Recoil studies of photonuclear reactions on natCu, natAg, natTa, and 197Au at intermediate energies

The recoil properties of nuclides produced in the photonuclear reactions on natCu, natAg, natTa, and 197Au induced by bremsstrahlung of end-point energies (E o) of 250 to 1000 MeV have been investigated using the thick-target thick-catcher method. The obtained mean ranges of produced nuclides smoothly increase with an increase of the mass difference (ΔA) between products and target, and show E 0-independence at E 0≥600 MeV, reflecting the limiting behavior above (3, 3) resonance region. The mean kinetic energies, T, deduced from the mean ranges show the following two components; (1) (γ, xn) products by giant-resonance and/or quasi-deuteron resonance absorption, (2) (γ, xnyp) products by mainly (3, 3) resonance absorption. Slightly rapid increase of T was found around ΔA=15, 18, 24, and 25 for natCu, natAg, natTa and 197Au, respectively, reflecting a change in mechanism. Kinematic properties of the product nuclei were calculated by using the PICA (Photon-Induced Intranuclear Cascade Analysis) code. The T calculated by the PICA code at E 0=400 MeV well reproduced the experimental results of natCu, but the same calculation for natAg, natTa, and 197Au gave lower mean kinetic energies than the experimental results.