dubnium

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dubnium

(do͞ob`nēəm), artificially produced radioactive chemical element; symbol Db; at. no. 105; mass number of most stable isotope 268; m.p., b.p., and sp. gr. unknown; valence +5. Situated in Group 5 of the periodic tableperiodic table,
chart of the elements arranged according to the periodic law discovered by Dmitri I. Mendeleev and revised by Henry G. J. Moseley. In the periodic table the elements are arranged in columns and rows according to increasing atomic number (see the table entitled
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, it has properties similar to those of niobiumniobium
, metallic chemical element; symbol Nb; at. no. 41; at. wt. 92.90638; m.p. about 2,468°C;; b.p. 4,742°C;; sp. gr. 8.57 at 20°C;; valence +2, +3, +4, or +5.
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 and tantalumtantalum
[from Tantalus], metallic chemical element; symbol Ta; at. no. 73; at. wt. 180.94788; m.p. 2,996°C;; b.p. 5,400±100°C;; sp. gr. 16.65 at 20°C;; valence +2, +3, +4, or +5.
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 Dubnium-268, the most stable istotope, has a half-life of 1.2 days.

In 1968 a Soviet team led by G. N. Flerov at the Joint Institute for Nuclear Research at Dubna announced the discovery of element 105. They claimed that in 1967 they had isolated isotopes with mass numbers 260 and 261 and half-liveshalf-life,
measure of the average lifetime of a radioactive substance (see radioactivity) or an unstable subatomic particle. One half-life is the time required for one half of any given quantity of the substance to decay.
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 of 0.1 sec and 3 sec, respectively, by bombarding americium-243 atoms with neon-22 ions. In 1970 the same team announced that by using the same americium and neon isotopes but a different detection technique they had created an isotope of element 105 with mass number 261 and a half-life of 2 sec; they suggested that element 105 be named nielsbohrium to honor the Danish physicist Niels BohrBohr, Niels Henrik David
, 1885–1962, Danish physicist, one of the foremost scientists of modern physics. He studied at the Univ. of Copenhagen (Ph.D. 1911) and carried on research on the structure of the atom at Cambridge under Sir James J.
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. In 1970, an American research team led by A. Ghiorso at the Lawrence Berkeley National Laboratory announced that, while they had been unable to confirm the Dubna group's results, they had synthesized an isotope of element 105 by another route. They bombarded californium-249 atoms with nitrogen-15 ions to create an isotope with mass number 260 and a half-life of 1.6 sec. Disputing the Soviet claim of discovery, the Americans suggested the name hahnium to honor the German chemist and physicist Otto HahnHahn, Otto
, 1879–1968, German chemist and physicist. His important contributions in the field of radioactivity include the discovery of several radioactive substances, the development of methods of separating radioactive particles and of studying chemical problems by the
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.

An international committee set up to resolve such disputes decided in 1992 that the Berkeley and Dubna laboratories should share credit for the discovery. The syntheses of at least nine isotopes of dubnium, with half-lives ranging from 1.2 sec (Db-259) to 34 sec (Db-262), have been confirmed. In 1994 a committee of the International Union of Pure and Applied Chemistry (IUPAC), convened to resolve naming disputes for the transactinide elementstransactinide elements
, in chemistry, elements with atomic numbers greater than that of lawrencium (at. no. 103), the last member of the actinide series. See transuranium elements.
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, recommended that element 105 be named joliotium, symbol Jl, after the French physicist Frédéric Joliot-CurieJoliot-Curie
, French scientists who were husband and wife. Frédéric Joliot-Curie , 1900–1958, formerly Frédéric Joliot, and Irène Joliot-Curie , 1897–1956, daughter of Pierre and Marie Curie, were married in 1926.
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. In 1997 the name dubnium was accepted internationally for element 105, in recognition of the pioneering work done at the Dubna laboratory.

See also synthetic elementssynthetic elements,
in chemistry, radioactive elements that were not discovered occurring in nature but as artificially produced isotopes. They are technetium (at. no. 43), which was the first element to be synthesized, promethium (at. no. 61), astatine (at. no.
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; transuranium elementstransuranium elements,
in chemistry, radioactive elements with atomic numbers greater than that of uranium (at. no. 92). All the transuranium elements of the actinide series were discovered as synthetic radioactive isotopes at the Univ.
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.

dubnium

[′düb·nē·əm]
(chemistry)
A chemical element, symbolized Db, atomic number 105, a synthetic element; the thirteenth transuranium element.

dubnium

a synthetic transactinide element produced in minute quantities by bombarding plutonium with high-energy neon ions. Symbol: Du; atomic no. 105