Author :
Kim, H.J. ; Lee, H.S. ; Bhang, H.C. ; Choi, J.H. ; Dao, H. ; Hahn, I.S. ; Hwang, M.J. ; Jung, S.W. ; Kang, W.G. ; Kim, D.W. ; Kim, S.C. ; Kim, S.K. ; Kim, T.Y. ; Kim, Y.D. ; Kwak, J.W. ; Kwon, Y.J. ; Lee, J. ; Lee, J.H. ; Lee, J.I. ; Lee, M.J. ; Lee, M.H.
Abstract :
The response of CsI(Tl) crystals to nuclear recoils and gammas down to 3 keV has been studied, and it has been demonstrated that the pulse shape discrimination capability for CsI(Tl) is better than that for NaI(Tl). Extensive study of internal background of CsI powder was performed and a lot of efforts have been made to reduce the internal background sources such as 137Cs and 87Rb. The 137Cs concentration of 2 mBq/kg was achieved successfully in the CsI powder using ultra-pure water for whole extraction process. The Rb concentration was successfully reduced to be less than 1 ppb by the recrystallization method. The CsI(Tl) crystal used for the experiment was grown with the ultra-low background CsI powder and a dimension of the CsI(Tl) crystal is 8times8times30 cm3 which corresponds to weight of 8.7 kg. The number of photoelectrons is measured to be about 4-6/keV with a RbCs photocathode PMT. The background of CsI(Tl) crystals were measured in the shielding of 30 cm thick mineral oil, 15 cm thick lead, 5 cm thick polyethylene and 10 cm copper at the 700 m minimum depth of underground laboratory at YangYang Pumped Storage Power Plant in Korea. The WIMP search with low background CsI(Tl) crystals has been carried out by the Korean Invisible Mass Search (KIMS) Collaboration and the lower limit on WIMP-nucleon cross section are reported.
Keywords :
caesium compounds; cosmic ray apparatus; dark matter; hypothetical particles; photocathodes; photomultipliers; recrystallisation; solid scintillation detectors; thallium; 137Cs; 87Rb; CsI(Tl) crystals; CsI:Tl; KIMS Collaboration; Korean Invisible Mass Search Collaboration; RbCs photocathode PMT; WIMP-nucleon cross section; YangYang Pumped Storage Power Plant; cold dark matter; extraction process; internal background sources; nuclear recoils; photoelectrons; polyethylene; pulse shape discrimination capability; recrystallization method; ultrapure water; weakly interacting massive particle searches; Cathodes; Crystals; Minerals; Petroleum; Powders; Power measurement; Pulse shaping methods; Shape; Thickness measurement; Water resources; CsI(Tl); Dark matter; WIMP; internal background; pulse shape discrimination;
