mardi 4 février 2020 à 14:00
Nuclear fission is a complex process that involves the largest scale collective motion. In this process, initial excitations are transformed into large deformations until the nucleus splits. At low excitation energy, the fission-fragment distributions are strongly affected by the single-particle shell structure of the nucleons. Despide 80 years of intense research, a complete microscopic quantum description of the fission process is still lacking and models need to rely on the available experimental information. Nevertheless, experimental access to full isotopic fragment distributions has been parcial and scarce until recently.
A solution based on in-flight fission in inverse kinematics induced by surrogate reactions was carried out in GANIL, resulting in the first experiments accessing to the excitation energy of a collection of fissioning systems together with their corresponding fission-fragment distributions. In these experiments, a 238-U beam at coulomb energies impinged on light targets to produce fissioning systems by transfer and fusion reactions. Fissioning systems were identified through the recoil-nucleus measurement and the fragments resulting from the consequent fission decay were detected using the VAMOS spectrometer.
Results from this experimental campaign will be presented. The impact of the excitation energy will be discuss based on the isotopic fission yields. Kinetic observables, such as the velocity, reconstructed in center of mass, and the total kinetic energy of the fragments, will be also discussed. The impact of structure effects is investigated by means of the neutron content of the fragments at scission.
These new results represent a big step forward in the description of the fission process, with implications from fundamental to applied physics.