SiPM Scintillation Detector Development for a Fast-Neutron Detector*

For the development of a new fast-neutron detector to be used in invariant-mass spectroscopy of neutron-unbound states at the Facility for Rare Isotope Beams, silicon photomulitplier (SiPM) sensors are being evaluated and scintillator configurations are being tested. Many large-area fast-neutron detectors use plastic scintillator as a material with a high hydrogen ratio to effectively detect neutrons, and photo-multiplier tubes (PMTs) to detect the scintillation light with excellent timing. The position of the neutron interaction is often deduced from the time-difference of the signals from a pair of PMTs at opposite ends of a long detector bar. This poses limits to the position resolution and multi-hit capabilities of neutron detectors. As an alternative, a design using SiPM arrays is being developed. For this purpose, SiPM test kits have been assembled by undergraduate students at several MoNA Collaboration institutions and were tested using cosmic rays, radioactive sources, and an 11-MeV neutron beam at the Triangle Universities Nuclear Laboratory. Different configurations regarding sensor placement, optical coupling, and reflective wrapping were compared. The results of these tests help to benchmark detector simulations. The goal is to develop a new fast-neutron detector with SiPM sensors and improved position resolution compared to current large-area neutron detectors.