Preparation of low-radioactive high-purity enriched ¹⁰⁰MoO₃ 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 (0νDBD) of the ¹⁰⁰Mo isotope using over 100 kg of ¹⁰⁰Mo embedded in 200 kg of ultra-pure Li₂¹⁰⁰MoO₄ bolometric crystals. Efficient purification technology was developed and adapted to purify ¹⁰⁰MoO₃ powder with a 5 kg per month production capacity. Based on the ICP-MS analysis of purified powder, the ²³²Th and ²³⁸U were reduced to <9.4 μBq/kg and <50 μBq/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 ²³²Th and ²³⁸U decay chains, reporting upper limits of <27 μBq/kg for ²²⁸Ac and <16 μBq/kg for ²²⁸Th. The ²²⁶Ra activity was acceptable at 110 ± 30 μBq/kg. In the last 3 years, 100 kg of pure ¹⁰⁰MoO₃ 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.