2008

BARC/2008/E/007B

AR

C/2008/E

/007

PERFORMANCE CHARACTERISTICS OF CaSO4: DY BASED INDIGENOUSTHERMOLUMINESCENT DOSIMETERS FOR ENVIRONMENTAL RADIATION MONITORING

byM. P. Chougaonkar, R. A. Takale, P.G. Shetty, Y. S. Mayya

andV. D. Puranik

Environmental Assessment Division

BARC/2008/E/007B

AR

C/2

008/

E/00

7

GOVERNMENT OF INDIAATOMIC ENERGY COMMISSION

BHABHA ATOMIC RESEARCH CENTREMUMBAI, INDIA

2008

PERFORMANCE CHARACTERISTICS OF CaSO4: DY BASED INDIGENOUSTHERMOLUMINESCENT DOSIMETERS FOR ENVIRONMENTAL RADIATION MONITORING

by

M. P. Chougaonkar, R. A. Takale, P.G. Shetty, Y. S. Mayya

and

V. D. PuranikEnvironmental Assessment Division

BIBLIOGRAPHIC DESCRIPTION SHEET FOR TECHNICAL REPORT(as per IS : 9400 - 1980)

01 Security classification : Unclassified

02 Distribution : External

03 Report status : New

04 Series : BARC External

05 Report type : Technical Report

06 Report No. : BARC/2008/E/007

07 Part No. or Volume No. :

08 Contract No. :

10 Title and subtitle : Performance characteristics of CaSO4:Dy based indigenousthermoluminescent dosimeters for environmental radiation monitoring

11 Collation : 26 p., 11 figs., 3 tabs.

13 Project No. :

20 Personal author(s) : M.P. Chougaonkar; R.A. Takale; P.G. Shetty; Y.S. Mayya; V.D. Puranik

21 Affiliation of author(s) : Environmental Assessment Division, Bhabha Atomic ResearchCentre, Mumbai

22 Corporate author(s) : Bhabha Atomic Research Centre,Mumbai-400 085

23 Originating unit : Environmental Assessment Division,BARC, Mumbai

24 Sponsor(s) Name : Department of Atomic Energy

Type : Government

Contd...

BARC/2008/E/007

BARC/2008/E/007

30 Date of submission : April 2008

31 Publication/Issue date : May 2008

40 Publisher/Distributor : Associate Director, Knowledge Management Group andHead, Scientific Information Resource Division,Bhabha Atomic Research Centre, Mumbai

42 Form of distribution : Hard copy

50 Language of text : English

51 Language of summary : English, Hindi

52 No. of references : 19 refs.

53 Gives data on :

60

70 Keywords/Descriptors : DYSPROSIUM; CALCIUM SULFATES; ACCURACY;THERMOLUMINESCENT DOSEMETERS; PERFORMANCE TESTING; ENVIRONMENT;RADIATION MONITORING; GAMMA RADIATION; FEASIBILITY STUDIES;DOPED MATERIALS

71 INIS Subject Category : S46

99 Supplementary elements :

Abstract : Dysprosium doped calcium sulphate based Thermoluminescent Dosimeter (TLD) cards,generally used for personal dosimetry applications in India were redesigned and modified to suit theenvironmental gamma radiation monitoring applications. Characteristics of the new TLDs, necessary forenvironmental gamma radiation monitoring were studied and found to be satisfactory in every respect.The TLDs were field tested together with the calcium fluoride powder based capsule TLDs and the resultswere found to be very satisfactory. This report describes the design parameters, characteristics of theTLDs and results of comparison studies between the two systems that were carried out in all the DAEinstallations where the environmental gamma radiation monitoring is being carried out for more than threedecades.

