Studies On Terrestrial Gamma – Radiation And Polonium- 210 ... · Studies On Terrestrial Gamma – Radiation And Polonium- 210 Activities In And Around Costal Uttarkannada S. D

Studies On Terrestrial Gamma – Radiation And Polonium- 210 Activities In And Around Costal Uttarkannada

S. D. M. Degree College, Honnavar 1

CHAPTER-I

INTRODUCTION:

All living organisms are continuously bombarded by radiation emanated

from naturally occurring radionuclide’s. There are two main sources of

background radiations, they are Terrestrial sources and Extra - terrestrial

sources.

Terrestrial sources: Terrestrial radiation is due to primordial radionuclide’s

such as 40

K , 238

U 232

Th present in varying amount in soil, rocks, water and

building materials and atmosphere. They were present at the origin of the earth

and have half lives that are of the same order of magnitudes as the age of the

earth. Although natural abundance of 40K ,238U and 232Th varies with

geological condition , they are widely distributed in the earth’s crust. Some

radionuclide like 232

Th has several members of its decay chain.

232Th ----->

228Ra ----->

228Ac ----->

228 Th ----->

224Ra ----->

220Rn 216Po -----

>212

Pb ----->212

Bi ---->

212Po ----->

208Pb (stable)

The artificial radiation is primarily from medical imaging. Other human

contributors include smoking, air travel, radioactive building materials,

historical nuclear weapons testing, nuclear power accidents and nuclear industry

operation. Radiation treatment for various diseases also accounts for some dose,

both in individuals and in those around them.

https://en.wikipedia.org/wiki/Medical_imaging



Extra - terrestrial sources: Cosmic rays that are extraterrestrial in nature are

important sources of external exposure. Cosmic radiations primarily consisting

of 87% proton, 12% alpha particles and 1% heavier nuclei. When these

radiations interacts with atoms and molecules in the atmosphere to create an air

shower of secondary radiation, including X-rays, muons, protons , pions,

electrons, and neutrons. The intensity of cosmic ray background increases

rapidly with altitude. The cosmic radiation at sea level usually manifests as 511

keV gamma rays from annihilation of positrons created by nuclear reactions of

high energy particles and gamma rays.

About 88% of the total exposure is from natural sources remaining 12%

is from artificial sources of radiation. Radiation from radio nuclides in earth’s

crust and in other terrestrial matrices give rise to both external and internal

exposure. Natural radiation levels generally remain constant with time but may

vary significantly with location due to variation in regional geology.

POLONIUM (210

Po):

Polonium is a chemical element with symbol Po with atomic number 84. It

was discovered in 1898 by Marie Curie and Pierre Curie. A rare and highly

radioactive element with no stable isotopes, polonium is chemically similar to

bismuth and tellurium, and it occurs in uranium ores.

https://en.wikipedia.org/wiki/Air_shower_(physics)https://en.wikipedia.org/wiki/Air_shower_(physics)https://en.wikipedia.org/wiki/X-rayhttps://en.wikipedia.org/wiki/Muonhttps://en.wikipedia.org/wiki/Protonhttps://en.wikipedia.org/wiki/Pionhttps://en.wikipedia.org/wiki/Electronhttps://en.wikipedia.org/wiki/Neutronhttps://en.wikipedia.org/wiki/Positronhttps://en.wikipedia.org/wiki/Chemical_elementhttps://en.wikipedia.org/wiki/Atomic_numberhttps://en.wikipedia.org/wiki/Marie_Curiehttps://en.wikipedia.org/wiki/Pierre_Curiehttps://en.wikipedia.org/wiki/Radioactivehttps://en.wikipedia.org/wiki/Isotopes_of_poloniumhttps://en.wikipedia.org/wiki/Bismuthhttps://en.wikipedia.org/wiki/Telluriumhttps://en.wikipedia.org/wiki/Uraniumhttps://en.wikipedia.org/wiki/Ore



2I0Po is a decay product of

210Bi which in turn is the decay product of

210Pb. It has a half life of 138.4 days and is an alpha emitter. The intermediate

isotope 210

Bi with a half life of five days is a β emitter. The main source of 210

Po

in the environment is 222

Rn, which is exhaled from earth's crust. 222

Rn ultimately

decays to the nuclides 210

Pb and 210

Bi. These radionuclides attach themselves to

aerosol particles and return to the earth by gravitational, electrostatic and by

atmospheric precipitation. The 222

Rn remaining within the earth's crust decays in

situ to 210

Pb and 210

Po. A small quantity of 210

Po also forms in the atmosphere

by the disintegration of 210

Bi and returns to the earth through atmospheric

precipitation. The first two processes are responsible for the supported 210

Po and

the third process is responsible for unsupported 210

Po.

