γ能谱符合相加效应修正方法及影响因素

Coincidence summing correction methods and influence factors ofγspectrum

在辐射环境质量监测中,多能核素的级联符合相加效应是影响γ能谱活度测量准确性的重要因素之一,为了提高待测样品分析的准确性,对结果进行符合相加修正是十分必要的。以^(152)Eu核素为例,根据峰总比不变性特点,获得探测器峰总比拟合公式,联合符合相加修正公式,全能峰效率公式,计算了^(152)Eu核素的符合相加修正因子,进一步采用Genie 2000符合相加蒙特卡罗程序对液体体源的^(152)Eu核素进行了符合相加修正。点源的修正结果与真值的相对偏差小于6%,体源修正结果与真值的相对偏差在±4%以内。通过点源符合相加修正因子与源到探测器距离的线性关系,可以得到符合相加效应可忽略的最小测量距离;体源样品的符合相加修正结果表明:同一介质的样品,高度越高,符合相加修正因子越小;自吸收效应会在低能端对样品的有效立体角产生较大影响,从而影响样品的符合相加修正因子。峰总比不变性与衰变纲图相结合的数值修正方法,不需要对不同位置处的点源总效率进行测量,与蒙特卡罗程序法相比,该方法无需对探测器进行工厂表征,不用对体源介质、密度和形状等参数进行描述;舍弃级联符合较严重的能量点后,可用于环境应急样品的符合相加修正。

[Background]In the radiation environmental quality measurement or emergency measurement,one of the factors that influence the measurement results ofγspectrum activity is the cascade coincidence summing effect of multienergy nuclides.[Purpose]This study aims to verify the accuracy of coincidence summing correction and analyze its influencing factors.[Methods]^(152)Eu nuclide was taken as an example object,the peak-to-total fitting formula of the detector was obtained according to the invariance characteristics of peak-to-total ratio.Combined with the coincidence summing correction formula and the full energy peak efficiency formula,and the coincidence summing correction factors of^(152)Eu nuclide were calculated,and the Genie 2000 Monte Carlo program was used to correct^(152)Eu nuclide of the bulk samples.[Results]The experimental results show that the relative deviation between the result and the true value is less than 6%of point source,and the relative deviation between the corrected results and the reference values is within±4%of bulk samples.Through the linear relationship between the point source coincidence summing correction factor and the distance from the source to the detector,the minimum measurement distance with negligible coincidence summing effect can be obtained.The results of coincidence summing correction of bulk samples show that the higher the sample height is,the smaller the coincidence summing correction factor is.[Conclusions]The numerical correction method combining peak-to-total ratio invariance and decay scheme,which does not require measurement of the point source total efficiency at different locations.Compared with the Monte Carlo program method,this method does not require factory characterization of the detector,nor does the parameters of the bulk sample such as medium,density and shape after abandoning the energies with serious cascade coincidence,hence be used for the coincidence summing corrections of the environmental emergency samples.In the low energy part,the self-absorption effect has a great influence on the effective solid angle of the sample,so that affecting the coincidence summing correction factor of the sample.