A cyclotron is a particle accelerator that is used to produce short-lived radionuclides. The cyclotron takes ions, either protons (p) or deuterons (d), and accelerates them to high speeds (or high energy) through the use of alternating electric fields. The particles are kept in a circular orbit by a strong magnetic field as they gain energy. Most cyclotrons used for producing PET radiotracers use particles (p or d) with an energy between 3 and 19 million electron volts (MeV). These energetic particles are directed toward “targets” made of the starting element, and through a nuclear reaction, produce a different element, in this case one that decays by the emission of a positron. Common radionuclides used in PET have a half-life between 75 seconds and 110 minutes. The positron-emitting isotopes are transferred from the target to a computer controlled unit which makes the radiopharmaceutical that is used to monitor physiological processes in the body.