A Sodium Iodide (Tl) Total Absorption Spectrometer for High Energies

A scintillation counter employing a 70-lb NaI(Tl) crystal and a Swiss (AfiF) multiplier phototube has been tested with electrons of energy up to 600 mev. The plot of pulse height vs energy of incident electrons is found to be linear up to the highest energy tested (600 mev). Energy resolution of 16 per cent has been obtained at 350 mev. The crystal is 9 1/2 inches both in diameter and length. The incident radiation, which can be either electrons or gamma rays, induces a cascade electromagnetic shower within the mass of the crystal giving rise to light which enters the photomultiplier tube. Graphs showing linearity in energy response are presented as well as plots of line shape at constant energy of the incident particle. The procedure for obtaining line breadth semitheoretically is described, and the breadth so derived compared with the value obtained in actual practice. Details of the airtight crystal enclosure and of the crystal-photomultiplier optical coupling system are shown.