Initially the designation transuranic referred to an artificial element heavier than Uranium. Until the development of the atomic bomb only 92 elements were known to exist in nature. After that for a long time only the artificial elements Neptunium and Plutonium existed. Later more were added, created essentially by the addition of neutrons firstly and then successive transformation by for example β-decay. These elements called transuranic were all unstable with sometimes extremely short half-lives.