Dynamics of fission and quasi-fission revealed by pre-scission neutron evaporation

Abstract

The dependence of pre-scission neutron multiplicities (ν pre) on the mass-split and total kinetic energy in fusion-fission and quasi-fission has been measured for a wide range of projectile-target combinations. The data indicate that the fusion-fission time scale is shorter for asymmetric splits than for symmetric splits, whilst there is no dependence on TKE. For quasi-fission reactions induced using 64Ni projectiles, ν pre falls rapidly with increasing TKE, indicating that these neutrons are emitted near to or after scission. A new interpretation of both neutron multiplicities and mean energies (the neutron clock-thermometer) allows the extraction of time scales with much less uncertainty than previously, and also gives information about the deformation from which the neutrons are emitted.