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 sci ntillation 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). Tho se were obtained from the numbers of photoelectrons measured with seve ral 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 numb er 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. Ho wever, the above values do not include the uncertainties due to the no t known exact emission spectra and the photomultiplier response curves .