Due to the α activity of 210

Po, it produces greater biological effect than

210Pb the β emitter. The equivalent dose resulting from a single disintegration of

210Po is 1000 times greater than the decay of

210Pb (Parfenov, 1974). Hence it is

grouped under highly toxic radioisotopes. The total amount of 210

Po in the

earth's crust is approximately 2.3 x 10-14

% of the total weight. From the

geophysical point of view, polonium is very important because of the

substantial decay energy involved and the corresponding contribution to the

heat balance of the earth's crust (Parfenov, 1974).

210Po content in the soil varies widely throughout the globe from 8.14 Bq

kg-1

to 219 Bq kg-1

(Parfenov, 1974). US Atomic Energy Commission reports



the 210

Po content of various soils as 33 Bq kg-1

in brown soils, 58.1 Bq kg-1

in

bruizen soils, 55.87 Bq kg-1

in gray brown, etc.

210Po whose half life is 138 days has appreciable growth in vegetation

during single growing season and has an additional build up during food storage

reaching equilibrium in one year.

Polonium has 33 known isotopes, all of which are radioactive. They

have atomic masses that range from 188 to 220 u. 210

Po (half-life 138.376 days)

is the most widely available radionuclide. The longer-lived 209

Po (half-life 125.2

± 3.3 years, longest-lived of all polonium isotopes) and 208

Po (half-life 2.9

years) can be made through the alpha, proton, or deuteron bombardment of lead

or bismuth in a cyclotron.

210Po is an alpha emitter that has a half-life of 138.4 days; it decays directly to

its stable daughter isotope, 206Pb. A milligram (5 curies) of 210Po emits about as

many alpha particles per second as 5 grams of 226Ra. A few curies (1 Ci equals

37 GBq) of 210Po emit a blue glow which is caused by excitation of surrounding

air.

https://en.wikipedia.org/wiki/Isotopes_of_poloniumhttps://en.wikipedia.org/wiki/Radioactivityhttps://en.wikipedia.org/wiki/Atomic_masshttps://en.wikipedia.org/wiki/Atomic_mass_unithttps://en.wikipedia.org/wiki/Leadhttps://en.wikipedia.org/wiki/Bismuthhttps://en.wikipedia.org/wiki/Cyclotronhttps://en.wikipedia.org/wiki/Alpha_decayhttps://en.wikipedia.org/wiki/Decay_producthttps://en.wikipedia.org/wiki/Leadhttps://en.wikipedia.org/wiki/Radiumhttps://en.wikipedia.org/wiki/Curiehttps://en.wikipedia.org/wiki/Becquerelhttps://en.wikipedia.org/wiki/Excited_state



LIST OF TABLES:

Table1: Origin of 210

po from the uranium series

Element Symbol

Atomic

Number

Z

Mass

Number A

Half-Life

(T1/2) in

Radiation

given out

Uranium I UI 92 238 4.5X109yr α

Uranium X1 UX1 90 234 24.1 day β, γ

Uranium X2 UX2 91 234 1.17 min β, γ

Uranium II UII 92 234 2.52X105yr Α

Ionium Io 90 230 8.0X104yr α, γ

Radium Ra 88 226 1622 yr α, γ

Radon Rn 86 222 3.825 day Α

Radium A RaA 84 218 3.05 min α, β

Radium B RaB 82 214 27.0 min β, γ

Radium C RaC 83 214 20.0 min β, α, γ

Radium C′ RaC′ 84 214 1.6X10-4

sec Α

Radium C″ RaC″ 81 210 1.30 min Β

Radium D (Lead

210)

RaD

(Pb-210) 82 210 22 yr β, γ

Radium E

(Bismuth-210)

RaE

(Bi-210) 83 210 5 day Β

Radium F

(Polonium)

RaF

(Po-210) 84 210 138 day α, γ

Radium G (Lead) RaG

(Pb) 82 206 Stable lead



Table-2: Natural exposure levels in high background areas.

Kerala, India 1600mRy-1

Black Forest, Germany 1800mRy-1

Central City, Colorado 2200mRy-1

Guarapari, Brazil 17000mRy-1

Ref: Iyengar (1989)

Table-3: Estimated Annual Exposure of Man to Natural Sources of

Radiation

In Areas of Normal Background.

