10"2 10'110"8 10"7 10"6 10"5 10"4 10"3 10"2 10'1 1 10 100
Neutron energy - MeV
Relative angular dependence of Hs(ab(0.07) for electrons
2.0
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2. MeV 4. MeV
10. MeV
100
Angle of incidence - degrees
- 1 3 4 -
JAERI-Conf 95-014
Relative angular dependence of Hs)ab(3) for electrons
oCO
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Angle of incidence - degrees100
Relative angular dependence of Hs!ab(10) for electrons
oCD
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0 C20 40 60 80
Angle of incidence - degrees100
- 1 3 5 -
JAERI-Conf 95-014
Ambient dose equivalent:
H*(d) at a point in a radiation field, is the doseequivalent that would be produced by thecorresponding aligned and expanded field inthe ICRU sphere at a depth d on the radiusopposing the direction of the aligned field
A depth d = 10 mm is recommended for stronglypenetrating radiation
Directional dose equivalent:
at a point in a radiation field, is the doseequivalent that would be produced by thecorresponding expanded field in the ICRUsphere at depth d, on a radius in a specifieddirection, Q
A depth d = 0.07 mm is recommended forweakly penetrating radiation
- 1 3 6 -
JAERI-Conf 95-014
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Sv/Gy
0.01 0.1 1,Energy - MeV
- 1 3 7 -
JAERI-Conf 95-014
Photon dose conversion coefficients
0.01 0.1 1,Energy - MeV
Neutron dose conversion coefficients
"8 10"7 10"6 10"5 10"4 10'3 10'2 10"110 8 10 7 10 6 10 5 1 0 4 103 10 2 1 0 1 1 10 102 10
Energy - MeV
- 1 3 8 -
JAERI-Conf 95-014
Summary - Use of operational quantities
Monoenergetic dose equivalent conversion coefficientsrecommended by ICRP/ICRU (Joint Task Group)
Personal D.E. - HP(d)Ambient D.E. - H*(d)Directional D.E. - H'(d,Q)
rPhotons - KermaNeutrons - FluenceElectrons - Fluence
J L
* Calculate spectrum weighted conversion coefficients
* Measure primary quantity rates at calibration point (s"1)
* Calculate operational quantity rates (Sv s"1)
* Irradiate dosimeters8 or instruments for fixed time
* Calibration factor = Dosimeter response/delivered D.E.a) On suitable phantom .
- 1 3 9 -
JAERI-Conf 95-014
1.5 The Australian Radiation Laboratory Intercomparison ofPersonal Radiation Monitoring Services in the Asia/Pacific Region
byNeville J. Hargrave and Joseph G. Young
BACKGROUND
In February 1985 the International Commission on Radiation Units and Measurements (ICRU)(I) recommendednew operational quantities for individual monitoring for the purpose of radiation protection from externalsources. In order to determine to what extent the ICRU recommendations had been implemented in theAsia/Pacific region, the Australian Radiation Laboratory (ARL) conducted an intercomparison of PersonalRadiation Monitoring Services (PRMSs) in the region. The intercomparison was conducted in 1991/1992 andwas partially funded by the IAEA. This paper outlines the results of the intercomparison. A detailed report™and journal article0' may be consulted for more information.
PRELIMINARY
A total of 29 organisations from 16 countries in the region participated. Thirty-two different types of dosemeterwere submitted for evaluation. Extremity dosemeters were not considered. Twenty-five dosemeters of eachtype were submitted for evaluation. All intercomparison dosemeters were kept in a low background area andwere only removed from it to perform the exposures. Dosemeters were returned to participants for assessmentwith some information regarding the exposure conditions. Participants informed ARL of their results and theprocedures they used. The anonymity of participants was maintained.
RADIATION EXPOSURES
Seven different exposures were performed. Three exposures were made to '"Cs gamma rays (Beams A, B &C). This was the principal intercomparison beam because it was used by most participants as the standardcalibration source for their PRMSs. Three X-ray beams were selected from those recommended in theInternational Standards Organisation (ISO) document No. 4037, "X and Gamma Reference Radiations forCalibrating Dosemeters and Dose Ratemeters and for Determining their Response as a function of Energy"(<).The effective energies of the beams selected were 33 keV (Beam D), 79 keV (Beam E) and 202 keV (Beam F)The last exposure involved beta rays of maximum energy 2.0 MeV at the calibration distance from a '"Sr^Ysource (Beam G).
