Title: Search for cosmic dark matter by means of ultra high purity NaI(Tl) scintillator,
Abstract: The dark matter search project by means of ultra high purity NaI(Tl)
scintillator is now underdevelopment. An array of large volume NaI(Tl)
detectors whose volume is 12.7 cm$\phi\times$12.7 cm is applied to search for
dark matter signal. To remove radioactive impurities in NaI(Tl) crystal is one
of the most important task to find small number of dark matter signals. We have
developed high purity NaI(Tl) crystal which contains small amounts of
radioactive impurities, $<4$ ppb of $^{nat}$K, 0.3 ppt of Th chain, 58
$\mu$Bq/kg of $^{226}$Ra and 30 $\mu$Bq/kg of $^{210}$Pb. Future prospects to
search for dark matter by means of a large volume and high purity NaI(Tl)
scintillator is discussed.