就地HPGeγ谱仪测量隧道空气中氡平衡因子技术研究

Study on Radon Progeny Concentrations Measurement in Tunnel by In-situ HPGeγ Spectrometry

对就地HPGeγ谱仪测量隧道空气中氡平衡因子的方法进行了研究。就地HPGeγ谱仪可直接测量隧道中214Pb(或214Bi)的特征γ射线,其计数来自于空气与岩石中214Pb(或214Bi)的贡献。利用214Pb(或214Bi)不同能量特征γ射线的计数率及其效率转换因子建立方程组,并采用期望最大(EM)算法对方程组进行求解,得到空气中214Pb(或214Bi)的活度浓度。218Po无法通过就地HPGeγ谱仪直接测量,但可通过214Pb的活度浓度计算得出。在一常年封闭的隧道中连续测量24 h,按不同时长获取8个能谱,分别计算出不同时段空气中214Pb和214Bi的活度浓度,由此计算出218Po的活度浓度,并得到隧道空气中氡平衡因子。通过对测量结果的验证认为该方法是可行的。

The method was studied to determine the radon equilibrium factor in tunnel by in - situ HPGeγ/spec- trometry. The characteristic γ rays of ^214pb （^214Bi） in tunnel could be detected by in -situ HPGe γ/spectrome- try directly, but the contributions for count rates were from air and rocks in tunnel, respectively. The systems of equations composed of count rates, efficiency factors and activity concentrations of ^214Pb （^214Bi） in the air and rocks were constructed. The system of equations were solved by the expectation maximization algorithm （EM） to obtain the activity concentrations of ^214Pb （^214Bi） in the air. Although ^218Po wasnt able to be measured by in -situ HPGe detector directly, its concentration could be calculated on the basis of ^214Pb. An experiment had been performed for 24 hours in a perennial closed tunnel, and 8γ/-spectrums were obtained. The concentra- tions of ^214pb and 2t＋Bi in the air were calculated respectively. Then the concentrations of ^218po were calculated in accordance with the concentrations of ^214Pb and ^214Bi. And this method was feasible by verification the re- suits.