View
151
Download
1
Category
Preview:
Citation preview
QUANTITIES AND UNITS USED IN RADIATION PROTECTION
H.L ANIL RANJITHHEAD, DIVISION OF RADIATION PROTECTION
ATOMIC ENERGY AUTHORITY
QUANTITIES:
ARE MEASURABLE CHARACTETISTICSEg LENGTH, DOSE ETC.
UNITS
ARE USED TO DESCRIBE THE QUANTITYEg METERS, GRAYS ETC.
RADIATION UNITS
• TO MEASURE RADIOACTIVITY• TO EXPRESS ENERGY OF
RADIATION EMITED• TO EXPRESS AMOUNT OF
ENERGY DEPOSITED IN THE BODY
• TO QUANTIFY BIOLOGICAL DAMAGES TO IRIDIATED TISSUES
ACTIVITY
• NO.OF DESINTEGRATIONS PRE SECOND
• 1Bq = 1 dis/s
• ORDER OF MAGNITUDE
THE CURIE
1 Curie (Ci) = Activity of 1g of 226Ra
1g of 226Ra disintegrate 3.7x1010 atoms per second
1 Ci = 3.7 x 1010 dis/s
1 Ci = 3.7 x 1010 Bq
1 Ci = 37 GBq
ENERGY OF RADIATION
ELECTRON VOLTS
1eV = 1.6 X 10 –19 J COBALT- 60 RADIOACTIVE MATERIAL EMITS TWO GAMMA RADIATIONS OF ENERGIES 1.17 MeV AND 1.32 MeV.
DOSE
USES AS A GENERIC TERM THAT CAN APPLY TO ANY OF THE RELEVANT
DOSIMETRIC QUANTIES
EXPOSURE
IN A GENERIC SENSE TO MEAN THE PROCESS OF BEING EXPOSED TO
RADIATION
Exposure Unit
•Is a measure of ionization produced in air
•Is used only for X and radiation
•Is valid for quantum energy less than 3 MeV
X Unit
1 X unit = 1 C/kg air
One exposure unit is defined as that quantity of x or gamma radiation that produces in air, ions carrying 1 coulomb of change( of either sign) per kg air.
Exposure Exposure is measured under conditions of electronic
equilibrium For photon energies above about 3 MeV, the ranges of
secondary electrons become a significant fraction of the photon attenuation lengths and the departure from equilibrium may be significant
Thus, exposure is not defined above photon energies of 3 MeV
Roentgens (2/3)
• Is symbolized by R
• was used as the exposure unit before SI system was adopted
• is still being used.
Roentgen
Is defined as the quantity of x or gamma radiation that produces ions carrying one statcoulomb of charge of either sign per cubic centimeter of air at STP. Charge of the electron=1.6x10-19C =4.8x10-10sC
1C =3x109 sC
13
KERMA
KERMA (Kinetic Energy Released in a Material):– Is the sum of the initial kinetic energies of all charged
ionizing particles liberated by uncharged ionizing particles in a material of unit mass
– For medical imaging use, KERMA is usually expressed in air
SI unit = joule per kilogram (J/kg) or gray (Gy)
1 J/kg = 1 Gy
14
Mean absorbed dose in a tissue or organ
The mean absorbed dose in a tissue or organ DT is the energy deposited in the organ divided by the mass of that organ.
