The presented project has two main objectives. The first one is the realization (building, calibration, data taking and data analysis) of a first experiment with the FALSTAFF detector in its configuration with two detection arms. In such a configuration, FALSTAFF will be able to detect in coincidence both fragments emitted by fast-neutron triggered fission reactions. These neutrons will be provided by the neutron beam of SPIRAL2-NFS in GANIL. The advantage of using direct kinematics is the ability to determine on an event-by-event basis the excitation energy of the fissioning nucleus by the measurement of the incident-neutron kinetic energy.
For this first experiment, we will have a uranium 235 target. 235U is the main source of fission neutrons in nuclear reactors and therefore at the heart of the system. Hence, the understanding of neutron-induced fission of 235U is essential and the rather exclusive data FALSTAFF will provide, with not only the identification of the fission fragments but also their kinematics will permit to reconstruct also the fissioning system. Such a measurmement in direct kinematics have never been done, to our knowledge, with the accuracy we are aiming at.
To perform this exepriment, we have improved and added detection capabilities to the FALSTAFF spectrometer, in particular with the financial support of the Région Normandie over the last two years. This experiment will be completed by a work to be done on a theoretical model developed by our collaborators of CEA-Cadarache. We will compare our detailled data with predictions of the model and have the model evolve, according to the laws of nuclear physics in order to obtain results from the model close to the data. Such a test of this model on as complete data as those we will obtain with FALSTAFF have never been done so far.