Performance of a photomultiplier at liquid-helium temperature

The performance of a Hamamatsu R7725-mod photomultiplier has been studied at liquid-helium temperature. When cooling from 300 to 8 K, the quantum efficiency decreases by about 10% and the gain by about 30%, afterpulses become less probable, but the dark rate increases, down to the lowest temperature measured. There is no indication against using a photomultiplier at liquid-helium temperature.