Free neutron

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A free neutron is a neutron that exists outside of an atomic nucleus. While neutrons can be stable when bound inside nuclei, free neutrons are unstable and decay with a half-life of just under 15 minutes. Particles inside the nucleus are typically resonances between neutrons and protons, which transform into one another by the emission and absorption of pions. The only possible decay mode, via the weak nuclear force, is into a proton, an electron, and an electron antineutrino, the proton and electron forming a hydrogen atom:

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Even though it is not a chemical element, the free neutron is often included in tables of isotopes. It is then considered to have an atomic number of zero and a mass number of one.

Nuclear fission reactors naturally produce free neutrons; their role is to sustain the energy-producing chain reaction. The intense neutron radiation is also used to produce various radioisotopes through the process of neutron activation.

Experimental nuclear fusion reactors produce free neutrons in copious amounts as a waste product. However, it is these neutrons that possess most of the energy, and converting that energy to a useful form has proved a difficult engineering challenge to nuclear physicists.

Free neutron

See also