Characterization of a pure CsI crystal at low temperature for a dark-matter search

Scintillators are widely used as detectors to search for dark matter. In this study, we studied the scintillation properties of a pure CsI crystal to confirm that the crystal has good properties for searching for dark matter at low temperatures. To confirm if the pure CsI crystal has suitable properties for detecting dark matter, we investigated its scintillation properties by using alpha particles and gamma rays in temperature range from 300 - 10 K. The light yield, alpha/gamma ratio, and decay time were measured for each temperature, and it the alpha and the gamma signals could be separated by using a pulse shape discrimination. The light yield increased as the temperature decreased, and the light yields due to alpha particles and gamma rays were found to be about 80,000 photons/MeV. The decay times of alpha particles and gamma rays increased as the temperatures was decreased. Because pure CsI at low temperatures have twice the number of photoelec-trons per MeV than the CsI:Tl detector at room temperatures, we confirm that CsI has a low threshold energy at low temperatures which is an advantage when searching for low-mass dark matter.