Simulation Study On The Background Contribution Of Material Around The Point Electrode Of High Purity Germanium Detector

Dark matter is one of the important constituents of the universe.Exposing the mysterious veil of dark matter particles is of great significance for humans to re-understand the material world.At present,the dark matter candidate particles with the highest voice and high probability that can be detected by experiments are weakly interacting massive particles（WIMPs）predicted based on the supersymmetric theory.There are three most feasible detection schemes,and direct detection is one of them.As one of the experiments with extremely low background,the direct detection of dark matter is to achieve an extremely low background.The China Dark Matter Experiment（CDEX）is located in the world’s thickest underground laboratory,the China Jinping Underground Laboratory（CJPL）,which provides superior geographical conditions for China’s extremely low background experiments.This subject is based on the background physics case energy spectrum of the CDEX-1B experiment.By investigating the analysis of the low energy region background by the dark matter direct detection experimental groups at home and abroad,it is found that one of the background sources that causes the energy spectrum of the low energy region to rise is:all kinds of daughters produced by the decay of the daughter ²¹⁰Pb of radon in the material near the germanium crystal.They can penetrate into the germanium crystal from the P⁺electrode surface of the point electrode high-purity germanium detector,thereby contributing to the background.Therefore,the research on this background case is very important to improve the sensitivity of dark matter detection in CDEX experiments.In view of this background case,by using Geant4 simulation software,this topic selects and verifies the physical process that can accurately describe the physical behavior characteristics of heavy charged particles on the surface of the material;On the basis of ensuring the correctness of the physical process,the daughter ²¹⁰Pb of radon To verify the correctness of the simulation program,refer to the simulation results of the Super CDMS experimental group on the surface case,because the simulation experiment has been in good agreement with the actual measurement data;After confirming that the simulation program is correct,use the prototype detector of CDEX-1B to set a ²¹⁰Pb point source and an ideal electronic device on the P⁺electrode surface.By comparing the simulation experiment and the energy spectrum of the background physical case in the CDEX-1B experiment,it is possible to qualitatively give the magnitude of the contribution of each ²¹⁰Pb decay daughter to the background of the low energy region.