Recoil Study of 27Al(γ,2pn)24Na Reaction at Intermediate Energies

Photofission of209Bi at intermediate energies

The reaction yields of 63 radionuclides with the mass numberA= 56 − 135 produced in the photofission of209Bi by bremsstrahlung of end-point energies (E0) from 450 to 1100 MeV have been measured using a catcher foil technique with the aid of intensive chemical separation. The charge distribution was well reproduced by a Gaussian function with the most probable charge (Zp) expressed by a linear function ofA,i.e.,Zp=RA+S, and with theA-independent full width at half maximum (FWHMCD). The charge distribution parametersR,Sand FWHMCDwere independent ofE0above 600 MeV, reflecting the resonance nature in photonuclear reactions at intermediate energies. The weighted mean values atE0≥ 600 MeV wereR= 0.421 ± 0.001,S= 0.6 ± 0.1 and FWHMCD= 2.1 ± 0.1 charge unit (c.u.). The numbers of pre- and post-fission neutrons were deduced to be νpre= 12 ± 1 and νpost= 1.4 ± 0.3, respectively, assuming the Unchanged Charge Distribution (UCD). Based on the charge distribution parameters, the symmetric mass yield distributions with the most probable massApof 96 ± 1 mass unit (m.u.) and the width FWHMMDof 33 ± 1 m.u. were also obtained. The characteristics of the charge and mass yield distributions are discussed by referring to those for197Au based on the results of calculations using the Photon-induced Intranuclear Cascade Analysis code combined with the Generalized Evaporation Model (PICA3/GEM).

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 onnatV,natCu,93Nb,natAg,natTa, and197Au, respectively, induced by bremsstrahlung of end-point energies (E0) from 600 to 1100 MeV, have been investigated using the thick-target thick-catcher method based on the two-step vector model. The measured forward-to-backward ratios (F/B) were found to be independent of the mass difference (ΔA) between a product (Ap) and a target (At) and also of At. The recoil velocities ν 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 E0= 400 MeV was also performed. It was found that although the code well reproduces the experimental results ofnatV andnatCu, 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 At≥ 100. The parameter values of εs= T/(ΔA/At), the average kinetic energy of the emitted particles in a random-walk process of both the photon- and proton-reactions, were found to increase along with an increase of At, but change slopes to become constant above At= 100.