Studies of scintillation properties of CaMoO₄ at millikelvin temperatures

Application of CaMoO₄ as a scintillation target in cryogenic rare event searches relies on the understanding of scintillation properties of the material at the temperatures at which these detectors operate. We devised and implemented a detection module with a low-temperature photomultiplier from Hamamatsu (model R8520-06) powered by a Cockcroft-Walton generator. The detector module containing the CaMoO₄ crystal was placed in a ³He/⁴He dilution refrigerator and used to measure scintillation characteristics of CaMoO₄ in the millikelvin temperature range. At the lowest temperature achieved, the energy resolution of CaMoO₄ for 122 keV γ from a ⁵⁷Co source is found to be 30%, and the fast and slow decay constants are 40.6 ± 0.8 μs and 3410 ± 50 μs, respectively. The temperature variation of the CaMoO₄ decay kinetics is discussed in terms of a three-level model of the emission center