Study of fast neutron detector for COSINE-100 experiment

Abstract

A monitoring system for fast neutrons is planned in the COSINE experiment, a dark matter experiment with NaI crystals. We pursued several R&D approaches for a neutron detector using a liquid scintillator (LS). A pulse shape discrimination (PSD) technique is used for the identification of neutron events and the PSD properties of two different LS were compared. A good separation power between neutrons and gamma has been achieved for energies between 200 keVee to 1500 keVee. The combination of alumina adsorption, filtration, and water extraction is effective in purifying the LS, which leads to reduction in the alpha contamination by Po-210 of more than a factor of two. The measured activities of the internal alpha are 0.36 +/- 0.04 mBq/kg and 0.21 +/- 0.03 mBq/kg before and after purification, respectively.