All exposures were performed at normal incidence on a perspex/paper combination phantom under conditionsapproximating an aligned and expanded beam. Except for the 90Sr/'0Y exposure, all beams were monitoredusing ionisation chambers. Tests made on the phantom using both ionisation chambers and thermoluminescentdosemeters (TLDs) could not detect any difference between it and a solid perspex phantom. Apart from BeamA, participants were not told the radiation qualities used. After they had reported their assessments they weretold the unknown qualities and invited to make another assessment. Precise details of the irradiation conditions,calculation methods and factors used are reported elsewhere(H>.
RESULTS
There was little uniformity in dose reporting. Services reported their results in terms of mR, (iC/kg, in absorbeddose to air, tissue or water in units of rad or Gy, and in terms of dose equivalent in rem or Sv with one reportingin terms of effective dose equivalent. Only 4 services reported routinely in terms of the ICRU operationalquantities (deep or shallow doses), however many were able to convert their usual result correctly. As a matterof interest relating to the time taken for the survey, it took four months for all the questionnaires to be returned.The return of the dose assessments was similarly slow. The quickest took 3 weeks, the slowest 21 weeks. Fromreplies to a questionnaire sent out prior to the commencement of the intercomparison it was indicated that 50%of services were not equipped to assess unknown radiation beams. The holders used by services ranged fromquite complex, to extremely simple where only LiF with no filtration was used.
A summary of the results reported by participants for the penetrating dose equivalent H^IO) is shown in theTable. The results show the ratio of each participant's reported penetrating dose equivalent to the deliveredpenetrating dose equivalent. A ratio of less than 1.0 indicates that the dose has been underestimated. Theabsence of some ratios in Table is due to several reasons. The participant may have experienced technicaldifficulties during assessment, the dosemeter submitted for evaluation may not have been suitable for the beam
- 1 4 0 -
JAERI-Conf- 95-014
under investigation, the dosemeter could have been damaged in transit, or the participant did not return anassessment.
The repeatability of a participant's assessment procedures is also shown in the third column of the Table as therelative standard deviation of the 7 dosemeters used for Beam A.
There was a large variation in the doses for the transit/control dosemeters from 10's to 100's of microgray. Oneparticipant had to contend with a control dose of 5 mGy. This probably explains why some participants haddifficulty measuring doses of around 150 nGy. In one country the control doses seemed to vary depending onwhether the service was located in capital city or remote from it.
The majority of services had a repeatability of better than ±7% as measured by the standard deviation of 7dosemeters exposed to the same dose of a known radiation ('"Cs). For this beam, 30% of participants reportedthe correct result within 5%, however, 50% of participants underestimated the dose.
Of the 33 participants, 13 identified the unknown beams to within 15 keV and 4 identified the energy range towithin ±150 keV. The remaining 16 participants could not identify the unknown beams. Only 9 participantsidentified that Beam G was due to a beta exposure. When told that the beam was due to beta radiation 11 out ofthe 13 who assessed the beam were within ±50% of the correct value.
Doses of various levels were chosen by for several reasons. A value of 2 mSv was used for the repeatabilitytest. It was expected that this would be greater than any transit or storage dose. A value close to 10 mSv waschosen for a test of the calibration accuracy of the participants and a small value of close to 0.3 mSv to see howwell allowances for transit exposures could be made.
Beam D (effective energy 33 keV) was a very heavily filtered beam and the penetrating dose equivalent of0.260 mSv was the lowest dose used in the intercomparison. Seven participants were within ±5%, while 23were within ±30% of the delivered dose. Some participants, even when informed of the beam energy foundassessment difficult as they assumed that it was more lightly filtered than it was. Two participantsunderestimated the dose by a factor of approximately 10 while another participant overestimated the dose by afactor of 5.
It is interesting to note, that of the 9 participants who claimed they could perform beta dosimetry only 6correctly identified Beam G as a beta source, whilst 3 participants who stated in'their questionnaire they couldnot perform beta dosimetry successfully identified Beam G. The ratios calculated from the reported superficialdose equivalent and the delivered dose equivalent varied from 0.73 to 1.68. Four of the nine participantsreported a dose within ±5% of the delivered dose.
