# How accurately we know the standard $^{252}$Cf(sf) neutron multiplicity?

## TL;DR

This paper investigates the potential unrecognized uncertainties and correlations in the measurement of the neutron multiplicity of the $^{252}$Cf spontaneous fission source, which is crucial for neutron standards and nuclear data accuracy.

## Contribution

It highlights the neglected issue of unrecognized uncertainties and correlations in neutron multiplicity measurements and provides a case study to evaluate their impact.

## Key findings

- Potential unrecognized uncertainties in $^{252}$Cf neutron multiplicity measurements.
- Correlations between different experiments may affect the accuracy of neutron standards.
- The study emphasizes the need for more comprehensive uncertainty analysis in nuclear data evaluations.

## Abstract

Small uncertainties obtained for the Neutron Standards have been associated with possible missing correlations in the input data, with an incomplete uncertainty budget of the employed experimental database or with unrecognized uncertainty sources common to many measurements. While further detailed studies may improve the first two issues, the issue of potential unrecognized uncertainties and correlations between different experiments has long been neglected. We address this gap with a test-case study ons the evaluation of the total neutron multiplicity of the $^{252}$Cf(sf) source, which is included in the evaluation of the Thermal Neutron Constants within the Neutron Standards.