分层γ扫描技术中点源定位的蒙特卡罗方法

摘要

Large amounts of low and intermediate level radioactive waste (LILW) will be produced and piled up with the nuclear power industry development and the increasing widespread application of radioisotopes.The types of nuclides and the activity of the radioactive waste should be measured before the radioactive waste is disposed.Segmented gamma scanning (SGS) measure is an important technique of quantitative analysis for nuclear scrap and radioactive waste.However,when point source location changes,both the relative attenuation distance and scale efficiency are not corresponding,which causes errors of counts of detectors on activity estimation.This study is based on 12 different positions counts method and through Monte Carlo simulation methods,records waste barrels with uniform filling of polyethylene samples.It will find the max & min counts records with BeerLambert attenuation law to value the turning radius,so that it can determine the location of radioactive nuclides in the current segment.Thus,the problem of the attenuation distance,scale efficiency non-correspondence of the radionuclide in different location which lead to SGS estimate error of point source activity is solved.%随着核工业发展和放射性同位素的广泛应用,产生大量中、低放射性废物.中、低放射性废物长期贮存前要对放射性废物的核素种类、活度等进行测量.分层γ扫描(SGS)测量技术是一种无损检测桶装核废物的手段,但是在测量过程中会遇到放射性核素所在的位置变化,则相对衰减距离、效率刻度不对应,导致估计活度结果误差较大.本工作首先将当前层平均分成12份分别进行计数,并通过实验和蒙特卡罗模拟方法,记录以均匀聚乙烯样品填充对废物桶径向不同偏心位置的探测器的计数.由12个位置的探测器计数得到两个最值,并根据γ射线在样品中衰减规律计算得到放射性核素距桶轴的距离,从而确定放射性核素在当前层的位置.结果表明:此方法可求出放射性核素所在的位置从而估计点源在桶内旋转半径,对应使用该旋转半径下的自吸收校正因子、探测效率和衰减校正效率,提高了SGS估计的精度.