Li2100deplMoO4 Scintillating Bolometers for Rare-Event Search Experiments.

We report on the development of scintillating bolometers based on lithium molybdate crystals that contain molybdenum that has depleted into the double-ß active isotope 100Mo (Li2100deplMoO4). We used two Li2100deplMoO4 cubic samples, each of which consisted of 45-millimeter sides and had a mass of 0.28 kg; these samples were produced following the purification and crystallization protocols developed for double-ß search experiments with 100Mo-enriched Li2MoO4 crystals. Bolometric Ge detectors were utilized to register the scintillation photons that were emitted by the Li2100deplMoO4 crystal scintillators. The measurements were performed in the CROSS cryogenic set-up at the Canfranc Underground Laboratory (Spain). We observed that the Li2100deplMoO4 scintillating bolometers were characterized by an excellent spectrometric performance (∼3-6 keV of FWHM at 0.24-2.6 MeV γs), moderate scintillation signal (∼0.3-0.6 keV/MeV scintillation-to-heat energy ratio, depending on the light collection conditions), and high radiopurity (228Th and 226Ra activities are below a few µBq/kg), which is comparable with the best reported results of low-temperature detectors that are based on Li2MoO4 using natural or 100Mo-enriched molybdenum content. The prospects of Li2100deplMoO4 bolometers for use in rare-event search experiments are briefly discussed.

Single crystals of undoped Li2WO4 and Li2W1-0.0125Mo0.0125O4: formation enthalpies, heat capacity in the temperature range 320-997 K.

The Li2WO4 single crystal was first grown by applying the Czochralski technique with weight control and low-temperature-gradients. A single crystal of Li2WO4 is one of the perspective materials for researching rare events. The heat capacity for a Li2W1-0.0125Mo0.0125O4 single crystal has been determined by DSC calorimetry in the temperature range 320-997 K for the first time. No anomalies in the heat capacity associated with phase transitions were found. The standard formation enthalpy for the Li2WO4 single crystal was studied using reaction calorimetry. It has been shown that the relation of standard formation enthalpies for Li2W1-xMoxO4 (x = 0.15-0) with function (1-x)W + xMo are close to linear, which allows one to predict the thermodynamic properties for single crystals with isotopes Li2W1861-0.0125Mo1000.0125O4 and Li2W186O4. It was shown that single crystals with isotopes are more thermodynamically stable than without isotopes.