Detection of small light pulses and pulse height resolution of a fine mesh photomultiplier tube

The pulse height resolution of a fine mesh photomultiplier tube and its ability to distinguish zero photoelectrons from greater than zero have been measured as a function of the mean number of photoelectrons per pulse and of the magnetic field magnitude and orientation. The fraction of the charge ejected from the photocathode that is collected at the anode, and therefore the effective photostatistics, is greatest when the field is oriented along the pmt axis. In practice, FMPMT gain is quite low in this orientation and low-noise electronics must be used to realize the benefit of the more efficient charge collection.