Combined model of photonucleon reactions

A combination of the semimicroscopic, exciton, and evaporation models is used to describe photonucleon reactions induced in medium-mass and heavy nuclei by photons of energy below the mesonproduction threshold. Two mechanisms of the photoexcitation of nuclei are considered. These are the formation of a giant dipole resonance (GDR) at energies in the range E _γ ≲ 30 MeV and quasideuteron photoabsorption, which is dominant at energies in the region E _γ ≳ 40 MeV. The densities of particle-hole states appearing in the exciton model are calculated on the basis of the Fermi gas model. Our combined model takes into account the multiparticle emission of preequilibrium particles. The influence of isospin conservation and collective phenomena on photonucleon emission by giant dipole resonances is considered. The combined model is used to describe cross sections for photonucleon reactions proceeding on the ^40,48Ca, ⁹⁰Zr, ¹³⁹La, ¹⁴²Nd, and ¹⁸¹Ta nuclei, as well as difference (E _γmax = 85–55 MeV) bremsstrahlung photoneutron spectra for the ⁶³Cu, ¹¹⁵In, ¹¹⁸Sn, ¹⁸¹Ta, ²⁰⁷Pb, ²⁰⁹Bi, and ²³⁵U nuclei and bremsstrahlung photoproton spectra for the ⁹⁰Zr nucleus at the energies of E _γmax = 22, 25, and 34 MeV.