Neutron background measurements with a hybrid neutron detector at the Kuo-Sheng Reactor Neutrino Laboratory

TL;DR

This study measures neutron backgrounds at the Kuo-Sheng Reactor Neutrino Laboratory using a hybrid detector, providing detailed background characterization crucial for neutrino experiments and demonstrating the detector's applicability to similar rare-event studies.

Contribution

It introduces a hybrid neutron detector setup and analysis method for in situ neutron background measurement in a neutrino laboratory environment.

Findings

Neutron fluxes are quantified using an iterative unfolding algorithm.

Neutron-induced backgrounds from ambient radioactivity and reactor operation are negligible.

The detector and analysis methods are applicable to other rare-event experiments.

Abstract

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.