Recoil properties of radionuclides formed in photospallation reactions on complex nuclei at intermediate energies

The recoil properties of 14, 24, 26, 31, 21 and 20 radionuclides formed in photospallation reactions on V-nat, Cu-nat, Nb-93, Ag-nat, Ta-nat, and Au-1 97, respectively, induced by bremsstrahlung of end-point energies (E-o) fro m 600 to 1100 MeV, have been investigated using the thick-target thick-catc her method based on the two-step vector model. The measured forward-to-back ward ratios (F/B) were found to be independent of the mass difference (Delt aA) between a product (A(p)) and a target (A(t)) and also of A(t). The reco il velocities v from the first step and the mean kinetic energies T of the residual nuclei in the second step were deduced and discussed by comparing with the reported results on proton-induced reactions. A comparison with T values calculated by the PICA (Photon-Induced Intranuclear Cascade Analysis ) code at E-o = 400 MeV was also performed. It was found that although the code well reproduces the experimental results of V-nat and Cu-nat, the same calculation for heavier targets gives T values lower than the experimental results, indicating some nuclear-structure effect, such as a medium effect notably at A(t) greater than or equal to 100. The parameter values of epsi lon (s) = T/(DeltaA/A(t)), the average kinetic energy of the emitted partic les in a random-walk process of both the photon- and proton-reactions, were found to increase along with an increase of A(t), but change slopes to bec ome constant above A(t) = 100.