TL response of sodalime glass at high doses

TL response of sodalime glass at high doses

Nuclear Instruments and Methods in Physics Research A 505 (2003) 407–410 TL response of sodalime glass at high doses F.A. Baloguna,*, F.O. Ogundareb,...

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Nuclear Instruments and Methods in Physics Research A 505 (2003) 407–410

TL response of sodalime glass at high doses F.A. Baloguna,*, F.O. Ogundareb, M.K. Fasasia a

Centre for Energy Research and Development, Obafemi Awolowo University Ile-Ife, Nigeria b Department of Physics, University of Ibadan, Ibadan, Nigeria

Abstract The possibility of using sodalime glass as a TL material for high-dose measurements and in accident dosimetry has been investigated. The structure of the glow curves, including the number of peaks was found to be dose and annealing temperature dependent. However, a linear relationship was obtained between the glass response and dose in the dose range studied. Variation in the responses of the glass after repeated use was obtained to be 4%. Variation in batch sensitivity was also found to be not more than 5%. The fading rate of the glass response at room temperature is small. r 2003 Elsevier Science B.V. All rights reserved. PACS: 87.66.Sq Keywords: Thermoluminescence; TL; Dosimetry; Sodalime glass; Fading; Sensitivity

1. Introduction Reliable dosimetric techniques are required in some industrial and scientific applications of radiation (e.g. food processing, nuclear power plant, radiation sterilization, etc.) where personnel may be accidentally exposed to very high-dose levels. Many of the dose measuring techniques available at these dose levels are expensive and significant effort has to be invested in them to obtain large output [1]. Solid-state techniques based on thermoluminescence (TL) dosimetry are cheaper methods that have been suggested by several authors for high-dose measurements [1]. The saturation effect display by glow-peaks in many of the available TL dosemeters at high doses is however a serious factor militating against the *Corresponding author. E-mail address: [email protected] (F.A. Balogun).

acceptance of this technique in both high-dose measurements and accident dosimetry. Possibility of using biological tissue and inorganic materials in high-dose measurements and in particular in accident dosimetry has been investigated [2]. One of the reasons why these were considered was because they are common in most laboratories and can easily be used after a radiation accident to estimate dose. Another material that is common in many laboratories is glass. Glass has been reported to have potential to serve as a TL dosemeter [3,4]. In a study of plain and microscopic slide glasses [5], a simple glow curve with a glow peak at 200 C was obtained. Dose–response curves showed linearity over a wide range of doses. Sensitivity in the microscopic slide glass was shown to be up to 3 times higher than was obtainable for the plain glass samples. In a similar study using a semiconductor doped Vycor glass [6], a TL glow curve

0168-9002/03/$ - see front matter r 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0168-9002(03)01109-4

F.A. Balogun et al. / Nuclear Instruments and Methods in Physics Research A 505 (2003) 407–410

with a maximum at 220 C was obtained. A TL dose–response curve of this material showed linearity over a dose range of 1 mGy to 500 Gy with a low fading rate at room temperature. The site-dependent TL of copper (I) ions in silica glass irradiated to a test dose of 0.72 kGy has also been reported [7]. The aim of the present work is to investigate the TL properties of sodalime glass and to ascertain its possible use for high-dose measurements and in accident dosimetry. Sodalime glass is a common material in almost all the laboratories and therefore if fully studied and developed for high-dose measurements, it will become a reliable means of estimating the doses of personnel who may be accidentally irradiated.

2. Experimental details A commercially available and unleached clean sodalime silicate glass of known purity with approximate composition of 73 w/o SiO2, 3.5 w/o (K2, Na)O, 9 w/o CaO, 4 w/o MgO, 0.2 w/o Al2O3 was cut into smaller bits of equal sizes and masses. Cleaning of the glass was effected by ultrasonic scrubbing with detergent followed by rinsing in distilled water, then trichloroethylene, acetone and ethyl alcohol in that order. At each stage, doubly de-ionized distilled water was used to remove the cleaning liquids from the glass. The glass samples were then dried in hot air. Irradiations of the glass samples were performed at room temperature using a 60Co irradiator gamma cell (1.25 kGy/h) at the Centre for Energy Research and Development (CERD), Obafemi Awolowo University, Ile-Ife. Some of the samples were annealed before irradiation using a wellcalibrated annealing machine at the Federal Radiation Protection Service, University of Ibadan, Ibadan. The annealing temperatures used are 200 C, 300 C and 400 C for 1 h. The TL glow curves of the irradiated glass were recorded in a nitrogen atmosphere using the Victoreen TL reader (Model 2800M) available at CERD. The glow curves were read out at a heating rate of 10 C/s.

