Number of photoelectrons from a photomultiplier cathode coupled with a NaI(Tl) scintillator

Absolute numbers of photoelectrons from several PMT photocathodes coupled with NaI(Tl) scintillators were measured for the several energies of gamma-rays. Typically, 6.85 × 103 photoelectrons were obtained with a resolution of 13% for 662 keV gamma-rays of 137Cs.