Sources

Annual Exposure (mRy-1

)

External Internal Total

Cosmic rays

Ionizing component

Neutron component

Cosmogenic nuclides

28.0

2.0

- -

--

--

1.5

28.0

2.0

1.5

Primordial nuclides in soils and

rocks

Potassium-40

Rubedium-87

Uranium-238 series

Thorium-232 series

12.0

--

9.0

14.0

18.0

0.6

95.0

19.0

30.0

0.6

104.0

33.0

Total 65.0 134.1 194.1

By: Iyengar (1989)



Table-4: Singly occurring radio nuclides of terrestrial origin

Radionuclide

Abundance (%) Half-life (Years) Principal

Radiation

40K 0.012 1.2610

9 -

87V 0.25 610

15

87Rb 27.9 4.810

10

-

115In 95.8 6.010

14

-

123Te 0.87 1.210

13 EC

138La 0.089 1.1210

11

-

142Ce 11.07 >510

16

144Nd 23.9 2.410

15

148Sm 11.27 >210

14 -

176Lu 2.6 2.210

10

-

190Pt

0.013 6.910

11

EC-Electron Capture



Table-5: Gamma absorbed dose recorded in some places of Karnataka and

its comparison with all India and World average.

Gamma absorbed dose

nGyh-1

Region Reference

Literature values

77.4-146.2 Shimoga Anandaram (1998)

50-250 Mysore Nagaiah (1996)

75 Karnataka

Average

Nambi et al (1987)

24-85 World range UNSCEAR (1988)

89 All India

Average

Nambi etal (1987)



SIGNIFICANCE OF THE STUDY:

The occurrence of radio nuclides varies from place to place on the globe

depending on regional geology and geography. For example, the high

background radiation along the coastal belt of South India, places like Brazil

etc, has been found due to the presence of monazite sand. Relatively high

background radiation levels were also observed in some parts of Singhbhum

District, India, Southern Saskatchewan, Germany etc., due to the presence of

granites. The local population in such localities receives relatively a higher

radiation dose. Several researchers have measured the 210

Po activity in and

around nuclear power plants such as Kalpakkam and Kaiga (near the study

area of the present investigation). Measurement shows that 210

Po activity is

considerably high in these regions than other areas. Thus the characterization of

the various environmental matrices with respect to their radioactivity content is

essential for correlation of dose estimates.

The geology of Uttara Kannada includes Granites, Lateritic rocks, Iron

ore, Bauxite ore etc., and Soil types include lateritic soil, alluvial soil, red loamy

soil, cotton soil etc. As granites contain higher concentration of 235U and 232

Th

and also 40

K, one can expect higher terrestrial radiation level in this region.

Consequently, dose to population in this region could be higher than normal. It

was therefore proposed to study radiation level and 210

Po activity in various

environmental matrices of Costal uttarakannada. This type of work has not been

carried out so far in this part of the country and happens to be first of its kind.



OBJECTIVES:

The objectives of the present study were,

1. Estimation of ambient gamma exposure level in and around Costal Uttara

Kannada and hence to assess annual dose to the population.

2. Estimation of 210

Po in Soil, Rocks, sand and Minerals, collected from

various locations in and around Costal Uttara Kannada.



CHAPTER-II

REVIEW OF LITERATURE

I. AMBIENT GAMMA RADIATION LEVEL:

1. The World average for terrestrial gamma radiation dose rate is about 59

nGyh-1

UNSCEAR (2009) , The overall terrestrial gamma dose in Spain

as 53. nGyh-1

Quindos et al (1994). The average gamma ray dose at

outdoor environments of Canada (Grasty, Carson JM, et al (1984) ranges

from 18-44 nGyh-1

in Bulgaria (Vassilev 1991) with an average of 70

nGyh-1

for the outdoor and an average of 75 nGyh-1

for the indoor

environs. The Malaysian average is 92 nGyh-1

but the highest average

terrestrial gamma radiation dose rates was recorded in Rembau district is

383 18 nGyh-1 which is 4 times higher than Malaysian average and 6

times higher than world average.

