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Applied Radiation and Isotopes 66 (2008) 86–89

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Application of commercial glasses for high dose measurement using thethermoluminescent technique

Pradeep Narayan�, K.R. Senwar, S.G. Vaijapurkar, D. Kumar, P.K. Bhatnagar

Defence Laboratory, Radiation Dosimetry, Ratanada Palace, Jodhpur, Rajasthan 342011, India

Accepted 18 July 2007

Abstract

Commercial glasses under this study showed linear thermoluminescence (TL) response in gamma dose range 100Gy to 10 kGy, glow

peaks between 175 and 200 1C, fading under dark and room light 2.86–7.36% and 10.42–20.82%, respectively, in 24 h and 34.86–70.80%

under sunlight in 5 h after exposure. The TL glass dosimetric results have been found to be reproducible within 76.0%. Glasses have

been observed as thermally unstable and its TL sensitivity reduces after annealing. The TL response of the glasses has been found to

reduce by 7.40–51.49% after first annealing of the samples at 400 1C for 15min. The trace element study suggests that presence of

impurities has no role in TL sensitivity of glasses rather imperfections and dislocations in the lattice are the major contributor in the

formation of TL centers. Commercial glasses can serve as good TL material for gamma irradiator and gamma chamber dosimetry. The

various radiation parameters for glass TL dosimetry have been studied in detail and presented.

r 2007 Elsevier Ltd. All rights reserved.

Keywords: Thermoluminescence; TLD reader; Commercial glass; High dose dosimetry

1. Introduction

Dosimetry is an essential requirement for qualityproduct in radiation processing of medical and consumerproducts. Radiation processing has emerged as an expand-ing technology with numerous applications in health careproducts sterilization, sewage and hospital waste treat-ment, polymer modification, food processing and R&D,etc. Radiation processing generally requires high-gammadose of the order of kilogray depending upon the type ofthe material and requirements. All parts of the productmust receive an absorbed dose within certain prescribedlimit. Adequate dosimetry with proper statistical controlsand documentations is the key part of the quality control,which is necessary to assure that the products are properlytreated (Ferrar, 1999).

Glasses are generally made of silica as the basic materialwith certain additional trace elements as per its intendedapplication. Sands are also made of silica and have been

e front matter r 2007 Elsevier Ltd. All rights reserved.

radiso.2007.07.018

ing author.

ess: pradeep_narayan@rediffmail.com (P. Narayan).

reported as thermoluminescence (TL) dosimetric materialfor high dose and accidental dosimetry (Vaijapurkar et al.,1998). TL in common natural materials, e.g., naturalquartz present in sand provides a useful method for directmeasurement of absorbed radiation (Fathony, 1999). Inrecent past, glasses have been reported for its high doseradiation dosimetric properties (Quezada and Caldas,1999; Caldas and Quezada, 2002; Caldas and Teixeira,2002, 2004; Narayan et al., 2004, 2005c; Zheng et al., 1998).The dosimetric characteristics show that commercialglasses may be applied to high dose dosimetry in the doserange of 50Gy to 20 kGy depending on their evaluationtechnique (Caldas and Teixeira, 2002; Zheng et al., 1998).Colored commercial glasses can also be used in high doseTL gamma dosimetry in the dose range 50Gy to 100 kGy(Caldas and Teixeira, 2004). Glasses can be sensitized withgamma radiation to detect lower gamma doses for personalmonitoring and can have potential to measure accidentaldoses also (Narayan et al., 2005a). Some of the high-temperature laboratory glasses are sensitive enough to beused for personal monitoring and therapeutic dose evalua-tion (Narayan et al., 2005b). Gamma irradiated commercial

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0

50

100

150

200

250

300

350

0 2000 4000 6000 8000 10000 12000 14000

TL

Out

put (

Arb

itrar

y U

nit)

TG2TG3TG4TG5

Dose (Gy)

TG1

Fig. 1. TL output of 60Co exposed glasses at different doses

(0.1–11.8 kGy).

