Radioassay and Purification for Experiments at Y2L and Yemilab in Korea

Two major rare-process search experiments, COSINE-100 for WIMP dark matter and AMoRE for neutrinoless double beta decay, have been running at the Yangyang underground laboratory (Y2L) in Korea for about four years. In order to measure radio-activities of materials in both experiments, a number of ultra-low radioactivity measurement detectors have been developed and are now operational. For radioassays of raw materials and detector components, an ICP-MS, an argon gas ionization counter, and a number of HPGe detectors are being used. Three silicon PIN diode-based radon chamber detectors have been either upgraded or constructed for accurate measurements of atmospheric radon in a radon reduction system. A fourteen element HPGe detectors array was installed in 2016 for more sensitive measurements and larger sample capacities than those could be tested in two single crystal HPGe detectors. Since the Y2L space is too small to accommodate the next phases of both experiments, a new underground laboratory, called Y emilab, is being constructed in Jeongseon, Korea with a factor of ten more space (~2,800 m²) and a ~1,100 m overburden compared to ~200 m² and ~700 m at Y2L. The future experiments require detector materials with substantially lower background levels than those in the current ones. Various types of scintillating crystals such as CaMoO₄, Li₂MoO₄, and NaI(Tl) are being grown with purification methods specifically developed for the raw materials. A summary on radioassay and purification results for experiments at Y2L and Yemilab in Korea will be presented.