Ca toward the Study of Neutrinoless Double Beta Decay by CANDLES

CANDLES used ⁴⁸Ca to study the neutrinoless double beta decay (0vββ) to explore the mystery of the universe, such as lepton number violation, Majorana neutrino, and matter anti-matter asymmetry. The recent CANDLES III experiment achieved a lower limit on the half-life of 0vββ decay at 5.6 × 10²² years and the effective Majorana neutrino mass of ≤ 2.9 − 16 eV at 90% C.L. However, producing large quantities of ⁴⁸Ca is challenging. Utilizing laser isotope separation (LIS) is crucial in overcoming this challenge and enabling the mass production necessary for the CANDLES study of 0vββ.

Studies have shown that a laser diode with a single frequency of 422.792 nm can deflect ⁴⁸Ca from an atomic beam due to the isotope shift of ⁴⁸Ca and other isotopes. An atomic beam generator, laser irradiation unit, collection system, and monitor and control system are necessary for mass production. The use of microchannel capillaries can improve the performance of sheet-like atomic beam generators by reducing inter-atomic scattering and maintaining high beam intensity with a small divergence angle. The laser system, which utilizes multiple slave lasers, can produce a power of 2W and efficiently separate ⁴⁸Ca, achieving a production rate of 10 grams/year. The most effective materials for collecting and coating thin films are being researched. The new design for the main chamber that will increase production capacity to 2 mol/year and 300 kg/year will be presented.