We report in situ neutron background measurements at the Kuo-Sheng Reactor Neutrino Laboratory (KSNL) by a hybrid neutron detector (HND) with a data size of 33.8 days under identical shielding configurations as during the neutrino physics data taking
. The HND consists of BC-501A liquid and BC-702 phosphor powder scintillation neutron detectors, which is sensitive to both fast and thermal neutrons, respectively. Neutron-induced events for the two channels are identified and differentiated by pulse shape analysis, such that background of both are simultaneously measured. The fast neutron fluxes are derived by an iterative unfolding algorithm. Neutron induced background in the germanium detector under the same fluxes, both due to cosmic-rays and ambient radioactivity, are derived and compared with the measurements. The results are valuable to background understanding of the neutrino data at the KSNL. In particular, neutron-induced background events due to ambient radioactivity as well as from reactor operation are negligible compared to intrinsic cosmogenic activity and ambient $gamma$-activity. The detector concept and analysis procedures are applicable to neutron background characterization in similar rare-event experiments.
We report the performance and characterization of a custom-built hybrid detector consisting of BC501A liquid scintillator for fast neutrons and BC702 scintillator for thermal neutrons. The calibration and the resolution of the BC501A liquid scintilla
tor detector are performed. The event identification via Pulse Shape Discrimination (PSD) technique is developed in order to distinguish gamma, fast and thermal neutrons. Monte Carlo simulation packages are developed in GEANT4 to obtain actual neutron energy spectrum from the measured recoil spectrum. The developed methods are tested by reconstruction of 241AmBe(alpha, n) neutron spectrum.
