Photofission of²⁰⁹Bi at intermediate energies

Abstract

Photofission / 209 Bi / Bremsstrahlung / Intermediate energies / Thick-target thick-catcher method / Charge and mass yield distributionsSummary. The reaction yields of 63 radionuclides with the mass number A = 56 − 135 produced in the photofission of 209 Bi 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 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 CD ). The charge distribution parameters R, S and FWHM CD 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 CD = 2.1 ± 0.1 charge unit (c.u.). The numbers of pre-and post-fission neutrons were deduced to be ν pre = 12 ± 1 and ν 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 FWHM MD of 33 ± 1 m.u. were also obtained. The characteristics of the charge and mass yield distributions are discussed by referring to those for 197 Au 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

“…The overhelming productions of 7 Be and 22 Na from the targets with the (N/Z) t lager than the N/Z of these nuclides may suggest the production of these two nuclei after some neutron emissions from the excited targets. It is instructive that in photofission of 197 Au at E0 м 600 MeV an average number of the pre-fission neutron is deduced to be 11 from the unchanged charge distribution (UCD) assumption [33]. Further measurements of the other light nuclides such as 11, 14 C, 26 Al, and 36,39 Cl would help to elucidate the trend discussed above.…”

“…5. The details for the analysis of the mass distribution curves for spallation [23,32], photopion reaction [24] and fission [33] were reported. The mass yields of 7 Be, 10 Be, 22 Na, 24 Na and 28 Mg are clearly different from the values expected from the mass yield distributions of fission.…”

“…Comparison of the yields of 7 Be, 10 Be,22 Na, 24 Na and28 Mg with the mass yields of spallation, fission and photopion reaction obtained from 197 Au target at E 0 ϭ 1000 MeV[23,24,32,33].…”

A simple description of the temperature dependence of the width of the fission-fragment mass yield in 197 Au and 209 Bi at intermediate energies

“…The experimental data for the width and A prob for 197 Au obtained at the bremsstrahlung of end-point energies 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, and 1100 MeV are taken from Refs. [13,18]. The corresponding experimental data for 209 Bi evaluated at the bremsstrahlung of endpoint energies 40, 65, 85, 600, and 700 MeV are taken from Refs.…”

Photofission of 197Au and 209Bi at intermediate energies

“…MeV have been investigated using the thick-target thick-catcher method [1][2][3]. The recoil properties such as the forward-to-backward ratio F/B and the kinetic energy T of the residual nuclei were discussed by comparing with those of photospallation products and also with the literature data on proton-induced reactions.…”