Metastable isomers are produced through nuclear reactions. The excited state of the nucleus will de-excite by emission of gamma rays until the nuclear ground state is reached.
Isotopes in a metastable condition are designated with a 'm', for example 99mTc.

In cyclotrons charged particles are circular accelerated to bombard atoms. Short-lived positron-emitting isotopes are produced for Positron Emission Tomography (PET) imaging (e.g. F-18).

See also Linear Accelerator, Metastable Condition, Meson, Fluorodeoxyglucose, Electric Polarization.