Performance validation of the first arm of FALSTAFF: ²⁵²Cf and ²³⁵U fission fragment characterisation

The renewed interest for the study of nuclear fission is mainly motivated by the development of GEN-IV reactor concepts, mostly foreseen to operate in the fast neutron energy domain. To support this development, new high-quality nuclear data are needed. In this context, a new experimental setup, the FALSTAFF spectrometer, dedicated to the study of nuclear fission is under development. Employing the double-velocity (2V) and energy-velocity (EV) methods, the fission fragment mass before and after neutron evaporation will be deduced and the correlation between prompt neutron multiplicity and fragment mass will be determined. The first arm of the spectrometer is achieved. It is composed of two SED-MWPC detectors (a combination of a foil to produce secondary electrons and a Multi-Wire Proportional Chamber to detect them) and an axial ionization chamber. The SED-MWPC give access to the velocity (V) via time-of-flight and position measurements. The ionization chamber measures the fragment kinetic energy (E) and the energy loss profile. Preliminary results for spontaneous fission of ²⁵²Cf and from the thermal-neutron induced fission experiment on ²³⁵U, performed at the Orphee reactor (CEA-Saclay, France), are presented. The results show that for ²⁵²Cf the simulated velocity and energy distributions have a rather good agreement with experimental distributions while for ²³⁵U, the agreement is less good and in both cases the velocity distribution is slightly distorted for the light fragment peak compared to simulations