DISCUSSION
The new operational quantities have not been adopted by the vast majority of participants in the Asia/Pacificregion. Four participants routinely report their results in terms of the ICRU new operational quantities and theseresults were reported in units of Sv, rem or Gy. Of the remaining participants, 8 routinely report their results interms of exposure (R or C kg'1), 2 report absorbed dose to the skin or body (Gy or rad), 6 report absorbed dose toair (Gy) and 10 report dose equivalent to skin (Sv). Some participants report dose equivalent to air (3participants, Sv) and to water (1 participant, Sv).
Most participants have underestimated the delivered dose equivalents for all seven beams. Several dosimetryservices can satisfactorily measure the new ICRU operational quantities, for radiation at normal incidence. Theperformance of participants was best for l37Cs gamma rays, whilst the assessment of the unknown X-ray beamqualities proved difficult for the majority of participants.
Since most participants use l37Cs as their standard calibration source it was anticipated that the performance ofparticipants should be best for these beams. This was the case. Most participants reported similar ratios forBeams A, B and C. However, several participants reported ratios which varied by approximately a factor of 2 orgreater. In general, for all three "7Cs beams, participants underestimated the dose.
The performance of the majority of participants for the X-ray Beams E and F was disappointing with the scatterin the participants assessments greater than that observed for the l37Cs exposures and for Beam D, the 33 keV X-ray beam. Because most participants use l37Cs as their calibration source and since most detectors have a
- 1 4 1 -
JAERI-Conf 95-014
maximum response to photons between 20 to 40 keV, this may account for the better performance for thesebeams. In addition, problems resulting from the magnitude of the transit and storage doses for some participantsmay have had some bearing on the error in energy estimation thus leading to poor dose assessments.
Part of the reason for the difficulty in making an accurate assessment of the Hp(10) and H,(0.07) by participantsappears to be that services have used different methods, and different numerical values for the conversionfactors. It is therefore very difficult to assess the performance of participants when some have used differentconversion factors from those used at ARL to calculate H/IO) and H,(0.07), whilst others have used the samefactors as ARL, but a different method of calculation.
Participants results were not modified to take into account the different conversion factors and methods used bythem. The combination of different conversion factors and different methods of calculation had the effect that insome cases the agreement with ARL was fortuitous.
Eleven participants successfully estimated the energy of the unknown X and gamma ray beams, with oneparticipant demonstrating excellent accuracy. Many participants have not developed their dosimetry service to a"level where beta radiation can be identified.
CONCLUSIONS
The repeatability of the assessment procedures, expressed as one standard deviation, is better than ±7% for thevast majority of participants. Participants used a variety of methods and conversion factors for calculating thesuperficial and penetrating dose equivalents. Because of the confusion regarding the correct method forcalculating the new operational quantities and the lack of consistency in choice of the conversion factors theremay well be value in recommending the adoption of a consistent set of data for use in the region and supplying aprotocol on its use. Beta dosimetry is not widely catered for in the Asia/Pacific region. Less than 50% ofparticipants could correctly identify an unknown beam quality. For those participants using the same methodsand conversion factors good agreement was obtained.
Twelve participants estimated the delivered penetrating dose equivalent to better than ±30% for the six photonbeams. The majority of participants underestimated both the superficial and penetrating dose equivalents. Thescatter in results was greatest for the X-ray beam qualities.
The type of phantom to be used for dosemeter calibration is a major concern. The adoption of a commonlyaccepted calibration method would allow direct comparison of results from service to service, both within acountry and internationally.
ACKNOWLEDGMENT
The financial assistance of the International Atomic Energy Agency who partly funded this project (ResearchContract 6012/R1 /RB) is gratefully acknowledged.
REFERENCES
1. International Commission on Radiation Units and Measurements (ICRU) "Determination of DoseEquivalents Resulting from External Radiation Sources". Bethesda, MD, 1985; Report 39.
2. J G Young and N J Hargrave "Intercomparison of Personal Radiation Monitoring Services in theAsia/Pacific Region" ARL/TR110, October 1992.
3. J G Young and N J Hargrave "Intercomparison of Personal Radiation Monitoring Services in theAsia/Pacific Region" Radiation Protection Dosimetry, Vol 51, No 2, pp 79-85 (1994)
4. International Standards Organisation (ISO), "X and Gamma Reference Radiations for CalibratingDosemelers and Dose Ratemeters and for Determining their Response as a Function of Energy", ISO4037-1979.
