NUMBERS OF SCINTILLATION PHOTONS PRODUCED IN NAI(TL) AND PLASTIC SCINTILLATOR BY GAMMA-RAYS

The W(S)-value, which is defined as an average energy expended per scintillation photon, was determined to be 17.2 +/- 0.40 eV for a NaI(Tl) phosphor and 60.8 +/- 4.3 eV for a plastic scintillator(NE-102A). Those were obtained from the numbers of photoelectrons measured with several combinations of a photomultiplier tube and a NaI(Tl) or a NE-102A scintillator. The number of photoelectrons, which was measured by the photomultiplier tube as a vacuum photodiode, was converted to the number of scintillation photons by using an averaged quantum efficiency (Q(e)) of each photomultiplier photocathode and a calculated collection efficiency (f(c)) of the scintillation photons at the photocathode. However, the above values do not include the uncertainties due to the not known exact emission spectra and the photomultiplier response curves.