Calculations of capture cross sections and gamma-ray spectra as a tool for testing strength function models

The impact of the low energy behaviour of the E1 and the M1 gamma-ray strength functions on statistical model calculations of radiative neutron capture was studied for targets with mass numbers between 55 and 197. We found strong support for models of the E1 strength function with a non-zero limit if the transition energy tends to zero. Such a low energy behaviour is predicted in theoretical work by Kadmenskij et al. and by Sirotkin. The employed strength functions are derived from a generalized Lorentzian in case of E1 and a standard Lorentzian in case of M1 and E2 radiation. The parameters of these strength functions are based on independent experimental data. No normalizations were applied to the strength functions. We, therefore, recommend to use these strength functions in reaction model calculations for applied purposes. (author). 61 refs, 8 figs, 3 tabs