放射性活度测量中HPGe γ谱仪自吸收修正的研究

Study on self-absorption correction of HPGe gamma spectrometer in radioactivity measurement

    摘要
  • 摘要:
    目的  为进一步研究相同几何参数下，不同样品密度对HPGe γ谱仪放射性活度测量结果的影响，建立自吸收修正函数曲线，为HPGe γ谱仪在放射性活度测量中的自吸收修正提供参考。
    方法  制备10种密度不同的环境样品，分成2组后，1组加入1 g标准钍粉末，另1组加入1 g标准铀镭平衡粉末，混合均匀后封装。对实验所测量的能谱进行分析，用最小二乘法对不同密度样品的计数率进行二次函数拟合，得出自吸收系数。使用无源效率刻度软件模拟不同密度样品的探测效率，通过探测效率计算自吸收系数。对2种方法得出的结果进行分析比较。
    结果  用实验测量和无源效率刻度2种方法得到的自吸收系数，拟合获得232Th子体核素和226Ra子体核素不同能量峰的自吸收系数与样品密度的关系曲线。自吸收系数实验值与模拟值变化趋势大致相同， 232Th γ射线各能量点的自吸收系数相对误差最大值为6.99%，226Ra γ射线各能量点的自吸收系数相对误差最大值为8.51%。自吸收系数实验值与无效源刻度模拟值之间的相对误差不超过10%。
    结论  在密度相同的情况下，自吸收效应对低能区的影响比高能区大。2种方法建立的自吸收修正曲线相对误差较小，规律一致，在日常测量中可以采用这2条曲线对样品自吸收进行修正。

     

    Abstract:
    Objective  A self-absorption correction function curve was established to provide reference for the self-absorption correction of HPGe γ spectrometer to further study the influence of different sample densities on its radioactivity measurement under the same geometric parameters.
    Methods  Ten kinds of environmental samples with different densities were prepared and divided into 2 groups. One was added with 1 g of standard thorium powder, and the other was added with 1 g of standard uranium radium balance powder. The samples were mixed well and packaged. The energy spectrum measured in the experiment was analyzed. The counting rate of samples with different densities was fitted with a quadratic function using the least squares method, and the self-absorption coefficient was obtained. The detection efficiency for samples with different densities was simulated using the sourceless efficiency calibration software, and the self-absorption coefficient was calculated from the detection efficiency. The results obtained by the two methods were analyzed and compared.
    Results The self-absorption coefficient is obtained by experimental measurement and passive efficiency scale, and its relationship with the sample density of 232Th and 226Ra daughter nuclides with different energy peaks is determined by fitting. The variation trend of the self-absorption coefficient is roughly the same as that of the simulated value. The maximum relative error of the self-absorption coefficient of each energy point is 6.99% for 232Th gamma ray and 8.51% for 226Ra gamma ray. The relative error between the experimental value of the self-absorption coefficient and the simulated value from the passive scale is not more than 10%.
    Conclusions  At the same density, the effect of self-absorption on the low-energy region is greater than that on the high-energy region. The relative error of the self-absorption correction curve established by the two methods is small, and the law is consistent. The two curves can be used to correct sample self-absorption in daily measurements.

     

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