可作为校准检定用标准剂量计的能量补偿型高气压电离室改进

Development of energy compensated high pressure ionization chamber as standard dosimeter for metrological verification

在电离辐射计量检定工作中,标准剂量计的测量结果通过检定逐级传递到工作计量器具,以实现单位统一和量值准确可靠。由于环境水平γ射线剂量率较低,国际上常用的PTW-UNIDOS系列标准剂量计无法满足需要。针对这一特点,结合蒙特卡罗方法对高气压电离室的X射线、γ射线和宇宙射线响应特性进行模拟计算,进行了能量补偿型高气压电离室改进。测试结果表明:剂量率约30μGy/h时,能量补偿型高气压电离室在87ke V^1.25 Me V能量范围内相对于^(137)Csγ射线的响应偏差不大于6%,宇宙射线和^(137)Csγ射线的响应偏差不大于10%,在0.5μGy/h^1 m Gy/h范围内相对固有误差为-3%,0.5μGy/h时的重复性为0.7%,校准因子的不确定度为4%(k=2),可作为环境水平标准剂量计在校准检定工作中使用。

In the ionizing radiation metrology work, the measurement results of the standard dosimeters are transferred to working metrological instruments through verification in order to achieve a unified unit and accurate and reliable quantity value. Due to low environmental gamma ray dose rate, the common PTW - UNIDOS series standard dosimeter can not meet the requirements for verification. An energy compensated high pressure ionization chamber was developed for this feature. The response characteristics of high pressure ionization chamber for X ray, gamma ray and cosmic ray were simulated using Monte Carlo method. Test results showed that the response deviation within the energy range of 87 keV-1.25 MeV for the ^137Cs gamma ray was less than 6% when the dose rate was about 30 μGy/h, the deviation in cosmic rays and ^137Cs gamma ray response was less than 10% , relative intrinsic error was -3% in the dose rate range ofO. 5 μGy/h^-1 mGy/h, the repeatability was 0.7% when the dose rate was 0.5 μGy/h, and the uncertainty of the calibration factor was 4% （k = 2）. The energy compensated high pressure ionization chamber can be used as a standard dosimeter in calibration and verification at environmental levels.