窄束X射线半价层测量法标定电子直线加速器的能量.pdf

　第37卷第4期 原 子 能 科 学 技 术 Vol. 37 ,No. 4 　2003年7月 Atomic Energy Science and Technology J uly 2003 窄束 X 射线半价层测量法标定 电子直线加速器的能量 严慧勇 ,唐传祥 ,李泉凤 ,石成玉 (清华大学 工程物理系 ,北京　100084) 摘要 :X 射线半价层测量法是一种常用的低能电子直线加速器能量标定方法 ,本文对窄束 X 射线半价层 的测量方法进行了讨论。利用 MonteCarlo 程序 MCNP4B 对窄束 X 射线半价层进行了计算和分析 ,并 与实测数据进行了比较 ,测量数据与 MCNP4B 计算结果符合得很好。此外 ,还讨论了准直锥的长度和 材料、准直缝的尺寸、靶的厚度和材料等因素对半价层的影响。 关键词 :半价层 ;窄束 ;宽束 ;MCNP4B 程序 中图分类号: TL53 　　　文献标识码 :A 　　　文章编号 (2003) Calibration of the Energy of an Electron Linac by Measuring the Narrowbeam Xray Halfvalue Layer YAN Huiyong , TAN G Chuanxiang , L I Quanfeng , SHI Chengyu ( ) Depart ment of Engineering Physics , Tsinghua U niversity , Beijin g 100084, China Abstract : The halfvalue layer ( HVL ) of the broadbeam Xray is often used to calibrate the energy of an electron linac , but in some cases the measurement of the broadbeam Xray HVL is not convenient . Therefore , the measurement of the narrowbeam Xray HVL as a method to calibrate the energy of an electron linac is discussed in the paper. The MonteCarlo code , MCNP4B is used to calculate and analyze the narrowbeam Xray HVL , meanwhile the narrowbeam Xray HVLs are measured for the 2. 5 , 4 , 6 and 9 MeV electron linacs. There is a good agreement between the measured HVLs and the MCNP4Bcalculated results. Also , the length of a primary collimator , the width of a collimator slot , the thickness of a target and such other factors ’influence on HVL is discussed , and