The timing capability of photomultipliers (PMTs) can be inferred from the basic laws of electron motion. The relationships between time dispersion and field strength, initial electron energy, angle of emission, and electrode spacing follow from these laws. For conventional PMTs, the major contribution to dispersion arises from the cathode-to-first-dynode region. The field gradient at the cathode primarily determines the timing. This is verified by examining the electron motion in non-uniform electric fields. The contribution from interdynode transitions is small for linear focussed PMTs. Monte Carlo simulations of output waveforms from scintillators agree with measurements. The performance of threshold, zero crossing, and constant fraction (CF) discriminators is examined, revealing the superiority of the CF types. Two organizations have made detailed timing measurements, some of which show sub-nanosecond jitter. Proximity focussed PMTs from Hamamatsu confirm time dispersion measured in picoseconds.
Electric fields, electron production, and electron motion at the stripper foil in the Los Alamos Proton Storage Ring
