UNNILPENTIUM

(UNP) also called element 105, hahnium, or nielsbohrium an artificially produced radioactive transuranium element in Group Vb of the periodic table. The discovery of unnilpentium, like that of unnilquadium (element 104), has been a matter of dispute between Soviet and American scientists. The Soviets may have synthesized a few atoms of element 105 in 1967 at the Joint Institute for Nuclear Research in Dubna, Russia, U.S.S.R., by bombarding americium-243 with neon-22 ions, producing isotopes of element 105 having mass numbers of 260 and 261 and half-lives of 0.1 second and 3 seconds, respectively. Because the Dubna group did not propose a name for the element at the time they announced their preliminary dataa practice that has been customary following the discovery of a new elementit was surmised by American scientists that the Soviets did not have strong experimental evidence to substantiate their claims. Soviet scientists contended, however, that they did not propose a name in 1967 because they preferred to accumulate more data about the chemical and physical properties of the element before doing so. After completing further experiments, they proposed the name nielsbohrium. In 1970 a group of investigators at the Lawrence Radiation Laboratory of the University of California at Berkeley announced that they had synthesized isotope 260 of element 105, whereupon they proposed the name hahnium for the element, in honour of Otto Hahn, the discoverer of nuclear fission. The American team could not duplicate the Soviet experiment; but, when its members bombarded californium-249 with the nuclei of nitrogen-15 atoms, they produced hahnium-260, which had a half-life of about 1.6 seconds. As further evidence of their discovery, the scientists at Berkeley measured the amount of energy emitted by hahnium-260 as it decayed, as well as the elements produced in the process; these characteristics were quite different from those of previously known elements in the periodic system. The International Union of Pure and Applied Chemistry recommended that the element be named unnilpentium. atomic number 105 mass of most stable isotope 260 electronic configuration 2-8-18-32-32-11-2or (Rn)5f 146d37s2