Calculations of particle energy spectra resulting from the photonuclear reactions at energies below the meson production threshold have been carried out in the framework of combining the pre-equilibrium exciton model and the quasideuteron model. A 2p-2h initial state in the exciton model is assumed because the quasideuteron absorption is the dominant process in the energy region above giant resonance. With this combined model the subsequent secondary interactions of the emerging particle with the rest of the nucleus following the initial photon-nucleus interaction are appropriately taken into account. The experimental difference energy spectra of fast photoneutrons from several elements (Al, Cu, In, Sn, Ta, Pb, Bi, and U) at bremsstrahlung energies of 55 and 85 MeV were compared with the theoretical predictions. General agreements in both spectral shapes and cross sections are obtained. The relative yields of the reactions ($\gamma ,xn$) resulting from monoenergetic photons on ${}_{}{}^{127}{}_{}{}^{}\mathrm{I}$ at 50, 100, and 150 MeV are also predicted reasonably well by the combined model together with the conventional evaporation theory.

NUCLEAR REACTIONS ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}(\gamma ,x)$, ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}(\gamma ,x)$, ${}_{}{}^{115}{}_{}{}^{}\mathrm{In}(\gamma ,x)$, ${}_{}{}^{118}{}_{}{}^{}\mathrm{Sn}(\gamma ,x)$, ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}(\gamma ,x)$, ${}_{}{}^{207}{}_{}{}^{}\mathrm{Pb}(\gamma ,x)$, ${}_{}{}^{209}{}_{}{}^{}\mathrm{Bi}(\gamma ,x)$, ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}(\gamma ,x)$, $E_{\gamma }=55\mathrm{} \mathrm{and} 85$ MeV bremsstrahlung. ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}(\gamma ,x)$, $E_{\gamma }=110\mathrm{}$ MeV bremsstrahlung. ${}_{}{}^{127}{}_{}{}^{}\mathrm{I}(\gamma ,xn)$, $E_{\gamma }=50, 100, \mathrm{and} 150$ MeV. Pre-equilibrium exciton, quasideuteron, and statistical compound nucleus models analyses.

• Received 2 December 1976

DOI:https://doi.org/10.1103/PhysRevC.16.1812