Evaluation of Covariance Data for Chromium, Iron and Nickel Contained in JENDL-3.2

Abstract

An evaluation has been made for the covariances of neutron cross sections of ⁵²Cr, ⁵⁶Fe, ⁵⁸Ni and ⁶⁰Ni contained in JENDL-3.2. Reactions considered were the threshold reactions such as (n, 2n), (n, nα), (n, np), (n, p), (n, d), (n, t) and (n, α), the radiative capture reaction above the resonance region, and the inelastic scattering to discrete and continuum levels. Evaluation guidelines and procedures were established during the work.

A generalized least-squares fitting code GMA was used in estimating covariances for reactions of which JENDL-3.2 cross sections had been evaluated by taking account of many measured data. For cross sections that had been evaluated by nuclear reaction model calculations, the KALMAN code, which yields covariances of cross sections and of associated model parameters on the basis of the Bayesian statistics, was used in conjunction with reaction model codes EGNASH and CASTHY.

The evaluated uncertainties of a few percent to 30% in the cross sections look reasonable, and the correlation matrices show understandable trends. Even though there is no strict way to confirm the validity of the evaluated covariances, tools and procedures adopted in the present work are appropriate for producing covariance files based on JENDL-3.2. The covariances obtained will be compiled into JENDL in the near future. Meanwhile, new sets of optical model and level density parameters were proposed as one of byproducts obtained from the KALMAN calculations.

KEYWORDS:

• covariance
• evaluations
• neutron cross sections
• JENDL-3.2
• structural materials
• GMA
• KALMAN
• guidelines
• recommendation
• chromium 52
• iron 56
• nickel 58
• nickel 60