transuranium elements

transuranium elements, in chemistry, radioactive elements with atomic numbers greater than that of uranium (at. no. 92). All the transuranium elements of the actinide series were discovered as synthetic radioactive isotopes at the Univ. of California at Berkeley or at Argonne National Laboratory; in order of increasing atomic number they are neptunium, plutonium, americium, curium, berkelium, californium, einsteinium, fermium, mendelevium, nobelium, and lawrencium. Of these only neptunium and plutonium occur in nature; they are produced in minute amounts in the radioactive decay of uranium.

Much of the study of the transuranium elements has taken place at the Lawrence Berkeley National Laboratory (at Berkeley, Calif.) and at the Joint Institute for Nuclear Research in Dubna, Russia; workers at both locations share credit for the independent discovery of rutherfordium, dubnium, and seaborgium (at. no. 104 through 106), which are the first three transactinide elements. A German team at the Institute for Heavy Ion Research at Darmstadt discovered bohrium, hassium, meitnerium, darmstadtium, roentgenium, and copernicium (at. no. 107 through 112). Researchers at Japan's RIKEN Linear Accelerator Facility in Wako have been credited with the discovery of nihonium (at. no. 113). The Dubna laboratory, with assistance from Lawrence Livermore National Laboratory, Calif., synthesized flerovium, moscovium, livermorium, and oganesson (at. no. 114 through 116 and 118); and, with assistance from Vanderbilt Univ. and the Oak Ridge National Laboratory, Tenn., tennessine (at. no. 117). The Berkeley team claimed to have produced livermorium and oganesson, but later retracted the claim for after other laboratories failed to reproduce Berkeley's results and a reanalysis of their data did not show the production of the element.

Up to and including fermium (at. no. 100), the transuranium elements are produced by the capture of neutrons; the transfermium elements are synthesized by the bombardment of transuranium targets with light particles or, more recently, by projecting medium-weight elements at targets of other medium-weight elements (see also synthetic elements).

Isotopes of the transuranium elements are radioactive because their large nuclei are unstable, and the transactinide, or superheavy, elements in particular have very short half-lives. However, on the basis of theories of nuclear structure, physicists have predicted that certain transactinide elements may have relatively stable isotopes. For example, an isotope of flerovium with mass number 298 (comprising 114 protons and 184 neutrons) should be very stable and resemble lead in its chemical properties. However, the three isotopes of flerovium that are claimed to have been synthesized have fewer than the requisite 184 neutrons.

See G. T. Seaborg and W. D. Loveland, The Elements beyond Uranium (1990); L. R. Morss and J. Fuger, ed., Transuranium Elements (1992); G. T. Seaborg and A. Ghiorso, The Transuranium People (1999).

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