ABSORBED DOSE(1/2)• MEASURES THE ENERGY
DELIVERED TO ANY MATERIAL
• IN RADIATION PROTECTION THE MATERIAL CONCERNED IS
THE TISSUE OR ORGAN OF THE HUMAN BODY
ABSORBED DOSE(2/2)
• DEFINED AS THE “ENERGY ABSORBED
PER UNIT MASS OF ANY MATERIAL”
• UNIT USED “GRAY” OR “RADS”
1GRAY (Gy) = 1J/kg
1RADS = 100 ergs/g
100 RADS = 1 Gy
EQUIVALENT DOSE(1/2) QUANTIFY THE BIOLOGICAL DAMAGE TO THE ORGAN OR
TISSUE IRRIDIATEDThe same dose levels of different radiations (ie photons and neutrons) do not have the same level of biological effect
Radiation weighting factor, wR(related to radiation quality)
EQUIVALENT DOSE(2/2)
• BIOLOGICAL EFFECTS OF AN EXPOSURE ON A ORGAN OR TISSUE DEPEND ON:
• ENERGY TRANSMITTED TO THE ORGAN OR TISSUE BY RADIATION
• HAMFULNESS OF THE TYPE OF RADIATION INVOLVED (DEGREE OF POWER OF IONIZATION)
Radiation weighting factors, wR
1 Type and energy ranges
Radiation
weighting
factor, wR
115
10 20105 5
Photons, all energiesElectrons and muons, all energiesNeutrons, energy < 10 keV
10 keV to 100 keV100 keV to 2 MeV> 2 MeV to 20 MeV> 20 MeV
Protons, other than recoil protons, energy > 2
MeVAlpha particles, fission fragments, heavy nuclei
20
1) All values relate to the radiation incident on the body, or, for internal sources, emitted from the source.
Neutron radiation weighting factors30
25
20
15
10
5
0
wR
Neutron energy - MeV10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 1 10 102
ICRP Recommendation
ICRP Approximation
EFFECTIVE DOSE
Different body tissues have different biological sensitivities to the same radiation type and dose
Tissue weighting factor, wT
EFFECTIVE DOSE• MEASURES THE RISK OF
BIOLOGICAL DAMAGE TO WHOLE BODY TAKING THE RADIOSENSITIVITIES OF TISSUE IRRIDIATED IN TO ACCOUNT
• MEASURES THE RISK REGARDLESS OF EXPOSURE INVOLVED.( INTERNAL, EXTERNAL, PARTIAL OR TOTAL)
• MEASURES IN THE UNIT OF.
“SIEVERT”( Sv )
Roentgen (3/3)
1R = 0.0087 J/kg of airIR = 0.0087 Gy = .87 RadIR = 0.0096 J/kg in TissueIR = 0.0096 Gy in TissueIR = .96 Rad in Tissue1 R = 1 Radfor x and rays IR = 1 rem = .01 Sv
Multipliers of the equivalent dose to an organ or tissue to account for the different sensitivities to the induction of stochastic effects of radiation.
Tissue or organ wT Tissue or organ wT
Gonads 0.20 Bone marrow (red) 0.12 Colon 0.12 Lung 0.12 Stomach 0.12 Bladder 0.05 Breast 0.05 Liver 0.05 Oesophagus 0.05 Thyroid 0.05 Skin 0.01 Bone surface 0.01 Remainder 0.05 TOTAL 1.00
Tissue weighting factors
Committed Dose
Is a useful subsidiary dosimetric quality to express dose to body during certain time following an intake of radioactive material to the body.
Note : The dose delivery to the body during the above period is at varying rates.
Committed Equivalent Dose
Defined as the time integral of the equivalent dose rate and denoted by HT( )
= integration time in years following the intake.
If t is not specified
Integration time is taken as
50 years for adults
70 years for children
Committed equivalent dose: The quantity H(), defined as;
where to is the time of intake, HT(t) is the equivalent dose rate at time t in an organ or tissue T and is the time elapsed after an intake of radioactive substances.When is not
specified it will be taken to be 50 years for adults and to age 70 years for intakes by children.
H H t dtTt
t
o
o
.
Committed effective dose:
The quantity E(), defined as ;
where HT() is the committed equivalent dose to tissue T over the integration time and WT is the tissue weighting
factor for tissue T. When is not specified it will be taken to be 50 years for
adults and to age 70 years for intakes by children.
E W HT TT
.
Collective Dose(1/2)
Is used to express dose to a group or a population.
Takes account of the no of people exposed to a source and the average dose to the individual.