3. Results and discussion 3.1. Glow curve The TL glow curves of the glass (unannealed and those annealed at 200 C, 300 C and 400 C for 1 h) irradiated to a test dose of 1.25 kGy are shown in Fig. 1. It can be seen from the figure that the structures of the glow curves are different. As the annealing temperature increases, more peaks than observed at lower annealing temperatures are seen in the glow curve. However for very high doses, no difference is observed in the structures of the glow curves obtained after the samples have been pre-irradiation annealed at these temperatures (see Fig. 2). Also presented in Fig. 3 are the glow curves of the glass obtained at different doses. The figure revealed that the structures of the glow curves are also dose dependent. The number of peaks varies, at some doses three peaks are observed around 160 C, 227 C and 274 C, while at very high doses only one peak is observed around 274 C. The 227 C peak is likely to be the peak that was found by Erknol et al. [5] and Justus and Huston [6] as 200 C and 220 C, respectively. These observed glow curve structure dependent on dose and annealing temperature may be explained by the expected change in defect concentration of the glass through heat treatment and irradiation [8]. In fact, Jayanta and unheated 200°C 300°C 400°C

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F.A. Balogun et al. / Nuclear Instruments and Methods in Physics Research A 505 (2003) 407–410 unheated 200°C 300°C 400°C

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Fig. 2. Glow curves of the glass irradiated to a test dose of 5 kGy at different annealing temperatures. 62.5Gy 1250Gy 1875Gy 5000Gy

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measurements; its response should be linear with dose in the high-dose region. In order to determine this relationship, pieces of the glass of equal sizes were exposed to doses from 20 Gy to 2  104 Gy and read out in the TL reader. Fig. 4 shows this response. The response of the glass caused by the irradiation is taking to be the integral over the whole glow curve. This is because the number of peaks varies with dose. The figure shows that the response of the glass is linear with dose in the dose range considered. 3.3. Reproducibility

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Fig. 3. Glow curves of the glass irradiated to a different doses.

Radhaballah [7] had earlier reported the generation of aluminium hole centres in silica glass through irradiation. Therefore, the observed variance in glow curve structures may be attributed to likely creation and/or redistribution of defects by heat treatment and irradiation. This argument is further supported by the fact that the glass is made of many ions including aluminium.

Since the glass is re-usable, how economic it is will depend on how many times it can be used before it looses its TL potential. Ideally, TL material should be re-usable at least for a sufficient number of times. In order to determine how the sensitivity of the glass varied with repeated use, a selection of pieces of the glass was taken, and annealed at 400 C for 1 h, exposed and read out a number of times. The number of cycles used was 8 and it was found that the response does not vary by more than 4% over this number of cycles.

3.2. Response with dose 3.4. Batch sensitivity The response of a personal dosemeter should ideally be proportional to dose, hence if the sodalime glass is to be suitable for high-dose

The responses of some pieces of the glass that have undergone the same treatment are not

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is shown in Fig. 5. The figure shows that the glass initially has a fast fading rate and after about 2 days the fading rate reduced dramatically and the intensity almost approach a constant value with delay time.

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Fig. 5. Fading characteristic of the sodalime glass.

expected to vary too much in order for it to be a reliable TL material. To test this, a batch containing 10 pieces of the glass was selected and annealed, exposed to the same dose and read out. The mean of the responses of these pieces within the batch was obtained. It was found that the response of each of the piece within the batch does not vary by more than 5% from their mean. 3.5. Fading Since it may take some time after a radiation accident has occurred before an access to the glass is possible, a desirable property of the glass that must be studied is fading. This is the property that tells for how long a material can hold any signal stored in it. To investigate this, a batch of the pieces of the glass was given a test dose of 1.25 kGy. Some of these were read out immediately. Others were kept at room temperature for a later time. Some of these were read at some interval of days after storage. A plot of the response against delay time

The high-dose TL properties of sodalime glass have been investigated. Glow curve structure of the glass was found to be dependent on dose and annealing temperature. This has been attributed to possible change in defect concentration through heat treatment and irradiation. The response of the glass to irradiation was found to be linear with dose in the dose range considered. Reproducibility of results after repeated use of the glass was also obtained to be acceptable. The rate at which the glass loses any signal stored in it was found to be small. All these results in an indication that the glass may be a reliable material for measuring high doses.

References [1] Y.S. Horowitz, M. Moscovitch, Nucl. Instr. and Meth. A 243 (1986) 207. [2] C.L.P. Mauricio, L.A.R. Rosa, P.G. Cunha, Radiat. Prot. Dosim. 11 (3) (1985) 185. [3] S. Crofts, D.D. Weaver, R. Mathews, Radiat. Prot. Dosim. 65 (1–4) (1996) 381. [4] B.L. Justus, A.L. Huston, T.L. Johnson, Appl. Phys. Lett. 68 (24) (1996) 3377. [5] A.Y. Erknol, S. Yasar, B. Karakale, Radiat. Phys. Chem. 46 (4–6) (1995) 111. [6] B.L. Justus, A.L. Huston, Appl. Phys. Lett. 67 (1995) 1779. [7] J. Chaudhuri, D. Radhaballabh, J. Phys.: Condens. Matter 6 (1994) 3987. [8] S.W.S. Mckeever, J.A. Strrain, P.D. Townsend, P. Uvdal, PACT 9 (1983) 123.