0

10

20

30

40

50

60

70

80

TG2 TG4

% T

L f

adin

g in

5 h

ours Under Dark

Under LabSunlight

TG1

Sample

TG3 TG5

Fig. 2. TL fading in 5 h of 60Co gamma exposed (2 kGy dose) under

different environmental conditions.

P. Narayan et al. / Applied Radiation and Isotopes 66 (2008) 86–89 87

glasses have been studied in detail for its application in highdose dosimetry using TL techniques and reported.

2. Experimental techniques

The commercial glasses available in our environmentsuch as in houses and other public places were used for TLanalysis after exposing it with 60Co gamma radiation.Clean glass samples were crushed in metal pot to make finemicro grain size (150–200 mm). The powder samples werepacked in black paper pouch (10mm� 10mm) and sealedto restrict light exposure during irradiation and transport.Exposures were given in 60Co based gamma chamber(GC 900), BRIT Make with central dose rate of 125Gy/h.The exposed samples were read in Harshaw 2000 B andNulceonix 1009I TLD readers. Both the TLD readers wereoperated under standard procedure for reproducible read-ing. Reproducibility (72%) of TLD readers were checkedusing standard reference source and multiple reading ofunexposed standard TL samples. The TL instruments werecalibrated up to 450 1C temperature. Forty-seven numbersof commercial glasses were exposed to 2 kGy of gammadose and studied for its sensitivity, glow peak position andfading under room condition.

Five suitable glasses (TG1, TG2, TG3, TG4 and TG5)among all the 47 studied glasses were screened out forfurther study on the basis of moderate TL sensitivity,glow peak temperature (150–200 1C), nature of glow curve(single peak) and lower fading in 24h. The samples wereexposed with different doses of 60Co gamma radiation andTL output measured for linearity study. The gamma exposed(2 kGy) samples were stored in different environmentalconditions (dark, laboratory condition and direct sunlight)for studying the influences of environmental condition on theglass detectors. The glass samples were also studied forreproducibility check and the effect of heat treatment(successive annealing at 400 1C for 15min) on its sensitivity.Presence of impurities and trace elements (Cu, Mn, Cr, Fe,Zn, Mg, Sr, Na, K, Ca and Ni) were also studied usingatomic absorption spectrometer (Model no. 2380, Perkin-Elmer, UK made) for correlation with TL sensitivity.

3. Result and discussion

3.1. Linearity

The TL output of the glasses exposed with different dosesof 60Co gamma radiation is shown in Fig. 1. The glasses havebeen responded linearly up to 10kGy. Beyond 10kGy,glasses reaches in sub-linearity region due to filling of most ofthe electron traps by radiation produced free electrons. As theexposure increased further the TL response became furtherslower but still in increasing mode up to 50kGy. The glasseshave been found to saturate beyond 50kGy, as all TL centersseem to be filled by the free electrons produced by radiation.Single calibration factor can serve the purpose of high dosegamma dosimetry up to 10kGy using TL property of

commercial glasses, however, dosimetry up to 50kGy ispossible with extrapolation technique using calibration graph.

3.2. Environmental effects on TL response

Percentage fading of the gamma exposed (2 kGy) glasssamples under different environmental conditions in 5 h isshown in Fig. 2. The samples show 3–5%, 5–12% and35–71% fading under dark, room light and sunlightstorage conditions, respectively. This suggest that TLcenters are prone to photoluminescence by visible as wellas by UV rays. The fading even under dark conditionreflects that phosphorescence may also be the contributingfactor in TL signal losses. The fading estimation can helpto incorporate corrections during dosimetry, if identicalconditions are not maintained while reading all thesamples.

