Maximum Scintillation Yield in NaI(Tl)

The linear energy transfer ( LET ) dependence of the scintillation yield in liquid argon was previously obtained experimentally over the wide range from 1 to 10 4 MeV/g/cm 2 of LET . In the present paper, this LET dependence is compared with that in NaI(Tl) given in the paper of Murray and Meyer. From the similarity between the LET dependence of NaI(Tl) and that of liquid argon, it is suggested that a flat top of the scintillation yield in NaI(Tl) gives the maximum scintillation yield. This maximum yield is due to a 100% recombination efficiency of electron-hole pairs and to each electron-hole pair recombination resulting in one scintillation photon from the Tl activator. Based on this suggestion and the recent measured average energy, the W p -value, to produce one scintillation photon in NaI(Tl) for ∼1 MeV electrons by Miyajima et al. , the W p -value at the flat top in NaI(Tl) is obtained to be 12.4 -0.8 +1.0 eV. This value is in agreement with the W p -values (10.5∼10.7 or 11.4 eV) calculated here by the Shockley model.