Mechanism of s-wave and p-wave neutron resonance capture in light and medium-weight nuclei

Capture gamma-ray spectra of ¹⁶O, ²⁸Si and ³²S have been measured to investigate the mechanism of neutron capture in s-wave and p-wave resonances with large reduced neutron width. Observed gamma-ray transitions from the 434-keV p₃/₂-wave resonance of ¹⁶O exhibit typical features of valence neutron capture in light nuclei. For the 565-keV and 806-keV p₃/₂-wave resonances of ²⁸Si, a particle-vibrator coupling model indicates that in these resonance states core excitation is essential to explain the observed partial radiative widths. There is also some possibility of core excitation in the 203-keV p₁/₂-wave resonance capture in ³²S. Moreover, a strong correlation between partial radiative widths and spectroscopic factors of the final states was found for gamma-ray transitions from the 188-keV s-wave resonance of ²⁸Si and the 103-keV s-wave resonance of ³²S. A discussion follows on the particle-core coupling scheme in these resonance capture transitions.