Neutron irradiation is the exposure of a material to a flux of neutrons, which, because neutrons are uncharged, penetrate deeply and interact with atomic nuclei rather than being stopped by the electron cloud, producing displacement damage and, in some cases, transmutation products within the material ^[1]. The primary consequence in structural materials is the creation of lattice defects: an energetic neutron transfers kinetic energy to an atom, knocking it from its lattice site into an interstitial position and leaving a vacancy, and such primary knock-on atoms generate cascades of further displacements whose accumulated point defects evolve into dislocation loops, voids, and clusters under continued exposure ^[2]. Neutron irradiation is distinguished from charged-particle irradiation by the neutrality and deep penetration of the incident particle, which enables bulk rather than surface damage, and from simple thermal exposure by the displacement cascades and transmutation elements introduced by nuclear reactions ^[1]. The effects on properties—changes in strength, ductility, swelling, and embrittlement—arise from the accumulation and rearrangement of irradiation-induced defects and from transmutation gases, and are characterized in terms of displacement dose, typically expressed as displacements per atom ^[2]. Its defining mechanism is nuclear interaction producing atomic displacements deep within the solid ^[3].