Resonance analysis of ¹⁴⁷Sm(n,α) cross sections : comparison to optical model calculations and indications of nonstatistical effects

We have measured the Sm-147(n,alpha) cross section from 3 eV to 500 keV and performed an R-matrix analysis in the resolved region (En>700 eV) to extract α widths for 104 resonances. We computed strength functions from these resonance parameters and compared them to transmission coefficients calculated using optical model potentials similar to those employed as inputs to statistical model calculations. The statistical model often is used to predict cross sections and astrophysical reaction rates. Comparing resonance parameters rather than cross sections allows more direct tests of potentials used in the model and hence should offer greater insight into possible improvements. In particular, an improved α+nucleus potential is needed for applications in nuclear astrophysics. In addition to providing a more direct test of the α+nucleus potential, the α-width distributions show indications of nonstatistical effects.