| High purity germanium(HPGe)gamma spectrometer is widely used in the fields of environment,nuclear power and medicine due to its high energy resolution and nondestructive measurement.In practical applications,most of radioactive samples are fabricated to volume sources.Although the ?-ray spectra of the volume sources can be obtained by using a HPGe detector,efficiency calibration is required to make sure the content of the radionuclides.However,the common-used efficiency calibration that based on standard radioactive sources is often operationally complicated,time-consuming and difficult to evaluate errors.Recently,the mathematical efficiency calibration and the efficiency calibration with the combination of source measurement and mathematical calculation are increasingly popular.In this paper,the accuracy,the application limitations and fields of the methods that apply in the mathematical efficiency calibration or the combined efficiency calibration are compared and analyzed.The main focuses and conclusions of this research are as follows:1?A set of measurement system is designed.The system can realize precise autolocation,reduce human error and protect operator's safety.With this system,the detection efficiencies of standard point sources at different locations and the detection efficiencies of cylindrical volume source at various heights are obtained.2?In the combined efficiency calibration,the source measurement and mathematical calculation are employed to locate the position of the representative point,respectively.Consequently,the detection efficiencies of soil volume source at different given heights are calculated.Compared with the source measured results,the relative deviation between experimental and computational methods is within 5%,and the internal structure differences in the detector does not affect the positioning of the representative point.Furthermore,the depths of the virtual point detector under different ?-ray energy are calculated by the efficiency of standard point source at a specific position.The results show that the relative deviation between calculated and experimental detection efficiency for volume source is decreased with the adding of source height.When the distance between the volume source and the detector exceed the bottom radius of the source,the relative deviation is within 10%.3?In the mathematical efficiency calibration,the physical models of the measurement targets are established by using GEANT4 software after obtaining the precise size parameters?matrix component and density of the detector and volume source,and the efficiencies of volume source under different heights are obtained.The simulation results inform that the relative deviation of detection efficiency between the simulation and the experiment results is within 3%.Based on the traditional numerical integration methods,a new and more accurate numerical integration method is proposed,which can be used to calculate the detection efficiency of volume source.This method is a combination of mathematical calculation and Monte Carlo simulation,which can keep the relative deviation of detection efficiency between the calculated value and the experimental value within 8%.This new proposed numerical integration method can be applied in practical efficiency calibrations of the volume source and can also be considered for the compilation of general volume source efficiency calibration software because of its high accuracy and fast calculation speed. |
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