Barium and xenon isotope yields in photopion reactions of 133Cs

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).

Target-dependence of light fragment production in photonuclear reactions at intermediate energies

Yields of7Be,10Be,22Na,24Na and28Mg produced fromnatB,natC,natO,23Na,27Al,natSi,natS,natCl,natK,natCa,natV,55Mn,natFe,59Co,natNi,natCu,89Y,natAg,natIn,141Pr,159Tb,165Ho and197Au in irradiations with bremsstrahlung having maximum end-point energies up to 1200 MeV were measured by γ-ray spectrometry (7Be,22Na,24Na and28Mg) and accelerator mass spectrometry (10Be). The yields of heavier fragments,39Cl,43, 44m, 44g, 46, 47, 48Sc,59Fe, and56, 57, 58, 60Co, were also measured by γ-ray spectrometry in order to survey the relative contribution of fragmentation to spallation and/or fission in the mass yield curves. A distinct difference of the target mass-dependence of these yields has made it possible to disentangle the contributions of photospallation and photofragmentation processes. It was found that the neutron-to-proton ratios of targets strongly affect the formation of the nuclei by fragmentation as revealed in the yields of the isotopic pairs as well as of the single isotopes. The photon results were compared with those of proton-induced reactions, and no clear effect due to the difference of the initial interactions of photons and protons with nuclei was found in the fragment yields.