Transactinide Elements
Transactinide Elements, chemical elements with an atomic number greater than 103. They are called transactinide (meaning beyond actinide) elements because they have atomic numbers greater than those of the elements of the actinide series.
Transactinide elements are not known to exist in nature. Eleven transactinide elements have been produced artificially by using particle accelerators to project a beam of ions against materials composed of such elements as californium or bismuth. When moving at the proper speed, the nuclei of some of the ions combine with the nuclei of atoms of the target material, forming atoms of a transactinide element. All the known transactinide elements are radioactive, with half-lives ranging from a fraction of a second to a few minutes. More than one isotope has been produced for most of these elements.
The production of transactinide elements has been carried out chiefly at the University of California at Berkeley, the Joint Institute for Nuclear Research at Dubna in Russia, and the Heavy Ion Research Laboratory at Darmstadt in Germany. Controversy and uncertainty have surrounded the discovery of many of the transactinide elements because the production of the elements is difficult and their presence is usually deduced from indirect evidence.