Measurement of the background activities of a  100Mo-enriched powder sample for an AMoRE crystal material by using fourteen high-purity germanium detectors

The Advanced Molybdenum-based Rare process Experiment (AMoRE) in its second phase will search for neutrinoless double-beta (0νββ) decay of 100Mo in 200 kg of molybdate crystals. To achieve the zero-background level in the energy range of the double-beta decay Q-value of 100Mo, the radioactive contamination levels in AMoRE crystals should be low. Enriched molybdenum trioxide powder, 100EnrMoO3, enriched to 95.73% abundance of the 100Mo isotope is used to grow the AMoRE crystals. A shielded array of fourteen high-purity germanium detectors with 70% relative efficiency each was used for the measurement of background activities in a sample of 9.6-kg powder. The detector system named the CAGe located at the Yangyang underground laboratory was designed for measuring low levels of radioactivity from natural radioisotopes or cosmogenic nuclides such as 228Ac, 228Th, 226Ra, 88Y, and 40K. The activities of 228Ac and 228Th in the powder sample were 0.88 ± 0.13 and 0.669 ± 0.089 mBq/kg, respectively. The activity of 226Ra was measured to be 1.19 ± 0.42 mBq/kg. The activity of 88Y was 0.101 ± 0.016 mBq/kg. The activity of 40K was found as 36.0 ± 4.1 mBq/kg.