- 1 4 2 -
JAERI-Conf 95-014
TABLE
Ratios of each participant's reported penetrating dose equivalent to the delivered penetratingdose equivalent and the reproducibility of the participant's assessment indicated as a %standard deviation.
ParticipantNo.
1
23*4
567
89
10*11121314
15*1617
18*192021
22*23*2425
2627282930
31*
32*33*34
3536
38*
BeamA
1.48
0.990.780.360.470.921.010.71
0.92
0.931.040.960.92
0.97
0.90
0.980.85
0.93
1.000.950.790.990.980.700.980.92
1.05
1.230.951.02
%sd
4.61.26.95.92.33.86.71.33.0
4.36.82.4
3.0
2.42.6
13.62.84.9
5.60.81.9
2.63.94.70.6
2.3
5.4
2.013.7
2.2
B
1.53
1.000.810.370.470.971.02
0.710.92
1.011.240.99
1.01
1.020.97
0.870.840.97
• 0.93
0.940.80
0.971.031.490.990.94
0.99
1.290.52
1.10
C
1.531.170.700.20
0.390.871.000.71
0.98
1.050.790.980.76
1.010.83
0.960.890.59
1.291.080.83
0.931.050.361.050.90
1.151.14
0.82
D
0.121.17
1.17
0.75
0.790.87
1.000.951.271.040.701.06
0.670.88
1.010.87
0.961.100.63
0.800.77
0.961.041.160.92
1.05
0.065.13
1.40
E
0.17
1.48
0.490.47
1.000.870.480.942.152.470.900.741.08
0.980.91
0.77
0.920.68
0.800.49
0.961.140.440.840.71
0.66
0.151.34
1.56
F
0.64
1.001.410.390.480.960.850.40
0.84
1.150.750.71
0.77
0.880.68
1.140.780.71
0.900.65
0.860.840.040.97
0.69
1.10
0.490.77
1.00
* See text for an explanation of missing results.
- 1 4 3 -
JAERI-Conf 95-014
APPENDIX 2
Summary of Answers to the Questionnaire on Calibrationof Dosimeters and Survey Instruments for Photons
- 1 4 4 -
JAERI-Conf 95-014
Summary of answer to the Questionnaireon
Calibration of Dosimeters and Survey Instruments for photon
l.Traceability system
1.1 In your country, are the performance and procedure of thecalibration for radiation monitoring equipments determinedby law or regulation?
Answer
National law
Specific regulation
Others
No answer
Number of answer
5
5
5
3
1.2 Omitted
1.3 What kind of calibration field is prepared at the nationalstandard laboratory(or the secondary laboratory) in yourcountry?
Type
Gamma dose
X-ray dose
Beta dose
Neutron dose
Radioactivities
Source or Nuclide1 3 7 C s
6 0 Co
2 2 6 R a
241Am
others
90Sr-Y
H 7 P m
2 0 <Tl
2 4 1 , _
Am-Be252Cf226Ra-Be2 3 9 _ _
Pu-Beothers
Number of answer
13
12
4
6
5 1Cr,5 7Co
13
9
7
7
7
4 (Mod-D,0 1)
2
2
reactor
3
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JAERI-Conf 95-014
1.4 Does your national standard laboratory(or the secondarylaboratory) have the specific relationship on calibration toother country's or international's standard laboratory?
Answer
Yes
No
Number of answer
11
4
1.5 In measurements of photon dose,what kind of radiation unitis used for the transfer of radiation standard in yourcountry?
Answer
C/kq ,C/(kq*hr)
R,R/hr
Gy,Gy/hr
Others
Number of answer
5
14
6
Sv 1
1.6 In measurements of photon dose,what kind of standardmeasuring equipments is used at the national standardlaboratory(or the secondary standard laboratory)?
Free air ionization chamber(GJJ)Graphite cavity chamber (NPL256O)Reference graphite chamber & sensitive electronics(BARC)Cavity ionization chamber (Shonka-Wyckoff,air equivalentplastic walled(Exradin))Ionization chamber 30cc(IONEX2303)Free air chambers,graphite ion chambers(NPL)Ionization chamber(Nuclear Enterprises Ltd.)Spherical ionization chamber(LS-01,OMH Hungary)
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JAERI-Conf 95-014
2.Application of the new operational quantities
2.1 What kind of radiation units are used for personal monitoringand area monitoring in your country?
(1)Personal monitoring
Answer
Sv
Others
Number of answer
14
R 3, rem 3, rad 1
(2)Area monitoring at radiation fields
Answer
R,R/hr
C/kg,C/(kg*hr)
Gy,Gy/hr
Sv,Sv/hr
Others
Number of answer
10
0
4
11
rem 1
2.2 What is the situation of your country on the practicalapplication of the new operational quantities in the ICRUreports?
