The High Efficiency Neutron Spectrometry Array (HENSA) is a state-of-the-art detection system for neutron background spectrometry in low radioactivity facilities, such as underground laboratories, and for the measurement of secondary neutrons produced by cosmic-rays.

Currently, the research with HENSA is focused on the study of the neutron background affecting different experiments at the Laboratorio Subterráneo de Canfranc (LSC, Spain) and the characterization of the ambient neutron background by cosmic-rays during solar cycle 25. Early versions of HENSA have been already used for neutron background measurements at the LSC and the shallow-underground laboratory Felsenkeller in Dresden, Germany.

The HENSA detector has been developed as a joint effort by researchers from different international institutions: Instituto de Física Corpuscular (IFIC/CSIC-UV, Spain), Technical University of Catalonia (INTE-UPC, Spain), Universidad Complutense de Madrid (UCM, Spain), Helmholtz-Zentrum Dresden-Rossendorf (HDZR, Germany), TRIUMF (Canada).

High energy neutrons are produced as secondary particles from interactions of cosmic-rays with atoms in the atmosphere. Cosmic-ray neutrons are the main component of the ambient neutron background at ground level and high altitudes. The total flux and the spectral distribution of cosmic-ray neutrons depend mainly on: the solar activity, the geomagnetic position and the altitude. Cosmic-ray neutrons are interesting for a wide range of areas, such as space weather, single event upset (SEU) in microelectronics, cosmic-rays physics and environmental radiation dosimetry.

Neutrons are a challenging source of radiation background affecting experiments dealing with rare event searches. In underground facilities, despite cosmic-ray neutron background is largely suppressed, radiogenic neutrons are still produced in the surrounding materials of the facility (rocks and walls) by means of (alpha,n) reactions and spontaneous fission. These neutrons have a large penetrability in matter and they are able to induce background signals in the detectors used for nuclear astrophysics, neutrino and dark matter experiments.