用于校准剂量(率)仪的低能X光子能谱测量技术

The Spectrum Measurement Technology of Low Energy Photon for Calibrating Dosemeters and Doserate Meters

在低能X参考辐射场中校准剂量(率)仪时,从空气比释动能到剂量当量的转换系数与光子能量分布及入射角等因素有很大的关系,简单地应用ISO4037《校准剂量仪和剂量率仪及确定其光子能量响应的X和γ标准辐射》中所给推荐值将产生很大的不确定度。能谱测量方法可以准确地得到能注量谱各方面信息,进而得到正确的转换系数。论文阐述了能谱测量技术的基本原理及方法,应用PTW软X射线电离室完成了低能参考辐射场特性测试,选用CdZnTe探测器对参考辐射场进行能谱测量,并利用蒙特卡罗方法解谱。由解谱结果计算得到的转换系数与德国PTB实验室的计算值最大相对偏差为8.9%,与ISO4037-3《场所剂量仪和个人剂量仪的校准及其能量响应和角响应的确定》推荐值最大相对偏差为18.2%。

For calibrating dosemeters and doserate meters in the low energy X reference radiation field ,the con- version coefficients from air kerma to dose equivalen have a strong dependence on the factors like the energy distribution and the incidence angle. Use the conversion coefficients given in IS04037 《X and gamma reference radiation for calibrating dosemeters and doserate meters and for determining their response as a function of photon energy》 directly can produce a large uncertainty. Measuring the spectra is helpful for knowing about energy and fluence spectra ,so a more exact conversion coefficient can be calculated from the spectra if necessary. In the paper, the basic principle and method of the spectrum measurement technology will be described. A soft X - ray ionization chamber of PTW was used for the test of characteristics data of the reference radiation field, the CdZnTe detectors was used for the spectra measurment, and the Monte Carlo method will be used for he unfolding of the pulse height spectrum. The largest deviation between the conversion coefficients calculated from the unfolding spectra results and the values given by PTB laboratory and the ISO standard《 Calibration of Area and Personal Dosemeters and Dosemeters and the Measurement of their Response as a Function of Photon Energy and Angle of Incidence》 are 8.9% and 18.2%.