Directional Detection and Fissile Material Identification with the nFacet 3D detector

Laboratoire de Physique Corpusculure de Caen, France

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Published online: 6 November 2025

Abstract

Source localisation is a critical point in nuclear safeguard and security, but it is currently an over-looked concept. Source search using counters is the standard method but is very time-consuming when the environment is complex or unknown. We introduce the nFacet 3D system, a portable gamma and neutron radiameter with directional capabilities, to fill the gap of directional detectors. We present here the results of the measurement campaign done at the STUK facility in Finland to assess the performance of the system in the field. Infield resolution below 5° for both ¹³⁷Cs and ⁶⁰Co at 5 and 10 meters away was demonstrated using machine learning techniques. High sensitivity to neutrons was shown, allowing long-range detection of a source at least 50 meters away, with possible detection up to 80 or 100 meters away. Gamma source separation capabilities were shown using energy window selection techniques, and good stability across variable environments in terms of count rates was demonstrated. The high angular resolution, with high detection range, gamma separation capabilities, and stability across the environment enables source localisation and detection on a large scale, making nFacet suitable for a wide range or security-related applications.