| 释义 |
‖ thorium Chem.|ˈθɔərɪəm|
[f. Thor, the Norse deity + -ium in other names of metals.
So named by its discoverer Berzelius 1828–9: see Kongl. Vetenskaps-Acad. Handlingar 1829, p. 1. The French having called the earth thorine (see thorina) named the metal thorinum, which prevailed also in England for many years.]
1. A rare metallic element discovered by Berzelius in the mineral thorite, and subsequently found in small quantities in some other rare minerals. Symbol Th. Also attrib.
Now noted as one of the radio-active elements.
1832Encycl. Brit. (ed. 7) VI. 401/2 Thorina, which constitutes an oxide of thorium, has been hitherto found only in a black mineral.., thorite. Ibid. 402/1 The only known compound of thorium and oxygen is thorina. 1868Watts Dict. Chem. V. 785 Thorinum, or Thorium. Atomic Weight, 115·72; Symbol, Th. 1881Ibid. VIII. 1967 Thorium..is not isomorphous with any other known element. Ibid., Thorium Oxide [ThO2]..Chloride [ThCl4]..Nitrate..Sulphate [etc.]. 1898Sir W. Crookes Addr. Brit. Assoc. 24 Rays..emitted by thorium and its compounds. The thorium rays affect photographic plates through screens of paper or aluminium, and are absorbed by metals and other dense bodies. 1903Daily Chron. 27 Nov. 8/3 He [Sir W. Ramsay] pointed out that the thorium emanations were an ephemeral gas which in two minutes ceased to exist. 1907Athenæum 31 Aug. 244/2 Thorium..gives no fewer than seven radio-active products, in the following order: mesothorium, radiothorium, thorium X, thorium emanation, and thorium A, B, and C.
2. Special Combs.: thorium lead, (a) the isotope lead 208, which is the final decay product of the series of radioactive transformations beginning with the common isotope of thorium; (b) used attrib. (with hyphen) to designate a method of isotopic dating, and results obtained with it, based upon measurement of the relative amounts in rock of thorium 232 and its ultimate decay product, lead 208; thorium series, the series of isotopes produced by the radioactive decay of thorium 232 (the major natural isotope), each member resulting from the decay of the previous one.
1914Phil. Mag. XXVIII. 827 It may be concluded with reasonable certainty [though erroneously] that thorium lead is unstable. 1946F. E. Zeuner Dating Past x. 319 The thorium-family begins with the element thorium (atomic weight 232). In the course of its disintegration, 6 atoms of helium are given off, and thorium-lead remains. 1955Bull. Amer. Geol. Soc. LXVI. 1141/2 The low thorium-lead age for the zircon could have been the result of addition of thorium to the mineral. Ibid., The analysis..demonstrates that small amounts of uranium lead and major amounts of thorium and thorium lead are very loosely bound, chemically. 1971I. G. Gass et al. Understanding Earth ii. 46/1 (heading) Uranium-lead.., lead-lead..and thorium-lead..methods.
1913Chem. News 28 Feb. 97/2 The parent of ionium, the product in the uranium series corresponding with radio-thorium in the thorium series, is still experimentally unknown. 1955I. Kaplan Nucl. Physics x. 207 In the actinium and thorium series, the mass numbers are given by the expressions 4n + 3 and 4n, respectively. 1973J. Yarwood Atomic & Nucl. Physics viii. 246 There are three main series of radioactive elements: the uranium, thorium, and actinium series, leaving out, for the present, the comparatively recently discovered neptunium series. |