1

Performance Characteristics of CaSO4:Dy based indigenous

Thermoluminescent Dosimeters for Environmental Radiation

Monitoring

M. P. Chougaonkar, R. A. Takale, P. G. Shetty, Y. S. Mayya and V. D. Puranik

Environmental Assessment Division, Bhabha Atomic Research Centre, Mumbai, 400085

Abstract:

Dysprosium doped calcium sulphate based Thermoluminescent Dosimeter (TLD) cards, generally used for personal dosimetry applications in India were redesigned and modified to suit the environmental gamma radiation monitoring applications. Characteristics of the new TLDs, necessary for environmental gamma radiation monitoring were studied and found to be satisfactory in every respect. The TLDs were field tested together with the calcium fluoride powder based capsule TLDs and the results were found to be very satisfactory.

This report describes the design parameters, characteristics of the TLDs and results of comparison studies between the two systems that were carried out in all the DAE installations where the environmental gamma radiation monitoring is being carried out for more than three decades.

Introduction:

Environmental monitoring of all the nuclear facilities under Department of Atomic

Energy (DAE) is an important programme of the Health Safety and Environment Group,

BARC, under which releases of radioactivity to the environment, solid, liquid or gaseous

wastes if any, are monitored. The programme assesses adequacy of the controls, set by the

international bodies like International Atomic Energy Agency (IAEA) and in Indian

context, Atomic Energy Regulatory Board (AERB) on the release of radioactive materials

to the environment. The programme also assures the public at large that the nuclear

industry does not add to the radiation levels in the environs of the establishment. Radiation

monitoring, in High Background Radiation Areas (HBRAs), is also important to study the

2

effects of the elevated radiation levels on the human health and to attempt a possible

correlation between them.

Thermoluminescent Dosimeters (TLDs) offer a very reliable and inexpensive tool

for measuring the gamma radiation dose since the TLDs are very sensitive; reusable and do

not require constant manual attendance or other infrastructural facilities like electricity,

water etc. They can therefore be deployed at any remote place where no infrastructure

facilities exist. The information stored in the TLDs remains stored unless heated and thus

they are useful in monitoring remote locations by mailed TLDs in which the TLDs are

mailed to the designated organisation, deployed at a location for a predetermined period of

time, retrieved and sent back to the monitoring laboratory where they are read off and the

radiation exposure evaluated.

Environmental gamma radiation monitoring, using TLDs, around all the nuclear

facilities in India is being carried out for over three decades (1-4) using this methodology.

The TLDs have also been used in the indoor dosimetry of the High Background Radiation

Areas (HBRAs) in the southwestern state of Kerala (5-7), in addition to various research

projects for baseline surveys in different regions in India.

Materials:

These programmes have essentially been based on naturally occurring calcium

fluoride powder as TLD phosphor. Fifty mg of the processed calcium fluoride powder in

the particle size range 75-150 μm, properly processed and annealed, is filled in two brass

capsules of 8mm length, 3mm ID & 1mm wall thickness through a constant volume

3

vibrator dispenser. Two such capsules sealed in a watertight packet make one TLD as

shown in (Fig. 1). The loose powder in the grain size 75-150 μm ensures higher sensitivity

while the cylindrical geometry ensures the near isotropic response to gamma rays. The

brass capsule also makes the dosimeter response less energy dependent.

Fig. 1: A Photograph of a typical powder based TL dosimeter using brass filled CaF2 powder. (a) Brass capsules, (b) Brass capsules opened, (c) TLD packet and (d) TLD packed in PVC; ready for deployment.

These TLDs have been thoroughly tested for performance characteristics as set by

American National Standards Institute (ANSI)(8) and have been found to be quite

satisfactory for environmental gamma radiation monitoring in India (Table I). Participation

in many International Inter-comparisons of Environmental Dosimeters (IIEDs), in

collaboration with US Department of Energy (US DoE) has proved the efficacy of this

system (Fig. 2) (9). It was observed that the values obtained by the laboratory using CaF2

based TLDs have always been within 10% of the organisers’ values and as seen in the

4

figure, the overall performance of the TLDs vis a vis the IIEDs has been within 4% of the

organisers’ values.

Table 1: Performance Characteristics of CaF2 Powder based environmental TLDs(11)

Characteristics Performance of CaF2 powder based TLDs.

