Gamma-Ray Resolution of Larger NaI(Tl) Scintillators

Abstract

The various factors affecting the gamma-ray energy resolution of NaI(Tl) scintillation spectrometers have been investigated experimentally with commercially packaged 2.5- and 5-in. diam scintillators and routinely available 3- and 5-in. photomultipliers. The resolution contains contributions from the scintillator light yield, photocathode efficiency, intrinsic resolution due to the material NaI(Tl) and two terms involving the effects of various spatial inhomogeneities in the packaged scintillator and photomultiplier. Insofar as possible these contributions are experimentally separated. The poorer resolution of the 5-in. systems is in about equal measure caused by their smaller light yield, their larger spatial inhomogeneities and the lower efficiency of the 5-in. photomultipliers in producing and collecting cathode electrons.