Side feeding patterns and nuclear lifetime determinations by the Doppler shift attenuation method in (α,nγ) reactions

gamma rays were measured at several angles in both singles and coincidence mode in the Sn-119(alpha, n gamma)Te-122 reaction at 15 MeV on a thick target. Lifetimes of excited states in Te-122 were determined from a Monte Carlo Doppler shift attenuation method (DSAM) analysis of the Doppler broadened lines shapes of gamma rays de-exciting the levels. A comparison of several deduced lifetimes with recent results obtained with the (n, n') reaction allowed us to validate the choice of a parameter used to calculate the contribution of the side feeding times. The ingredients of the DSAM line-shape analysis (stopping power, description of instrumental line shapes, and side feeding evaluation) are presented in some detail. It is concluded that with proper treatment of side feeding, a DSAM line-shape analysis of peaks in singles or coincidence spectra obtained following the (alpha, n gamma) reaction is able to provide rather accurate values for the lifetimes of levels with low and medium spins.