1 Energy dependence + 20 % between 50 and 1250 keV.

2 Environmental exposure response + 1 %of the true exposure using Ra226 calibration.

3 Fading 3 % in 3 months of continuous exposure.

4 Directional response Nearly isotropic.

5 Self dose- rate 26.8 μGy /year.

6 Precision + 5 %.

7 Accuracy (1 -20 mR range) + 10 %.

0.0 0.2 0.4 0.6 0.80.0

0.2

0.4

0.6

0.8

Y = 0.96(+/- 0.03)X r = 0.99

BAR

C va

lues

(mG

y)

Organiser's values (mGy)

Fig. 2: Results of different International Inter-comparisons of Environmental Dosimeters. The slope of the correlation curve, 0.96 (1 expected) indicates that the performance of the TLDs has been consistently within 4% of the organisers’ values.

5

Being powder based, this system is labor intensive and cannot cater to increased

requirement of environmental monitoring and other R&D activities like population

dosimetry in the HBRAs in India and other multi-institutional R&D projects. In order to

meet the increased demand for monitoring new stations, it was necessary to go for new,

state of the art, TLDs together with a fully automatic TLD reader system. This was

achieved by using an indigenously developed automated PC based TLD badge reader

system (10) wherein 50 TLDs can be loaded at a time and read off one after the other using

the automatic badge reader system

The card based TLD system on the other hand, used in personal monitoring

purposes, uses CaSO4:Dy as TL phosphor, first prepared by Yamashita et al (12), (<70μm

grain size) and is used in the form of Teflon embedded discs (13.3mm dia. & 0.8mm thick)

containing 70mg of CaSO4:Dy and 210 mg of Teflon. Three such discs are mechanically

clipped over three symmetrical circular holes each of diameter 12mm, on a nickel-plated

aluminum card (52 mm X 30 mm X 1 mm). The first disc is sandwiched between a pair of

1mm of aluminum and 1mm of Cu filters, copper filter being nearer to the disc. The

second disc is sandwiched between a pair of 1.5mm thick plastic filters. The third disc is

positioned under a circular open window. The various filters help in gamma, X-ray and

beta dose estimation. The readout of the disc under 1mm of Al and 1mm of Cu filters gives

directly the gamma dose. The TLD badge is covered with a wrapper and sealed in a

polythene pouch. The pouch protects the card from radioactive and chemical

contamination. The dosimetric characteristics of the TLD badge have been studied in

details and are reproduced in Table 2.

6

Table 2: Performance characteristics of the TLD using CaSO4:Dy powder (13)

Characteristics Performance of CaSO4:Dy based card TLDs.

1 Energy dependence ± 20% for 30keV to 3MeV

2 Environmental exposure response ± 8% of the true exposure using Cs137 calibration

3 Fading < 7 % in 6 months

4 Directional response Non - isotropic

5 Self dose- rate 120 µGy/year

6 Precision ±10%

7 Accuracy (1 -20 mR range) ±25%

Preliminary performance tests were carried out using these TLDs (without any

modifications) together with the CaF2 based powder TLDs. Based on the experiences, the

card TLDs were thoroughly modified and were subjected to rigorous quality control tests

in the laboratory as well as tests in the field. What follows in the report is the results of the

tests that were carried out and also the performance of the TLDs vis a vis powder based

TLDs.

Feasibility tests:

In order to assess the feasibility of using the CaSO4:Dy based personal monitoring

TLDs for the purpose of environmental gamma radiation monitoring, a preliminary

performance test was carried out by deploying the CaF2 powder based environmental TLD

and CaSO4:Dy card based personal TLDs together.

Two field test experiments were carried out to study the feasibility of use of

personnel monitoring TLDs in the environmental gamma radiation monitoring

applications(14). In the first, twelve personnel monitoring TLDs together with

7

environmental TLDs were deployed in the normal background areas for a period of three

months. The agreement between the two readings based on the TLD systems was found to

be rather poor and was attributed to the facts that the personnel monitoring TLDs, being

card shaped, are less isotropic in response compared to CaF2 TLDs, which are made of

powder filled in cylindrical brass capsules. In addition, the personnel monitoring

dosimeters, in the existing design, can yield the gamma radiation dose based on only one

disc. There is no mechanism to check the reproducibility of the reading that is possible in

the case of environmental TLD.

