Neutron capture

Neutron capture is a nuclear reaction where a nucleus absorbs a free neutron, transforming into a heavier isotope. This fundamental process powers stellar nucleosynthesis, shapes isotope ratios in nature, and underpins both civilian and military nuclear technology.

When a neutron enters a nucleus, the two merge in microseconds. The resulting nucleus is typically unstable and releases energy—either as gamma radiation (radiative capture) or by emitting other particles. This reaction rate depends sensitively on neutron speed; slow neutrons are "captured" more readily by certain elements, while fast neutrons behave differently. Temperature, material density, and nuclear cross-sections all influence capture probability.

Neutron capture is essential to stellar alchemy: it synthesizes heavy elements like iron and gold in stars and supernovae, seeding the cosmos with matter we find today. In reactors, controlled capture in uranium-235 or plutonium-239 sustains the chain reaction that generates power. Conversely, neutron capture in reactor materials causes them to become radioactive—a key engineering challenge.

The process also powers isotope production for medicine and research, enables dating via radiocarbon methods, and explains why boron absorbs neutrons so efficiently (used in reactor control rods).

Related

Nuclear fission, Isotope, Nucleosynthesis, Radioactivity, Boron, Stellar evolution