Transuranium element

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.

Overview

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, other than neptunium and plutonium. 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/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.

Discovery and naming of transuranium elements

The majority of the transuranium elements were produced by three groups:

A group at the University of California, Berkeley, under three different leaders:
- Edwin Mattison McMillan, first to produce a transuranium element:
  - 93. neptunium, Np, named after the planet Neptune, as it follows uranium and Neptune follows Uranus in the planetary sequence (1940).
- Glenn T. Seaborg, next in order, who produced:
  - 94. plutonium, Pu, named after the dwarf planet Pluto, following the same naming rule as it follows neptunium and Pluto follows Neptune in the pre-2006 planetary sequence (1940).
  - 95. americium, Am, named because it is an analog to europium, and so was named after the continent where it was first produced (1944).
  - 96. curium, Cm, named after Pierre and Marie Curie, famous scientists who separated out the first radioactive elements (1944).
  - 97. berkelium, Bk, named after the city of Berkeley, where the University of California, Berkeley is located (1949).
  - 98. californium, Cf, named after the state of California, where the university is located (1950).
- Albert Ghiorso, who had been on Seaborg's team when they produced curium, berkelium, and californium, took over as director to produce:
  - 99. einsteinium, Es, named after the theoretical physicist Albert Einstein (1952).
  - 100. fermium, Fm, named after Enrico Fermi, the physicist who produced the first controlled chain reaction (1952).
  - 101. mendelevium, Md, named after the Russian chemist Dmitri Mendeleev, credited for being the primary creator of the periodic table of the chemical elements (1955).
  - 102. nobelium, No, named after Alfred Nobel (1956).
  - 103. lawrencium, Lr, named after Ernest O. Lawrence, a physicist best known for development of the cyclotron, and the person for whom the Lawrence Livermore National Laboratory and the Lawrence Berkeley National Laboratory (which hosted the creation of these transuranium elements) are named (1961).

A group at the Joint Institute for Nuclear Research in Dubna, Russia (then the Soviet Union) who produced:
- 104. rutherfordium, Rf, named after Ernest Rutherford, who was responsible for the concept of the atomic nucleus (1966).
- 105. dubnium, Db, an element that is named after the city of Dubna, where the JINR is located. Also known in Western circles as "hahnium" in honor of Otto Hahn (1968).
- 106. seaborgium, Sg, named after Glenn T. Seaborg. This name caused controversy because Seaborg was still alive, but eventually became accepted by international chemists (1974).
- 107. bohrium, Bh, named after the Danish physicist Niels Bohr, important in the elucidation of the structure of the atom (1981).

A group at the Gesellschaft für Schwerionenforschung (Society for Heavy Ion Research) in Darmstadt, Hessen, Germany, under Peter Armbruster, who produced:
- 108. hassium, Hs, named after the Latin form of the name of Hessen, the German Bundesland where this work was performed (1984).
- 109. meitnerium, Mt, named after Lise Meitner, an Austrian physicist who was one of the earliest scientists to become involved in the study of nuclear fission (1982).
- 110. darmstadtium, Ds named after Darmstadt, Germany, the city in which this work was performed (1994).
- 111. roentgenium, Rg named after Wilhelm Conrad Röntgen, discoverer of X-rays (1994).
- 112. copernicium, Cn named after astronomer Nicolaus Copernicus (1996).

List of the transuranic elements

Actinides
- 93 neptunium Np
- 94 plutonium Pu
- 95 americium Am
- 96 curium Cm
- 97 berkelium Bk
- 98 californium Cf
- 99 einsteinium Es
- 100 fermium Fm
- 101 mendelevium Md
- 102 nobelium No
- 103 lawrencium Lr

Transactinide elements
- 104 rutherfordium Rf
- 105 dubnium Db
- 106 seaborgium Sg
- 107 bohrium Bh
- 108 hassium Hs
- 109 meitnerium Mt
- 110 darmstadtium Ds
- 111 roentgenium Rg
- 112 copernicium Cn
- 113 ununtrium Uut*
- 114 ununquadium Uuq*
- 115 ununpentium Uup*
- 116 ununhexium Uuh*
- 117 ununseptium Uus*
- 118 ununoctium Uuo*

*The existence of these elements has been confirmed, however the names and symbols given are provisional as no names for the elements have been agreed on.

Super-heavy atoms

Super-heavy atoms, (super heavy elements, commonly abbreviated SHE), are the transactinide elements beginning with rutherfordium (atomic number 104).^{[citation needed]} They have only been made artificially, and currently serve no useful purpose because their short half-lives cause them to decay after a few minutes to just a few milliseconds, which also makes them extremely hard to study.^[3]^[4]

Super-heavy atoms have all been created during the latter half of the 20th century and are continually being created during the 21st century as technology advances. They are created through the bombardment of elements in a particle accelerator, for example the nuclear fusion of californium-249 and carbon-12 creates rutherfordium. These elements are created in quantities on the atomic scale and no method of mass creation has been found.^[3]

References

^ "Price of Plutonium". The Physics Factbook.
^ Rodger C. Martin and Steven E. Kos. "Applications and Availability of Californium-252 Neutron Sources　for Waste Characterization" (pdf).
^ ^a ^b Heenen, P. H.; Nazarewicz, W. (2002). "Quest for superheavy nuclei". Europhysics News. 33: 5. doi:10.1051/epn:2002102.
^ Greenwood, N. N. (1997). "Recent developments concerning the discovery of elements 100-111". Pure and Applied Chemistry. 69: 179. doi:10.1351/pac199769010179.