Photofission of Bi-209 at intermediate energies

摘要

The reaction yields of 63 radionuclides with the mass number A = 56 - 135 produced in the photofission of Bi-209 by bremsstrahlung of end-point energies (E-0) 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 reproduce a Gaussian function with the most probable charge (Z(p)) 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 E-0 greater than or equal to 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 v(pre) = 12 +/- 1 and v(post) = 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 FWHMMD of 33 I m.u. were also obtained. The characteristics of the charge and mass yield distributions are discussed by referring to those for Au-197 based on the results of calculations using the Photon-induced Intranuclear Cascade Analysis code combined with the Generalized Evaporation Model (PICA3/GEM). [References: 55]