More on the scintillation response of NaI(Tl)

The NaI:Tl scintillation response has been studied for over four decades. Two of the significant conclusions that have been made from these studies (with respect to using NaI(Tl) to detect gamma rays and X-rays) are: (1) the NaI(Tl) scintillation response is nearly linear (especially over limited energy ranges) and (2) the NaI(Tl) scintillation response has significant nonproportionalities; while these conclusions may at first appear to be inconsistent with each other, upon further consideration these conclusions are not mutually exclusive. In fact, these conclusions are fully consistent with each other. Published results typically confirm only one of these conclusions (as it was likely the intention to study either linearity or proportionality, but not both) and are not always presented such that direct comparisons can be made with other results. Consequently, it is critical that both the intent of the study and the means with which the results are presented be appropriately considered. Otherwise, it is possible to make inaccurate conclusions about both linearity and proportionality. To facilitate accurate conclusions and meaningful comparisons, this study defines a fully consistent nomenclature, examines some of the subtleties which must be considered when comparing scintillation response results, and uses a review of the literature to demonstrate both the definitions and the subtleties.