Dark Matter Search Experiment with Csl(Tl) Crystal

Abstract

We are preparing an experiment for dark matter (WIMP) search using CsI(Tl) crystal. The detection threshold of a large CsI(Tl) crystal coupled with green extended PMTs was down to 2 keV, and the pulse shape discrimination power of the crystal shows better separation of nuclear recoil from background electron signals than NaI(Tl). With these characteristics, CsI(Tl) is another good material for WIMP search experiment. The disadvantage of CsI(Tl) is the internal background from cesium and rubicium ratioisotopes. In this report, the measurements and reduction of these ratioisotopes are described, and a perspective for the experiment is presented.