Reaction-rates for Sm-146 production in supernovae

Correlations of the Nd-142/Nd-144 ratio with the Sm/Nd ratio in some meteorites have been previously explained by the alpha-decay of long-lived Sm-146. In order to account for these observations, a necessary production ratio for Sm-146/Sm-144 in the gamma-process of 0.1-0.7 was deduced. The ratio [Gd-148(gamma, n)Gd-147]/[Gd-148(gamma, alpha)Sm-144], which plays the dominant role in the production of Sm-146/Sm-144, has been redetermined in the present Letter by improved statistical model calculations. Utilization of folding potentials for the alpha-channel reduce the (gamma, alpha) rate by a factor of 3, which would enhance the production ratios, previously predicted at the lower limit of the allowed range 0.1-0.7. However, additional improvements in the treatment of nuclear level densities also reduce the (gamma, n) rate by a factor of 0.4. Thus, in total the new cross section calculations result, at best, in only a modestly enhanced production ratio of Sm-146/Sm-144