Elements in the periodic table with atomic numbers from 90 to 103 (thorium to lawrencium); i.e., elements with a higher atomic number than actinium, which has an atomic number of 89. These are also called "rare earth metals." they include most of the well-known elements found in nuclear reactions. Actinides with atomic numbers higher than 92 do not occur naturally but are produced artificially by bombarding other elements with particles. Some of the actinides include plutonium, curium, and californium.