Mass production of ultra-pure NaI powder for COSINE-200

COSINE-200 is the next phase experiment of ongoing COSINE-100 that aims to unambiguously verify annual modulation signals observed by DAMA and reach world competitive sensitivity on low-mass dark matter search. To achieve physics goal COSINE-200, successful production low-background NaI(Tl) detectors crucial it must begin from mass ultra-low background NaI powder. A clean facility for mass-producing pure-NaI powder has been constructed at Center Underground Physics (CUP) in Korea. Two years operation determined efficient parameters purification provided a total 480 kg ultra-pure hand. The potassium concentration produced powders varied 5.4 11 ppb, maximum capacity 35 per 2 weeks was achieved. Here, we report our operational practice with powder, which includes raw purification, recycling mother solution, recovery residual melt after crystal growth.