2. In India, the average gamma absorbed dose in Karnataka as reported by

Nambi et al (1987) amounts to 85 nGyh-1

and All India Average reported

by the same group is 89 nGyh-1

. In the environs of Goa external dose

rates range from 30-87.8 nGyh-1

with a geometric mean of 70.3 nGyh-1

(Avadhani et al ,1998). In Singhbhum district, India gamma dose rates

range from 75.7 to 200.1nGyh-1

. Further they have found higher dose

rates near granite rocks (Raghuvanshi et al, 1994). Gamma absorbed dose

recorded in and around Shimoga by Anandaram (1998) ranges from 77.4



to 146.2 nGyh-1

.Gamma absorbed dose recorded in and around Mysore

by Nagaiah (1996) ranges from 50 to 250 nGyh-1

.

3. Olarinoye et al (2010) have measured the background radiation level at

the vicinity of three campuses of two major tertiary institutions in Minna,

Nigeria, using a portable Geiger-Mueller tube – based environmental

radiation dosimeter. They have reported the dose rate ranging from 0.125

– 0.184 . They have also reported the annual effective dose as

0.189 .

4. Maharana et al (2010) have measured gamma radiation levels (indoor and

outdoor) in the villages surrounding the uranium-enriched regions around

Jaduguda, India, using card-based CaSO(4):Dy thermoluminescent

dosemeters. They have reported the annual indoor and outdoor gamma

dose values as 980 and 924 , respectively.

5. Gerald Pinto et al (2010) have measured the gamma absorbed dose rates

in Udupi and Karkala taluks of coastal Karnataka, India, using the GM-

Survey meter. They have reported the dose rate ranging from 70 to

123

6. WENG Jianqing et al (1992~2004) have measured the ambient gamma

radiation level in Qinshan Nuclear Power Plants (QNPP) Base, the

northeast of Zhejiang Province using thermoluminescent dosimeter

(TLD). They have reported the dose rate ranging from 84 - 113 nGyh-1

,

with an average of 96nGyh-1

in the 13 years.

http://www.sciencedirect.com/science/article/pii/S100180420860010X



7. IdrishMiah (2003) has measured Indoor gamma dose rate in air using

TLDs in the Dhaka district, Bangladesh. He has reported the average

annual effective dose and the collective dose equivalent for the residents,

respectively as, 0.86 mSv and 172.2 man-Sv.

8. Sreenath Reddy et al (2010) have measured the natural background

gamma radiation levels in the Hyderabad and its surroundings,

India,using thermoluminescence (TL) dosimeters and Geiger-Muller

based R-survey meter. They have reported the dose rate ranging from

226 - 506 nGyh-1

for urban Hyderabad and 190- 462 nGyh-1

for

surroundings of Hyderabad.

9. Mohanty et al (2003) have measured The external gamma dose rate level

of Erasama coastal Region, eastern coast of Orissa, India. They have

reported the absorbed gamma dose rates in air due to the naturally

occurring radionuclides ranging from 650 - 3150 nGyh-1

, with a mean

value of 1925 718 nGyh-1.

10. Senthilkumar et al (1996) have measured Gamma absorbed dose rates in

air outdoors from soil samples collected from Thanjavur (Tamil Nadu,

India) using g-ray spectrometry. They have reported the dose rate

ranging between 32 nGy.h -1

and 59.1 nGy.h -1

, with an arithmetic mean

of 43.3 ±9 nGy.h -1

.

11. Sriharsha et al (2008) have measured the gamma exposure rate in Mysore

and Chamaraj Nagar district, Karnataka, India using Environmental

http://www.jmp.org.in/searchresult.asp?search=&author=B+Senthilkumar&journal=Y&but_search=Search&entries=10&pg=1&s=0



radiation dosimeter. They have reported the dose rate varying 122.7 to

231.4 nGyh-1

inside the temples and between 141.8 to 340.2 nGyh-1

outside the temples of the region. They have also reported the indoor dose

rate varying 112.2 to 197.5 nGyh-1

, with a median of 127.0 nGyh-1

. and

outdoor dose rate varying 140.9 to 298.4 nGyh-1

, with a median of

216.2nGyh-1

II. 210

Po IN THE ENVIRONMENTAL MATRICES:

INTERNATIONAL STATUS:

1. Richard B. Holtzman (1980) has reported the mean intake of 210Po as 0.06

Bq/day in U.S diets.

2. Fernando P. Carvallho (1995) has measured the 210Po in food stuffs. An

activity concentration of 210

Po as 0.23 Bq/Kg in rice, 0.18 Bq/Kg in

potato, 0.054 Bq/kg in leafy vegetables and 0.023 Bq/kg in non leafy

vegetables has been reported.

