Orateur
Description
The study of nuclear fission yields has a major impact on the characterization and understanding of the fission process and is mandatory for reactor applications. In the framework of a collaboration between the LPSC, the CEA and the ILL, a program of actinide fission yield measurements is ongoing at the LOHENGRIN spectrometer. Different experimental observables are achievable: mass yields, charge distributions, isomeric ratios, spectroscopic kinetic energy distributions, ionic charge – kinetic energy correlations etc. The Lohengrin separation power is better than 𝐴 Δ𝐴 > 400 allowing a mass identification up to A~160 with usual actinide target. The fission product separation is carried out according to their mass-over-ionic charge and velocity. However, the measurement of very low fission yields in the symmetry region and in the heavy far asymmetric wing of the distributions may be affected by contaminations with masses from the peaks of the fission distribution that undergo ionic charge exchange due to collisions with residual gas in the spectrometer. The velocities of such artefact ions then differ by about 5% from those of the normal ions satisfying the separator condition. Thus, an additional velocity measurement via a Time-of-Flight (ToF) system can reject such
background artefact ions and improve the precision of the mass yield measurements. For this purpose, the ToF condition is added to the presently practiced ΔE-E analysis with a split-anode ionization chamber. The new ToF system uses two 50 nm thin Si3N4 foils as transmission detectors. The emitted electrons are detected and serve as start and stop signals respectively. The flight distance is approximately 50 cm. Based on the upgrade of the Lohengrin spectrometer, the presentation deals with the future experimental program of interest for the nuclear data evaluation needs for applications. The new data require a specification of bias and uncertainty quantifications in order to apply statistical test
on fission models to assess the validity of physical assumptions and to propagate their consequences on nuclear data evaluation.
