Correction of the chemical composition effect for soil samples in gamma spectrometry is very important to perform at low emission energy (<100 keV). This study presents an intensive Monte Carlo simulation using Geant4 code of CERN which investigates several items in this subject. First, it is confirmed that for soil samples, in presence of chemical composition effect, correction of the density effect at low energy is not sufficient to produce an accurate efficiency calibration of the detector. Chemical composition effect must also be corrected. Second, it was found that the slope of the linear fit to the decrease of the efficiency as a function of % of average chemical composition for a given emission energy is density independent. This is a new result which could be used to develop new efficiency correction methods against chemical composition effect. Finally, the usual method of correcting the efficiency using the simple ratio between the self absorption factor of the gamma ray inside the sample and inside the calibration standard, was found unable to correct the chemical composition effect for soil samples.

校正γ光谱法中土壤样品的化学成分效应对于在低发射能量（<100 keV）下进行非常重要。这项研究提出了使用CERN的Geant4代码进行的深入蒙特卡洛模拟，该模拟研究了该主题中的几个项目。首先，已确认对于土壤样品，在存在化学成分效应的情况下，在低能量下校正密度效应不足以产生检测器的准确效率校准。化学成分的影响也必须纠正。其次，发现对于给定的发射能量，线性拟合对效率降低的斜率与平均化学组成的百分比的函数关系与密度无关。这是一个新结果，可用于开发针对化学成分效应的新效率校正方法。最后，发现使用样品内部和校准标准内的伽玛射线自吸收系数之间的简单比率来校正效率的常用方法，无法校正土壤样品的化学成分效应。