Effects of channel and potential radiative transitions in the 17O(γ,n0)16O reaction

The angular distribution for the 17O(γ,n0)16O reaction was observed throughout the excitation energy region 4.3--7 MeV and at angles of 900 and 1350. The ground-state radiation widths for resonances in this energy region were extracted from the data. The value of the radiation width for the d/sub 5/2/ → d/sub 3/2/ spin-flip transition at 5.08 MeV was found to be approximately 1/3 of the value expected for a pure single-particle transition. The implications that this result has for the nuclear structure of 17O is discussed. The effects of potential radiative capture were observed directly in a photoneutron reaction for the first time. At the location of the 5.38-MeV, 3/2- resonance in 17O, an anomalous symmetric dip was observed in the cross section at both reaction angles. The data were interpreted in terms of a general R-matrix reaction theory which includes the effects of internal, channel, and potential radiative capture in a self-consistent manner. The neutron channel was defined by incorporating an R-matrix analysis of the 16O(n,n)16O reaction into the present interpretation. The anomalous minimum at 5.38 MeV was found to be due to a unique feature of channel capture. The R-matrix prediction for the total cross section was extrapolated into the keV region and the significance that this cross section has for stellar nucleosynthesis is disucssed