Measurement of the ambient neutron flux and spectral distribution at the Canfranc Underground Laboratory

TL;DR

This study provides the first comprehensive measurement of ambient neutron flux and spectral distribution in an underground laboratory, crucial for rare-event physics experiments and understanding neutron backgrounds.

Contribution

It presents the first long-term, full spectral characterization of neutron flux in an underground setting using the HENSA detector.

Findings

Thermal neutron flux measured at 3.4(2) x 10^{-6} cm^{-2} s^{-1}

Total neutron flux is 14.8(2) x 10^{-6} cm^{-2} s^{-1}

Spectral distribution characterized over a broad energy range

Abstract

We report on the measurement of the ambient neutron flux and its energy distribution over a broad range of neutron energies, conducted in Hall A of the Canfranc Underground Laboratory using the High Efficiency Neutron Spectrometry Array (HENSA). In particular, we obtained a thermal neutron flux of $3.4(2) \times 10^{-6}$ cm$^{-2}$ s$^{-1}$ and a total energy-integrated flux of $14.8(2) \times 10^{-6}$ cm$^{-2}$ s$^{-1}$. This work represents the first long-term measurement of the total neutron flux, with full spectral characterization across a wide energy interval, performed in an underground laboratory to date. The results are relevant for rare-event search experiments located underground, ranging from nuclear astrophysics to astroparticle physics.