Background Studies and Understanding for High-Purity Germanium Detector at Kuo-Sheng Neutrino Laboratory

To observe the neutrino-nucleus coherent scattering and dark matter searching, a detection system with ultra-low energy high purity germanium detector has been built up by TEXONO Collaboration in Kuo-Sheng Nuclear Power Plant. Due to the rarity and small recoil energy of these processes, understanding the background sources and their contribution to the energy spectrum are the key factors in this experiment. By using a data analysis toolkit called ROOT which was developed by CERN to reproduce the background, comparing to the experimental data, we can estimate the upper limit of Tritium beta decay activities in HPGe crystal. In data analysis, the p-type Germanium detector has a surface effect which will distort the energy deposit in the surface of Ge crystal, a charge collection efficiency function is to determine the energy loss because of the surface effect. By ROOT and a simulation toolkit GEANT4, we can try to find out the possible structure of charge collection efficiency in Ge surface.