In the second exercise, 105 personnel monitoring TLDs were deployed together

with environmental TLDs in HBRAs for a period of four months. The retrieved TLDs

were processed by the respective units using their established protocols. The exposures

were expressed in the units of air kerma (μGy) and normalized for a period of 90 days.

It was observed that the readings obtained in the HBRAs showed good agreement.

Correlation analysis carried out between these data with the environmental TLDs along Y-

axis and the personnel monitoring TLDs along X-axis (Fig. 3) indicated a good linear

correlation between personnel monitoring and environmental TLDs, having a regression

coefficient of 0.96. The slope of the line is 1.07, very near to the expected value of unity.

The performance of the personal TLDs in environmental gamma radiation monitoring in

the HBRAs is as seen in Fig. 3.

The observation was also in concordance with the earlier observation (15) and

indicates that the TLDs used for personal monitoring purpose are suitable for

environmental dosimetry too if the radiation levels are higher than normal. In the case of

8

readings in low background areas however, where the air dose values ranged between 89-

218 μGy/90 days, the agreement between the two dosimeters was rather poor implying that

the personnel monitoring TLDs could not be used in the normal radiation background areas

in the present form and needed modifications.

0 200 400 600 800 1000 1200 1400 1600 1800 20000

200

400

600

800

1000

1200

1400

1600

1800

2000

μGy

μGy

Y = 1.07(+/- 0.01) Xr = 0.96n = 105

CaF 2 b

ased

env

ironm

enta

l TLD

s

CaSO4:Dy based PMS TLDs

Fig. 3: Intercomparison of PMS (CaSO4:Dy based) TLDs with EAD (CaF2 based) TLDs.

Following modifications were therefore made in the CaSO4:Dy based card TLDs to

make the personal monitoring TLD badge useful in the environmental monitoring:

1. Change in the dopant concentration: In place of the phosphor with 0.05% Dy,

concentration of 0.2% was used. This increased the sensitivity of the phosphor from 29

times the TLD 100 for 0.05% Dy concentration to 35 times that of TLD 100 for

CaSO4:Dy with 0.2% (16,17).

9

2. No. of elements for gamma radiation measurements: Rather than using only one

disc for gamma radiation as is done in personal TLD, two discs were covered with

1mm copper filters so that the reproducibility of the reading could be verified. At the

same time, the modified TLD consists of only two elements instead of three as in

personal TLD, thereby reducing the reading time by 33 %.

3. Copper filters for both the discs: Unlike in the personal monitoring TLDs, both the

discs were covered with 1 mm Copper filters from both the sides thereby making the

TL response less energy dependent.

4. Redesigning of plastic cassette: The plastic cassette covering the TLD card was

completely modified so as to be able to remove the exposed card and load it easily in

the TLD reader.

The TLD cards were prepared by fixing two discs with the wire clamps and were

placed in the cassette so that the discs were properly covered by the copper strips. This was

achieved with the help of a notch made on the card as well as in the cassette. The TLD

assembly is as shown in Fig 4.

.

Fig. 4: A typical photograph of Card based TLD using CaSO4: Dy phosphor.

10

The TLD discs as well as cards were thoroughly washed with acetone and dried.

The discs were then fixed on the cards with the help of spring clips. The TLDs were then

annealed at 250oC for the period of 3 hours in an oven with air circulation. After the

annealing, the oven was switched off and the TLDs were allowed to cool down naturally to

room temperature.

Background readings of all the TLDs were then recorded using automatic TLD

badge reader indigenously developed by BARC (18). Only those discs were selected that

showed the background reading within 10% of the average reading of about 15 counts.

The modified TLDs were subjected to various performance checks as follows.

