Growth and Optical Properties of a Cs2Mo2O7 Single Crystal

A Cs2Mo2O7 single crystal, a molybdenum-based crystal as research and development scintillation material for future neutrinoless double beta decay experiments under milli-Kelvin temperatures, was grown by the Czochralski method. The grown crystal was prepared as a sample for measurements of its optical properties. The sample was cooled down from room temperature to 10 K, and temperature dependence of emission spectrum and decay time were measured. We used a light emitting diode as an excitation source for the emission spectra measurements and a pulsed-type laser for the decay time due to its high intensity. The intensity of emission spectrum and the decay time increased as the temperature decreased. We estimated the optical energy bandgap via a transmittance measurement at room temperature. As far as we know, it is the first time to grow a large Cs2Mo2O7 crystal and to study its luminescence properties. Moreover, we grew a well-studied Li2MoO4 crystal as a reference to compare the light output of the Cs2Mo2O7 at 10 K. Through these results, the Cs2Mo2O7 crystal found to be a candidate scintillator for the future neutrinoless double beta decay experiments. © 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.11sci

Growth and development of pure Li2MoO4 crystals for rare event experiment at CUP

© 2020 IOP Publishing Ltd and Sissa Medialab. The Center for Underground Physics (CUP) of the Institute for Basic Science (IBS) is searching for the neutrinoless double-beta decay (0 nu beta beta) of Mo-100 in the molybdate crystals of the AMoRE experiment. The experiment requires pure scintillation crystals to minimize internal backgrounds that can affect the 0 nu beta beta signal. For the last few years, we have been growing and studying Li2MoO4 crystals in a clean-environment facility to minimize external contamination during the crystal growth. Before growing (Li2MoO4)-Mo-100 crystal, we have studied (Li2MoO4)-Mo-nat crystal growth by a conventional Czochralski (CZ) grower. We grew a few different kinds of Li(2)(nat)MO(4)crystals using different raw materials in a campaign to minimize impurities. We prepared the fused Al2O3 refractories for the growth of ingots. Purities of the grown crystals were measured with high purity germanium detectors and by inductively coupled plasma mass spectrometry. The results show that the Li2MoO4 crystal has purity levels suitable for rare-event experiments. In this study, we present the growth of Li2MoO4 crystals at CUP and their purities11sci

Alpha backgrounds in the AMoRE-Pilot experiment

© 2022, The Author(s).The Advanced Mo-based Rare process Experiment (AMoRE)-Pilot experiment is an initial phase of the AMoRE search for neutrinoless double beta decay of 100Mo, with the purpose of investigating the level and sources of backgrounds. Searches for neutrinoless double beta decay generally require ultimately low backgrounds. Surface α decays on the crystals themselves or nearby materials can deposit a continuum of energies that can be as high as the Q-value of the decay itself and may fall in the region of interest (ROI). To understand these background events, we studied backgrounds from radioactive contaminations internal to and on the surface of the crystals or nearby materials with Geant4-based Monte Carlo simulations. In this study, we report on the measured α energy spectra fitted with the corresponding simulated spectra for six crystal detectors, where sources of background contributions could be identified through high energy α peaks and continuum parts in the energy spectrum for both internal and surface contaminations. We determine the low-energy contributions from internal and surface α contaminations by extrapolating from the α background fitting model.11Nsciescopu

First results from the AMoRE-Pilot neutrinoless double beta decay experiment

The advanced molybdenum-based rare process experiment (AMoRE) aims to search for neutrinoless double beta decay (0νββ) of100Mo with ∼ 100kg of 100Moenrichedmolybdenumembeddedincryogenicdetectorswith adualheatandlightreadout.Atthecurrent,pilotstageofthe AMoRE project we employ six calcium molybdate crystals withatotalmassof1.9kg,producedfrom48Ca-depletedcalcium and 100Mo-enriched molybdenum (48deplCa100MoO4). The simultaneous detection of heat (phonon) and scintillation (photon) signals is realized with high resolution metallic magnetic calorimeter sensors that operate at milli-Kelvin temperatures. This stage of the project is carried out in the Yangyang underground laboratory at a depth of 700 m. We report first results from the AMoRE-Pilot 0νββ search with a 111 kg day live exposure of 48deplCa100MoO4 crystals. No evidence for 0νββ decay of 100Mo is found, and a upper limit is set for the half-life of 0νββ of 100Mo of T0ν 1/2 > 9.5×1022 years at 90% C.L. This limit corresponds to an effective Majorana neutrino mass limit in the range mββ≤(1.2−2.1)eV. © The Author(s) 201911sciescopu