A method of measuring gamma-ray relative intensities was developed which used a germanium .bent-crystal spectrometer as a monochromator. The response function of a Nai detector to the essentially monoenergetic gamma rays, obtained from the diffracted beam of the spectrometer, was recorded in a multichannel analyzer. The composite spectrum due to all the gamma rays was then recorded in the analyzer. A computer program was written to normalize the response functions to unit area and to determine, by minimizing the sum of the squares of the deviations, the linear combination of monoenergetic response functions that best represents the composite spectrum. The intensity of a gamma ray is then proportional to the adjusted area under the monoenergetic response function. The relative intensities of the gamma rays of Tm 169 obtained by electron capture from Yb 169 were measured.
Brown, Joseph Emerson and Hatch, E. N., "A computer method for determining by least squares gamma ray relative intensities using a bent-crystal monochromator" (1964). Ames Laboratory Technical Reports. 90.