Methods, Results and Discussion (19):

1) Determination of Lowest Detectable Dose (LDD):

Freshly annealed TLDs were taken and the background readings were recorded

using the automatic TLD badge reader. Average background readings and the standard

deviation were determined. As seen in Fig. 5, the average background were found to be 15

± 3 counts. The distribution of the 70 such background readings was observed to be normal

and 61 of the 70 readings were found to be within 2σ, indicating the closeness of the data.

The same TLDs were then used for determination of calibration factor. Ten TLDs

each were exposed to a standard 137Cs gamma-source (662 keV), traceable to IAEA

primary standards, for known exposures of 88,176,264 and 352 μGy respectively. The

calibration factor was found to be 0.48 μGy/count and is shown in Fig. 6. Based on the 3

11

times standard deviation of the background readings, the LDD was determined as

3*3*0.48 ∼ 5 μGy. The LDD of the TLDs was therefore 5 μGy.

10 15 200

2

4

6

8

10

12

14 Average counts 15 + 3LDD = 3*3*0.48 = 4.3 μGy

Num

ber o

f occ

uran

ces

TL Counts

Fig. 5 Distribution of background TL signal of 77 freshly annealed TLDs. 90% of the TLDs

are seen to have the background between 15± 2.98. The standard deviation of 2.98 gives

the LDD of 5 μGy.

0 50 100 150 200 250 300 3500

100

200

300

400

500

600

700

800 Response = 5 + 2.07*calibration doseCalibration factor = 1/2.07 = 0.48 μGy/counts

TL (c

ount

s)

DOSE (μGy)

Fig. 6: A typical calibration factor. Reciprocal of the slope of the dose response line

(counts/μGy) gives the calibration factor (μGy/counts)

12

2) Energy Dependence:

CaSO4 based TLDs, due to the high Zeff. are known to exhibit energy dependence if

proper care is not taken. The dosimeters, as described above, are designed in such a way

that the phosphor discs are covered on both sides by a 1mm thick copper filter for

attenuation of low energy photons. The energy dependence of the arrangement was

assessed by exposing 10 TLDs each to 88 μGy of X-ray/gamma radiation of various

energies. Three sets of readings were taken for various arrangements viz.

i) Only bare cards were exposed.

ii) Cards only with plastic cassettes were exposed

iii) Cards with 1mm copper filters in the plastic cassettes were exposed to the gamma

radiations

In each case, the TL response for energies, either of X-ray or gamma radiation was

compared with that for 137Cs (662keV). Fig. 7 shows the normalised TL response for the

TLDs for each energy normalised with respect to that due to 662 keV (137Cs source). It is

worth noticing the facts that

1. In the first two arrangements, where there was no metallic filter, the dependence of

the response on energy is quite prominent and there is hardly any difference in the

TL response.

2. When the TLD card is covered with 1 mm copper filter encased with plastic

cassette is practically energy independent.

13

0 200 400 600 800 1000 1200 1400

0.1

1

10

Rela

tive

TL in

tens

ity

Energy (keV)

No Filter Only Plastic Filter Plastic + 1mm Copper

Fig. 7: Energy dependence of TLDs. The TLDs with copper filter of 1 mm thickness is seen

to be sufficient to make the TLDs almost energy independent of the gamma/X-ray energy.

3) Accuracy and Precision

Freshly annealed TLDs were given a known exposure of 126, 189 and 252 μGy

using a 137Cs gamma source and were read off. The exposure values were evaluated using

the calibration factor and the precision and accuracy were calculated as shown in Table 3.

It is seen from the Table that the precision of the readings is about 5% of the

delivered value while the accuracy is within 7% of the delivered value. American National

Standard Institute criteria for environmental TL dosimeters (ANSI N545) specify that the

field results should be within 30% of the delivered values. It is seen from the table that all

the values are well within the limit specified in ANSI N545.

14

Table 3: Accuracy and Precision of the CaSO4:Dy card based environmental TL Ds.

