Recoil Studies of Photonuclear Reactions at Intermediate Energies

抄録

A review is given on the recoil studies of photonuclear reactions on complex nuclei at intermediate energies. Recoils of 167 radionuclides formed in the photonuclear reactions of ²⁷Al, ^natV, ^natCu, ⁹³Nb, ^natAg, ^natTa, and ¹⁹⁷Au, induced by bremsstrahlung of end-point energies (E₀) from 600 to 1100 MeV, have been investigated by the thicktarget thick-catcher method. The recoil velocity from the first step and the mean kinetic energy of the residual nuclei in the second step were deduced based on the two-step vector velocity model and discussed by comparing with the reported results on proton-induced reactions. Recoils of ²⁴Na produced from ²⁷Al, ^natV, ^natCu, ^natAg, and ¹⁹⁷Au are of special interest from a viewpoint of a change in the production mechanism with respect to target mass. Reaction yields of 58 and 63 radionuclides produced in the photofission of ¹⁹⁷Au and ²⁰⁹Bi, respectively, were also measured at E₀ = 300-1100 MeV by a catcher foil technique with the aid of intensive chemical separation. The fission characteristics such as the charge and mass distributions and the numbers of pre- and post-fission neutrons were determined. These results were compared with the calculations using the Photon-induced Intranuclear Cascade Analysis 3 code combined with the Generalized Evaporation Model code.