dub·ni·um  (dōōb'nē-əm)  n. Symbol Db An artificially produced radioactive element with atomic number 105 whose most long-lived isotopes have mass numbers of 258, 261, 262, and 263 with half-lives of 4.2, 1.8. 34, and 30 seconds, respectively. Also called unnilpentium. See Table at element. [After Dubna, Russia, the location of the United Institute of Nuclear Research.] |
dubnium
an artificially produced radioactive transuranium element in Group Vb of the periodic table, atomic number 105. The discovery of dubnium (element 105), like that of rutherfordium (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 data-a practice that has been customary following the discovery of a new element-it 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.
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