The work performed at CENBG took place in a revaluation campaign of the fission cross-section U(n,f) in the range of fast neutrons (1-6.5 MeV). It is possible to measure this cross-section from the number of detected fission fragments, the neutron flux incident on the target and the number of target nuclei.
- Fission fragments were detected by 2 photovoltaic cells.
- The number of target nuclei was determined from the number of α particles from the U decay measured with a Si detector.
- The estimation of the neutron flux is the most delicate measurement, the neutron flux can be deducted from the activity of monitoring targets (such as gold foils, fission rate of U), or from the elastic scattering (n,p) of neutrons by a polypropylene film of several microns in thickness. It was this latest method that was used since the (n,p) scattering cross-section is known with a much higher precision (1%) than for the other above-mentioned reactions. The protons were detected with a Si surface barrier detector.
EXPERIMENTAL SET UP