Speaker
Description
LA-UR-21-29120
Historically, there is little to no consistency between the various types of nuclear fission data in our libraries (Patrick Jaffke, NSE 190, 258 (2018)), despite the fact that we know these observables to be correlated through the joint fission process underlying them all. For instance, the energies and multiplicities of prompt neutrons and gamma rays are correlated through the excitation energy of the fission fragments, but are usually evaluated separately with different types of models or, in some cases, entirely based on experimental data.
To address these inconsistencies and potential biases that arise from them, correlated fission models have been developed in the last decade. One can, for instance, use the LANL-developed, Monte Carlo Hauser-Feshbach statistical decay code, CGMF (P. Talou, et al., CPC 269, 108087 (2021)), to calculate the prompt emission of neutrons and gamma rays from highly excited fission fragments, conserving energy, momentum, spin, and parity at each step in the decay. This code ultimately yields the desired $\langle\nu_p \rangle$ and PFNS within the same framework. However, these models do not predict $\langle\nu_p \rangle$ and PFNS to the precision needed for nuclear data evaluations and the application simulations they serve as the model parameter space is too large. To this end, experimental data for these observables need to be included in a formal evaluation procedure.
Here, we present the first of such an evaluation for $\langle\nu_p \rangle$ of major actinides underpinned by CGMF. We show, for instance, for the case of $^{239}$Pu(n,f) $\langle\nu_p \rangle$ that in addition to being able to reproduce experimental $\langle\nu_p \rangle$, the evaluation also produces reasonable results for other prompt observables that are comparable with available experimental data. Moreover, these evaluated data performed well in simulating various integral responses when combined with more recent $^{239}$Pu(n,f) PFNS and fission cross sections.
Acknowledgments
Work at LANL was carried out under the auspices of the National Nuclear Security Administration (NNSA) of the U.S. Department of Energy (DOE) under contract 89233218CNA000001. We gratefully acknowledge partial support of the Advanced Simulation and Computing program at LANL and the DOE Nuclear Criticality Safety Program, funded and managed by NNSA for the DOE.