A snippet-based algorithm for practical covariance estimation in Feynman-α analysis

Research output: Contribution to journalResearch articleContributedpeer-review

Abstract

In the context of Feynman-α analysis, the bunching technique is a widely used method for synthesizing neutron count data with larger bin widths by aggregating counts from smaller bin widths. For each bin size T[jls-end-space/], the variance-to-mean ratio (Formula presented) is computed, forming the basis for determining the α parameter. However, the points on the (Formula presented) curve are inherently correlated due to the bunching process. As a result, uncorrelated fitting methods that rely solely on the standard errors of (Formula presented) fail to provide accurate estimates for α and its uncertainties. A proper treatment of these correlations requires incorporating the covariance matrix of the (Formula presented) points into the fitting procedure. In practice, estimating this covariance matrix from real measurements is challenging and demands a large amount of data, while its theoretical estimation remains an open problem. This paper investigates alternative approaches to reliably determine α and its uncertainties. Our analysis confirms that uncorrelated fits, neglecting the covariance matrix, fail to provide reliable uncertainties as correlations are significant. Conversely, including an accurately estimated covariance matrix yields correct results for α and its uncertainties. Since direct estimation of the full covariance matrix requires extensive data, entailing significant measurement time and computational effort, a new method is proposed. This method enables the estimation of the necessary covariance information within practical limits of measurement time and computational resources. These findings reinforce the theoretical foundation of Feynman-α analysis and offer a robust framework for accurately fitting correlated data arising from the bunching technique.

Details

Original languageEnglish
Article number112241
JournalAnnals of nuclear energy
Volume233
Publication statusPublished - Aug 2026
Peer-reviewedYes

External IDs

Mendeley 63d4ddad-2840-35f4-9679-df4b0935d12c
unpaywall 10.1016/j.anucene.2026.112241

Keywords

Keywords

  • Rossi-α, Kinetic parameters, Variance-to-mean, Covariance-to-mean, Correlated data fitting, Feynman-α, Bunching technique