The efficient use of photomultiplier tubes for recording spectra

The experimental value of the signal-to-noise ratio (S/N) was used as a criterion for comparing different photomultiplier tubes and for assessing the relative merits of pulse-counting and dc measurement. For tubes with S-11 and S-20 photocathodes at room temperature, no significant difference was found between pulse-counting and dc methods. When different tubes were compared, other factors being equal, those with smaller cathodes gave higher S/N values. A comparison was also made between a cooled S-1 cathode photomultiplier tube and a p-i-n photodiode at room temperature. The photomultiplier tube was found to have a S/N many times higher than the photodiode.