Neutron Cross Section Uncertainties in the Thermal and Resonance Regions

Abstract

In the Atlas of Neutron Resonances, special care was expended to ensure that the resonance parameter information reproduces the various measured thermal cross sections, as well as the infinite dilute resonance integrals for Z = 1-100. In contrast, the uncertainties of the recommended quantities do not match those generated from the uncertainties of the resonance parameters. To address this problem, the present study was initiated to achieve consistency for 15 actinides and 21 structural and coolant moderator materials. This is realized by assigning uncertainties to the parameters of the negative-energy resonances and changing, if necessary, significantly the uncertainties of the low-lying positive-energy resonances. The influence of correlations between parameters on the derived uncertainties is examined and discussed.

Calculations of Maxwellian-averaged Cross Sections and Astrophysical Reaction Rates Using the ENDF/B-VII.0, JEFF-3.1, JENDL-3.3 and ENDF/B-VI.8 Evaluated Nuclear Reaction Data Libraries

“…• The unresolved-resonance region, described by the average resonance parameters as reported in Atlas [12] and determined in recent investigation [47,48].…”

“…by Mughabghab [17]. These cross sections were produced to independently verify the data, and are calculated from neutron-resonance parameters and nuclear systematics [12,47,48]. Mughabghab [17] followed two approaches, termed the detailed cross section method and the comparative method, to determine σ Maxw γ (30keV ) .…”

Development of Covariance Capabilities in EMPIRE Code

“…In general, these are correlations for the same resonance, discussed in more detail by Mughabghab [13].…”

“…Detailed discussion of the first scenario, along with its application to the neutron radiative capture on 55 Mn, was done by Mughabghab and Obložinský [13]. Restricting adjustment to the parameter uncertainties led to a considerable modification of the Atlas data.…”

“…We mention here covariances for 13 [11] released in 2006. In addition, there was a considerable effort to deliver preliminary covariances for the WPEC Subgroup 26 which resulted in covariance estimates for 36 materials.…”