Hjerpe Thomas, Samuelsson Christer
Department of Radiation Physics, The Jubileum Institute, Lund University, University Hospital, 221 85 Lund, Sweden.
Radiat Environ Biophys. 2002 Sep;41(3):225-30. doi: 10.1007/s00411-002-0158-3. Epub 2002 Jul 4.
Stationary and mobile field gamma spectrometry is a useful tool for rapid estimation of environmental radioactivity inventories on and in the ground. A weak point however, is that the depth distribution of the activity in the ground must be known in order to calculate the true activity per unit area or unit mass from an observed photon fluence rate. A promising method for converting incoming spectral data into both true activity content and depth distribution in real time is the peak-to-valley method, which is based on an analysis of the ratio between count rates from primary and forward-scattered photons. In this study the peak-to-valley method was adapted to car-borne mobile gamma spectrometry, where the depth distribution of (137)Cs is fitted to a Lorenz function. Results from field experiments with a large HPGe detector, utilising point sources at different depths, are presented. It was found that the method can be useful for mobile measurements with a measuring time of 5-10 min for activity concentrations of about 100 kBq.m(-2) or higher, resulting in an uncertainty in the estimate of the true activity of about 50%.
固定场和移动场伽马能谱法是快速估算地面及地下环境放射性总量的一种有用工具。然而，一个不足之处在于，为了根据观测到的光子注量率计算单位面积或单位质量的真实活度，必须知道地下活度的深度分布。一种将输入光谱数据实时转换为真实活度含量和深度分布的有前景的方法是峰谷法，该方法基于对初级光子和前向散射光子计数率之比的分析。在本研究中，峰谷法被应用于车载移动伽马能谱法，其中将¹³⁷Cs的深度分布拟合为洛伦兹函数。给出了使用大型高纯锗探测器、利用不同深度点源进行的野外实验结果。结果发现，对于活度浓度约为100 kBq·m⁻²或更高的情况，该方法对于测量时间为5 - 10分钟的移动测量可能有用，这导致真实活度估计的不确定度约为50%。
