Understanding internal backgrounds of NaI(Tl) crystals toward a 200~kg array for the KIMS-NaI experiment

摘要

The Korea Invisible Mass Search (KIMS) collaboration has developedlow-background NaI(Tl) crystals that are suitable for the direct detection ofWIMP dark matter. With experience built on the KIMS-CsI programs, the KIMS-NaIexperiment will consist of a 200~kg NaI(Tl) crystal array surrounded by layersof shielding structures and will be operated at the Yangyang undergroundlaboratory. The goal is to provide an unambiguous test of the DAMA/LIBRA'sannual modulation signature. Measurements of six prototype crystals showprogress in the reduction of internal contaminations of radioisotopes. Based onour understanding of these measurements, we expect to achieve a backgroundlevel in the final detector configuration that is less than 1~count/day/keV/kgfor recoil energies around 2~keV. The annual modulation sensitivity for theKIMS-NaI experiment shows that an unambiguous 7$\sigma$ test of the DAMA/LIBRAsignature would be possible with a 600~kg$\cdot$year exposure with this system.