Photofission of 209Bi at intermediate energies

The reaction yields of 63 radionuclides with the mass number A = 56 - 135 produced in the photofission of 209Bi 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 of A, i.e., Zp = RA + S, and with the A-independent full width at half maximum (FWHMCD). The charge distribution parameters R, S and FWHMCD were independent of E0 above 600 MeV, reflecting the resonance nature in photonuclear reactions at intermediate energies. The weighted mean values at E0 > 600 MeV were R = 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 mass Ap of 96±1 mass unit (m.u.) and the width FWHMMD of 33 ± 1 m.u. were also obtained. The characteristics of the charge and mass yield distributions are discussed by referring to those for 197Au based on the results of calculations using the photon-induced intranuclear cascade analysis code combined with the generalized evaporation model (PICA3/GEM). (orig.)