This paper reports a measurement of the differential photoneutron cross section of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ at 65°, between $E_{\gamma }$=30 and 100 MeV. Tagged photons, monochromatic to within 2.6 MeV, were used, thus allowing the cross sections to a wide range of final states to be observed. The results are compared to the photoproton cross section of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, which was measured previously, under similar conditions. Comparisons are also made with calculations based on the quasi-deuteron model, and with calculations by Gari and Hebach, and Cavinato et al. These latter calculations incorporate two-body effects by the inclusion of meson exchange currents. The agreement between these calculations and the measured cross section is in contrast to predictions of a direct, single-nucleon knockout model of the reaction mechanism, indicating the importance of two-body effects in the photoreaction process for energies greater than 50 MeV.

• Received 30 June 1987

DOI:https://doi.org/10.1103/PhysRevC.37.13