Development of Reactor Neutrino Detector for Measurement of Neutrino Mixing Angle Theta_13

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The aim of this research is to develop a reactor neutrino detector to measure neutrino mixing angle theta_13 accurately. In order to accurately measure the mixing angle theta_13, it is necessary to develop a detector with accurately known detection efficiency. Further more it is necessary to place such detectors near the reactor (〜a few 100m) and at oscillation maximum (〜1.6km) to cancel systematic uncertainties by comparing two detector data. As R&D for the detector the following studies were performed.1. A boring study was performed at an actual detector position in the site of the power station. The gamma-ray background and cosmic-ray background were measured at the actual depth where the detector is planned to locate. Simulators are developed based on such data and detector structure and depth are designed using the simulators. The information of geology is used to investigate about possible method of digging the underground area.2. A prototype detector, which consists of 900 liter liquid scintillator and 7 liters of Gadolinium loaded liquid scintillator. Neutrino like signals were generated by using Am-Be radioactive source and detection efficiency for the reactor neutrino events are studied. Especially, Gadolinium gamma ray peak was successfully observed which can not be observed in a small test system.3. KASKA will use 1200 photomultipliers. Test experiments for some candidate PMTs were performed, such as uniformity of the response, timing resolution, etc. and 10 inch PMT was selected for the KASKA experiment.Other R&D such as stability test of liquid scintillator, development of front end electronics, wire based detector calibration system.Finally letter of intent for the KASKA experiment is written based on those research.