Total Monte Carlo of the fission model in GEF and its influence on the nuclear evaporation in TALYS

Abstract: Features recently added to the nuclear reaction software TALYS allow the use of the GEF model as a fission fragment generator. GEF generates data for fission fragment yields, total excitation energy (TXE), total kinetic energy (TKE) and individual fragment excitation energies (E') with their standard deviations through Monte Carlo simulations for TALYS. In this work a framework named McPUFF was developed to couple GEF and TALYS and study the propagation of uncertainties in fission fragment data. The GEF model has a set of 94 parameters which were changed in order to produce perturbed output data. Both GEF and TALYS were modified to allow implementation of the Total Monte Carlo (TMC) method which is a method for handling the propagation of uncertainties throughout the simulation process. The developed framework allows the user to control aspects of the nuclear reaction using a set of input files. It is designed to be fast and memory efficient, performing simulations in parallel and storing all results in an object structure. A demonstration of the framework for the neutron induced fission of 235U, 238U and 239Pu was performed. Randomly perturbed sets of fission fragment data were created by GEF and fed into TALYS for simulation of the evaporation process using a Hauser-Feshbach statistical model. The impact that the perturbation of parameters in GEF has on results from TALYS were investigated for prompt particle multiplicity and energy. The results showed that a perturbation of parameter values in GEF by 3 percent has significant effects on values for fission observables produced by TALYS. The TALYS results for 235U showed an uncertainty for prompt neutron multiplicity of σn = 0.16 neutrons with an uncertainty for the neutron energy of σϵn = 0.03 MeV. The corresponding values for the uncertainty of the prompt γ-ray multiplicity were σγ = 0.10 γ-rays with an uncertainty for the γ-ray energy of σϵγ = 0.02 MeV. An investigation of how changes in the angular momentum of the fission fragments affects the evaporation process in GEF and TALYS was performed through the perturbation of the GEF parameter Jscaling. The results highlighted the need to scrutinize the handling of angular momentum in TALYS.