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 in the laboratory, 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.”
Heavy transuranic elements are difficult and expensive to
produce, and their prices go up rapidly with atomic number.
As of 2008, weapons-grade plutonium cost around $4,000/gram
(or roughly 150 times more than gold),[1] and californium
cost $60,000,000/gram.[2] Due to production difficulties,
none of the elements beyond californium have industrial
applications or were ever produced in macroscopic
quantities.
Transuranic elements that have not been discovered, or have
been discovered but are not yet officially named, use
IUPAC's systematic element names. The naming of transuranic
elements is a source of controversy.
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