作者：滕忠斌^1,2, 田丽霞¹, 宋明哲², 倪宁², 张曦², 魏可新²

作者单位：1. 东华理工大学, 江西 南昌 330013;
2. 中国原子能科学研究院, 北京 102413

关键词：空腔理论;限制的阻止本领比;EGSnrc;电离室

摘要：

当使用基于空腔理论的石墨空腔电离室绝对测量γ射线空气比释动能时，需要考虑空腔体积的大小变化对测量结果准确度的影响。利用EGSnrc程序计算得到10~5 000 cm³的球型石墨空腔电离室的石墨和空气的限制的阻止本领比（L△（E）/ρ）_c，air、入射光子与空腔气体直接作用沉积能量的份额F_air和Spencer-Attix空腔理论修正因子k_SA。结果表明对于⁶⁰Co和¹³⁷Cs能量的光子，在计算（L△（E）/ρ）_c，air时选择合适的△值可以使k_SA的值保持在0.998~1.000之间。此外k_SA的大小随空腔体积的增大有逐渐减小的趋势。表明在设计和使用较大体积（≥50 cm³）的石墨空腔电离室时需要考虑合适大小的k_SA值，以保证空腔理论计算值和绝对测量结果的准确。

Study of the accuracy of γ-rays air kerma calculated by cavity theroy using Monte-Carlo method
TENG Zhongbin^1,2, TIAN Lixia¹, SONG Mingzhe², NI Ning², ZHANG Xi², WEI Kexin²
1. East China University of Technology, Nanchang 330013, China;
2. China Institute of Atomic Energy, Beijing 102413, China
Abstract: When people absolutely measure the γ-rays air kerma using a cavity chamber based on cavity theory, it is necessary to consider the impact of the different sizes of the cavity volume on the accuracy of the measurement results. Based on the calculation of EGSnrc code,the restricted stopping-power ratios graphite to air,(L△(E)/ρ)_c,air,the fraction of dose caused by photon interacting with cavity gas,F_air,and the Spencer-Attix correction factor, k_SA,have been obtained,when the cavity volume changes from 10 cm³ to 5000 cm³.The results show that for photons of ⁶⁰Co and ¹³⁷Cs source, selecting the appropriate $\Delta $ value,during the calculation of (L△(E)/ρ)_c,air,can keep the k_SA between 0.998-1.000.And the k_SA gradually decreases with the increase of cavity volume.Thus, to obtain accurate results of cavity theory calculation and absolute measurement, the appropriate value of k_SA needs to be considered carefully when designing or using a large volume (≥ 50 cm³) graphite-walled cavity ionization chamber.
Keywords: cavity theory;restricted mass stopping power ratios;EGSnrc;cavity chamber
2019, 45(6):13-18  收稿日期: 2018-09-10;收到修改稿日期: 2018-10-15
基金项目: 国家自然科学基金（11505028）；核技术应用教育部工程研究中心开放基金资助项目（HJSJYB2015-12）
作者简介: 滕忠斌(1993-),男,山东聊城市人,硕士研究生,专业方向为核科学与技术
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