3. Korenkov et al (2000) have measured the 210Po content in the superficial

soil layer of Moscow. They have reported the activity range of 210

Po as

30-50 Bk/kg.

4. Ashraf E.M. Khater and H.A. AL-Sewaidan (2008) have measured the

210Po content in the selected phosphate fertilizers samples used in Saudi

Arabia. They have reported the activity range of 210

Po as 0.5–110 Bqkg-1

with a mean value of 25 Bqkg-1

.

http://www.ncbi.nlm.nih.gov/pubmed?term=Korenkov%20IP%5BAuthor%5D&cauthor=true&cauthor_uid=10900787



5. Che Abdul Rahim Mohamed et al (2006) have measured the 210Po and

210Pb content in in sediment around the Sabah water at Teluk Brunei,

Sipitang, Teluk Kimanis, Kota Kinabalu and Kuala Penyu in Malaysia.

They have reported the activity range of 210

Po as 0.413 dpm/g to 8.491

dpm/g and 210

Pb as 0.023 dpm/g to 2.767 dpm/g.

NATIONAL STATUS:

1. Rajan et al (1980) have reported the activity 0.12 Bq kg -1in Sweet potato,

0.23Bq kg -1

in Spinach for 210

Po respectively from the Kalpakkam

region.

2. Karunakara et al(1993) have investigated 210Po activity in the two types

of vegetation species collected from Kaiga. They have reported 210

Po

activity in Careya arborea to range from 1.81-5.16 Bq kg-1

In Terminalia

paniculata the 210

Po activity ranges from 2.82-5.20 Bq kg-1

.

3. Karunakara et al (1993) have reported geometric mean of 97.89Bq kg-1as

the activity of 210

Po in soil samples of Kaiga.

4. Anandaram(1998) has measured 210Po activity concentration in the soils

of Shimoga and has reported it to vary form 4.7- 43.5 Bq kg-1

.

5. Similar type of measurement by Nagaiah(1996) in the soils of Mysore

reports 210

Po activity to vary from 7.6-37.3 Bq kg-1

.

6. Raja and Shahul Hameed (2010) have measured the 210Po and 210Pb

content in the sediments of Parangipettai Coast, South East Coast of



India, They have reported the activity concentration of 210

Po and 210

Pb in

sediments as 4.38 Bq kg -1

and 2.31Bq kg -1 respectively.

7. Marbaniang et al (2010) have measured the 210Po content in the soil

samples at Domiasiat uranium deposit area, West Khasi Hills,

Meghalaya, India. They have reported the mean activity of 210

Po in soil

as124.8 +/-5.7 Bq kg-1

.

http://www.ncbi.nlm.nih.gov/pubmed?term=Marbaniang%20DG%5BAuthor%5D&cauthor=true&cauthor_uid=19242810



CHAPTER-III

ABOUT STUDY AREA: COSTAL UTTARAKANNADA DISTRICT:

The Uttara Kannada district is located in Karnataka state of India

between north latitudes130 55’ 02”to 15

0 31’ 01” and east longitudes 74

00’35”

to 75010’ 23”.The total area of Uttara kannada district is 10291 sq.km and the

total population in the district is around 14.36 lakh (as per 2011census), out of

which rural population constitutes 10.18 lakh. The District experiences tropical

monsoon climate.Genarally the weather is hot and humid on the coastal areas

throughout the year. The district falls under the Hilly agro climatic zone except

for western parts of Karwar, Ankola, Kumta, Honnavar and Bhatkal taluks

which fall under coastal agroclimatical zone. The temperatures start rising from

January to May. The highest day time temperatures rise sometime up to 380C.

Average annual rainfall is around 1166.3 - 3672.5 mm.

The geographical conditions are most favorable in the formation of

different types of soils. Heavy rainfall and alternative seasons of heat and cold

have lead to the formation of lateritic soil. Such lateritic rocks are the parent

material of rock types in and around Uttara kannada. The dense forest of

Western Ghats have provided very conducive environment for soil formation.

The hills of Western Ghats are covered by iron rich lateritic soil which is

reddish brown in colour. The narrow strip of Sharavathi enriches the river banks

and the flood plains with alluvial soil, which is the most potential soil for

agriculture. Along the coast the costal alluvial soil is occurring on western most



parts of the district. The most rugged hilly parts of the district are covered by

hilly type soil and surrounded by lateritic soil having less rugged features. On

eastern parts, the lateritic soils change to red loamy soils. Some parts on eastern

most parts of Mundgod taluk are covered by semi black cotton soils. In the

district there are two big and two medium sized industries and 7736 small

industries are located in the district. Main surface water resources Kali and

Kadra rivers are used for generating electricity Major Atomic power plant is

situated in the bank of River Kali at Kaiga.

