Measurement of Neutron Inelastic Scattering Cross Sections for 209Bi from Threshold up to 18 MeV

Abstract

The interest in 209Bi, the only stable isotope of this element, originates from its proposed use in the spallation module and as moderator/coolant of an accelerator driven system (ADS). Inelastic scattering that constitutes 30% of the total neutron cross section of 209Bi is a major contributor to uncertainties in predicted ADS parameters. New data were obtained for production cross sections of 19 transitions up to about 18 MeV, incident energy. One transition was observed per excited level for the first 8 levels. From the measured gamma‐ray production cross sections, total and level inelastic cross sections were deduced. The experiment was performed at GELINA, with a white neutron spectrum, at 200 m flight path length using the time‐of‐flight method. The gamma rays from the 209Bi(n,n′γ)209Bi reaction were detected with two large volume HPGe detectors and the neutron flux was monitored with a multilayer 235U fission chamber. For the main transitions the inelastic cross section is given with an incident neutron energy resolution ranging from 1.1 keV at 1 MeV to 35.7 keV at 10 MeV within overall statistical error of less than 5%.