neutronirradiation

Neutron irradiation is the exposure of a material or biological specimen to a flux of free neutrons. Neutrons are uncharged and can penetrate deeply, so irradiation sources such as nuclear reactors or spallation sources are commonly used. The resulting energy spectrum can be thermalized (thermal neutrons) or rich in higher-energy fast neutrons, depending on moderators and shielding.

During irradiation, neutrons interact with nuclei by elastic and inelastic scattering, neutron capture (n,γ), and other reactions that transmute nuclides (for example (n,p) or (n,α)). These interactions alter the isotopic composition of the material and deposit energy, which can modify physical properties or induce radioactivity.

In materials science, irradiation can cause displacement damage as atoms are knocked from lattice sites, creating vacancies and interstitials. This can lead to irradiation hardening or embrittlement, swelling, phase changes, and gas production (notably hydrogen and helium) within the material. Activation is another consequence: target nuclei capture neutrons and become radioactive isotopes, which decay with characteristic half-lives and contribute to residual radioactivity and heat.

Applications of neutron irradiation include materials testing under reactor-relevant conditions, neutron activation analysis for trace element quantification, and neutron radiography for imaging. It also enables production of radioisotopes used in medicine and industry, such as cobalt-60.

Safety and handling considerations are central to neutron irradiation. Induced radioactivity requires shielding (often water and dense concrete), remote handling, and careful dosimetry and monitoring of facilities, personnel, and affected regions.