防护水平X射线电离室的校准及不确定度分析

防护水平电离室剂量计是辐射防护的主要计量器具,需要在窄谱参考辐射质下进行检定和校准。利用EGSnrc软件模拟了参考辐射质X射线能谱,分析得到的能谱分辨率和平均能量与ISO 4037-1推荐值的最大偏差分别为7.1％和1.04％,均满足规范要求。依托60~250kV X射线空气比释动能国家基准装置,在窄谱系列参考辐射质下完成了距离X光机1m处参考点的空气比释动能量值复现;然后通过替代法对两个传递电离室进行校准并完成量值传递;最后利用传递电离室复现的2.25m处的空气比释动能率对PTW-32002球形电离室进行校准,获得相应的校准因子,校准因子相对扩展不确定度为2.2%(k=2)。

Calibration and Uncertainty Analysis of Protective Level X-ray Ionization Chambers

The protection level ionization chamber dosimeters are main measuring instrument for radiation protection and need to be calibrated under narrow spectrum series reference radiation qualities. The EGSnrc software was used to simulate the X-ray energy spectrum of the reference radiation quality. The maximum deviations of the spectral resolution and average energy obtained from the analysis and the recommended values of ISO 4037-1 were 7.1% and 1.04%, respectively, which met the specification requirements. Based on the (60~250) kV X-ray air kerma national primary standard, the air kerma at the reference point of 1m from the X-ray tube spot was reproduced under the narrow spectrum series reference radiation quality, and then two transfer ionization chambers were calibrated and transferred by the substitution method.Finally, the PTW-32002 spherical ionization chamber was calibrated by using the air specific release kinetic energy rate at 2.25m reproduced by the transfer ionization chamber, and the corresponding calibration factor was obtained. The relative expanded uncertainty of the calibration factor was 2.2%(k=2).