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Hassium is a chemical element with symbol Hs and atomic number 108, named after the German state of Hesse. It is a synthetic element (an element that can be created in a laboratory but is not found in nature) and radioactive; the most stable known isotope, 269Hs, has a half-life of approximately 9.7 seconds, although an unconfirmed metastable state, 277mHs, may have a longer half-life of about 130 seconds. More than 100 atoms of hassium have been synthesized to date.〔 In the periodic table of the elements, it is a d-block transactinide element. It is a member of the 7th period and belongs to the group 8 elements. Chemistry experiments have confirmed that hassium behaves as the heavier homologue to osmium in group 8. The chemical properties of hassium are characterized only partly, but they compare well with the chemistry of the other group 8 elements. In bulk quantities, hassium is expected to be a silvery metal that reacts readily with oxygen in the air, forming a volatile tetroxide. ==History== The synthesis of element 108 was first attempted in 1978 by a Russian research team led by Yuri Oganessian and Vladimir Utyonkov at the Joint Institute for Nuclear Research (JINR) in Dubna, using reactions that would generate the isotopes hassium-270 and hassium-264. The data was uncertain and they carried out new experiments on hassium five years later, where these two isotopes as well as hassium-263 were produced; the hassium-264 experiment was repeated again and confirmed in 1984.〔 Hassium was officially discovered in 1984 by a German research team led by Peter Armbruster and Gottfried Münzenberg at the Institute for Heavy Ion Research (Gesellschaft für Schwerionenforschung) in Darmstadt. The team bombarded a target of lead-208 with accelerated nuclei of iron-58 to produce 3 atoms of the isotope hassium-265. Due to this issue, a controversy arose over who should be recognized as the official discoverer of the element. The IUPAC/IUPAP Transfermium Working Group (TWG) recognised the GSI collaboration as official discoverers in their 1992 report. They stated that the GSI collaboration was "more detailed and, of itself, carries conviction", and that while the combined data from Dubna and Darmstadt confirmed that hassium had been synthesized, the major credit was awarded to the GSI. This statement came in spite of the combined data also supporting the Russian 1983 discovery claim and the TWG also acknowledging that "very probably element 108 played a role in the Dubna experiment."〔〔 (Note: for Part I see Pure Appl. Chem., Vol. 63, No. 6, pp. 879–886, 1991)〕 The name ''hassium'' was proposed by Peter Armbruster and his colleagues, the officially recognised German discoverers, in 1992, derived from the Latin name (''Hassia'') for the German state of Hesse where the institute is located.〔 Using Mendeleev's nomenclature for unnamed and undiscovered elements, hassium should be known as ''eka-osmium''. In 1979, during the Transfermium Wars (but before the synthesis of hassium), IUPAC published recommendations according to which the element was to be called ''unniloctium'' (with the corresponding symbol of ''Uno''), a systematic element name as a placeholder, until the element was discovered (and the discovery then confirmed) and a permanent name was decided on. Although widely used in the chemical community on all levels, from chemistry classrooms to advanced textbooks, the recommendations were mostly ignored among scientists in the field, who either called it "element 108", with the symbol of ''(108)'' or even simply ''108'', or used the proposed name "hassium".〔 In 1994 a committee of IUPAC recommended that element 108 be named ''hahnium'' (Hn) after the German physicist Otto Hahn, after an older suggestion of ''ottohahnium'' (Oh)〔 in spite of the long-standing convention to give the discoverer the right to suggest a name, so that elements named after Hahn and Lise Meitner (meitnerium) would be next to each other, honoring their joint discovery of nuclear fission. This was because they felt that Hesse did not merit an element being named after it.〔 After protests from the German discoverers and the American Chemical Society, IUPAC relented and the name ''hassium'' (Hs) was adopted internationally in 1997.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hassium」の詳細全文を読む スポンサード リンク
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