Laterite Soil:

Laterite is a soil and rock type rich in iron and aluminum, and is

commonly considered to have formed in hot and wet tropical areas. Nearly all

lateritic are of rusty-red coloration, because of high iron oxide content. Laterite

(brick stone) occurs all along the coastal part and is restricted to the upper part

of the rock formation and is one of the important building stones of the district.

Alluvial Soil:

Alluvial soils are formed mainly due to silt deposited by Indo-Gangetic-

Brahmaputra Rivers. In coastal regions some alluvial deposits are formed due to

wave action. Rocks of the Himalayas form the parent material. Thus the parent

material of these soils is of transported origin.

https://en.wikipedia.org/wiki/Ironhttps://en.wikipedia.org/wiki/Aluminiumhttps://en.wikipedia.org/wiki/Iron_oxide



Characteristics:

They are immature and have weak profiles due to their recent origin.

Most of the soil is Sandy and clayey soils are not uncommon.

The soil is porous because of its loamy (equal proportion of sand and

clay) nature.

Porosity and texture provide good drainage and other conditions

favorable for agriculture.

Chemical Properties:

The proportion of nitrogen is generally low.

The proportion of Potash, phosphoric acid and alkalies are adequate

The proportion of Iron oxide and lime vary within a wide range.

Granite:

Though both granite and gneiss share common mineralogy, they differ in

the mode of origin. While, granite represents a typical igneous rock, gneiss is a

metamorphosed form of granite formed under specific temperature and pressure

within the earth's crust. However, they exhibit similar physical features. Both

are hard rocks and generally occur below the lateritic cover in some parts of

Uttara Kannada district.



Figure 1Geological Map of the Study Area



CHAPTER-IV

NUCLEAR INSTRUMENTATION:

1. MICRO R SURVEY METER

MICRO R SURVEY METER (Type: UR 705) manufactured by Nucleonic

Systems is exclusively meant for low level radiation measurement. It is an ideal

choice for environmental radiation monitoring and also for geological

prospecting for radioactive minerals.

SPECIFICATIONS OF MICRO R SURVEY METER

MICRO R SURVEY METER (Type: UR 705) manufactured by

NUCLEONIX SYSTEMS is primarily designed to measure low level gamma



and X-radiation. This portable survey meter, designed around integrally coupled

1” X 1” NaI (Tl) Scintillator to a 1

“ PMT, will offer an optimum

performance in counting low level Gamma radiation dose rate

TABLE-6: TECHNICAL SPECIFICATIONS OF SURVEY METER

Detector NaI (Tl) Scintillator, 1” d X 1” h Coupled to

Photomultiplier Tube. Detector assembly is

inside the survey meter enclosure.

Calibration Accuracy Better than +/- 10% (Specified with a Cs -137

standard source) from 100µR h-1

onwards.

Acquisition mode CPS: 0-50000 , CPM 0-5000

Dose rate 1-10000 µR h-1

Over range It can Show over range above the 10,000 µR h-1

Data Storage Can store up to 1000 data readings. Stored data

can be recalled back on to the display

Display Indication Dot Matrix LCD display for dose rate

Sensitivity 1 µR h-1

or 0.01 µ Sv h-1

User Interface START, STOP, PROG, STORE, INC, DEC,

POWER ON command buttons for setting of

parameter and operation of the instrument.

Power 6V, DC , BPL Excel or DURACELL ULTRA ,

Size AA , MN 1500 LR 6 (4 X 1.5V) Alkaline

cells

Dimension 106 W X 196 L X 95 H in mm ( Approx)

Weight 2 Kg



Block diagram Description:

A. +5V Regulator Output:

Unit draws power from +6V (1.5Vx4) dry cells. A low dropout regulator

provided, regulates and gives out +5V. This also provides signal for low battery

indication.

B. HV Circuit

This is a blocking oscillator based on DC to DC converter circuit which

generates required HV to the Plastic Scintillator assembly, gamma probe.

C. Gamma Detector Probe:

This is a 1”x1” NaI or 2”x2” NaI optically coupled to 1’ or 2” PMT. Also

it contains HV bleeder circuit required for the probe assembly.

