Resonance structure in the ${}_{}{}^{28}{}_{}{}^{}+\mathrm{n}$ system has been investigated by performing neutron total cross section and capture γ-ray measurements. A detailed analysis of resonance parameters was carried out up to a neutron energy of 2.75 MeV. Level densities were determined for s- and p-wave resonances, as well as neutron strength functions and partial radiative widths. The neutron strengths are compared with existing model calculations. The neutron width of at least one T=(3/2 level has been determined, providing a measure of isobaric spin mixing. Whereas other workers previously reported a strong correlation between the reduced neutron widths (${\Gamma }_{\mathrm{n}{}^l}$) and total radiative widths, we observe no significant correlation between ${\Gamma }_{\mathrm{n}{}^l}$ and the partial radiative widths for ground state transitions. We conclude that radiative capture in ${}_{}{}^{28}{}_{}{}^{}+\mathrm{n}$ does not proceed via a simple valence mechanism, but must involve several competing doorway states. The observed M1 strength in ${}_{}{}^{29}{}_{}{}^{}\mathrm{Si}$ is lower than that reported for ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ from inelastic electron scattering, suggesting either a considerable fragmentation or a significant reduction due to the presence of the additional neutron.

• Received 9 February 1987

DOI:https://doi.org/10.1103/PhysRevC.36.585