Role of the density, density effect and mean excitation energy in solid-state detectors for small photon fields
Role of the density, density effect and mean excitation energy in solid-state detectors for small photon fields
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DOI：
10.1088/1361-6560/aa562e
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发表时间：
2017-02-21
影响因子：
3.5
通讯作者：
Benmakhlouf, Hamza
中科院分区：
文献类型：
--
作者：
Andreo, Pedro;Benmakhlouf, Hamza
最近发表的一些关于小光子束剂量测定的出版物旨在促进理解固态探测器在小视场中的响应。他们中的一些人将敏感探测器材料相对于水的质量密度或电子密度的响应差异分配给响应。这项工作分析了一些探测器材料在 0.5 cm 半径的 6 MV 光子束中的质量和电子密度 (rho, n(e))、密度效应 (delta) 和平均激发能 (I 值) 的作用，其基本原理是探测器的响应主要取决于探测器与水的阻止功率比。还研究了电子密度以及电子单次和多次散射对体积缩放的探测器响应的影响。探测器材料为水、金刚石和硅，并且还包含其他材料以保证分析的一致性。对停止功率比的 (rho, I, delta) 依赖性的详细分析表明，密度效应 delta 取决于电子密度和介质的 I 值，但并不像通常假设的那样仅取决于质量密度 rho。这导致阻止功率比对 I 值的双重依赖性，并质疑“密度扰动因子”或仅以 rho 形式对探测器响应的常见解释的充分性。响应的差异可以用探测器与水的阻止功率比的变化来描述，这主要是由于不同的 I 值以及较小程度的不同电子密度值造成的。研究发现，在低能量下，探测器材料内蒙特卡罗计算的电子注量谱的趋势仅取决于它们的 I 值。在任何能量下都没有观察到仅依赖于质量密度或密度效应。受限 CEMA 与水的比率（作为吸收剂量比的替代）的趋势遵循 1 MeV 处的阻止功率比的趋势，这是本研究中微分受限 CEMA 分布的最可能的能量。结论是 I 值和 d 对 (I-2, rho Z/A, beta) 的依赖性的综合效应控制着限制性 cema 值，并且 rho 或 delta(rho, beta) 都不能单独解释不同探测器材料的不同响应。结果表明，对于本研究中的小型非缩放体积和缩放体积，C-Delta,C-det 实际上是恒定的，并且在这两种情况下，电子散射对受限 cema 值的贡献约为 2%。
A number of recent publications on small photon beam dosimetry aim at contributing to the understanding of the response of solid-state detectors in small fields. Some of them assign the difference in response to the mass density, or to the electron density, of the sensitive detector material relative to that of water. This work analyses the role of the mass and electron density (rho, n(e)), density effect (delta) and mean excitation energy (I-value) of some detector materials in a 6 MV photon beam of 0.5 cm radius, its rationale being that the response of a detector depends critically on the stopping-power ratio detector-to-water. The influence on the detector response of volume scaling by electron density, and of electron single and multiple scattering, is also investigated. Detector materials are water, diamond and silicon, and additional materials are included for consistency in the analysis. A detailed analysis on the (rho, I, delta) dependence of stopping-power ratios shows that the density effect delta depends both on the electron density and on the I-value of the medium, but not on the mass density rho alone as is usually assumed. This leads to a double dependence of stopping-power ratios on the I-value and questions the adequacy of a 'density perturbation factor' or of common interpretations of detector response in terms of rho alone. Differences in response can be described in terms of the variation of stopping power ratios detector-to-water, mainly due to different I-values and to a lesser extent to different values of electron density. It is found that at low energies the trend of Monte Carlo-calculated electron fluence spectra inside the detector materials depends solely on their I-values. No dependence on mass density or density effect alone is observed at any energy. The trend of restricted-cema ratios to water (as a substitute of absorbed dose ratios) follows that of stopping-power ratios at 1 MeV, the most probable energy of differential restricted-cema distributions in this study. It is concluded that the combined effect of the I-value and the dependence of d on (I-2, rho Z/A, beta) governs the restricted-cema values, and that neither rho or a delta(rho, beta) alone explain the different response of diverse detector materials. The results show that, for the small non-scaled and scaled volumes in this work, C-Delta,C- det is practically constant and that in both cases the contribution of electron scattering to the restricted-cema values is about 2%.