Scintillating Bolometer Crystal Growth and Purification for NeutriNoless Double Beta Decay Experiments

A crucial step in understanding the physics of our universe, and a current priority for DOE’s Nuclear Physics program, is elucidating the nature of neutrinos. Experiments probing the nature of the neutrino are searching for the rare nuclear process of neutrinoless double-beta decay (0νββ). The state-of-the-art bolometer-based experiment is the Cryogenic Underground Observatory for Rare Events (CUORE) at Gran Sasso, Italy. Although CUORE is the most sensitive 0νββ experiment to date, further background reduction is needed to clearly observe this rare process. The next generation 0νββ detectors will be more sensitive, using a detector with particle identification to better reject background events. CUPID (CUORE with Particle Identification) is a ton-scale 0νββ experiment. The CUPID Group includes researchers from more than 30 institutions in 7 countries, including US researchers at MIT, ANL, BNL, LBNL, LLNL, UC Berkeley, UCLA, USC, and Yale. Phase IIA will continue the successful collaboration between RMD and MIT, working with the international CUPID Interest Group. Phase IIA research will optimize crystal growth of ultra-pure lithium molybdate, scale up crystal size, and implement procedures that maintain the radio-purity throughout processing. Detector crystals will be sent to MIT and the CUPID Group to evaluate detector performance. The final step will be to incorporate enriched 100Mo into our processes and provide crystals for a demonstration experiment to qualify the material. The ultimate goal is to enable full-scale production of detector crystals and become a qualified U.S. supplier of crystals for the CUPID experiment. Phase I involved developing synthesis and purification procedures, crystal growth, and fabrication and testing of zinc molybdate and sodium molybdate bolometers. Crystals were successfully tested by MIT at the CSMSN laboratory in France. Phase II continued and expanded this research, including investigating lithium molybdate. Crystals of sodium molybdate up to 600 grams and lithium molybdate up to 400 grams have been grown. Lithium molybdate crystals are presently being tested by the researchers at MIT. Commercial Applications and Other Benefits: Our intent is to develop a U.S. based capability for producing crystals and scintillators for rare event experiments. If successful, the resulting detector technology will be applicable to many experiments in addition to 0νββ. The commercial revenues will come from sales to several very large international physics research efforts. In addition, the processes developed will be directly applicable to production of many other commercial scintillation materials where the increased purity will lead to better detector performance, giving RMD a competitive advantage.