The Positron emission reference article from the English Wikipedia on 24-Jul-2004
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Positron emission

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Nuclear processes
Radioactive decay processes
Nucleosynthesis

Positron emission is a type of beta decay, referred to as "beta plus" (β+). In beta plus decay, a proton is converted to a neutron via the weak nuclear force and a beta plus particle (a positron) and a neutrino are emitted. Isotopes which emit positrons include C-11, N-13, O-15 and F-18; for example:

These isotopes are used in positron emission tomography.

See also Beta decay