In
chemistry,
transuranium elements (also known as
transuranic elements) are the
chemical elements with
atomic numbers greater than 92 (the atomic number of
uranium). None of these elements are stable; they
decay radioactively into other elements.
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).
Those that can be found on earth now are artificially generated synthetic elements, via nuclear reactors or particle accelerators. The half lives of these elements show a general trend of decreasing with atomic number. There are exceptions, however, including dubnium and several isotopes of curium. Further anomalous elements in this series have been predicted by Glenn T. Seaborg, and are categorised as the “island of stability.”
