High-energy photoneutrons from 12C

Abstract

Photoneutron spectra from the reaction 12C(γ, n) 11C were measured at bremsstrahlung end-tip energies from 64 to 128 MeV in 2 MeV steps. The spectra were obtained simultaneously at five angles (30°, 60°, 90°, 112° and 142°) using time-of-flight techniques. The measured cross sections for a fixed neutron energy exhibit kinematic resonances corresponding to the emission of a single neutron from the 1p shell in 12C. The observed angular distributions of these 1p shell neutrons are forward asymmetric, the asymmetry increasing with neutron energy. The results are compared with single-particle and cluster theories. It was found that the angular distributions and the differential cross section at 90° can best be explained by a quasi-alpha model. It is therefore concluded that dynamic correlations between nucleons in the same shell are more important than those between nucleons in different shells.