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بخشی از مقاله انگلیسیعنوان انگلیسی:Development ofa personal dosimeter badge system using sintered LiF:Mg,Cu,Na,Si TL detectors for photon -elds~~en~~

Abstract

The badge system of personal thermoluminescence (TL) dosimeter for photon fields using LiF:Mg,Cu,Na,Si TL material, which was developed by Korea Atomic Energy Research Institute (KAERI) a few years ago, was developed by taking advantage of its dosimetric properties including energy dependencies. A badge filter system was designed by practical irradiation experiments supported by computational modeling using Monte Carlo simulation. Design properties and dosimetric characteristics such as photon energy response and angular dependence of new TL dosimeter system examined through the irradiation experiments are presented. Based on the experiments for the developed dosimeter, it is demonstrated that the deep dose response of dosimeter provided the value between 0.78 and 1.08, which is within the design limit by ISO standard. This multi-element TL dosimeter badge system allows the discrimination of the incident radiation type between photon and beta by using the ratios of the four TL detectors. Personal TL dosimeter using sintered LiF:Mg,Cu,Na,Si TL detectors has the ability to measure a personal dose equivalent Hp(d) for a wide range of photon energies.

۱ Introduction

Thermoluminescence dosimetry is the most widely used technology for evaluating the personal and environmental radiation exposure. Lithium uoride (LiF) is a well-known thermoluminescent (TL) dosimetry material used in environmental and personal monitoring due to its high sensitivity, stability and tissue-equivalency.

The -rst interest in the thermoluminescent phenomenon of LiF for dosimetry was by Daniel et al. (1953) from the University ofWisconsin. Since then many experimental doping agents were used with LiF. The TLD material based on LiF that has been studied most extensively is LiF:Mg,Ti, which is widely used in personal dosimetry and available in the market under trade names like TLD-100 and its variations, TLD-600 and TLD-700 which contain diFerent concentrations oflithium isotopes (Vij, 1993). Since the introduction ofLiF:Mg,Ti (TLD-100), many new types ofTL materials have been developed and used to evaluate the personal dose equivalent in various radiation -elds. Many researches for developing the more advanced thermoluminescence materials have been accomplished. Nakajima et al. (1978) were the -rst to describe the properties ofLiF doped with Mg, Cu and P impurities, namely, a high sensitivity and a good tissue equivalency. This material, LiF:Mg,Cu,P, has been improved and commercialized by Chinese (GR-200), Polish (MCP–N) and USA (TLD-100H, TLD-600H, TLD-700H) (Bos, 2001).

In Korea, Doh et al. (1989) developed powdered type ofLiF doped with magnesium, copper, sodium and silicon, and undertook a study on its characteristics about a wide range ofdopants concentration in the 1980s. After Doh et al. proposed LiF doped with four dopants, Kim et al. (1989) found out that the response of LiF:Mg,Cu,Na,Si: for low energy photons was higher than that ofLiF:Mg,Cu,P in the aspect ofdosimetric properity. In the 1990s, more concrete researches on the powder type LiF:Mg,Cu,Na,Si TL phosphor have been accomplished by Korea Atomic Energy Research Institute (KAERI) (Nam et al.,1998, 1999). This powder type TL phosphor has about 2 times higher sensitivity in comparison with LiF:Mg,Cu,P. However, the powder type TL phosphor has many disadvantages for the practical handling ofthe material. Therefore, it is necessary to develop a suitably shaped solid type TL detector for application in practical dosimetry -elds. During the last few years the LiF:Mg,Cu,Na,Si TL material has been studied for practical pellet type TL detector by Nam Y.M. et al., the dosimetry group ofhealth physics department in KAERI (Nam et al., 2000). But the sensitivity ofdeveloped pellet type TL detectors did not exceed 50% ofChinese GR-200A, and had poor reusability, that is, a decrease of10% ofthe readout values after a reuse of 8 times (Nam et al., 2001). Based on these previous studies by Nam et al., the sensitivity and reusability ofthe pellet type LiF:Mg,Cu,Na,Si TL detectors were improved by modi-cation ofthe dopants concentration and the parameters ofthe preparing procedure. The optimum concentration ofdopants for pellet type LiF:Mg,Cu,Na,Si TL detectors was investigated as Mg: 0:2 mol%, Cu: 0.05 mol%, Na: 0.9 mol% and Si: 0.9 mol% (Lee et al., 2002). Now a days, it has become possible to produce a mechanically stable and eLcient TL detector using LiF:Mg,Cu,Na,Si, which is a newly developed TL material in a personal TL dosimetry -eld.

The objective ofthis study was to design and develop the badge system ofa multi-element personal TL dosimeter using LiF:Mg,Cu,Na,Si TL detectors by taking advantage ofits sensitivity, tissue-equivalency and energy dependencies to allow the measurement ofpersonal dose equivalent Hp(d). The design ofdosimeter was accomplished by the practical irradiation experiments that are supported by a computational simulation with MCNP code, and then the developed dosimeter was tested in terms ofits dosimetric characteristics such as photon energy response and angular dependence.

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