Answer
Now applied
Will be introduced in future
Refused
Others
Number of answer
5
7
0
applied partially 3
2.3 Please see P.4.
2.4 What kind of (conversion) coefficient do you use to convertexposure (or Air Kerma) into the operational quantities?
Answer
ICRU 39
ICRU 47
ICRP 51
Others
Number of answer
1
6
3
C.Coef.for IAEA phantom 1Wills,Grosswendt 1
2.5 Please see P.5
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JAERI-Conf 95-014
2.3 How are the standards for these quantities produced andsupplied for calibration?
Based on exposure/air kerma calibration and application ofICRU recommended factors.
ICRU dose equivalent standards are produced by multiplyingexposure standards by dose equivalent conversion factorswhich was suggested by ICRU Report 47.
1.Measurements are made using a cuboid water phantom of30cm cubic.A small volume tissue equivalent chamber is usedfor measurement of dose in phantom and air kerma in air.2.Use of published conversion factors for air kerma toambient dose equivalent.
1.Calibration of radiation sources with transfer chamberspreviously calibrated at PSDL.2.Measurement of exposure rate at calibration point withoutPMMA phantom and irradiation of dosimeters on the phantom.3.Compute the delivered dose equivalent using Air-Kerma todose equivalent factors.
Measure Air Kerma,apply published correction factors toobtain Sv.
By using standard chamber to calibrate output of radiationsources at various distances.Both cylinder and sphereionization chambers are calibrated in Exposure unit.Thesphere ionization chambers are recently compared totravelling standard ionization chamber of IAEA in Air Kermaunit.
By using international standard source.
1.Calibration performed free in air in term of exposure unit.2.Exposure then converted to air kerma.3.Air Kerma converted to H (10) using available data.
ICRP and ICRU publications.
Calibration of dosimeter.Use of calibrated source.Participation in intercomparison measurements of dosimeters.
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JAERI-Conf 95-014
2.5 Specify some topics or comments on the application of thenew operational quantities in your country.
Main difficulties are due to instruments not being scaled inthem.3.Monitoring Equipments for photon dose and theircalibration.
There are still some confusions in the use of calibrationphantom and conversion coefficient.lt is difficult to measureHo,H in the mixed field of photon and neutron.The design andthe calibration of personal dosimeters used for the measurementof H (0.07) should be improved in the future.
p
Problems on how to change the display unit from the old to thenew quantity instruments.Use of appropriate phantom for more reasonable results inirradiation of personal dosimeters.
We are interested in updating our system, but we need moreclarifications especially on the proper use of the .operationalquantities.While it has been started in TLD calibration,theproblem of using the data for a sphere phantom in a set-up of30cm cubic IAEA water trunk still comforts the SSDL staff.Theprocedure for calibration of survey meters is not revised norupdated.
People are not familiar with new quantities.And most ofinstruments are using old unit.
There are some research worries on developing the method ofmeasuring and colic Hp(10) quantities by TLDs.
Ambient dose equivalent is applied to both area monitoring andpersonal monitoring.
To be introduced when it will be international applied.
H (d) has not been applied yet, since we have not got ICRU spherephantom.
At present new operational quantities are not being used at SSDL.
1.Individual monitoring calibration methods,errors and theirassessment,S.C.Misra,P.S.Rao,Lecture delivered at workshop onindividual monitoring,BARC.2.Impact of new operational quantities on the calibration ofpersonal,environmental monitoring systems,and radiologicalprotection instruments.A.S.Pradhan.Proceedings of the conferencecum workshop on radiation standards and measurements,BARC,1993.
Adoption of the new operational quantities will take for sometimesince must of the survey meters and pendosimeters being used byclients are still in the mR/h,mR units.
