The actinide elements are unusual in that most of them were synthesized in a particle accelerator after 1940. Only three naturally occurring members of the group, thorium, protactinium and uranium, were known before that date.
Uranium was the first of the actinides to be discovered, having been found in 1789 by the German chemist, Martin Heinrich Klaproth, on examination of pitchblende, a uranium ore. Thorium came next, identified by the Swedish chemist, J÷ns Jacob Berzelius, in 1828, and protactinium followed, almost a hundred years later, discovered by O. Gohring and K. Fajans in 1913.
The remaining elements, known collectively as the transuranium elements, because they follow uranium in the periodic table, do not occur naturally (although neptunium and plutonium have recently been discovered in very small quantities); but developments made in the understanding of atomic structure in the first half of the twentieth century made possible the techniques necessary for their synthesis. Neptunium was the first to be produced, in 1940, by the American scientists, Edwin McMillan and Philip Abelson, and new elements were regularly created in the following years.
Most of these syntheses took place in the cyclotron at the University of Berkeley, in California (hence the names, berkelium and californium), and the outstanding scientist in this field is Glenn Seaborg who, in 1951, was the joint recipient of the Nobel Prize for Chemistry.
