Demonstration of photomultiplier tube operation at 29 K

We describe measurements of gain, dark current, and detection efficiency obtained while cooling a Hamamatsu R5912-02-MOD photomultiplier tube from room temperature to 29 K. We found that the PMT operated normally down to 29 K, with a reduced gain and detection efficiency at the lowest temperatures. Furthermore, we found that the dark count rate increased as the temperature decreased. We conclude that these PMTs appear to be adequate for the requirements of the CLEAN experiment.