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arXiv · 2512.19857

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

S. E. A. Orrigo·J. L. Tain·N. Mont-Geli·A. Tarifeño-Saldivia·L. M. Fraile·M. Grieger·A. Quero-Ballesteros·J. Agramunt·A. Algora·D. Bemmerer·F. Calviño·G. Cortés·A. De Blas·I. Dillmann·R. García·E. Nacher
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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), with a total livetime of 248 days. 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 ambient neutron flux that includes a full spectral characterization across a wide energy interval (from $10^{-4}$ eV to 20 MeV), 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.

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S. E. A. Orrigo, J. L. Tain, N. Mont-Geli, A. Tarifeño-Saldivia, L. M. Fraile, M. Grieger, A. Quero-Ballesteros, J. Agramunt, A. Algora, D. Bemmerer, F. Calviño, G. Cortés, A. De Blas, I. Dillmann, R. García, E. Nacher. 2025-12-22. Measurement of the ambient neutron flux and spectral distribution at the Canfranc Underground Laboratory. https://doi.org/10.1140/epjc%2Fs10052-026-16064-6

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