D. Pulse Amplifier/ Discriminator Circuit

This receives negative tail pulses from the gamma probe and amplifies these

signals considerably before they are passed into discriminator followed by

which to monostable, to generate TTL SIGNALS. Input stage of amplifier is a

charge sensitive stage.

E. Real Time Clock (Optional)

This is a signal RTC chip with battery backup. It is provided only in case

the user specifically orders the unit with RTC. This facilitates the user to log

and store dose rate and RTC information simultaneously. Note: In normal

Micro-R Survey Meter RTC is not provided.



F. Microcontroller and Associated Circuit Blocks:

TTL pulses from the detectors are counted in a digit BCD counter, which

is interfaced to microcontroller. These counts are read by microcontroller,

counted for a Time Constant (TC) and shown on a LCD dot-matrix display in

terms of dose rate, CPS or CPM. There is a choice of three TCs, for the user.

The user interface to the unit is through keypad consisting of SIX

command buttons. Unit has additionally EEPROM chip which allows the user

to store readings up to 1000. Future the stored data readings can be down loaded

into PC under the control of data communication software. There is an RS232

port provided (optionally) for connecting to PC for data transfer. This unit

works on dry cells 4x1.5V (6V).



CHAPTER-V

METHODOLOGY:

AMBIENT GAMMA LEVEL:

The ambient gamma exposure in the environs of Costal Uttarkannada was

measured using an environmental radiation dosimeter (sensitivity 1R/h).

Measurements were made 1m above the ground level both in disturbed and

undisturbed areas of study locations.

210Po ANALYSIS

COLLECTION OF ENVIRONMENTAL SAMPLES:

SOIL:

An area of about 10 sq. meter on an open, undisturbed and level ground

surface, away from public road and building was selected. After removing the

top layer of vegetation and root a pit was dug up to 6 centimeters. The soil from

the pit was collected in a polythene bag and sealed. The radiation level was also

noted using radiation dosimeter.

Sample processing:

The soil sample collected from various sampling locations was dried

overnight in oven at 1100C and cooled.

ACTIVITY OF 210

Po IN SOIL

210Po is volatile. Processing of the samples at high temperature is likely to

lead to loss of polonium. So wet ashing of environmental samples was carried at



a temperature of 90°C for the radiochemical separation of 210

Po. Initially the

radionuclide’s were leached from the sample using nitric acid. After obtaining

the white residue the sample was treated with 10 ml of concentrated

hydrochloric acid and evaporated to near dryness. This procedure was repeated

5 to 6 times so as to bring the sample into HC1 medium. Finally the residue was

treated with 400 ml of 0.5N hydrochloric acid and stirred. If any turbidity

occurs the solution was filtered through Whatman 42 filter paper. The solution

was used for the analysis of 210

Po by electrochemical displacement method.

SPONTANEOUS DEPOSITION OF 210

Po

The sample solution was kept on a magnetic stirrer provided with heating

arrangement. The temperature of the solution was maintained between 90° C to

95° C. About 100 mg of ascorbic acid was added to the solution to reduce ferric

ions in the solution to ferrous ions which otherwise would interfere in the 2I0

Po

deposition. A clean, brightly polished and background counted (on both sides)

silver disc (0.1 cm thick and 3.5 cm dia) was suspended into the solution.The

solution was then stirred using the magnetic stirrer for a period of 6 hours.

Distilled water was added in small dose occasionally to maintain the level of

solution as well as to wash 210

Po sticking to the beaker and glass rod. At the end

of the plating period, the disc was removed, washed with distilled water, ethyl

alcohol and dried under IR lamp. It was then counted both sides for alpha



activity in an alpha counting system. The 210

Po activity was calculated using the

relation.

Where,

A = Activity in Bq kg-1

S = Background subtracted sample counts per sec

SD = Standard deviation = (Cs / Ts2+ Cb / Tb

2)

½

Cs and Cb are the sample and background counts respectively,Ts and Tb

are the sample and background counting periods respectively (s).

ε = Efficiency of the alpha counting system (%)

W = Mass of the dry sample taken for analysis in g

M = Moisture content in the sample (%)

Ep = plating efficiency (%)

The plating efficiency of the Po was determined through Po standard of known

activity spiked in the sample. The sample was brought to solution from using

radiochemical procedures as explained above. The Po in the solution was placed

on a silver planchet and the percentage of recovery was calculated using the

alpha counts obtained.



