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中子监测器，用于测量环境中子。含有Gd- 157的闪烁体具有很高的热中子捕获截面（254,000 b），可能是高灵敏度的中子监测仪。以下是本研究的结果。(1)用GSO闪烁体探测中子：观察了GSO闪烁体对热中子的响应。用低强度中子源对Gd-158的热中子捕获产生的79.5 keV和182 keV的伽马射线进行了确认，对2”Φ x 2”的GSO晶体获得了14%的高探测效率。在Pb、无氧Cu和石蜡块的良好屏蔽条件下，将计划应用于测量非常低通量的环境中子。(2) GSO闪烁体的闪烁脉冲形状：利用高速数字示波器结合脉冲高度测量闪烁的脉冲形状。为此研制了脉冲形状分析系统，测量了不同Ce浓度的GSO晶体以及其他LSO、BGO和BaF_2闪烁晶体的闪烁衰减时间。所开发的脉冲形状分析系统可有效地对晶体中u系核中的α和污染物进行鉴别。本研究提供了GSO闪烁体高灵敏度中子监测仪的相关知识。

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,