Method for least-squares analysis of gamma-ray scintillation spectra using a bent-crystal monochromator

Abstract

A method is presented for determining gamma-ray relative intensities using features of the conventional least-squares analysis of a NaI pulse-height spectrum combined with the crystal-diffraction method. In studying the gamma rays from a radioactive source, a bent-crystal spectrometer is used as a gamma-ray monochromator to obtain monoenergetic gamma rays using a strong line source. The individual response functions of a NaI detector to these monoenergetic gamma rays are recorded in a multichannel analyzer. The NaI detector is then directly exposed to a second thin line source of the same source material, placed on the focal circle of the monochromator, and the composite pulse-height spectrum in the NaI detector of all gamma rays from the source is recorded. The relative intensities of the gamma rays are then determined by a least-squares adjustment of the appropriate linear combination of monochromatic response functions to obtain the best fit to the composite pulse-height spectrum. The relative intensities of gamma rays from 169Tm following electron capture of 169Yb obtained with this method show good agreement with those obtained using the crystal-diffraction method.