Measurement of the neutron flux at spallation sources using multi-foil activation

TL;DR

This study employs activation analysis with multiple elements and Bayesian unfolding to measure and characterize the neutron flux spectrum from thermal to hundreds of MeV at a spallation source.

Contribution

It introduces a comprehensive method combining multi-foil activation and Bayesian spectrum unfolding for accurate neutron flux measurement across a wide energy range.

Findings

Successful measurement of neutron flux from thermal to hundreds of MeV.

Effective unfolding of the neutron spectrum with limited correlations.

Detailed uncertainty evaluation in activation analysis.

Abstract

Activation analysis is used in this work to measure the flux of a fast neutron beamline at a spallation source over a wide energy spectrum, extending from thermal to hundreds of MeV. The experimental method is based on the irradiation of multiple elements and measurements of activation {\gamma}-lines using a High Purity Germanium detector. The method for data analysis is then described in detail, with particular attention to the evaluation of uncertainties. The reactions have been chosen so to cover the whole energy range, using mainly (n,{\gamma}) for thermal and epithermal neutrons, and threshold reactions for the fast region. The variety of these reactions allowed for the unfolding of the neutron spectrum, using an algorithm based on a Bayesian statistical model, and limited correlations have been found between the energy groups.