Characterization of neutron and high purity germanium detectors with advanced data acquisition system and measurement of neutron background at the Kuo-Sheng neutrino laboratory

The rare event experiments for both in the new physics and the standard model studies such as; neutrino physics, weakly interacted massive particle (WIMP) investigations, neutrinoless double beta decay searches and so on, highly desires background suppression and understanding. Therefore in this study at the Kuo-Sheng Neutrino Laboratory (KSNL), two major components of background due to photon and neutron interactions were investigated with complete characterized high-purity Germanium (HPGe) detectors and a neutron detector with a hybrid structure (HND). HND and HPGe detectors were exposed with a data size of 33.8 and 347 days respectively to ambient and cosmic events under the same identical shielding configuration where the data acquisition system was designed in advanced level for labeling cosmic and ambient backgrounds. The measured nuclear recoil spectrum on HND is constructed into the fast neutron energy spectrum by an iterative unfolding method and projected into the Ge-recoil spectrum by Geant4 simulation. Thus, the background contribution due to neutron interaction with the measured photon background in HPGe spectra was obtained. Moreover, some X-ray emission lines of germanium due to neutron capture in HPGe detector were used to estimation of neutron flux, whose result proved that the measured and estimated neutron fluxes are consistent. Therefore, this method can be used for estimation on low energy and low background experiments in underground laboratories. The results are valuable to background understanding on the neutrino and WIMP studies at the KSNL. In particular, the ambient radioactivity due to neutron interaction is negligible compared to photon activity.