Photoneutrons from 13C at photon energies up to 14 MeV

Abstract

The photoneutron yield of 13C was measured as a function of the maximum bremsstrahlung energy up to 14.5 MeV. The cross section for the 13C(γ, n) 12C reaction was obtained by using the inverted matrix method of Penfold and Leiss. The integrated cross sections from threshold to 10 MeV and to 14 MeV are 2 and 16 MeV ·mb, respectively. These values are in agreement with earlier experiments. The cross-section curve shows peaks at 6.2, 7.5, 8.2, 9.1, 11 and 13 MeV, the last two being in the pygmy resonance energy region. The angular distributions of photoneutrons were measured at different values of E γmax . The data were analyzed for the distribution of neutrons from each peak. The significant features of the cross-section curve and the angular distributions of neutrons from the peaks are discussed and compared with the theoretical ones reported by several authors. The integrated cross section from the threshold to 10 MeV is much smaller than those calculated on the basis of a pure single-particle model. The neutrons in the pygmy resonance energy region follow a 1+0.46 sin 2θ angular distribution, while a 1+1.5 sin 2θ distribution is expected from the single-particle picture of the pygmy resonance. These discrepancies are interpreted in terms of the mixing of core excitations and single-particle excitations.