Energy Dependent Calculations of Fission Product, Prompt, and Delayed Neutron Yields for Neutron Induced Fission on $^{235}$U, $^{238}$U, and $^{239}$Pu

TL;DR

This study performs energy-dependent calculations of fission product yields and neutron emissions for uranium and plutonium isotopes, using statistical decay models and Bayesian adjustments, to compare with experimental data and explore second chance fission effects.

Contribution

It introduces a comprehensive energy-dependent modeling approach for fission yields and neutron emissions, incorporating Bayesian parameter adjustments and analysis of second chance fission impacts.

Findings

Calculated yields agree with experimental data across energies.

Bayesian adjustments improve model accuracy at specific energies.

Second chance fission influences delayed neutron yield energy dependence.

Abstract

We perform energy dependent calculations of independent and cumulative fission product yields for $^{235}$U, $^{238}$U, and $^{239}$Pu in the first chance fission region. Starting with the primary fission fragment distributions taken from available experimental data and analytical functions based on assumptions for the excitation energy and spin-parity distributions, the Hauser-Feshbach statistical decay treatment for fission fragment de-excitation is applied to more than 1,000 fission fragments for the incident neutron energies up to 5 MeV. The calculated independent fission product yields are then used as an input of $\beta$-decay to produce the cumulative yield, and summation calculations are performed. Model parameters in these procedures are adjusted by applying the Bayesian technique at the thermal energy for $^{235}$U and $^{239}$Pu and in the fast energy range for $^{238}$U. The calculated fission observable quantities, such as the energy-dependent fission yields, and prompt and delayed neutron yields, are compared with available experimental data. We also study a possible impact of the second chance fission opening on the energy dependence of the delayed neutron yield by extrapolating the calculation.