RESULTS AND DISCUSSIONS:

TABLE-7: AMBIENT GAMMA EXPOSURE LEVEL IN THE STUDY

AREA

Sl.No. Location No. of

Readings

Absorbed Dose

in

Annual

Effective Dose

in

1

SDMCollege

Surroundings

60 76.3 93.5

2 ITI College 60 77.9 95.5

3 APMC Ramthirtha 60 86.7 106.3

4

Lateritic stone

Quarry

60

82.6 101.3

5

Indore stadium

Behind SDM college

60 96.7 118.6

6

Anjumanabad ,

Bhatkal

60

95.6 117.2

7

Near Karki

Mudaganapati

Temple

60

81.5 100.0

8 Apsarkonda 60 82.6 101.3

9

Granitic stone

Quarry near Karwar

60 131.3 161.0

10

Chandavar Stone

Quarry

60

119.4 146.4

11 Aresamikere 60 75.4 92.5

12 Kalsanmoote 60 61.1 74.9

13

Manki College

Ground

60

69.9 85.7

14 Anantavadi 60 73.8 90.5

15 Hosapattana bridge 60 62.4 76.5

16 Muroor Kumta 60 66.9 82.0

17 Kasarkod beach 60 45.6 55.9



Figure 2: Variation of Dose rate with Location

The knowledge of natural radiation level is very important due to the fact

that it accounts for the largest contribution to collective dose received by man.

This study provides the base line data required to assess the exposure of

population in areas of high natural radioactivity chosen for this study. The

ambient gamma levels have been measured at 17 different regions present in the

Uttara Kannada District The measurements have been made using

environmental radiation dosimeter ER-705. The results are summarized in Table

7

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

Dose rate in (nGyh-1)

Dose rate in (nGy/h)



It can be seen that the mean gamma dose rates vary from 45.6 to 131.3

nGyh-1

. Similar to the observations made elsewhere, ( Bruno Sansoni 1982,

Nagaiah,1996 Anandaram,1998)) higher than normal dose rates were found in

the regions where granitic outcrops were prominent and granite quarrying is

taking place. Granitic quarry near Karwar, Chandavar stone quarry, fall under

this category. Indoor stadium behind SDM college premises, Anjumabad in

Bhatkal, though the places are lateritic , the dose rates in these places were

found to be relatively high compared to the dose rate in Manki college ground,

Hosapattana Bridge, Kalsanmoote, etc. Very low dose rate was observed in the

Kasarkod beach, which is slightly low compared to dose rate of 75 nGy.h-1

in

Karnataka (Nambi etal 1987, BARC highlights, 1988) and is significantly low

compared to the dose rate observed near areas such as Ullal beach,

Manavalakurichi (Kerala), Kalpakkam beach, South west coast of Tamilnadu,

etc., where monazite is known to occur. Since the number of observations made

at sea level was small as compared to readings taken elsewhere in the study

area. Abnormal weather conditions and rough sea conditions might have

influenced significantly in obtaining such low dose rates. More definitive

conclusions can be drawn only after studying primordial radionuclide

distribution in this region.

The gamma dose rate in the Granitic quarry near Karwar, Chandavar

stone quarry, premises were found to be 131.3 and 119.4 respectively, which



are marginally high compared to the dose rates observed in general. It is known

that elevated levels of uranium, thorium and decay products are generally

present in granites. The higher radiation levels around these places are

obviously due to the presence of granitic outcrops in these regions.

The values of gamma dose rate obtained in the present study are

comparable with those obtained in the other environs and also with the world

average. They are well within the ranges of values observed at other places.



CONCLUSIONS AND SCOPE FOR FUTURE STUDY

The measurement of environmental is very much important, since

inhabitants of earth are continuously being exposed to such radiations ever since

the birth of this planet. In this respect monitoring of harmful health effects

caused by such radiations to the general public becomes highly essential. The

readings shown in this study have been taken very much painstakingly during

all the three seasons with the available resources and equipments. The authors

express their sincerest gratitude to the UGC for its constant encouragement and

support during all the stages of this project.

The Analysis of 210

Po as proposed in the project earlier is due on the part

of authors because of shortage of funding and will be taken up for the future

studies.



PHOTOGRAPHS

Behind S.D.M College

APMC Ramathirtha



Kasarkod Beach

Lateritic Stone Quarry



Lateritic Stone Quarry at Manki

Action Photograph



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