transuranium element

n. transuranic element, chemical element with an atomic number greater than 92 (which is the atomic number of uranium)

In chemistry, transuranium elements (also known as transuranic elements) are the chemical elements with atomic numbers greater than 92.Of the elements with atomic numbers 1 to 92, all but four (technetium, promethium, astatine, and francium) occur in easily detectable quantities on earth, having stable, or very long half life isotopes, or are created as common products of the decay of uranium.All of the elements with higher atomic numbers, however, have been first discovered artificially, and other than plutonium and neptunium, none occur naturally on earth. They are all radioactive, with a half-life much shorter than the age of the Earth, so any atoms of these elements, if they ever were present at the earth's formation, have long since decayed. Trace amounts of neptunium and plutonium form in some uranium-rich rock, and small amounts are produced during atmospheric tests of atomic weapons. The Np and Pu generated are from neutron capture in uranium ore with two subsequent beta decays (²³⁸U → ²³⁹U → ²³⁹Np → ²³⁹Pu).
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An element with an atomic number higher than 92 (uranium's atomic number). Transuranium elements are unstable and occur in extremely low concentrations (if at all) in nature. Most are made artificially.