J. H. Barker

Line shapes of doppler shifted γ-rays from coincidence and singles spectra in measurements of nuclear lifetimes

Abstract A procedure is described for extracting nuclear lifetimes from the analysis of line shapes of γ-rays from either coincidence or singles spectra obtained from Doppler-shift attenuation experiments. The nuclear and electronic stopping powers in a given slowing down medium are independently adjusted to give the line shape and lifetimes of “standard” Doppler-shifted γ-rays, the lifetimes of which have been determined by other independent methods. The stopping power thus calibrated is then used to determine the lifetimes of other transitions from Doppler-shift attenuation experiments in the same stopping medium. Line shapes are obtained by including the effects (a) of the recoils that escape the target, (b) of the decay of other levels into the state in question, (c) of the γ-or particle-detection angles and their corresponding solid angles, (d) of the integration over the distribution of recoils in the singles experiments including angular correlation effects to a good approximation for angles of observation ≤30° to the beam direction, and (e) of the detector response assumed to be gaussian. Lifetimes are obtained from comparison with experiment using both a line shape fitting technique and the F ( τ ) or centroid-shift technique.