COLLECTIVE DOSE(2/2)
DEFINED AS,
THE PRODUCT OF THE NUMBER OF INDIVIDUAL EXPOSED TO A SOURCE AND THEIR AVERAGE DOSE
UNIT: MAN SIEVERT (man Sv)
Is there RADIATION in this room?
Background Radiation
•Natural Background Radiation•Background Radiation Due to Man Made Sources.
NATURAL BACKGROUND RADIATION
• TERRESTRIAL SOURCES• EXTRA TERRESTRIAL SOURCES ( COSMIC RADIATION )
Natural sources of radiation… (2.4 mSv.y-1)
Cosmic…(0.4 mSv.y-1)
…from earth’s crust (0.4 mSv.y-1)
…via ingestion (0.3 mSv.y-1)
…via inhalation (1.3 mSv.y-1)
C. Torudd ; Swedish Radiation Protection Institute
...internal
External terrestrial irradiation 0.4 mSv y- Varies considerably with soil and rock type
Unusually high background in a few places in e.g.•Esperito Santos, Brazil•Kerala, India•Guandong province, ChinaUp to 50 µGy h-1 compared to 0.1 µGy h-1
External extra terrestrial radiation (Cosmic radiation)Estimated spectrum of secondary particles in the atmosphere from cosmic radiation
Heinrich et al 1999 (0.4 mSv.y-1)
Cosmic radiationDose and ambient dose equivalent during a flight from Bangkok to Copenhagen
External irradiation: Natural background dose rates from external sources (mSv.y-1)
Internal irradiation via
inhalation, 1.2 mSv.y-1
(mainly indoor radon)
Reasons for elevated levels of indoor radon
•elevated levels of 238U and 232Th series in the ground
•building material with elevated levels of 238U and 232Th series
•tight houses (cold climate…)
Internal irradiation via
ingestion40K•abundance 0.0188% in potassium (K)(0.15 mSv.y-1)
Also•uranium and thorium series(0.15 mSv.y-1)
Man-made Radiation
• Cigarette smoke• Consumer products
– Building materials– Smoke detectors
• Industrial use• Medical use• Nuclear power • Nuclear fall out
…and artificial sources of radiation
Medical examinations…(0.4 mSv.y-1)
C. Torudd ; Swedish Radiation Protection Institute
…and more artificial sources of radiation
...and nuclear weapons(0.005 mSv.y-1
atmospherical tests)
Nuclear fuel cycle…(0.0002 mSv.y-1)
C. Torudd ; Swedish Radiation Protection Institute
Nuclear power
Nuclear weapons
© Chernobylinterninform 1996
Chernobyl accident, April, 1986
Practical concequencies of Chernobyl accident
Effects of radiation and accident situation•600,000-800,000 persons in cleaning up work•Approximately 200,000 persons evacuated•Large areas of land abandoned (30 km zone etc.)
Other effects:•Cost estimated to 100 billion USD
Health concequencies of Chernobyl accident
Effects of radiation and accident situationSeen:•Immediate death of 30 persons •1800 children diagnosed with thyroid cancer (1998)Statistically:•15,000 deaths in cancer (global)
Other factors influencing health:•Poor food supply, social concequencies, anxiety
Source Mean effective dose (mSv)Natural background 2,4Medical examinations 0,4Nuclear tests in the atmosphere 0,005Chernobyl accident 0,002Nuclear fuel cycle 0,0002
Individual exposure of the world’s population due to ionising radiation,
year 2000
UNSCEAR
DO WE NEED RADIATION PROTECTION ?
Drinking Hot Coffee
Excess Temperature = 60º - 37 = 23º1 sip= 3ml3x 23= 69 calories
Lethal Dose= 4GyLD 50/60 = 4 GyFor man of 70 kg
Energy absorbed = 4 x 70 = 280 Joules = 280/418= 67 calories = 1 sip
X-ray
We live with1-3 mSv
Can kill4000 mSv
Radiation
Where to stop, where is the safe point?What are the effects of radiation?
What can radiation do?DeathCancerSkin BurnsCataractInfertilityGenetic effects
Recommended