Further study of undoped NaI scintillators with different purity

Several undoped NaI crystals of scintillation grade purity, selected for their different light emission under UV excitation at room temperature, were studied by gamma-ray spectrometry methods at liquid nitrogen (LN2) temperature using avalanche photodiode. The measured quantities covered the light output expressed in the e-h pair number, non-proportionality characteristics, energy resolution and finally the intrinsic resolution of the studied crystals. The performed measurements confirmed previous observations that the performance of the tested crystals in gamma spectrometry depends on the accidental doping by traces of impurities. To define them, the characterization of NaI crystals themselves by different analytical methods was used, like test of the emission spectra at room and liquid nitrogen temperatures, X-ray fluorescence analysis and then the inspection of light pulse shapes at LN2 temperature.