The distribution of E1 and M1 strength in ${}_{}{}^{157}{}_{}{}^{}\mathrm{Gd}$ compound nucleus has been studied. An investigation of capture of 2 and 24 keV neutrons in a ${}_{}{}^{156}{}_{}{}^{}\mathrm{Gd}$ target resulted in resonance-averaged intensities of primary gamma rays between 3.7 and 6.4 MeV. From these intensities the gamma-ray strength functions have been derived for E1 and M1 radiation. We compare several formulations of strength functions to these resonance capture and/or photoabsorption data. Further we use these prescriptions in calculations of the total average radiation width, radiative capture cross sections, and gamma-ray spectra, and compare them to available experimental information. By analyzing these results strong evidence was found for an E1 strength function which is based on a generalized Lorentzian, enhanced compared to spherical nuclei, with an energy-dependent spreading width and a nonzero limit as the energy tends to zero. For M1 radiation the giant resonance spin-flip mode is favored.

• Received 11 March 1992

DOI:https://doi.org/10.1103/PhysRevC.47.312