Data Covariances from RMatrix Analyses of Light Nuclei
Abstract
After first reviewing the parametric description of lightelement reactions in multichannel systems using Rmatrix theory and features of the general LANL Rmatrix analysis code EDA, we describe how its chisquare minimization procedure gives parameter covariances. This information is used, together with analytically calculated sensitivity derivatives, to obtain cross section covariances for all reactions included in the analysis by firstorder error propagation. Examples are given of the covariances obtained for systems with few resonances ({sup 5}He) and with many resonances ({sup 13}C ). We discuss the prevalent problem of this method leading to cross section uncertainty estimates that are unreasonably small for large data sets. The answer to this problem appears to be using parameter confidence intervals in place of standard errors.
 Authors:
 Publication Date:
 OSTI Identifier:
 22436777
 Resource Type:
 Journal Article
 Resource Relation:
 Journal Name: Nuclear Data Sheets; Journal Volume: 123; Conference: International workshop on nuclear data covariances, Santa Fe, NM (United States), 28 Apr  1 May 2014; Other Information: Copyright (c) 2014 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 73 NUCLEAR PHYSICS AND RADIATION PHYSICS; CARBON 13; CROSS SECTIONS; DATA COVARIANCES; HELIUM 5; LANL; MINIMIZATION; R MATRIX
Citation Formats
Hale, G.M., Email: ghale@lanl.gov, and Paris, M.W. Data Covariances from RMatrix Analyses of Light Nuclei. United States: N. p., 2015.
Web. doi:10.1016/J.NDS.2014.12.029.
Hale, G.M., Email: ghale@lanl.gov, & Paris, M.W. Data Covariances from RMatrix Analyses of Light Nuclei. United States. doi:10.1016/J.NDS.2014.12.029.
Hale, G.M., Email: ghale@lanl.gov, and Paris, M.W. 2015.
"Data Covariances from RMatrix Analyses of Light Nuclei". United States.
doi:10.1016/J.NDS.2014.12.029.
@article{osti_22436777,
title = {Data Covariances from RMatrix Analyses of Light Nuclei},
author = {Hale, G.M., Email: ghale@lanl.gov and Paris, M.W.},
abstractNote = {After first reviewing the parametric description of lightelement reactions in multichannel systems using Rmatrix theory and features of the general LANL Rmatrix analysis code EDA, we describe how its chisquare minimization procedure gives parameter covariances. This information is used, together with analytically calculated sensitivity derivatives, to obtain cross section covariances for all reactions included in the analysis by firstorder error propagation. Examples are given of the covariances obtained for systems with few resonances ({sup 5}He) and with many resonances ({sup 13}C ). We discuss the prevalent problem of this method leading to cross section uncertainty estimates that are unreasonably small for large data sets. The answer to this problem appears to be using parameter confidence intervals in place of standard errors.},
doi = {10.1016/J.NDS.2014.12.029},
journal = {Nuclear Data Sheets},
number = ,
volume = 123,
place = {United States},
year = 2015,
month = 1
}

We review the method for obtaining covariance information for lightelement reactions using Rmatrix theory. The general LANL Rmatrix analysis code EDA provides accurate covariances for the resonance parameters at a solution due to the search algorithm it uses to find a local minimum of the chisquare surface. This information is used, together with analytically calculated sensitivity derivatives, in the firstorder error propagation equation to obtain crosssection covariances for all reactions included in the analysis. Examples are given of the covariances obtained from the EDA analyses for np scattering and for the n+{sup 6}Li reactions used in the latest lightelement standardmore »

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