First test of a cryogenic scintillation module with a CaWO_4 scintillator and a low-temperature photomultiplier down to 6 K

摘要

Future cryogenic experiments searching for rare events require reliable, efficient and robust techniques for the detection of photons at temperatures well below that to which low-temperature photomultipliers (PMT) were characterised. Motivated by this, we investigated the feasibility of a low-temperature PMT for the detection of scintillation from crystalline scintillators at T=6K. The scintillation module was composed of a CaWO_4 scintillator and a low-temperature PMT D745B from ET Enterprises. The PMT responsivity was studied at T=290, 77 and 6K using γ-quanta from ~(241)Am (60 keV) and ~(57)Co (122 and 136 keV) sources. We have shown that the low-temperature PMT retains its single photon counting ability even at cryogenic temperatures. At T=6K, the response of the PMT decreases to 51+13% and 27 + 6%, when assessed in photon counting and pulse height mode, respectively. Due to the light yield increase of the CaWO_4 scintillating crystal, the overall responsivity of the scintillation modules CaWO_4 + PMT is 94 + 15% (photon counting) and 48 + 8% (pulse height) when cooling to T=6 K. The dark count rate was found to be 20 s~(-1). The energy resolution of the module remains similar to that measured at room temperature using either of the detection modes. It is concluded that commercially available low-temperature PMT are well suited for detection of scintillation light at cryogenic temperatures.