Neutrino-Less Double Beta Decay Experiment Using Ca $^{100}$ MoO $_{4}$ Scintillation Crystals

Search for neutrino-less double beta decay of ¹⁰⁰Mo is proposed using active method with Ca ¹⁰⁰MoO₄ scintillation 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 CaMoO₄ crystals 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 Ca ¹⁰⁰MoO₄ crystals with good energy resolution and low background. Further reduction of background induced by 48 Ca two neutrino double beta decay can be achieved by using ⁴⁸Ca depletion. We are planning to install several kilograms of Ca ¹⁰⁰MoO₄ crystals depleted in ⁴⁸Ca at underground laboratory for the neutrino-less double beta decay experiment in the near future.