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，以解决油基液体闪烁体的各种问题。在本研究中，当带电粒子通过液体时，将含有苯环的分子与荧光一起溶解在水中，从而获得荧光。含有苯环并能溶于水的分子有两种。一种是苯环表面活性剂，另一种是水溶性芳香液体。将不同种类的这类分子列出来，与不同浓度组合的PPO和bis-MSB等荧光剂一起混合在水中，用^<60>Co.的γ射线测量其光输出。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。在420nm波长的光下，我们可以制备出含水量82%、光输出蒽量7.2%、光衰减长度77cm的不燃液体闪烁体，或者通过在水中溶解表面活性剂和氟，制备出含水量81%、光输出蒽量4.0%、光衰减长度220cm的不燃液体闪烁体。这些光输出足够高，可以用于核实验和处理高电离粒子的基本粒子实验。另一方面，在等效8个月的加速试验中，这些液体闪烁体显示出老化特性。这仍然是一个悬而未决的问题。一个中微子实验正在设计中，这种基于水的液体闪烁体是候选体之一。

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.