Fission Fragment Yields Of $^{235}$U$(n_{th},f)$ Evaluated By The CCONE Code System

TL;DR

This paper introduces a new computational system using the CCONE code to evaluate and correlate multiple fission observables for $^{235}$U, improving upon previous methods that considered limited data types.

Contribution

The paper presents a novel integrated calculation system that simultaneously estimates various fission observables, enabling correlation studies and improved data evaluation.

Findings

Successfully reproduces experimental fission fragment yields

Demonstrates effective parameter optimization using Gaussian process and least squares

Shows good agreement with observed prompt neutrons and gamma emissions

Abstract

Fission fragment yield evaluations are one of the important nuclear data studies. Fission accompanies various physical observables such as prompt fission neutron, prompt fission gamma, and delayed-neutrons. When evaluating fission fragment yields, a study including correlations among those observables is essentially required. However, fission fragment yield data in the past JENDL libraries have been made by focusing only on experimental fragment yields, decay heats, and delayed neutron yields, and they have not been expanded into a wider range of fission observables. This is because the evaluation method adopted in the JENDL libraries could not study fission fragment yields and particle emissions from fragments simultaneously. To solve this problem, a calculation system with CCONE code is newly developed to estimate not only independent and cumulative fission fragment yields but also prompt fission neutron, prompt fission gamma, decay heats, and delayed-neutrons simultaneously. This system enables us to study a correlation between various fission observables. To determine lots of parameters in this system efficiently, a Gaussian process and a least square fitting are adopted. We tested the calculation system through a thermal neutron-induced fission on $^{235}$U. In this paper, we demonstrate the performance of the parameter search method and show that experimental fission fragment yield data and other observables resulting from fission are reproduced well by the new calculation system.