Response of doped alkali iodides measured with gamma-ray absorption and Compton electrons

Relative light yield and intrinsic energy resolution of NaI:Tl, CsI:Na and CsI:Tl crystals were investigated by means of the wide angle Compton coincidence technique in wide energy range from several keV up to 1 MeV. The experimental setup consisted of a high purity germanium (HPGe) detector and the tested scintillators were put at a close separation from the HPGe detector. The tested samples were cylinders of 25 mm diameter and height coupled to a photomultiplier. Compton electron responses were compared to the results obtained with γ-ray absorption peaks. A correlation between intrinsic resolution of the tested scintillation materials and their nonproportionality was observed. Substantial differences in intrinsic resolution measured for γ-ray absorption peaks and Compton electrons were registered in the energy range between 50 keV and 200 keV. The results were discussed in terms of electron scattering, pointing to δ-ray production as an important contribution for determination of scintillator intrinsic resolution.