Ununseptium

Ununseptium
Ununseptium is the temporary name of a superheavy artificial chemical element with temporary symbol Uus and atomic number 117. Six atoms were detected by a joint Russia–US collaboration at Dubna, Moscow Oblast, Russia, in November 2010.[1][2] Although it is currently placed as the heaviest member of the halogen family, there is no experimental evidence that the chemical properties of ununseptium match those of the lighter members like iodine or astatine and theoretical analysis suggests there may be some notable differences.

Discovery of Ununseptium
Author: Dr. Doug Stewart In 2009, the first atoms of element 117 were made in the Flerov Laboratory of Nuclear Reactions in Dubna, Russia. Evidence of the synthesis was published in April 2010, by scientific teams from Russia and the United States of America. The research effort, led by Yuri Oganessian, was a collaboration between the Joint Institute of Nuclear Research (Dubna, Russia); the Research Institute for Advanced Reactors, Dimitrovgrad; Lawrence Livermore National Laboratory; Oak Ridge National Laboratory; Vanderbilt University, Tennessee; and the University of Nevada, Las Vegas. The discovery has not yet been verified by IUPAC. Ununseptium's place in the periodic table is unofficial until IUPAC validates its existence. Ununseptium was made by a fusion reaction of element 20 with element 97: calcium-48 with berkelium-249. Calcium ions were formed into a beam in a cyclotron (a particle accelerator) and fired at a target layer of berkelium deposited 300 nm thick on titanium foil. The first bombardment lasted 70 days. The berkelium was bombarded with over 7 trillion calcium-48 ions per second, accelerated to about 10% of the speed of light. The data suggest five nuclei of interest were produced during the 70 day bombardment. As a consequence of the high energy of the impacts that created them, these nuclei instantly lost thermal energy by emitting four neutrons to form ununseptium-293. The ununseptium-293 (approximate half-life 14 ms) decayed by alpha emission into element 115 (ununpentium). In a second bombardment lasting 50 days, the speed of the bombarding calcium-48 ions was reduced. The resulting impacts were of lower energy and the single nucleus of interest that formed needed to emit just three neutrons to lose its excess energy, leading to the heavier ununseptium-294 isotope. The data suggest one atom of ununseptium-294 (approximate half-life 78 ms) was formed in the bombardment, decaying again to element 115. As a result of its position in Group 17 of the periodic table, ununseptium is expected to have chemical properties characteristic of the halogens. The effects of relativistic electrons, however, may result in partial metalloid properties. Too little of the element has been synthesized for its chemical properties to be confirmed. Jim Roberto from Oak Ridge said: "New isotopes observed in these experiments continue a trend toward higher lifetimes for increased neutron numbers, providing evidence for the proposed 'island of stability' for super-heavy nuclei." The joint teams at JINR in Dubna and Lawrence Livermore in California have published evidence for the synthesis of elements 113, 114, 115, 116, 117 and 118. IUPAC has accepted the discoveries of element 114 (flerovium/ununquadium) and element 116 (livermorium/ununhexium). It has not yet considered the evidence for the discovery of element 117 (ununseptium). IUPAC requires stronger evidence before it will confirm the synthesis of element 113 (ununtrium), element 115 (ununpentium), or element 118 (ununoctium).



Theoretical calculations in a quantum tunneling model with mass estimates from a macroscopic-microscopic model predict the alpha-decay half-lives of isotopes of ununseptium (namely, 289–303Uus) to be around 0.1–40 ms.[11home][12home][13home]