PICO-LON Project for WIMPs search

Highly segmented inorganic crystal has been shown to have good performance for dark matter search. The energy resolution of ultra thin and large area NaI(Tl) scintillator has been developed. The estimated sensitivity for spin-dependent excitation of 127I was discussed. The recent status of low background measurement at Oto Cosmo Observatory is reportedComment: 3 pages, 1 figure, Proceedings of TAUP200

High purity NaI(Tl) scintillator to search for dark matter

A high purity and large volume NaI(Tl) scintillator was developed to search for cosmic dark matter. The required densities of radioactive impurities (RIs) such as U-chain, Th-chain are less than a few ppt to establish high sensitivity to dark matter. The impurity of RIs were effectively reduced by selecting raw materials of crucible and by performing chemical reduction of lead ion in NaI raw powder. The impurity of $^{226}$Ra was reduced less than 100 $\mu$Bq/kg in NaI(Tl) crystal. It should be remarked that the impurity of $^{210}$Pb, which is difficult to reduce, is effectively reduced by chemical processing of NaI raw powder down to less than 30 $\mu$Bq/kg. The expected sensitivity to cosmic dark matter by using 250 kg of the high purity and large volume NaI(Tl) scintillator (PICO-LON; Pure Inorganic Crystal Observatory for LOw-background Neutr(al)ino) is 7$\times$10$^{-45}$ cm$^{2}$ for 50 GeV$/c^{2}$ WIMPs.Comment: 6 pages, 2 Figures, Proceedings of International Symposium on Radiation Detectors and Their Uses (ISRD2016). Talk given on 19th Jan. 2016 by K.Fushimi. To be published in Proceedings will be published as JPS conference proceedings (2016