Development of low-background CsI(Tℓℓ) crystals for WIMP search

Search for weakly interacting massive particles (WIMPs) is being carried out at the underground laboratory, Yangyang, Korea. Characteristics and internal background of CsI(Tℓℓ) crystal have been investigated. In our extensive R&D, we reduced internal background in the CsI(Tℓ)CsI(Tℓ) crystal. With the latest, we have achieved 5.50±0.10cpd (counts/keV/kg/day) at 10–15 keV low-energy region. Further reduction of internal background is foreseen with the CsI powder lately produced.