Development of Water-Based Liquid Scintillator for Elementary-Particle, Nuclear and Cosmic-Ray Experimental

本研究的目的是开发水基液体闪烁体，以解决与油基液体闪烁体相关的各种问题。本研究将含苯环的分子溶于水和荧光剂中，使带电粒子通过液体时产生荧光。有两种分子含有苯环，可以溶于水。一种是含苯环的表面活性剂，另一种是水溶性芳香液体。将各种类型的此类分子列出并与荧光剂如PPO和bis-MSB以各种浓度组合一起混合在水中，并使用来自γ-Co的γ射线测量其光输出<60>。如果样品显示出显著的光输出，则进一步研究其光衰减长度、闪点和稳定性。将表面活性剂和氟化物溶于水中，可制得含水量为82%，光输出为7.2%，对420 nm波长光衰减长度为77 cm的蒽不燃液体澄清剂;或含水量为81%，光输出为4.0%，光衰减长度为220 cm的蒽不燃液体澄清剂。这些光输出对于处理高电离粒子的核实验和基本粒子实验来说足够高。另一方面，在加速试验中，这些液体冷却剂在8个月的等效时间后显示出老化性能。这仍然是一个悬而未决的问题。正在设计一个中微子实验，其中这种水基液体闪烁体是候选者之一。

The aim of this research is to develop water-based liquid scintillator to solve various issues associated with the oil based liquid scintillators. In this research, molecules which contains benzene circle are dissolved in water as well as fluors in order to obtain fluorescence when a charged particle passes through the liquid. There are two kinds of molecules which contain the benzene circle and can be dissolved in the water. One is surfactant with the benzene circle and the other is water-solvable aromatic liquid. Various kinds of such molecules were listed up and mixed in water together with fluors such as PPO and bis-MSB with various combinations of concentrations and its light output was measured using γ-rays from ^<60>Co. If a sample showed a significant light output, its light attenuation length, flash point and stability were further investigated. We could make noninflammable liquid scintillators with 82% of water content, 7.2% Anthracene of light output and 77cm of light attenuation length for 420nm wavelength light, or 81% water content, 4.0% Anthracene of light output and 220cm of light attenuation length, by dissolving surfactant and fluors in water. These light outputs are high enough for nuclear experiments and elementary particle experiments which deal with high ionizing particles. On the other hand it turned out these liquid scintillators show aging properties after 8months equivalent period in acceleration tests. This is still a remaining issue. A neutrino experiment is being designed in which this water-based liquid scintillator is one of the candidates to be used.