Rossi-alpha Uncertainty Quantification by Analytic, Bootstrap, and Sample Methods to Inform Fitting Best Practices

TL;DR

This paper compares analytic, bootstrap, and sample methods for quantifying uncertainty in Rossi-alpha measurements, aiming to improve fitting practices and optimize measurement precision in nuclear safety applications.

Contribution

It validates a new bootstrap method for Rossi-alpha uncertainty quantification and provides guidelines for selecting bin widths and reset times.

Findings

Bootstrap method accurately estimates error bars

Guidelines improve measurement precision

Two-exponential model accounts for reflector effects

Abstract

The prompt neutron period (the negative reciprocal of the prompt neutron decay constant) can be estimated using the Rossi-alpha technique that is predicated on fitting Rossi-alpha histograms and of interest in nuclear criticality safety and nonproliferation [1, 2, 3]. The histograms are traditionally fit with a one-exponential model; however, recent work has proposed a two-exponential model to account for reflector-induced phenomenon [4, 5, 6]. Until recently, the uncertainty quantification for either model was inadequate (inaccurate and demanded large measurement times). Measurement uncertainty quantification by sample and analytic methods was developed and validated in Ref. [7]. The purpose of this transaction is to (i) validate a new bootstrap method by comparing bin-by-bin error bar estimates and (ii) demonstrate how to choose bin widths and reset times to optimize precision and accuracy.