Neutron/γ-ray discrimination based on the property and thickness controls of scintillators using Li glass and LiCAF (Ce) in a γ-ray field

Recently, various neutron detectors, such as scintillation detectors, are being developed as alternatives to 3He proportional counters. Here we focus on the thickness and property controls of inorganic scintillators used for thermal neutron detection in intense γ-ray fields without considering pulse shape discrimination (PSD) techniques. GS20TM (a lithium glass) and LiCaAlF6 crystals activated with Ce (LiCAF:Ce) scintillators with thicknesses of 0.5 and 1.0 mm, respectively, have been employed because they have faster decay times than other inorganic scintillators. Pulse signals generated by photomultiplier tubes, to which the scintillators were coupled, were inserted into a digital pulse processing unit with a sampling rate of 1 GHz, and the areas of waveforms were integrated for 360 ns. Neutron/γ-ray detections and discriminations were performed via pulse integrations without using PSD techniques. For GS20TM, the relative energy resolution values of the thermal neutron peaks were 11% and 12% in 0.5 mm and 1.0 mm thicknesses, respectively, and those for LiCAF:Ce were 18% and 36% in 0.5 mm and 1.0 mm thicknesses, respectively. In a 60Co γ-ray field, the neutron detection for GS20TM in a 0.5 mm thickness was possible at dose rates of up to 0.919 Gy/h; however, for LiCAF:Ce, neutron detection was possible at 0.473 Gy/h, and it failed at 0.709 Gy/h. The neutron/γ-ray discrimination of GS20TM was better than that of LiCAF:Ce due to its better energy resolution and higher detection efficiency (6Li content).