铀矿γ能谱测井多核素定量特征能量选择最优化计算——基于特定尺寸LaBr_3(Ce)单晶的钻孔γ谱探测

Optimization Calculating on Characteristic Energy Selecting for Determining Multi-radionuclide Content in Gamma-ray Spectra-log for Uranium Mine——Detecting Gamma Spectra in Borehole Based on Specified Size LaBr_3(Ce) Crystal

采用新型LaBr3(Ce)探测器的铀矿γ能谱测井可实现天然产状下对铀等多核素的直接定量。为了选择探测效果最优的特征能量,选定的Φ1.5×2英寸LaBr3(Ce)单晶对备选特征能量光子的探测能否获得较高的相对计数率是一个重要指标。此外,还要考虑是否存在重峰情况及受康普顿散射谱的影响程度。基于此,建立计算相对计数率的数学模型以及与实际钻孔探测条件一致的峰探测效率数值模拟计算模型,计算备选各特征能量的峰探测效率,进而求出可表征各分支相对计数率的指标,通过比较并结合实测仪器谱,分别选出了在该探测条件下对铀组、镭组和钍系核素定量分析最合适的特征能量。

Gamma-ray spectra-log technology for uranium mine using a new LaBr3（Ce） detector can determine contents of multi-radionuclide including uranium.In order to select the best characteristic energy in detecting effect for a target multi-radionuclide,whether a given small size Φ1.5＂×2＂ LaBr3（Ce） crystal can get a higher relative count rate for detecting characteristic energy gamma photons is an important performance parameter.Moreover,it must be taken into account that characteristic energy peaks may overlap and be affected by Compton scattering spectra.The present work establishes a mathematical formula for calculating relative count rate for a given characteristic energy and a mathematical model for numerical modeling characteristic peak detecting efficiency in accordance with practical borehole detecting conditions,and calculates the detecting efficiency and the parameter which is related to relative count rate for candidate characteristic energies.The optimal energies are selected for determining contents of the radionuclide from uranium group,radium group and thorium series under the given detecting condition by comparing the calculating results and combining with gamma spectrum measured from borehole.