Continuous Observation of Solar Neutrinos and Detection of Supernova Neutrinos

神冈是位于东京大学宇宙线研究所神冈地下实验室的水切伦科夫探测器。它是目前世界上正在工作的四个太阳中微子探测器中唯一的实时探测器。它还可以测量反冲电子的能量。由于这些特点，它的观测结果受到了高度重视。1990年，Kamiokande探测器进行了升级，例如用新的高性能系统取代了电子设备。然而，为了充分利用新的电子设备，电源和数据采集系统也必须进行升级；这是在本资助计划的支持下于1991年实现的。本研究项目的两个主题之一的神冈德太阳中微子观测的主要结果总结如下：(1)从8B Decay I…观测到的太阳中微子通量(2)反冲电子能谱用8B衰变中微子能谱来解释。(3)在实验不确定度范围内，白天和夜间的太阳中微子通量没有差别。(4)加上神冈二号观测，神冈德总共6年半的观测表明，太阳中微子通量与太阳活动的变化没有明显的时间变化。包括尚未公布的数据，截至2月底，神冈德观测的太阳中微子通量总计2140个活探测器日。这个研究项目的另一个主题是探测由大质量恒星引力坍塌引起的超新星爆炸产生的中微子爆发。虽然在本研究期间没有探测到中微子爆发，但我们银河系的恒星崩塌速率的世界最佳上限是0.44年。值得一提的是，在本研究项目期间，神冈的监测系统中安装了一个在线、半实时的中微子爆发监测(每15分钟一次)。这使我们能够在光学观测之前发现由银河系坍塌驱动的超新星爆炸。较少

Kamiokande is a water Cherenkov detector which is located at the Kamioka Underground Laboratory of Institute for Cosmic Ray Research, University of Tokyo. It is the only realtime detector out of the four solar-neutrino detectors currently at work in the world. It can also measure the energy of recoil electrons. Because of these characteristic features, its observation results have been highly valued. In 1990, the Kamiokande detector was upgraded by, e.g., replacing electronics with a new high-performance system. In order to fully exploit the new electronics, however, power supplies and data-acquisition sytem had also to be upgraded ; this was achieved in 1991 supported by the present Grant-in-Aid.Main results of the Kamiokande's solar-neutrino observation, which is one of the two subjects of this research project, obtained from the published data up to July, 1993 (corresponding to 1,667 live detector days), are summarized as follows.(1) The observed solar neutrino flux from ^8B decay i … More s about 50% of theoretical expectations.(2) The recoil-electron energy spectrum is explained by the ^8B-decay neutrino spectrum.(3) There is no difference between the day-time and nighttime solar-neutrino fluxes within experimental uncertainties.(4) Together with the Kamiokande-II observation, a total of 6 years and a half Kamiokande's observation shows no appreciable time variation of the solar-neutrino flux associated with the variation of the solar activity.Including the data which are not yet published, the total Kamiokande's solar-neutrino observation amounts to 2,140 live detector days up to the end of February, 1995.The other subject of this research project is detection of neutrino bursts from supernova explosions due to gravitational collapse of massive stars. Though no neutrino burst was detected during the term of this research project, a world best upper limit of the stellar collapse rate in our Galaxy, 0.44 yr^<-1> as of November, 1993, has been obtained. It should be mentioned that an on-line, semi-realtime neutrino-burst watch (in every -15 minutes) has been installed in the Kamiokande's monitoring system during the term of this research project. This enables us to discover a Galactic collapse-driven supernova explosion before it is observed optically. Less