A closer look at prompt fission data*

In this talk, I will provide a brief overview of recent advances in the modeling of the decay of fission fragments and the description of post-scission prompt data through the use of the FREYA and CGMF Monte Carlo fission event generators, which have been developed to describe the complex distributions and correlations of prompt neutrons and photons. Of fundamental interest are questions related to the dynamics of the fission process, the sharing of the excitation energy between the two fragments at scission, the production of angular momentum in each partner fragment, and the nuclear structure of neutron-rich nuclei formed in the fission process. Of particular interest to applications are correlations in energy, multiplicity and angle of the emitted particles, which can be used advantageously as signatures of the fission process.

FREYA and CGMF follow the de-excitation of the fission fragments produced right after scission, through successive emissions of prompt neutrons and photons until a final ground-state or isomeric state is reached. The energy and momentum vector of those particles in the laboratory frame are recorded at each stage of the decay, and for each initial fission fragment configuration. By computing this decay for a large number of fission events, the analysis of those simulated data to look for correlations and distributions is straightforward, e.g., n-n angular correlations and neutron multiplicity distribution P(nu).

I will present several recent results obtained using both CGMF and FREYA as standalone codes or integrated in MCNP. While some examples will be  taken from our recent review publication [1], other will touch upon more recent results, e.g., inferring fission yields from gamma-gamma-gamma coincidences.

[1] "Correlated Prompt Fission Data in Transport Simulations," P.Talou, R.Vogt, J.Randrup, M.E.Rising, S.A.Pozzi, et al, Eur. Phys. J. A 54, 9 (2018).