Line-Widths in Nal(Tl) Scintillation Counters for Low Energy Gamma-Rays

The line-width for a number of NaI(Tl) scintillation counters for low energy gamma-rays has been examined in detail down to an energy of 6 KeV. Below 100 KeV, the photomultiplier accounts for about half the relative variance. For energies in the range 30-40 KeV there is a curious anomaly in the line-width, interpreted as being associated with the K-edge of iodine at 33.2 KeV. The surface preparation of the crystal has an effect on the line-width which differs markedly from region to region over the whole energy range below about 100 KeV.