149-
JAERl-Conf 95-014
3.1 I your country,what kind of monitoring equipments do you usefor personal monitoring and area monitoring?
(l)Personal dosimeter
Answer
Film
TLD
Others
Number of answer
13
14
electronic dosimeter 1pocket dosimeter 3
(2)Survey meter,others
Answer
Ionization chamber
GM survey meter
Scintillation Survey Meter
Others
Number of answer
12
13
12
semi-conductor survey 1no answer 1
3.2 What kind of radiation sources do you use for the calibrationof personal dosimeters and survey meters?
(l)Personal dosimeter
Answer
137Cs
60Co
226Ra
241,
AmX-ray generator
Others
Number of answer
13
13
4
3
g_ . 125_ 131 _ 9S=_
Beta-source, I, I, Tc
( 2)Survey meter
Answer
137Cs
60Co
226Ra
Am
X-ray generator
Others
Number of answer
14
11
5
4
9
0
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JAERI-Conf 95-014
3.3 Do you use "phantom" for calibration of personal dosimeter?
Answer
Yes
No
Number of answer
11
4
Figure of Phantom
Shape & Size
slab
30x30x15
slab
30x30x15
slab
cubic
30x30x30
slab
40x40x15
Material
polyethylene
PMMA
perspex+water
perspex(IAEAwater phantom)
PMMA
Number of answer
1
3
1
4
2
- 1 5 1 -
JAERI-Conf 95-014
3.4 What is the calibration frequency of personal dosimeters andsurvey meters?
(l)Personal dosimeter
Answer
Once in a year
Once in 6 months
Once in 4 months
Once in 3 months
Once in 1 months
Others
Number of answer
1
3
1
3
1
6 Please see below.
(2)Survey meter
Answer
Once in 6 months
Once in a year
Others
Number of answer
3
7
5 Please see below.
3.4 Others.
(1) Personal dosimeterDepend on the monitoring period.
Once in a year for whole energy range.Once in 3 months forrespect to 40 & 1250 keV.
Once in a year for recabliration.Once in 3 months for initialcalibration.
Once in 1 or 3 months.
Complete calibration 5 yearly.Selected point annually-Regularweekly and daily test for quality assurance.
Once in 6 months for TLDs.Once in 3 months for Films.
(2) Survey meterOnce in a year.Anytime at it may deem necessary as in the eventof repair.
Once in 3 months,once in 6 months and once in a year.
Up to the users.
On request,usually between annually or 2 yearly.Some statesrequire calibration of survey meters annually. Some do not.
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JAERI-Conf 95-014
APPENDIX 3
Workshop Agenda and Participants' List
- 1 5 3 -
JAERI-Conf .95-014
Agenda of IAEA/RCA Workshopon Calibration of Dosimeters & Survey Instruments for Photons
M O N D A Y November 28 [Conference Room No.7]11:30 - 12:00 OPENING SESSION
Chairperson: S. Kobayashi ( NIRS: RCA National Coordinator of Japan )1. Opening Address R.V. Griffith (IAEA)2. Welcome Address 1) S. Machida (MOFA)
2) S. Yamazaki (STA)
3. Introducing of Workshop Director
Workshop Director K. Bingo (JAERI)
Deputy Director N. Sakurai (PNC)
4. Welcome Address by Workshop Director
K. Bingo
5. Introducing of Participants
6. Information from Secretariat : H.Murakami
12:00 - 13:30 LUNCH
SPECIAL LECTURE SESSION13:30 - 14:15
Chairperson: K.BingoFoundations on Gamma- and X-ray Monitoring Instruments
T.Watanabe14:15 - 15:05
Chairperson: N.SakuraiComputation of Dosimetric Quantities in External Radiation Protection
Y.Yamaguchi15:05 - 15:40 COFFEE BREAK15:40 - 16:20
Chairperson: R.V.GriffithDissemination of Exposure Standard and the Irradiation Field on ICRU OperationalQuantities (A Suggestion of Practical Calibration for Operational Quantities)
KJVlinami16:20 - 17:10
Chairperson: B.FooteWork of the ICRU and ICRP-ICRU Joint Task Group in Specifying OperationalQuantities for Radiation Protection
R.V. Griffith18:00 -19:30 RECEPTION
- 1 5 4 -
JAERI-Conf 95-014
TUESDAY November 29 [Conference Room No.7]
COUNTRY REPORT SESSION IChairperson: G.Ramanathan
9:25 - 9:45 BANGLADESH9:45 - 10:05 CHINA
10:10 - 10:45 COFFEE BREAKChairperson: W.Wanitsuksombat
10:45 - 11:05 INDIA11:05 - 11:25 INDONESIA11:25 - 11:50 JAPAN
12:00 - 13:30 LUNCH
COUNTRY REPORT SESSION DChairperson: S.S.Ahmad
13:30 - 13:50 KOREA
13:50 - 14:10 MALAYSIA14:10 - 14:30 MONGOLIA14:30 - 14:50 NEW ZEALAND
14:50 - 15:20 COFFEE BREAK
Chairperson: M.Begum
15:20 - 15:40 PAKISTAN15:40 - 16:10 PHILIPPINES (2 persons)16:10 - 16:30 THAILAND
16:30 - 17:00 VIETNAM (2 persons)17:00 - 17:15 Special talk on an accident in Vietnam
WEDNESDAY November 30 [Conference Room No.7]
DISCUSSION SESSION I : Overall Discussion for Instruments Calibration9:15 - 10:15
Chairperson: R.V.GriffithCalibration of Radiation Protection Instruments in Asia & Pacific Region
- Present Status and Future Subjects; What's necessary for upgrading?
