Study of Neutrino and Dark Matter by means of CaF_2

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The purpose of this research project is to study Dark Matter and mass of Neutrino by means of CaF_2 detector. Dark matters are strongly suggested to be new particles interacting weakly wiht nuclei. The ^<19>F in the CaF_2 detector has frequent interaction due to its spin thus the dark matter can be detected by obseving its recoil. Since CaF_2 detector has ^<48>Ca it can also be used to study double beta decay of ^<48>Ca which is one of promising methods to study properties of neutrinos.We constructed CaF_2 detector with active and passive shield. The whole system is in operation now. We had severe damage in our detector system due to the big earthquake last year. It has been recovered and we had minimum delay in our research project.It is essential to have low background system to search for above rare process. We achieved quite low background level which is comparable to other laboratories around the world. It should be noted that our detector system resides on the sea level though others are underground. Our future experiment in a underground laboratory is quite hopeful since usually 1 to 2 orders of magnitude of background level reduction is expected. The result was presented at the international symposium on "Weak and Electromagnetic Interactions in Nuclei" WEIN'95. Our achivement is summarized in the following.(1) The detector system has the lowest energy threshold (-3 keV) among similar systems with well studied efficiency and energy resolution.(2) Central CaF2 (Eu) crystal is viewed by pure CaF_2 crystal which act as active shield as well as light guide. It is a first detector which has 4pi active shield.(3) We studied radioactive contamination in the detector and established a way to reduce the background due to alpha emitters.We will be measuring the background level at the sea level until we reach the limit of the system. The we will move the detector to the underground laboratory and start full data taking.