Research on Pure Sodium Iodide as a Practical Scintillator

Pure Nal as a practical scintillator has been investigated in the temperature range of 125 K to 293 K. Previously reported limitations with photomultipliers and optical coupling methods have been overcome. New photomultipliers allow operating temperatures down to at least 77 K. Optical coupling was accomplished with silicone based coupling grease for temperatures down to 140 K. For lower temperatures, a gas interface was employed. Energy resolution of 14% at 122 KeV was obtained at a temperature of 125 K with a 5.1mm × 1.3mm encapsulated, air interface, Nal crystal. Data on relative pluse height and pluse height resolution are presented as a function of temperature. A brief concluding discussion on the advantages and limitations of pure Nal as a practical scintillator is also given.