10:15 - 10:40 Technical Demonstration No.l : R.V.Griffith
10:40 - 11:00 COFFEE BREAK11:00 - 12:00 Technical Demonstration No.2 : JAERI
12:00 - 13:15 LUNCH13:30 - 15:00 TECHNICAL EXERCISE PNC
INDIVIDUAL DISCUSSIONS
- 1 5 5 -
JAERI-Conf 95-014
THURSDAY December 1 [Conference Room No.8]
DISCUSSION SESSION II : Quality Assurance for Individual Monitoring9:15 - 10:15 PROPOSAL PRESENTATION
Chairperson: B.FooteProposal of IAEA/RCA Personal Dosimetry Intercomparison, Phase 2
R.V.GriffithResults of IAEA/RCA Personal Dosimeter Intercomparison, Phase 1
H.Murakami
10:15 - 10:45 COFFEE BREAK10:45 - 12:00 Comments from Participants & Discussion
Chairperson: R.V.Griffith
12:00 - 13:30 LUNCH13:30 - 15:00 Discussion
Chairperson: R.V.Griffith
15:00 - 15:30 COFFEE BREAK
15:30 - 17:00 Discussion and Conclusion
Chairperson: R.V.Griffith
17:00 - 17:15 CLOSING SESSIONChairperson: S.Kobayashi
1. Certificate Awarding
2. Closing Remarks: N.Sakurai
3. Closing : R.V.Griffith
17:45 - 19:30 DINNER
F R I D A Y December 2
TECHNICAL TOUR
TO: Electro-Technical Laboratory ( Primary Standard Laboratory of Japan )
- 1 5 6 -
JAERI-Conf 95-014
Participants' List for IAEA/RCA Workshop on Calibration (Nov.28-Dec.2,1995)
Participants:
Ms. Mahfuza BEGUMHealth Physics DivisionAtomic Energy CentreP.O.Box 164, RamnaDhaka 1000BANGLADESH
Mr. ZHANG QingliChina Institute of Radiation ProtectionP.O.Box 120Taiyuan Shanxi Province 030006CHINA
Mr. Ganesan RAMANATHANRadiation Standards SectionBhabha Atomic Research CentreTrombay, Bombay 400085INDIA
Mr. Susetyo TRUOKOPSPKR BATANJl. Cinere Pasar JumatP.O.Box 7043 JKSKLJakarta SalatanINDONESIA
Mr. Bong-Hwan KIMHealth Physics DepartmentKorea Atomic Energy Research InstituteP.O.Box 105, Yuseong-guTaejon 305-600KOREA
Mr. Abd.Aziz bin MHD.RAMLINuclear Energy UnitMinistry of Science,Technology and the EnvironmentPUSPATI Complex, Bangi43000 KajangSELANGOR DARUL EHSANMALAYSIA
Mr. Dashyn SHADRAABALCentral Environmental Research LaboratoryMinistry of Environment and NatureUlan Bator - 52MONGOLIA
- 1 5 7 -
JAERI-Conf 95-014
Mr. Syed Salman AHMADHealth Physics DivisionPINSTECHP.O.NiloreIslamabadPAKISTAN
Ms. Arlean ALAMARESPhilippine Nuclear Research InstituteCommonwealth AvenueP.O.Box 231DILIMAN 3004, Quezon cityPHILIPPINES
Ms. Nieva LINGATONGRadiation Health ServiceDepartment of HealthSan Lazaro Compound, Rizal Ave.Sta. CruzManilaPHILIPPINES
