Neutron-induced fission cross sections for ${}^{\text{nat}}$Pb and ${}^{209}\mathrm{Bi}$ were measured with a white-spectrum neutron source at the CERN Neutron Time-of-Flight (n_TOF) facility. The experiment, using neutrons from threshold up to 1 GeV, provides the first results for these nuclei above 200 MeV. The cross sections were measured relative to ${}^{235}\mathrm{U}$ and ${}^{238}\mathrm{U}$ in a dedicated fission chamber with parallel plate avalanche counter detectors. Results are compared with previous experimental data. Upgraded parametrizations of the cross sections are presented, from threshold energy up to 1 GeV. The proposed new sets of fitting parameters improve former results along the whole energy range.

• Received 10 February 2011

DOI:https://doi.org/10.1103/PhysRevC.83.044620