Investigation of scintillation properties of a CsI(Tl) crystal at low temperature for dark matter search

The Korea invisible mass search (KIMS) experiment used CsI(Tl) crystals coupled with photomultiplier tubes (PMTs) to detect signals from weakly interacting massive particles (WIMPs) at room temperature. It is expected that combining CsI(Tl) crystals with silicon photomultipliers (SiPMs) will enhance the detection performance. However, SiPMs must operate at low temperatures to reduce the dark count rate. In this study, we examined the temperature dependence of CsI(Tl) crystal properties, including light yield, α/β ratio, decay time, and pulse shape discrimination, before integrating it with a SiPM. The CsI(Tl) crystal was placed in a low-temperature chamber with a radiation source, and scintillation photons were detected by a PMT positioned outside the chamber. The response of CsI(Tl) to α-particles and γ-rays was examined across temperatures ranging from 10 K to 300 K.