A Study of 48deplCa100MoO4 Scintillation Crystals for the AMoRE-I Experiment

Advanced Molybdenum-based Rare process Experiment (AMoRE) searching neutrinoless double-beta (
$0\nu \beta \beta $
) decay of
¹⁰⁰
Mo from
^48depl
Ca
¹⁰⁰
MoO
₄
(CMO) scintillation crystals has been preparing CMO crystals for the phase-I stage, AMoRE-I. Nine CMO crystals with a total weight of 3.39 kg were produced by the FOMOS-Materials in Russia and delivered to the Yangyang Underground Laboratory (Y2L) in South Korea for about 2 years until the end of 2016. Acceptance tests of all the nine crystals on weight, dimension, transmittance, light output, energy resolution, and internal radioactivities were completed in the middle of 2017. We have set the upper limits of internal radioactivity levels for
²²⁸
Th,
²²⁶
Ra, and
²²⁷
Ac (daughters of
²³²
Th,
²³⁸
U, and
²³⁵
U), and the total alpha activity of U/Th in the crystals via a GEANT4 Monte Carlo simulation to achieve zero background in region of interest. We used a delayed-coincidence analysis to separate the alphas from gamma background events. Results of the acceptance tests showed that all the crystals are qualified for the AMoRE-I. We will present the test results of the nine crystals together with a reference crystal.