Livingstone J, Horowitz Y S, Oster L, Datz H, Lerch M, Rosenfeld A, Horowitz A
Center for Medical Radiation Physics, University of Wollongong, Wollongong, Australia.
Radiat Prot Dosimetry. 2010 Mar;138(4):320-33. doi: 10.1093/rpd/ncp272. Epub 2009 Nov 24.
The dose response of LiF:Mg,Ti (TLD-100) chips was measured from 1 to 50,000 Gy using 100 keV X rays at the European Synchroton Radiation Facility. Glow curves were deconvoluted into component glow peaks using a computerised glow curve deconvolution (CGCD) code based on first-order kinetics. The normalised dose response, f(D), of glow peaks 4 and 5 and 5b (the major components of composite peak 5), as well as peaks 7 and 8 (two of the major components of the high-temperature thermoluminescence (HTTL) at high levels of dose) was separately determined and theoretically interpreted using the unified interaction model (UNIM). The UNIM is a nine-parameter model encompassing both the irradiation/absorption stage and the thermally induced relaxation/recombination stage with an admixture of both localised and delocalised recombination mechanisms. The effects of radiation damage are included in the present modelling via the exponential removal of luminescent centres (LCs) at high dose levels. The main features of the experimentally measured dose response are: (i) increase in f(D)(max) with glow peak temperature, (ii) increase in D(max) (the dose level at which f(D)(max) occurs) with increasing glow peak temperature, and (iii) decreased effects of radiation damage with increasing glow peak temperature. The UNIM interpretation of this behaviour requires both strongly decreasing values of ks (the relative contribution of localised recombination) as a function of glow peak temperature and, as well, significantly different values of the dose-filling constants of the trapping centre (TC) and LC for peaks 7 and 8 than those used for peaks 4 and 5. This suggests that different TC/LC configurations are responsible for HTTL. The relative intensity of peak 5a (a low-temperature satellite of peak 5 arising from localised recombination) was found to significantly increase at higher dose levels due to preferential electron and hole population of the trapping/recombination complex giving rise to composite glow peak 5. It is also demonstrated that possible changes in the trapping cross section of the LC and the competitive centres due to increasing sample/glow peak temperature do not significantly influence these observations/conclusions.
在欧洲同步辐射装置上，使用100 keV的X射线，测量了LiF:Mg,Ti（TLD - 100）芯片在1至50,000 Gy剂量范围内的剂量响应。利用基于一级动力学的计算机化热释光曲线反褶积（CGCD）代码，将热释光曲线反褶积为各个热释光峰。分别确定了热释光峰4、5和5b（复合峰5的主要成分）以及峰7和8（高剂量水平下高温热释光（HTTL）的两个主要成分）的归一化剂量响应f(D)，并使用统一相互作用模型（UNIM）进行了理论解释。UNIM是一个包含辐照/吸收阶段和热致弛豫/复合阶段的九参数模型，同时包含了局域和非局域复合机制。在当前模型中，通过在高剂量水平下指数去除发光中心（LCs）来纳入辐射损伤的影响。实验测量的剂量响应的主要特征为：（i）f(D)(max)随热释光峰温度升高而增加；（ii）D(max)（出现f(D)(max)的剂量水平）随热释光峰温度升高而增加；（iii）辐射损伤效应随热释光峰温度升高而降低。对这种行为的UNIM解释要求ks（局域复合的相对贡献）的值随热释光峰温度强烈降低，并且峰7和8的俘获中心（TC）和LC的剂量填充常数的值与峰4和5所使用的值有显著差异。这表明不同的TC/LC构型是高温热释光的原因。发现峰5a（峰5的低温卫星峰，由局域复合产生）的相对强度在较高剂量水平下显著增加，这是由于俘获/复合复合体中优先的电子和空穴填充导致了复合热释光峰5。还证明了由于样品/热释光峰温度升高，LC和竞争中心的俘获截面的可能变化不会显著影响这些观察结果/结论。
