The Contribution of the NaI(Tl) Crystal to the Total Linewidth of NaI(Tl) Scintillation Counters

Monte-Carlo calculations have been performed to determine how much of the broadening of the output pulse of NaI(Tl) scintillation counters is due to the nonproportionality of response of NaI(Tl) to electrons, for incident photons of energy 10 KeV to 1 MeV. Interactions taking place in the crystal have been simulated in detail and take into account fluctuations in light output, due not only to the primary Compton and photoelectric processes, but also to energy-loss fluctuations in the ionizing process along the track of individual electrons. The contribution of these fluctuations is important at energies above 200 KeV but a substantial fraction of the experimental line broadening at low energies remains unaccounted for. It is suggested that the contribution of the crystal to the total broadening is quite sensitive to the shape of the electron response curve.