Neutron emission as a probe of fusion-fission and quasifission dynamics

Fusion and quasi-fission in the formation of heavy elements

“…This was conclusively shown experimentally for quasi-fission reactions [3] by the observed strong dependence of the extracted pre-scission neutron multiplicities (ν pre ) on the fragment total kinetic energy (TKE). This was not seen for fusion-fission [3,9]. The observation means that (many of) the neutrons identified as pre-scission are actually emitted after the TKE is determined.…”

“…The extracted time depends on the assumptions made, in particular in reactions forming heavy elements, depending sensitively on correct modeling of emission during fragment acceleration after scission [8]. This was conclusively shown experimentally for quasi-fission reactions [3] by the observed strong dependence of the extracted pre-scission neutron multiplicities (ν pre ) on the fragment total kinetic energy (TKE). This was not seen for fusion-fission [3,9].…”

“…Generally for fusion-fission, the number of neutrons in excess of statistical model predictions [4] has been used to determine an additional dynamical time, corresponding to the sum of the times to build up flux over the fission saddle point, and the time to move from saddle to scission [3]. The latter work made use of measured mean prescission neutron kinetic energies to help determine neutron lifetimes [5].…”

“…It can be sensitive in principle to time scales from 10 −22 to 10 −16 s. However, optimal interpretation of the measurements requires a priori knowledge of the dynamics, as well as neutron evaporation lifetimes [3] from all shapes encountered.…”

“…The neutron-clock method [3] counts the neutrons emitted from thermalization to breakup into two fragments (scisa e-mail: david.hinde@anu.edu.au sion). It can be sensitive in principle to time scales from 10 −22 to 10 −16 s. However, optimal interpretation of the measurements requires a priori knowledge of the dynamics, as well as neutron evaporation lifetimes [3] from all shapes encountered.…”