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Lawrencium is a synthetic chemical element with chemical symbol Lr (formerly Lw) and atomic number 103. It is named in honor of Ernest Lawrence, inventor of the cyclotron, a device that was used to discover many artificial radioactive elements. A radioactive metal, lawrencium is the eleventh transuranic element and is also the final member of the actinide series. Like all elements with atomic number over 100, lawrencium can only be produced in particle accelerators by bombarding lighter elements with charged particles. Eleven isotopes of lawrencium are currently known; the most stable is 262Lr with a half-life of 3.6 hours, but the shorter-lived 260Lr (half-life 2.7 minutes) is most commonly used in chemistry because it can be produced on a larger scale. A new isotope, 266Lr, with a half-life of 11 hours has been reported but not confirmed. Chemistry experiments have confirmed that lawrencium indeed behaves as a heavier homolog to lutetium in the periodic table, and is a trivalent element. It thus could also be classified as the first of the 7th-period transition metals: however, its electron configuration is anomalous for its position in the periodic table, having an s2p configuration instead of the s2d configuration of its homolog lutetium. This means that lawrencium may be less volatile than expected for its position in the periodic table and have a volatility comparable to that of lead. In the 1950s, 1960s, and 1970s, many claims of the synthesis of lawrencium of varying quality were made from laboratories in the Soviet Union and the United States. The priority of the discovery and therefore the naming of the element was disputed between Soviet and American scientists, and while the International Union of Pure and Applied Chemistry (IUPAC) established lawrencium as the official name for the element and gave the American team credit for the discovery, this was reevaluated in 1997, giving both teams shared credit for the discovery but not changing the element's name. ==History== In 1958, scientists at the Lawrence Berkeley National Laboratory claimed the discovery of element 102, now called nobelium. At the same time, they also attempted to synthesize element 103 by bombarding the same curium target used with nitrogen-14 ions. A follow-up on this experiment was not performed, as the target was destroyed. Eighteen tracks were noted, with decay energy around (9 ± 1) MeV and half-life around s; the Berkeley team noted that while the cause could be the production of an isotope of element 103, other possibilities could not be ruled out. While the data agrees reasonably with that later discovered for 257Lr (alpha decay energy 8.87 MeV, half-life 0.6 s), the evidence obtained in this experiment fell far short of the strength required to conclusively demonstrate the synthesis of element 103.〔 (Note: for Part I see Pure Appl. Chem., Vol. 63, No. 6, pp. 879–886, 1991)〕 Later, in 1960, the Lawrence Berkeley Laboratory attempted to synthesize the element by bombarding 252Cf with 10B and 11B. The results of this experiment were not conclusive.〔 The first important work on element 103 was carried out at Berkeley by the nuclear-physics team of Albert Ghiorso, Torbjørn Sikkeland, Almon Larsh, Robert M. Latimer, and their co-workers on February 14, 1961. The first atoms of lawrencium were reportedly produced by bombarding a three-milligram target consisting of three isotopes of the element californium with boron-10 and boron-11 nuclei from the Heavy Ion Linear Accelerator (HILAC). The Berkeley team reported that the isotope 257103 was detected in this manner, and that it decayed by emitting an 8.6 MeV alpha particle with a half-life of (8 ± 2) s.〔 This identification was later corrected to be 258103,〔 as later work proved that 257Lr did not have the properties detected, but 258Lr did.〔 This was considered at the time to be convincing proof of the synthesis of element 103: while the mass assignment was less certain and proved to be mistaken, it did not affect the arguments in favor of element 103 having been synthesized. Scientists at the Joint Institute for Nuclear Research in Dubna (then in the Soviet Union) raised several criticisms: all but one were answered adequately. The exception was that 252Cf was the most common isotope in the target, and in the reactions with 10B, 258Lr could only have been produced by emitting four neutrons, and emitting three neutrons was expected to be much less likely than emitting four or five. This would lead to a narrow yield curve, not the broad one reported by the Berkeley team. A possible explanation was that there was a low number of events attributed to element 103.〔 This was an important intermediate step to the unquestioned discovery of element 103, although the evidence was not completely convincing.〔 The Berkeley team proposed the name "lawrencium" with symbol "Lw", after Ernest Orlando Lawrence, inventor of the cyclotron. The IUPAC Commission on Nomenclature of Inorganic Chemistry accepted the name, but changed the symbol to "Lr". This acceptance of the discovery was later characterized as being hasty by the Dubna team.〔 : + → → + 5 The first work at Dubna on element 103 came in 1965, when they reported to have created 256103 in 1965 by bombarding 243Am with 18O, identifying it indirectly from its granddaughter fermium-252. The half-life they reported was somewhat too high, possibly due to background events. Later 1967 work on the same reaction identified two decay energies in the ranges 8.35–8.50 MeV and 8.50–8.60 MeV: these were assigned to 256103 and 257103.〔 Despite repeated attempts, they were unable to confirm assignment of an alpha emitter with a half-life of eight seconds to 257103. The Russians proposed the name "rutherfordium" for the new element in 1967:〔 this name was later used for element 104. : + → → + 5 Further experiments (Dubna 1969; Berkeley 1970) demonstrated an actinide chemistry for the new element, so by 1970 it was known that lawrencium is the last actinide.〔 In 1970, the Dubna group reported the synthesis of 255103 with half-life 20 s and alpha decay energy 8.38 MeV.〔 However, it was not until 1971, when the nuclear physics team at the University of California at Berkeley successfully performed a whole series of experiments aimed at measuring the nuclear decay properties of the lawrencium isotopes with mass numbers from 255 through 260,〔Silva, pp. 1641–2〕 that all previous results from Berkeley and Dubna were confirmed, apart from the Berkeley's group initial erroneous assignment of their first produced isotope to 257103 instead of the probably correct 258103.〔 All final doubts were finally dispelled in 1976 and 1977 when the energies of X-rays emitted from 258103 were measured.〔 In 1971, the IUPAC granted the discovery of lawrencium to the Lawrence Berkeley Laboratory, even though they did not have ideal data for the element's existence. However, in 1992, the IUPAC Trans-fermium Working Group (TWG) officially recognized the nuclear physics teams at Dubna and Berkeley as the co-discoverers of lawrencium, concluding that while the 1961 Berkeley experiments were an important step to lawrencium's discovery, they were not yet completely convincing; and while the 1965, 1968, and 1970 Dubna experiments came very close to the needed level of confidence taken together, only the 1971 Berkeley experiments, which clarified and confirmed previous observations, finally resulted in complete confidence in the discovery of element 103.〔〔 Because the name "lawrencium" had been in use for a long time by this point, it was retained by IUPAC,〔 and in August 1997, the International Union of Pure and Applied Chemistry (IUPAC) ratified the name lawrencium and the symbol "Lr" during a meeting in Geneva.〔 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「Lawrencium」の詳細全文を読む スポンサード リンク
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