Status of the International Neutron Cross-Section Standards File

Abstract

A report is given of the progress achieved in an IAEA Co-ordinated Research Project (CRP) to improve the cross-section standards. The objectives of the CRP, started in 2002, were initially the understanding of the origin of the strong uncertainty reduction in R-matrix model fits and the improvement of the evaluation methodology. These aims were extended in 2003 to the preparation of new evaluations for the standard 6 Li(n,t), 10 B(n,α), 10 B(n,α 1 ), 197 Au(n,γ), 235 U(n,f), and 238 U(n,f) reactions. The methodology, codes, and experimental database developed by Poenitz and Hale for the ENDF/B-VI standards evaluation were taken as the basis for the new evaluation. The major results achieved by the CRP participants include the testing and intercomparison of a number of codes that can be used in the standards evaluation, updating the database of experimental results, analysis of the reasons leading to the strong uncertainty reduction in model fits, and a study of the bias in evaluated data caused by the Peelles's Pertinent Puzzle (PPP) effect, which has been widely discussed in the nuclear data community since the ENDF/B-VI standards evaluation was completed. Preliminary results of the new standards evaluation are shown. The use of the new 235 U(n,f) cross section leads to better consistency in calculations of some important integral experiments.

NEA Working Party on International Nuclear Data Cooperation—Recent Achievements and Plans

“…The development of new standards is a complex international effort, including CSEWG in the United States, WPEC Subgroup 7 and an IAEA CRP on Standards [2,3]. These activities are closely intertwined.…”

Recent Advances in the ENDF/B Library

“…New evaluations will be prepared for 8 standard reactions 1 H(n,n), 3 He(n,p), 6 Li(n,t), 10 B(n,α), 10 B(n,α 1 ), 197 Au(n,γ), 235 U(n,f), and 238 U(n,f). In addition, 238 U(n,γ) and 239 Pu(n,f) will be evaluated because of strongly coupled databases with standards.…”

“…The CRP has made considerable progress; cross sections should be finalized in 2004, followed by covariances in 2005. See V. Pronyaev et al [3] for more details.…”

“…Among them are invited talks on cross-section standards [3], uranium evaluations [4], neutron resonance evaluations [5], and data validation [6]. • Charged particles: 20 materials (all LANL) -Protons: 3 H, 6 7 Li, 196 198 199 200 201 202 204 Hg -Deuterons: 2 3 H, 3 He, 6 7 Li, -Tritons: 3 H, 3 He, 6 Li, and 3-He: 3 He, 6 Li Neutron files were produced primarily by LANL, in particular for actinides. This is followed by ORNL evaluations in the neutron-resonance region motivated by criticality safety applications, and BNL-led work on fission products.…”