Ultra-violet wavelength shift for undoped CaF2CaF2 scintillation detector by two phase of liquid scintillator system in CANDLES

CANDLES is a project to search for neutrinoless double beta decay of 48Ca with CaF2CaF2 scintillators. An effective 4π4π active shield is achieved by placing the CaF2CaF2 crystals in a liquid scintillator. Energy resolution is improved by converting the ultra-violet light of the CaF2CaF2 scintillator into the visible region with a wavelength shifter dissolved in the liquid scintillator. The newly developed technique, “two phase system of liquid scintillator”, is presented. It will be used to exploit the unique features of the CANDLES system. Experiments to determine liquid scintillator composition will be described. Performance of CANDLES will be demonstrated with prototype detectors. Obtained results indicate that the proposed two phase technique is effective for CANDLES system which will utilize several tons of CaF2CaF2 scintillators.