Zirconium Evaluations for ENDF/B-VII.2 for the Fast Region

Abstract

We have performed a new combined set of evaluations for 90−96 Zr, including new resolved resonance parameterizations from Said Mughabghab for 90,91,92,94,96 Zr and fast region calculations made with EMPIRE-3.1. Because 90 Zr is a magic nucleus, 90 Zr is nearly spherical. Therefore, all even-even nuclei in the evaluation set were evaluated using EMPIRE's OPTMAN coupled channels code and a new soft-rotor optical model potential. This then led to improved (n,el) angular distributions, helping to resolve improper leakage in the older ENDF/B-VII.1β evaluation in KAPL proprietary, ZPR and TRIGA benchmarks. Another consequence of 90 Zr being a magic nucleus is that the level densities in both 90 Zr and 91 Zr are unusually low causing the (n,el) and (n,tot) cross sections to exhibit large fluctuations above the resolved resonance region. To accomodate these fluctuations, we performed a simultaneous constrained generalized least-square fit to (n,tot) for all isotopic and elemental Zr data in EXFOR, using EMPIRE's TOTRED scaling factor. TOTRED rescales reaction cross sections so that the optical model calculations are unaltered by the rescaling and the correct competition between channels is maintained. In this fit, all (n,tot) data in EXFOR was used for Ein > 100 keV, provided the target isotopic makeup could be correctly understood, including spectrum averaged data and data with broad energy resolution. As a result of our fitting procedure, we have full cross material and cross reaction covariance for all Zr isotopes and reactions.

Preequilibrium Asymmetries in the Pu239(n,f) Prompt Fission Neutron Spectrum

“…Models of nuclear fission reflect our understanding of the fission process. These models are used to inform nuclear data evaluations, which are then used to predict the performance of nuclear systems and reactors [1][2][3]. Despite the obvious need for a complete understanding of the fission process, we are only just now beginning to experimentally observe fundamental features of fission relating to the neutrons emitted during the fission process.…”

“…The details of multi-chance fission are not well known and are estimated from models with incomplete experimental validation [2][3][4]. A particularly unknown feature of second-chance fission is the transition from equilibrium prefission neutron emission to pre-equilibrium pre-fission neutron emission (illustrated in the bottom row of Fig.…”

“…Even recent experiments to measure the 239 Pu and 238 U PFNS [12,13] have assumed that their reported results are insensitive to the pre-fission pre-equilibrium component of the PFNS, but there is no experimental evidence to support or refute this claim. In terms of fission modeling efforts, Maslov et al [14], Rubchenya [15], the FREYA code [16], the CGMF code [17], and recent evaluations using the Los Alamos Model [3,[18][19][20] all use the exciton model [5,21,22] to describe the energy distribution of pre-equilibrium neutrons. This model inherently does not predict angular distributions, though Rubchenya [15] used a Kalbach-Mann (K-M) [23] angular distribution in conjunction with the exciton model to attempt to describe the angular effects.…”

Computational Study of Radiation Characteristics in the Niche of the Experimental Devices of the WWR-K Reactor

“…The user has the ability to model geometric three-dimensional configurations by setting the mathematical equations of the surfaces limiting them of the first, second and fourth degree, and filling them with an arbitrary material, setting the concentration of the nuclei of the elements that make up the substance. The ENDF/B-VII.1 library of cross sections for the interaction of neutrons with matter in the MCNP6 transport code was used [30]. In MCU-REA and MCNP6, the current configuration of the WWR-K reactor core was simulated with a real material composition.…”

Systematic study of the (n, 2n) reaction cross section for 121Sb and 123Sb isotopes

“…In the present work, the excitation functions of the 121 Sb 120 Sb m and 123 Sb 122 Sb reactions were measured at 12.50, 15.79 and 18.87 MeV neutron energies. The experimental results and latest evaluated data from JEFF-3.3 [9], JENDL/AD-2017 [10], ENDF/B-VIII.0 [11] and TENDL-2019 [12] libraries were compared with the each other. Specifically, the uncertainties in the measured cross section data were obtained through the covariance analysis method, which involves uncertainties from each source.…”