Delivered Dose (μGy) Observed dose (μGy) Precision % Accuracy %

126 123 ± 5.3 4 2

189 180 ± 8.8 5 5

252 234 ± 10.9 5 7

4) Angular dependence:

Angular dependence, an important characteristic of the TLDs, decides whether the

TLD is suitable for the environmental radiation monitoring as the radiation in environment

is incident from all the sides and it is essential that the response of the TLD is as isotropic

as possible. The TLDs were exposed at different angles of incidence from the point

radiation source. A known exposure of 20mR of 137Cs source was given to the TLDs and

were read off using the TLD badge reader.

The angular dependence of the TLDs, normalized to perpendicular incidence, is

shown in Fig. 8. It can be seen, from the figure, that the response at all the angles of

incidence is very much within 30% of the normal incidence and hence fulfills the ANSI

criteria. It may be remembered here that the work was carried out using a calibration

source that can be taken as a point source. Small variation in the distance between source

and the individual disc can matter in the response in the laboratory experiment whereas the

exposure in environment is from an infinite source and as such the variation in response

with respect to the true value is expected to be much smaller. The TLDs thus can be said

to be isotropic in response.

15

Fig. 8: Angular dependence of the TLD. TL response for all the TLDs was observed to be

within 10% of the normal incidence value excluding 900 angle.

5) Fading of the TL Signal

It is necessary to know the fading characteristics of the TLDs before they are put to

use. Earlier studies reported that the fading is typically 1% per month (4,5). These studies

were carried out for the modified design of CaSO4: Dy based TLDs. Freshly annealed

TLDs were given an exposure of 200 μGy and were stored in lead pot. Two TLDs were

read off at regular intervals ranging 4 days to 90 days. It was observed that there was a

fading of about 7% during the first month as shown in Fig. 9. Long-term fading studies are

in progress.

16

0 5 10 15 20 25 300.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Nor

mal

ised

exp

osur

e

No. of Days

Fig.9: Fading characteristics of the CaSO4:Dy card based environmental TLDs. About

7% loss in the signal over the period of 30 days is observed.

6) Field Tests

In the initial field studies, freshly annealed TLDs were deployed together with CaF2

based TLDs at 36 different locations for a period of 90 days. The retrieved CaF2 based

TLDs were read using the TLD reader used regularly for environmental TL monitoring

work while the modified TLDs were read using automatic TLD card reader. The data

collected over two such quarters, over the period of 180 days, was used in the present

analysis. The correlation between the results obtained using two different TLD systems, as

shown in Fig. 10. The correlation between the readings for card based modified TLDs

with the powder based environmental TLDs is seen to be excellent with a slope of 1.00

(expected 1) with correlation coefficient r of 0.99 and implies the goodness of fit. This

17

clearly indicates that the card based TLDs in the modified form are very much comparable

with the CaF2 based TLDs and can be used for the environmental gamma radiation

monitoring. It is worth noting that majority of the readings, 50 out of 72, are less than 500

μGy/90 days, thus it is clear that the TLDs after modifications in the design, are suitable

for environmental gamma radiation.

0 1000 2000 3000 40000

1000

2000

3000

4000

5000

Pow

der T

LD (μ

Gy/

90 d

ays)

Card TLD (μGy/90 days)

Y = 1.00 (+/-0.01)Xr = 0.99

Fig. 10: Intercomparison of the gamma radiation levels obtained using two different TLDs

36 locations. The slope of 1.00 (expected unity) indicates the excellent matching between

the modified TLDs and the ones that are in use for over three decades Fifty of 72 data

points are seen to be less than 500 μGy/a.

Based on the experience obtained during the work, the TLDs were deployed at all

the locations in all the DAE stations during the years 2006-07 on trial basis. CaF2 based

TLDs were also simultaneously deployed as the performance indicator. The comparison

between these two systems with a huge data of more than 1000 readings (Fig. 11) further

18

confirms, with the correlation parameters of slope =1 and r= 0.91, that the card based

TLDs have satisfied the performance criteria and the suitability of these TLDs for the

environmental gamma radiation dosimetry programme is established.

