Single Crystal Molybdates for Neutrinoless Double Beta Decay Experiments

75593-The Neutrinoless Double Beta Decay Underground Detector has been identified by the DOE as a high scientific priority for Nuclear Physics research; however, the current generation of proposed experiments to determine neutrino mass would require 500 kg of germanium (Ge), isotopically enriched to 86% in 76Ge, costing more than $100 million. Therefore, several alternate parent isotopes for neutrinoless double beta decay have been suggested as candidates. For example, the 100Mo isotope of molybdenum is particularly promising because it has a large decay energy, resulting in a signal above gamma ray backgrounds and corresponding to an increased decay rate. The nuclear structure of this relatively light nuclide has been shown to be simple enough to allow reliable calculation of the parameters needed to extract the effective neutrino mass from the measured half-life. However, these advantages can only be exploited if a detector can be constructed with both high detection efficiency and excellent energy resolution. The only known method is to construct a bolometer of a single crystal from a compound that contains a significant fraction of molybdenum. Therefore, this project will develop the bulk crystal growth of a single crystal molybdate (molybdenum oxide compound), so that large crystals can be routinely and cost-effectively grown. In Phase I, a target molybdate compound will be selected from preliminary candidates, based on theoretical considerations. Then, an un-enriched, oriented single crystal of approximately 2 cmwill be grown, and a 1 cm cube will be prepared for preliminary neutrino-detector experiments. Commercial Applications and Other Benefits as described by the awardee: Because the target molybdate compounds are acousto-optic materials, they should be well suited for such applications as acousto-optic modulators, frequency shifters, deflectors, and acousto-optic tunable filters. Based on results for lead molybdate, a possible use in low temperature scintillator applications is also contemplated, with luminescence arising from molybdenum oxide complexes.