A statistical model analysis of fluctuations in the elastic and inelastic proton scattering on 54Cr and 56Fe

Abstract

Excitation functions of the proton elastic scattering on the doubly even nuclei 54Cr and 56Fe have been measured together with the strong transitions to the 2 + first excited states at proton energies between 9 and 10 MeV and, for 56Fe only, between 11 and 12 MeV. Rapid cross-section fluctuations are found for scattering angles between 43° and 173°. Fourier analysis as well as autocorrelation functions are applied for data reduction. The interpretation is based on Ericson's statistical model following Moldauer's treatment. A coupled-channel calculation combined with the mean square variation of the cross sections allowed the separation of the direct and compound nucleus parts of the averaged cross sections. The angular distribution of the compound nucleus cross section is in agreement with Hauser-Feshbach calculations. The theoretically predicted enhancement of the compound elastic cross section by a factor of about 2 is confirmed. Mean level widths are deduced and found to be about 15 keV for 55∗Mn and 4 keV for 57∗Co at 17.6 MeV excitation energy in both cases. The mean level spacings D(J = 1 2 ) of these compound nuclei are determined to 0.2 keV for 55∗Mn and 0.07 keV for 57∗Co so that Γ/D(J = 1 2 ) ∼ 50 ⪢ 1 .