冷凝惰性气体源活度的小立体角绝对测量方法研究

Radioactive noble gases, such as Krypton-85 and Xenon-133, are one of the main products during nuclear power plants operation and nuclear test. Radioactivity measurements of such radionuclide is one of important tasks in the field of safe operation of nuclear power, and radiation environmental monitoring. So as to build our national traceable system for radioactive noble gaseous activity, and ensure the results of the related monitoring equipment accuracy and reliability, we will carry out the absolute measurement for radioactive gaseous activity in this program by using defined solid angle method for solidified noble gases, which has been widely used in the activity measurement for Radon-222. In detail, radioactive gas Krypton-85 will be solidified firstly, and the solid angle between the detector and the solidified source needs to be determined precisely before the absolute measurement for beta emitter in 4π steradian. So as to correct the spurious counts due to the gamma response in the detector, and also the self-absorption and scattering effects, on the radioactivity measurement, Monte Carlo simulation method will be used to determine the related correction factors. Finally, the result obtained in this program will be compared with that from the length compensation method based on internal gas proportional counters for validation.

放射性惰性气体（如Kr-85、Xe-133）作为核电运行和核试验中的主要产物之一，对其活度排放量的测量是核电安全运行监测和辐射环境监测的一项主要工作。为了建立我国的放射性惰性气体活度量值传递体系，确保相关监测设备测量结果的准确可靠，本项目中将借鉴目前在氡气活度绝对测量方法中精确度最高的冷凝氡源小立体角方法，开展冷凝惰性气体源的小立体方法活度测量方法研究。项目中将放射性惰性气体Kr-85冷凝成固体源，并通过精确测定探测器与冷凝固体源之间的相对立体角，实现惰性气体的4π总β活度绝对测量。为了修正γ计数、β射线源自吸收效应和散射效应对活度测量结果的影响，需通过蒙特卡罗方法来确定各项修正因子。测量结果将与基于内充气正比计数长度补偿法的结果进行对比，实现方法可行性验证。

放射性惰性气体（如Kr-85、Xe-133）作为核电运行和核试验中的主要产物之一，对其活度排放量的测量是核电安全运行监测和辐射环境监测的一项主要工作。为了建立我国的放射性惰性气体活度量值传递体系，确保相关监测设备测量结果的准确可靠，本项目中将借鉴目前在氡气活度绝对测量方法中精确度最高的冷凝氡源小立体角方法，开展冷凝惰性气体源的小立体方法活度测量方法研究。研究内容和取得的成果包括如下几个方面：1）开展了以氮气为载气的85Kr气体完全冷凝成固态的理论和实现方法。结果表明，本项目中建立的基于液氦制冷的冷凝装置可以实现5kpa以下85Kr气体源的冷却；2）开展了85Kr冷凝源的固定立体角活度测量方法研究。结果表明，在取气压强2kPa左右条件下，固定立体角法测量的冷凝85Kr源活度结果与基于正比计数器长度补偿法的85Kr气体活度测量结果相对偏差在2%以内；3）基于Geant4蒙特卡罗模拟程序，模拟了85Kr衰变产生的β射线在固定立体角装置舱室内的散射效应，并获得了考虑散射效应后的立体角几何因子；4）建立了一套基于塑料闪烁体和碘化铯晶体为探测系统的适用于惰性气体三是研制了基于塑料闪烁体和CsI晶体为探测器的惰性气体探测装置（如Kr-85、Xe-133），并初步进行了测试，该装置将为开展惰性气体活度相对测量和基于β-γ符合方法进行Xe-133的绝对测量奠定技术基础。