Study of the internal background of CsI(Tℓ) crystal detectors for dark matter search

Abstract

A search for particle cold dark matter with CsI(T,l) crystal is being prepared at the Cheong-Pyeong underground laboratory in Korea. The background spectra of CsI(Tl) crystal detectors in a prototype shield were obtained. The lowest background count rate of the test sample of crystals is measured to be 64.7+/-5.1 counts/keV/kg/day in the energy range of 5-20 keV. Quantitative estimation of residual radioactive isotope in CsI(Tl) was made using the GEANT4 Monte Carlo simulation. Analysis results show that CsI(Tl) crystal could be a good candidate for direct detection of WIMPs when the contamination level of cesium radioisotopes is reduced to under a few mBq/kg. (C) 2003 Elsevier Science B.V. All rights reserved.