高纯锗能谱仪^(125)I核素点源和体源绝对活度测量方法研究

Study on the absolute activity measurement method of^(125)I nuclide point source and volume source by HPGe spectrometer

通过^(125)I核素X射线和γ射线的符合相加特性,推导出了仅包含全能峰(27.3、35.5、31.2 keV)净计数率、符合峰(58.5、66.7 keV)净计数率和总谱净计数率的^(125)I活度计算公式,并通过宽能型和N型高纯锗谱仪分别对点源、活性炭盒源和液体源进行了验证。点源到探测器距离不大于5 cm测量时,绝对活度公式计算结果和参考值的相对偏差在±1.2%以内;活性炭盒对^(125)I核素的自吸收效应可以忽略,绝对活度计算公式不受^(125)I核素分布形式的影响,活性炭盒源正反面测量的相对偏差均在±1.4%以内;体积小于40 mL液体源的测量结果和参考值的相对偏差在±2.6%以内,液体源在测量时,样品高度不宜过高,以减少自吸收效应对符合相加峰的减弱效果。实验结果表明在不依赖标准物质和核素参数的情况下,推导的绝对活度计算公式可用于^(125)I核素放射性活度的精确测量。

This paper derived the^(125)I activity calculation formula based on the coincidence summing characteristics of^(125)I nuclide X-ray andγray.The formula only included the net counting rate of the full-energy peaks(27.3,35.5,31.2 keV),the net counting rate of the sum-peaks(58.5,66.7 keV)and the net counting rate of the total spectrum.The point source,activated carbon cartridge source and liquid source were verified by Broad-energy and N-type germanium spectrometer.When the distance from point source to detector was less than 5cm,the relative deviation between the calculated results of the absolute activity and the reference values was within±1.2%.The self-absorption effect of^(125)I nuclide in activated carbon cartridge could be ignored,and the absolute activity calculation formula was not affected by the distribution form of^(125)I nuclide.The relative deviation of front and rear measurements for activated carbon cartridge source was within±1.4%.The relative deviation between the measurement results and reference values of liquid source with volume less than 40mL was within±2.6%.The sample height should not be too high during the measurement of liquid source,so as to reduce the weakening effect of self-absorption on sum-peaks.The experimental results show that the absolute activity calculation formula derived in this paper can be used to accurately measure the activity of^(125)I nuclide without relying on standard substances and nuclide parameters.