Actinide Series
. Actinide Series, a series of 14 radioactive elements in the periodic table with atomic numbers 89 through 102. Only the first four elements in the series have been found in nature in appreciable amounts; the remainder have been produced synthetically. Those elements with atomic numbers of 93 and above are called transuranium elements . The elements constituting the actinide series are, in order of increasing atomic number, actinium, thorium, protactinium, uranium, neptunium, plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, and nobelium.