Fast neutron measurements with ~7Li and ~6Li enriched CLYC scintillators

摘要

The recently developed Cs_2LiYCl_6:Ce (CLYC) crystals are interesting scintillation detectors not only for their gamma energy resolution (＜ 5% at 662 keV) but also for their capability to identify and measure the energy of both gamma rays and fast/thermal neutrons. The thermal neutrons were detected by the ~6Li(n, α)t reaction while for the fast neutrons the ~(35)Cl(n,p)~(35)S and ~(35)Cl(n,α)~(32)P neutron-capture reactions were exploited. The energy of the outgoing proton or α particle scales linearly with the incident neutron energy. The kinetic energy of the fast neutrons can be measured using both the Time Of Flight (TOF) technique and using the CLYC energy signal. In this work, the response to monochromatic fast neutrons (1.9-3.8 MeV) of two CLYC 1" × 1" crystals was measured using both the TOF and the energy signal. The observables were combined to identify fast neutrons, to subtract the thermal neutron background and to identify different fast neutron-capture reactions on ~(35)Cl, in other words to understand if the detected particle is an a or a proton. We performed a dedicated measurement at the CN accelerator facility of the INFN Legnaro National Laboratories (Italy), where the fast neutrons were produced by impinging a proton beam (4.5, 5.0 and 5.5 MeV) on a ~7LiF target. We tested a CLYC detector ~6Li-enriched at about 95%, which is ideal for thermal neutron measurements, in parallel with another CLYC detector ~7Li-enriched at more than 99%, which is suitable for fast neutron measurements.