High-energy neutron-induced fission cross sections of natural lead and bismuth-209

The CERN Neutron Time-Of-Flight (n_TOF) facility is well suited to measure small neutron- induced ssion cross sections, as those of subactinides. The cross section ratios of ^natPb and ²⁰⁹Bi relative to ²³⁵U and ²³⁸U were measured using PPAC detectors. The fragment coincidence method allows to unambiguously identify the ssion events. The present experiment provides the first results for neutron-induced fission up to 1 GeV for ^natPb and ²⁰⁹Bi. A good agreement with previous experimental data below 200 MeV is shown. The comparison with proton-induced ssion indicates that the limiting regime where neutron-induced and proton-induced ssion reach equal cross section is close to 1 GeV.