Preparation of low-radioactive high-purity enriched (MoO3)-Mo-100 powder for AMoRE-II experiment

This paper describes preparing radiopure molybdenum trioxide powder enriched with Mo-100 isotope for the AMoRE-II experiment. AMoRE-II, the second phase of the AMoRE experiments, will search for the neutrinoless double-beta decay (0vDBD) of the Mo-100 isotope using over 100 kg of Mo-100 embedded in 200 kg of ultra-pure Li-2 (MoO4)-Mo-100 bolometric crystals. Efficient purification technology was developed and adapted to purify (MoO3)-Mo-100 powder with a 5 kg per month production capacity. Based on the ICP-MS analysis of purified powder, the Th-232 and U-238 were reduced to <9.4 mu Bq/kg and <50 mu Bq/kg, respectively. The concentrations of potassium, transition metals, and heavy metals were lower than 1 ppm. HPGe counting confirmed the reduction of progenies from the Th-232 and U-238 decay chains, reporting upper limits of <27 mu Bq/kg for Ac-228 and <16 mu Bq/kg for Th-228. The Ra-226 activity was acceptable at 110 +/- 30 mu Bq/kg. In the last 3 years, 100 kg of pure (MoO3)-Mo-100 powder was produced. The production yield for the final purified product was above 90%, while irrecoverable losses were under 1.5%, and all by-products could be recycled further.