Photofission of Bi-209 at intermediate energies

The reaction yields of 63 radionuclides with the mass number A = 56 - 135 produced in the photofission of 2 0 9 Bi by bremsstrahlung of end-point energies (E 0 ) from 450 to 1100 MeV have been measured using a catcher foiltechnique with the aid of intensive chemical separation. The charge distribution was well reproduced by a Gaussian function with the most probable charge (Z P ) expressed by a linear function of A, i.e., Z P =RA+S, and with the A-independent full width at half maximum (FWHM C D ). The charge distribution parameters R, S and FWHM C D were independent of E 0 above 600 MeV, reflecting the resonance nature in photonuclear reactions at intermediate energies. The weighted mean values at E 0 ≥ 600 MeV were R = 0.421 ′ 0.001, S = 0.6 ′ 0.1 and FWHM C D = 2.1 ′ 0.1 charge unit (c.u.). The numbers of pre- and post-fission neutrons were deduced to be v p r e = 12′1 and v p o s t = 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 A P of 96′1 mass unit (m.u.) and the width FWHM M D of 33′1 m.u. were also obtained. The characteristics of the charge and mass yield distributions are discussed by referring to those for 1 9 7 Au based on the results of calculations using the Photon-induced Intranuclear Cascade Analysis code combined with the Generalized Evaporation Model (PICA3/GEM).