0 1000 2000 3000 4000 50000

500

1000

1500

2000

2500

3000

3500

4000

4500

5000Y =1.00(+/- 0.009)X, r = 0.91Data points : 1053 From all the stations except Trombay

Dos

e m

easu

red

usin

g C

ard

TLD

(μG

y/q)

Dose measured using powder TLD (μGy/q)

Fig. 11: Intercomparison of the gamma radiation levels obtained using two different TLDs

at all the DAE establishments during the period 2006-2007. The slope of 1.00 (expected

unity) indicates the excellent matching between the modified TLDs and the ones that are in

use for over three decades.

Conclusions:

The CaSO4:Dy based card TLDs, which were modified based on the preliminary

field tests in HBRAs, were thoroughly studied for suitability in the environmental gamma

radiation monitoring applications. It was found that

1. The modified TLD have the LDD of 5 μGy.

19

2. With the introduction of 1 mm copper filter, the TLDs are almost energy

independent.

3. The TL response of the TLDs is almost isotropic.

4. The TLDs exhibit the precision and accuracy of 5 % and 7% respectively.

5. The TLDs show fading up to about 7% initially, although later on, there is no

further loss of signal.

6. Performance tests of the TLDs in the field indicate that the TLDs are very

much comparable with the CaF2 powder based TLDs.

The modified TLDs, which are card based and can be read on an automatic

TLD card reader, can be therefore used in the environmental radiation-monitoring

programme.

Acknowledgements:

Thanks are due to S/Shri O. P. Masand and Munish Kumar , PMS, RP&AD

for their kind help in analysing the PMS TLDs in the initial performance tests.

Thanks are also due to Shri S. Kannan Head, RP&AD and Smt. Ratna Pradip,

RSSD, BARC for modifying suitably and providing the automatic TLD badge

reader.

References:

1. Nambi, K.S.V. “Environmental radiation surveillance using thermoluminescent

dosimeters,” BARC report, BARC/I-575 (1979).

20

2. Basu, A. S., Bapat, V. N., Chougaonkar, M. P., Nambi, K. S. V. and Gurg R.P.

"Quarterly Radiation Monitoring Results for the Period 1988-1996 in RAPS Region

Using TLDs And Summarized Analysis for the Period 1982-1996",

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3. Chougaonkar M. P., Sarma, P. S., Lakshmanan, A. R. and Sadasivan, S. Two decades

of radiation monitoring around the environs of Nuclear Fuel Complex, Hyderabad

using TLDs. Proc. Nat. Symp. On Environment, B’lore Univ. June 2000, 230-234.

(2000).

4. Chougaonkar M. P. and Basu A. S., Environmental radiation dosimetry using TLDs:

quality assurance in performance; Nat. Seminar on Luminescence & its Applications

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Mayya Y. S. and Sadasivan S. “Results of Dosimetric Survey at High Background

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6. Shetty, P. G., Chougaonkar, M. P., Mayya Y. S. and Puranik, V. D. Analysis of

External Gamma Dose Levels in the Dwellings Situated in Elevated Natural

Radiation Areas of Kerala using Thermoluminescent Dosimeters (TLDs). Radat.

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7. Chougaonkar, M. P. Application of TL dosimetry in epidemiological studies in

HBRAs. Proc. NCLA-2006, Ed. S. V. Godbole et al, pp 92-96 (2006).

21

8. American National Standards Institute (ANSI) Performance criteria for

environmental radiation monitoring, N545 (1974).

9. Nambi, K.S.V., Bapat, V. N., David, M., Sundaram, V. K., Sunta, C. M. and Soman,

S. D. “Country-wide environmental radiation monitoring using TLDs,” Radiat. Prot.

Dosim. 28(1), 31-38, (1987).

10. S. Kannan, P. Ratna and M. S. Kulkarni “A new TLD badge with machine readable

ID for fully automated readout,” Rad. Prot and Env. 26, 251-253 (2003)

11. Vohra, K.G., Bhatt, R.C., Bhatt, B.C., Pradhan, A.S., Lakshmanan A.R. and Shastry

S. S. “Personnel dosimeter TLD badge based on CaSO4:Dy Teflon TLD disc,”

Health Phys. 38193-197, (1980).

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