基于放射性废物桶内所含介质材料和放射性核素分段均匀分布的假设, 采用蒙特卡罗程序模拟计算多种射线能量、多种样品密度条件下的线衰减系数和体源探测效率, 通过多元非线性拟合得到以线衰减系数和能量为自变量的体源探测效率函数。基于壳源法, 通过多个点源组合测试近似替代均匀体源的实验测量, 对3种能量射线和3种密度的样品进行验证实验, 利用蒙卡模拟与数值拟合结合方法和实验测量两种方式获得各自的体源探测效率, 完成活度估算。两种方式活度估算结果相对误差均小于23%。通过蒙卡模拟与数值拟合结合方法所得结果与实验结果基本吻合, 证明了该方法的有效性。

Efficiency calibration is one of the key problems to be solved in the activity detection of radioactive waste barrels. Based on the assumption of uniform distribution of media material and radionuclides contained in the barrel, Monte Carlo method was used to simulate line attenuation coefficients and body source detection efficiency under various energies and various sample densities. The body source detection efficiency function with linear attenuation coefficient and energy as independent variables is obtained by multivariate nonlinear fitting. And, based on the idea of shell source method, the experiment of the homogenous body source is approximately replaced by multiple point source combination measurement. Three kinds of energy ray and three kinds of density samples have been verified experimentally, and the detection efficiency is calculated respectively by the method of Monte Carlo simulation combining with numerical fitting and the method of experimental measurement. Then, the respective activity estimation results are obtained by solving the efficiency matrix equation, and, the relative error is less than 30%. The simulation results are basically consistent with the experimental result, which proves the effectiveness of the method.