Neutron activation

Science with neutrons
Foundations
Neutron temperature Flux, Radiation, Transport Cross section, Absorption, Activation
Neutron scattering
Neutron diffraction Small-angle neutron scattering GISANS Reflectometry Inelastic neutron scattering Triple-axis spectrometer Time-of-flight spectrometer Backscattering spectrometer Spin-echo spectrometer
Other applications
Neutron tomography Activation analysis, Prompt gamma activation analysis Fundamental research with neutrons: Ultracold neutrons, Interferometry Fast neutron therapy Neutron capture therapy
Infrastructure
Neutron sources: Research reactor, Spallation, Neutron moderator Neutron optics: Reflector, Supermirror Detection
Neutron facilities
America: HFIR, LANSCE, NIST CNR -SNS Oceania: OPAL Asia: J-PARC, HANARO Europe: BER II, FRM II, ILL, ISIS Neutron and Muon Source, JINR, SINQ Historic: IPNS, HFBR Under construction: ESS
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Neutron activation is the process in which neutron radiation induces radioactivity in materials, and occurs when atomic nuclei capture free neutrons, becoming heavier and entering excited states. The excited nucleus decays immediately by emitting gamma rays, or particles such as beta particles, alpha particles, fission products, and neutrons (in nuclear fission). Thus, the process of neutron capture, even after any intermediate decay, often results in the formation of an unstable activation product. Such radioactive nuclei can exhibit half-lives ranging from small fractions of a second to many years.

Neutron activation is the only common way that a stable material can be induced into becoming intrinsically radioactive. All naturally occurring materials, including air, water, and soil, can be induced (activated) by neutron capture into some amount of radioactivity in varying degrees, as a result of the production of neutron-rich radioisotopes.^{[citation needed]} Some atoms require more than one neutron to become unstable, which makes them harder to activate because the probability of a double or triple capture by a nucleus is below that of single capture. Water, for example, is made up of hydrogen and oxygen. Hydrogen requires a double capture to attain instability as tritium (hydrogen-3), while natural oxygen (oxygen-16) requires three captures to become unstable oxygen-19. Thus water is relatively difficult to activate, as compared to sodium chloride (NaCl), in which both the sodium and chlorine atoms become unstable with a single capture each. These facts were experienced at the Operation Crossroads atomic test series in 1946.