高能光子水吸收剂量辐射质转换因子的实验测量

摘要

Objective To briefly introduce the results of the international comparison of absorbed dose to water at National Institute of Metrology (NIM),and based on the results,to provide the beam quality correction factors for 9 common types of cylindrical ionization chambers.Methods In the 60Co γ primary standard dosimetry laboratory at NIM,the calibration factors of 9 types of cylindrical ionization chambers at the reference quality 60Co γ were measured.In the high-energy photon beams primary standard dosimetry laboratory at NIM,the calibration factors of the corresponding cylindrical ionization chambers at the reference quality 6,10 MV photon were also measured.Based on the obtained calibration factors,we calculated the beam quality correction factors of cylindrical ionization chambers which were then compared with the data given in IAEA TRS-398 protocol.Results The primary standard dosimetry laboratory of absorbed dose to water at NIM had the ability for the transmission and traceability of absorbed dose to water.Based on this result,the experiment values of the beam quality correction factors for tested cylindrical ionization chambers had a good agreement with the values given in IAEA TRS-398 protocol,with a relative deviation less than 0.9％.Generally,the measured beam quality correction factors were slightly smaller than the values in IAEA TRS-398 protocol,because the calibration factors in 60Co γ primary standard dosimetry laboratory at NIM are larger than the values given by International Atomic Energy Agency (IAEA) and the calibration factors in high-energy photon beams primary standard dosimetry laboratory at NIM are smaller than the values given by the International Bureau of Weights and Measures.Conclusion The primary standard dosimetry laboratory of absorbed dose to water at NIM could accurately measure the beam quality correction factors of users' cylindrical ionization chambers.%目的:简要介绍中国计量科学院(NIM)水吸收剂量国际比对结果,基于此实验给出9种常见指形电离室的辐射质转换因子.方法:在NIM60Coγ基准实验室测量9种型号指形电离室的基于60Coγ辐射场的校准因子,在NIM的高能光子水吸收剂量基准实验室测量这9种型号指形电离室的基于6、10 MV高能光子辐射场的校准因子,依据这两种校准因子,计算得到这9种指形电离室的辐射质转换因子.并与IAEA TRS 398报告中提供的数据相比较.结果:NIM水吸收剂量国家基准实验室已经具备水吸收剂量的量传和溯源能力,在此基础上,所测指形电离室的辐射质转换因子均与398报告符合较好,但普遍偏小,相对偏差不超过0.9％.这是由于NIM60Coγ基准实验室给出的校准因子比国际原子能机构给出的值偏大,而高能光子水吸收剂量基准实验室给出的校准因子比国际计量局给出的值偏小所致.结论:NIM的水吸收剂量国家基准实验室可以精确给出用户指形电离室的辐射质转换因子.