The physical mechanisms of neutron detection

Neutrons do not directly ionise the medium they pass through, unlike charged particles. Neutron detection is then based on nuclear reactions in which the neutron is typically lost and charged particles and/or γ-rays are generated in the final state. These are subsequently detected by appropriate sensors of various types, such as gas, scintillation, and solid-state detectors. Neutrons generated at large scale facilities (fission reactors or accelerator-driven plants) typically cover a very wide energy range. The nuclear reactions that are found to be effective at different energies make neutron detection on the one hand complex from an instrumental point of view, and on the other hand interesting from the point of view of the physics underlying the approach to be used. This article aims at presenting and discussing the main features of the nuclear reactions of interest in neutron detection in different energy ranges, and the physical processes that take place in typical sensors used as detection tools. This approach is intended to describe the entire physical process, from neutron-nucleus interaction to the physical sensor response, that represents the detection event.