Surface direct nuclear photoeffect in heavy deformed nuclei

Abstract

A mechanism of photon-induced direct knockout of a nucleon from the nuclear surface without formation of intermediate excited nuclear state is described. The effect plays an important role at least for the $(\ensuremath{\gamma},p)$ reaction on heavy nuclei in the energy region centered at about 30 MeV where the probability of formation of the giant dipole resonance is already small but quasideuteron photoabsorption still does not prevail. A compact model of the surface direct nuclear photoeffect (SDNP) in heavy deformed nuclei that can be used to calculate the differential $d\ensuremath{\sigma}({E}_{\ensuremath{\gamma}},\ensuremath{\vartheta})/d\mathrm{\ensuremath{\Omega}}$ and total $\ensuremath{\sigma}({E}_{\ensuremath{\gamma}})$ cross sections of the SDNP under adiabatic approximation is formulated. The model is applied to calculation of the $(\ensuremath{\gamma},p)$ reaction cross sections on $^{160}\mathrm{Gd}$ and $^{184,186}\mathrm{W}$. The importance of the SDNP effect for these nuclei at ${E}_{\ensuremath{\gamma}}\ensuremath{\sim}30$ MeV is demonstrated.