3.3. Long time TL fading

The result of long time (50 days) fading studies ofgamma-exposed (2 kGy) glasses under laboratory suggest10–21% TL signal loss in first 24 h after exposure. The TLfading has been observed to be more in first 5 h of

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exposure. The samples fade slowly as the time passes andtakes around 40–50 days in losing its 50% TL information.This will help in estimating the doses in case the samplecould not be read on time due to some reason.

3.4. Reproducibility

Different glass samples exposed with 2 kGy of gammaradiation have shown reproducible TL output within 76%as shown in Table 1. The evaluated uncertainty highlightsthe suitability and potential use of commercial glassdetectors for routine high dose measurement.

3.5. Effect of successive heat treatment on TL response

This study intends to evaluate the response of glassdetectors after successive annealing for its reusability.Large variations (18–57%) in the TL response of theglasses have been noted during five-cycle heat treatment at400 1C for 15min. TL sensitivities have been found toreduce by 7.40–51.49% after first heat treatment. Ingeneral, the effect of subsequent heat treatment after firstannealing is reduced. This may be due to the presence ofunstable electron trap in the glass lattice during manufac-turing process, which might have lost during first heattreatment. TG2 and TG4 glasses have shown little effect onits sensitivity after first annealing onwards (Fig. 3), suchtype of glasses can be reused after first heat treatment.Annealing at 400 1C for 15min has been found sufficient toremove unstable electron traps present before exposure.

Table 1

TL reproducibility of gamma-exposed commercial glasses

% Uncertainty in measurement (reproducibility), 96% CL

TG1 TG2 TG3 TG4 TG5

74.94 74.92 75.94 72.21 74.51

0

5

10

15

20

25

30

0 6

TL

out

put/d

ose

TG1TG2TG3TG4TG5

1 2 3 4 5

Frequency of Annealing

Fig. 3. Effect of successive thermal treatment on TL response of gamma-

exposed glasses.

The annealed sample must be cooled at least for 24 h atroom temperature for thermal stability of the samplesbefore exposure.

3.6. Correlation of TL response with trace element/

impurities in the glasses

This study found no correlation between TL sensitivityof commercial glasses and its composition. It seems thatimperfections and dislocations are the major contributingfactors in the formation of TL centers in commercial glasslattice. TL sensitivity could also be dependent on theprocess by which it was manufactured, such as annealingtemperature and melting point.

3.7. Precautions

Preparation of power samples for TL dosimetry is adangerous task. Eye protecting glass, protective apron andhand gloves must be used while preparing glass powdersamples. Facemask should also be used to protectinhalation of glass dust, as it is very toxic and injuriousto health.

4. Conclusion

All commercial glasses show TL properties but theirapplication for high dose measurement requires precisestudy for their radiation characteristics and environmentalstability. Their TL glow peaks lie in the temperature range175–220 1C and suited for most of the commercial TLDreaders. The glasses can be used for various applications ofgamma radiation dosimetry using TL techniques depend-ing on its sensitivity and TL fading. Commercial glasses aresuitable for high gamma dose measurement in the range of0.1–50 kGy. The commercial glasses for gamma dosemeasurement must be evaluated for its sensitivity, linearity,fading under different environmental conditions andreproducibility before use. The reproducible reading ofthe TLD reader is the prerequisite for the glass dosimetryusing TL technique. It must be checked either with thereference source or by using stable unexposed TL samples.Glasses are chemically inert, rigid, and insoluble, of

small size and are of very low cost. It requires very lessquality control in comparison to chemical dosimeters. Itcan serve as an additional dosimeter for gamma irradiatorand gamma chamber dosimetry. Glasses are the passivedetectors and can be kept along with the samples underexact irradiation conditions to know the dose by which thematerial is irradiated.

Acknowledgments

The authors wish to express their gratitude to Dr. M.P.Chacharkar, Director, and Shri G.L. Baheti, Head,Nuclear Radiation Management and Application Division,Defence Laboratory, Jodhpur (India) for their deep

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concern and encouragements in accomplishment of thisstudy.

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