Development of Highly Sensitive Neutron Monitor with GSO Scintillators

本研究旨在利用GSO（Gd_2SiO_5：Ce）闪烁体实现高灵敏度的中子监测器，用于环境中子的测量。具有254，000 B的热中子俘获截面的具有Gd- 157的闪烁体可以是高灵敏度中子监测器。以下是本研究的结果。(1)用GSO闪烁体进行中子探测：观测了GSO闪烁体对热中子的响应。用低强度中子源证实了热中子俘获产生的来自Gd-158的79.5 keV和182 keV γ射线，并在2”Φ x 2”GSO晶体上获得了14%的高探测效率。在铅、无氧铜和石蜡块的良好屏蔽条件下，将有可能应用于测量极低通量的环境中子。(2)GSO闪烁体的脉冲波形：用高速数字示波器测量了闪烁体的脉冲波形并结合脉冲高度的测定。研制了脉冲波形分析系统，测量了不同Ce浓度的GSO晶体和其它LSO、BGO和BaF_2闪烁晶体的闪烁衰减时间。脉冲波形分析系统的研制将有效地区分α粒子和晶体中U系列核的污染物，本研究提供了一种高灵敏度的GSO反应堆中子监测器的知识，

In this research, highly sensitive neutron monitors are intended to be realized for measurements of environmental neutrons with GSO (Gd_2SiO_5 : Ce) scintillators. The scintillator with Gd- 157, which has a very high cross section of 254,000 b for thermal neutron capture, may be a high sensitivity neutron monitor. Followings are the results from the present research.(1) Neutron detection with a GSO scintillators : The GSO scintillator response were observed for thermal neutrons. Gamma-rays of 79.5 keV and 182 keV from Gd-158 resulted by the thermal neutron capture were confirmed with a low intensity neutron source, and then a high detection efficiency of 14 % was obtained for a 2" Φ x 2" GSO crystal. Applications will be planed to measurement of very low flux of environmental neutrons will be possible with a good shield condition of Pb, Oxigen-free Cu, and Paraffin blocks.(2) Pulse shape of scintillation from a GSO scintillators : The pulse shapes of scintillation combining with the pulse height determination were measured with a high speed digital oscilloscope. A pulse shape analyzing system were developed for this purpose, and measured the decay times of scintillation from GSO crystals of different Ce concentrations, and other LSO, BGO and BaF_2 scintillation crystals. The developed pulse shape analyzing system will be effective for discrimination of alphas from contaminants of U-series nuclei in crystals.The present research provides the knowledge about a high sensitive neutron monitor of GSO scintillators,