Energy Resolution of ?-Radiation up to 18 MeV by Sodium Iodide Scintillation Counters

Abstract

The pulse-height distributions to be expected from scintillation counters using thallium-activated sodium iodide crystals have been investigated for ?-radiation of energies 6, 12, and 18 MeV. with two sizes of cylindrical crystal (2·5 cm. long by 2·5 cm. diameter and 7·5 cm. long by 4 cm. diameter). A Monte Carlo calculation of the partial shower process by which photons are absorbed in the crystals has given the probability distributions of ionization energy from homogeneous incident photons. The spreading of the distributions by statistical effects in the photomultiplier has been measured using light flashes of constant integrated intensity from a rotating mirror. The curves predicted by combining these two factors are compared with experimental pulse-height distributions for ?-radiation from proton bombardment of fluorine, boron, and lithium.