  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 = 6 K. The scintillation module was composed of a CaWO4
scintillator and a low-temperature PMT D745B from ET Enterprises. The PMT
responsivity was studied at T=290, 77 and 6 K using gamma-quanta from 241Am (60
keV) and 57Co (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 = 6 K, 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 CaWO4 scintillating crystal the overall
responsivity of the scintillation modules CaWO4+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 detection mode. It is
concluded that commercially available low-temperature PMT are well suited for
detection of scintillation light at cryogenic temperatures.
