Abstract A cryogenic detector system based on two 3. 3 kg high-purity CsI crystals was developed and characterized at approximately 95 K. Each crystal was coupled to dual-ended 3-inch photomultiplier tubes (PMTs) for scintillation readout. The measured light yields were 28. 7 0. 9 28. 7 ± 0. 9 and 29. 3 1. 0 29. 3 ± 1. 0 photoelectrons per keV electron-equivalent (PE/keV ₄₄ ee) for the two crystals, with corresponding energy resolutions of 7. 2% and 7. 7% (FWHM) at 59. 6 keV. The detector demonstrated excellent spatial uniformity, low intrinsic radioactivity, and stable operation over a continuous one-month period. Optical photon simulations using Geant4 reproduced the observed light collection trends, providing guidance for detector optimization. These results establish cryogenic pure CsI as a scalable technology for low-threshold rare-event searches.
Su et al. (Sat,) studied this question.