Experimental Studies of the Mechanism of Photon Absorption on Light Nuclei

Abstract

A measurement of the reaction 12 C (γ,p γ') has been made with tagged photons in the range 49.47<Eγ <70.24 MeV. The relative population of a triplet of states, (7/2-,1/2+ ,5/2+ ) at Eex ~7 MeV in the residual nucleus 11B, following the reaction 12 C (γ,p) has been made by directly resolving their de--excitation γ-­ray decay to the ground state of 11B. This measurement constitutes the highest resolution ever achieved in determining the excitation function of the residual nucleus after a (γ,p) reaction (~48 keV FWHM at Eex ~7 MeV). Comparison has been made with the data of Kuzin et al., who also measured the relative populations, with a resolution of ~270 keV at Eex ~7 MeV. The 7/2-,state at 6.74 MeV has been observed to be the most strongly excited state of the triplet in agreement with Kuzin et al. Disagreement has been found for the relative strengths of the 1/2 + and 5/2 + states in the triplet. An estimation of the maximum effect of angular correlations, between the ejected proton and de-excitation γ-­ray, has been included in the analysis. This effect increases the disagreement between the 2 measurements.