* Mr. Hikkaduwa L. ANIL RANJITHAtomic Energy Authority696, 1/1 Galle RoadColombo 3SRI LANKA
Ms. Warapon WANITSUKSOMBUTOffice of Atomic Energy for PeaceChatuchakBANGKOK 10900THAILAND
Mr. DANG Thanh LuongRadiation Dosimetry LaboratoryCentre of Radiation ProtectionVietnam National Atomic Energy Commission59 Ly Thuong Kiet StreetHanoiVIETNAM
Mr. PHO Due ToanVietnam National Atomic Energy Commission59 Ly Thuong Kiet StreetHanoiVIETNAM
- 1 5 8 -
JAERI-Conf 95-014
Others;Lecturers & Technical Advisor:
* Mr. Neville J. HARGRAVEAustralian Radiation LaboratoryLower Plenty Road, YallambieVictoria 3085AUSTRALIA
Mr. Brian J. FOOTENational Radiation Laboratory108 Victoria Street,P.O.Box 25099ChristchurchNEW ZEALAND
Mr. Richard V. GRIFFITHDivision of Nuclear SafetyInternational Atomic Energy AgencyWagramerstrasse 5, P.O.Box 100A-1400 ViennaAUSTRIA
Observer:
Mr. Si-Young CHANGHealth Physics DepartmentKorea Atomic Energy Research InstituteP.O.Box 105 YusongKOREA
* means the participants who did not attend the meeting.
- 1 5 9 -
JAERI-Conf 95-014
Japanese (Organizer):
MOFA Mr. Shinya MACHIDA
STA
MRS
JAERI
PNC
Lecturer:
Mr. Shigeru YAMAZAKI
Mr. Sadayoshi KOBAYASHI
Mr. Kazuyoshi BINGOMr. Kentaro MINAMIMr. Shigeru KUMAZAWAMr. Hiroyuki MURAKAMIMr. Yasuhiro YAMAGUCHIMr. Shigeru SHIMIZUMr. Yoshihiro OiMr. Michio YOSHIZAWAMr. Fumiaki TAKAHASHIMr. Tetsuya OISHIMr. Mikio FUJIIMr. Teruaki NAGANUMAMr. Masao OHSAWAMr. Kenji OGAWAMs. Tomoko MAEJIMAMs. Masae SEKINE
Mr. Naoyuki SAKURAIMr. Tamotsu NOMURAMr. Mitsunori SUZUKIMr. Keiyiro MIYABEMr. Tomohiro ASANOMr. Takumaro MOMOSEMr. Noboru KOJIMAMr. Satoshi MIKAMIMs. Kumi INABAMr. Norio TSUJIMURAMr. Noriaki ENDOMr. Hiroyuki NAGAIMr. Takahiro OTSUKAMs. Fumiko SUNADA
Mr. Tamaki WATANABE
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2.93072x10''
3.76616 x 10"7
4.45050 x 1<T"
caiaiMtt)0.238889
2.34270
8.59999 x 10!
1
252.042
0.323890
3.82743x10""
Btu
9.47813 x 10"'
9.29487 x 10"3
3412.13
3.96759 x 10"3
1
1.28506 x 10"3
1.51857 xlO"22
ft • Ibf
0.737562
7.23301
2.65522 x 10'
3.08747
778.172
1
1.18171 x lO""
eV
6.24150 x 10"
6.12082x 10"
2.24694 x 10"
2.61272x10"
6.58515 x 10n
8.46233 x 10'"
1
1 cal = 4.18605 J
= 4.184J
= 4.1855 J (15-C
= 4.1868 J(raKU8
(I:'If 4! lPS({A.Mi;j)
= 75 kgf-m/s
= 735.499 \V
Bq
3.7 x 10"
Ci
2.70270 x 10-
1
Gy I rad
1
0.01
100
1
C/kg
1
2.58 xlO"'
R
3876
1
Sv
1
0.01
rem
100
1
(86 «P 12/126 0
