Neutrino-Less Double Beta Decay Experiment Using Ca ¹⁰⁰MoO₄ Scintillation Crystals

Search for neutrino-less double beta decay of100Mo is proposed using active method with Ca100MoO4scintillation crystals which show the brightest scintillation light among variety of inorganic scintillation materials containing Mo. Study of X-ray luminescence and scintillation properties such as energy response, number of photoelectrons/keV, absolute light yield, decay time, pulse shape discrimination and radioactive contamination of CaMoO4crystals grown by the Czochralski method with different conditions are presented. Further R&D of resolution optimization, crystal quality improvement and background reduction are underway. Significant improvement of sensitivity to neutrino-less double beta decay can be achieved by using 10 Mo enriched Ca100MoO4crystals with good energy resolution and low background. Further reduction of background induced by 48 Ca two neutrino double beta decay can be achieved by using48Ca depletion. We are planning to install several kilograms of Ca100MoO4crystals depleted in48Ca at underground laboratory for the neutrino-less double beta decay experiment in the near future.