Studies of helium poisoning of a Hamamatsu R5900-00-M16 photomultiplier

We report results from studies of the helium poisoning of a 16-anode photomultiplier tube R5900-00-M16 manufactured by Hamamatsu Photonics. A tube was immersed in pure helium for a period of about four months and was periodically monitored using a digital oscilloscope. Our results are based on the analysis of waveforms triggered by the dark noise pulses. Collected data yield evidence of after-pulses due to helium contamination of the tube. The probability of after-pulsing increased linearly with the exposure time to helium but the phototube suffered only a small drop in gain, indicating generally strong resilience to helium poisoning.