Analysis of E1 radiative neutron capture based on the optical model

Abstract

Abstract The optical model formula of Lane and Mughabghab for E1 radiative neutron capture has been applied to resonance capture in 56 Fe and 90 Zr. It is shown that in general the optical model predicts the contributions to the radiative widths which are correlated with the neutron widths, except for a depletion factor α representing the proportion of E1 single-particle strength remaining near the neutron threshold. The degree of correlation between measured and calculated radiative widths is related to the ratio of the variances of these widths. This enables an estimate of the factor α. It is shown that the theoretical value for the ratio of the radiative to neutron widths is to a good approximation independent of the imaginary part of the optical potential. The calculated radiative width is thus well defined. The results are compared with those from the valence model and from experiment. The direct background contribution is found to be negligible compared to the average compound cross section. The contribution of d-waves to the radiative capture cross section is discussed.