neutronikiirgust

Neutron irradiation, or neutronikiirgust, is the exposure of a material or biological tissue to a flux of neutrons. Neutrons, being electrically neutral, penetrate matter efficiently and can cause ionization indirectly through nuclear interactions, as well as activate materials through transmutation. The effects depend on neutron energy, flux, and exposure duration.

Common neutron sources are nuclear reactors, which produce large thermal neutron fluxes; spallation sources and accelerator-driven systems generate fast neutrons or neutrons across a broad spectrum after moderation. Neutron energy is typically categorized as thermal (about 0.025 eV), epithermal, fast (MeV range), or moderated combinations.

Neutron interactions with matter include elastic scattering, inelastic scattering, and neutron capture (activation). Elastic collisions transfer kinetic energy to nuclei, causing displacement damage in materials. Absorption and (n,γ) reactions create radioactive nuclei, enabling neutron activation analysis but also leaving residual radioactivity. Neutron cross sections vary with energy and isotope; detectors and shielding are designed accordingly. In biology, neutrons are highly penetrating and produce biologically effective damage similar to high-LET radiation.

Applications include neutron activation analysis for qualitative and quantitative elemental analysis; production of medical and industrial radioisotopes; materials testing to assess radiation damage and performance in reactors or space environments; and, in some centers, neutron therapy as a treatment for certain cancers.

Safety and shielding rely on hydrogenous materials to slow and attenuate neutrons and on absorbers such as boron-10 for capture. Shielding design must account for secondary gamma rays from activation. Monitoring uses detectors like He-3 or BF3 proportional counters, fission chambers, and activation foils. Units of interest include neutron flux, fluence, and dose equivalent (sieverts).