作者：宋明哲, 滕忠斌, 倪宁, 侯金兵, 张曦, 魏可新, 刘蕴韬

作者单位：中国原子能科学研究院计量与校准技术国防科技重点实验室, 北京 102413

关键词：放射性计量学;复合效应修正;Nital方法;电离室;连续束γ射线

摘要：

该文总结目前国内外文献中用于获得电离室复合效应修正因子k_s的3种方法：实验外推法、双电压法以及Nital方法。在¹³⁷Cs γ射线辐射场中，分别使用上述3种方法计算300 cm³球型石墨空腔电离室的k_s，并详细地给出评估k_s测量不确定度的方法。在⁶⁰Co γ射线辐射场中，以同样的方式获得3种方法下的10 cm³球型石墨空腔电离室的k_s。结果显示，对于10 cm³和300 cm³电离室，由不同方法得到的复合修正因子k_s相差在0.64%之内。并且在⁶⁰Co γ射线辐射场中，通过比较1/I与1/V和1/V²的线性关系，得出剂量率在不大于38.65(66) Gy/h时10 cm³电离室的初始复合修正为复合效应修正的主要部分。

Study on the determination of the recombination correction of ionization chamber for continuous γ-ray beam
SONG Mingzhe, TENG Zhongbin, NI Ning, HOU Jinbing, ZHANG Xi, WEI Kexin, LIU Yuntao
Division of Radiation Metrology of China Institute of Atomic Energy, Beijing 102413, China
Abstract: Three methods, experimental extrapolation method, double-voltage method and Nital method, presently used to obtain the recombination correction factor k_s of the ionization cavity chamber were summarized. In the ¹³⁷Cs γ-ray radiation field, the k_s of a 300 cm³ spherical graphite cavity chamber were calculated by the above three methods, and the uncertainty of k_s obtained by the Nital method was given in detail. In the ⁶⁰Co γ-ray radiation field, the k_s of a 10 cm³ spherical graphite cavity ionization chamber were also obtained using those three methods. The results show that for the 10 cm³ and 300 cm³ cavity chambers, the k_s obtained by different methods differ within 0.64%. And in the ⁶⁰Co γ-ray radiation field, by comparing the linear relationship between 1/I and 1/V or 1/V², the initial recombination of the 10 cm³ cavity chamber dominates the total recombination losses at a dose rate of not more than 38.65(66) Gy/h.
Keywords: radiation metrology;recombination correction;Nital method;ionization chamber;continuous γ-rays
2020, 46(5):25-30  收稿日期: 2019-12-02;收到修改稿日期: 2020-01-22
基金项目:
作者简介: 宋明哲(1983-),男,吉林松原市人,硕士生导师,博士,研究方向为电离辐射计量
参考文献
[1] ANDREO P, BURNS D T, NAHUM A E, et al. Fundamentals of ionizing radiation dosimetry[M]. Berlin: Wiley-VCH, 2017: 513-524.
[2] KASE K R, BJARNGARD B E, ATTIX F H. The dosimetry of ionizing radiation, vol. Ⅱ[M]. New York: Academic Press, 1987: 169-243.
[3] 邬蒙蒙. Cs-137γ射线空气比释动能绝对测量的研究[D]. 成都: 成都理工大学, 2013.
[4] 吴金杰, 杨元第. 中能X射线空气比释动能的绝对测量[C]// 2010中国仪器仪表与测控技术大会论文集. 北京: 仪器仪表学报出版社, 2010.
[5] ALMOND P R. Use of a Victoreen 500 electrometer to determine ionization chamber collection efficiencies[J]. Medical Physics, 1981, 8(6): 901-904
[6] ALMOND P R, BIGGS P J, COURSEY B M, et al. AAPM's TG-51 protocol for clinical reference dosimetry of high-energy photon and electron beams[J]. Medical Physics, 1999, 26(9): 1847-1870
[7] WEINHOUS M S, WELI J A. Determining P_ion, the correction factor for recombination losses in an ionization chamber[J]. Medical Physics, 1984, 11(6): 846-849
[8] DE ALMEIDACE, NIATELMT. Rapport BIPM-1986/12: Comparison between IRD and BIPM exposure and air-kerma standards for cobalt gamma rays[EB/OL]. Paris: BIPM, 1986. https://www.bipm.org/en/publications/.
[9] BOUTILLON M. Volume recombination parameter in ionization chambers[J]. Physics in Medicine and Biology, 1998, 43(8): 2061-2072
[10] PIERMATTEI A, AZARIO L, ARCOVITO G, et al. Ion-recombination correction factor k_sat for spherical ion chambers irradiated by continuous photon beams[J]. Physics in Medicine and Biology, 1996, 41(6): 1025-1035
[11] PALMANS H, THOMAS R A S, DUANE S. Ion recombination for ionization chamber dosimetry in a helical tomotherapy unit[J]. Medical Physics, 2010, 37(6): 2876-2889
[12] BURNS D T, ROGERP. CCRI(I)/01-07: Characterization of the BIPM low-energy x-ray facility following a change of x-ray tube and high-voltage generator[EB/OL]. https://www.bipm.org/en/publications/, 2001.
[13] 李德红, 王培玮, 邬蒙蒙, 等. 137Csγ射线空气比释动能基准石墨空腔电离室的研制[J]. 计量学报, 2016(37): 324-327
[14] 李德红, 成建波, 王培玮, 等. γ射线空气比释动能测量不确定度分析[J]. 计量学报, 2016(37): 445-447
[15] 李景云, 郭文. ⁶⁰Co和¹³⁷Csγ射线参考辐射及测定其空气比释动能(率)的系列空腔电离室[J]. 辐射防护, 1996, 16(2): 88-97
[16] ALLISY-ROBERTS P J, KESSLER C, BURNS D T, et al. Summary of the BIPM. RI(I)-K5 comparison for air kerma in ¹³⁷Cs gamma radiation[J]. Metrologia, 2013, 50(Tech. Suppl.): 1-10
[17] ALLISY-ROBERTS P J, BURNS D T, KESSLER C, et al. Summary of the BIPM. RI(I)-K1 comparison for air kerma in ⁶⁰Co gamma radiation[J]. Metrologia, 2007, 44(1A): 1-15
[18] PARK S H, KIM H S, KIM Y K, et al. Saturation characteristics of the ionization chamber at a low dose rate[J]. Radiation Physics and Chemistry, 2005, 73(5): 248-253
[19] 测量不确定度评定与表示: JJF 1059.1—2012[S]. 北京: 中国质检出版社, 2012.