Measurement of Gamma-Ray Energies with Single Crystals of NaI(T1)

A new method is described for determining gamma-ray energies and intensities. The basis of the method is the observation of narrow pulse distributions (lines) in the scintillations of NaI(T1). Due to the presence of the iodine component, pair production and the photoelectric process produce relatively sharp lines in the pulse distributions. The Compton process may also be used in determining gamma-energies. Approximate theoretical curves of the pulse distribution are shown. Experimental spectra resemble the theoretical patterns, except for differences in intensities discussed in the text. Electronic as well as photographic techniques for obtaining spectra are described. With these methods well known spectra are confirmed and new results in the case of ${\mathrm{Ga}}^{66}$ are given. With a source of less than ${10}^{-9\mathrm{}}$ curie of ${\mathrm{K}}^{40}$ the energy of the gamma-ray has been determined to within two percent. The method described should make possible a new approach to the study of weak gamma-radioactivities and unknown gamma-ray spectra.