Neutron capture

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Neutron capture is a kind of nuclear reaction in which an atomic nucleus collides with a neutron and they merge to form a heavier nucleus. The process is also known as thermal capture.

Some nuclei are better at capturing a neutron than others. In order for a neutron to be captured it must be moving near the same speed (have a similar temperature or energy) as the target nucleus. A free relatively slow moving neutron is an unstable particle and has a half-life of about 15 minutes. When the neutron is captured the nucleus often releases its energy immediately as a gamma ray. The newly-formed nuclide may also undergo beta decay.

The process of neutron capture can proceed in two ways - as a rapid process (an r-process) or a slow process (an s-process). These two processes produce different isotopes. Some isotopes can only be produced by one or the other process.

Rapid neutron capture implies multiple neutron captures. These multiple captures usually produce an unstable nuclide which undergoes beta-decay to produce a stable nuclide. This process is more relevant to stars since there must be a large number of neutrons present.

Slow neutron capture implies a single neutron capture that produces a stable nuclide or that undergoes beta decay into a stable nuclide before another neutron capture occurs.

[edit] Uses

Neutron capture can be used to remotely detect the chemical composition of materials. This is because different elements release different characteristic radiation when they absorb neutrons. This makes it useful in many fields related to mineral exploration and security.