Optimization of cryogenic calorimetric detection with lithium molybdate crystals for AMoRE-II experiments

Abstract

The AMoRE collaboration is preparing for the second phase of the experiment, AMoRE-II, which will exploit a 100 kg of 100Mo isotopes to search for neutrinoless double beta decay from the isotope. Most of the 100Mo isotopes will be contained in the lithium molybdate (Li2MoO4) crystals, which will act as absorbers of cryogenic calorimeters coupled to MMC (metallic magnetic calorimeter) sensors. The detector array will have a total mass of approximately 200 kg with hundreds of detector modules. Hence, considerable effort has been taken to optimize the lithium molybdate crystal detector in terms of the detector performance and preparation procedure to build many detector modules in a reasonable schedule without compromising the detector performance. We found some critical experimental conditions to improve the energy resolution in a series of test experiments. In this paper, we discuss the effect of surface treatment and thermal link connection in improving the energy resolution from 14–15 keV to below 7 keV at 2.615 MeV, 208Tl gamma line, which is near the Q-value of the decay of 100Mo, 3.034MeV. We also report the high discrimination power for the separation of alpha particles using the simultaneous scintillation light detection with a test performed in the cryogen-free dilution refrigerator.

Light channel signal analysis with the lithium molybdate crystal R\&D detectors for AMoRE-II experiments

“…The MMC reads the temperature increase of the wafer due to the absorption of the scintillation light [7]. Detailed descriptions regarding the heat channel part can be found in [8][9][10][11]. A short description of different types of light detectors is mentioned in Table 1.…”

“…The energy of the scintillation signals from 2.615 MeV gamma rays for LMO crystals with AMoRE-II LD is found to be in the range of 2.1-2.5 keV, which corresponds to 0.80-0.96 keV/MeV. Thanks to the good light collection, we have demonstrated alpha rejection capabilities around ROI with more than 10 times the standard deviation[8,9]. In conclusion, we developed a light detector for AMoRE-II experiments and the performance showed promising results.…”

A study of event position dependence for the AMoRE-II R&D detectors with Li2MoO4 crystal absorbers

“…Fig 3(c), A crystal with a diffusive surface exhibited less pronounced position dependence than the polished surface. With a crystal with a diffusive surface, we vi demonstrated an energy resolution of around 7 keV with full width at half maximum (FWHM)[9].…”