tennessine tĕnˈəsēn [key], artificially produced radioactive chemical element; symbol Ts; at. no. 117; mass number of most stable isotope 294; m.p., b.p., sp. gr., and valence unknown. Tennessine is a member of Group 17 of the periodic table, the halogens, and may have properties similar to astatine.

In 2010 scientists from the Joint Institute for Nuclear Research in Dubna, Russia, announced that they had bombarded (2009) berkelium-249 atoms with calcium-48 ions to create two forms of tennessine. The Ts-294 isotope, with a half-life of 78 milliseconds, decayed through alpha-particle emission into dubnium (element 105), while the lighter Ts-293, with a half-life of 14 milliseconds, decayed down to roentgenium (element 111). The Russian researchers collaborated with American scientists at Vanderbilt Univ. and the Oak Ridge National Laboratory, which produced the berkelium used in the experiment. In 2015 the International Union of Pure and Applied Chemistry (IUPAC) confirmed the discovery. In 2016 the element's discoverers proposed the name tennessine, to honor the home state of the American collaborators, and the name was approved by IUPAC later that year.

See also synthetic elements; transactinide elements; transuranium elements.

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