| 释义 |
radio-ˈcarbon
Also radiocarbon.
[f. radio- 3 b + carbon.]
1. A radioactive isotope of carbon; spec. = carbon 14, which is formed in trace amounts by the effect of cosmic rays on atmospheric nitrogen. Also ellipt. for radio-carbon dating.
1940Physical Rev. LVII. 549/2 Large quantities of nitrogenous material have been exposed to neutrons for several months and will be shortly worked up for radio-carbon. 1946Ibid. LXIX. 672/1 The purpose of this letter is to..suggest that radiocarbon might be found in living matter especially in connection with the concentration of C13 for tracer uses. 1956W. F. Albright Archaeol. of Palestine (rev. ed.) i. 22 Radiocarbon has a ‘half life’ of some 5,600 years, and the count loses any significance beyond 25,000–30,000 years ago. 1957Times 11 Sept. 6/2 Recent studies using radiocarbon indicated that the yield of photosynthesis by the plankton of the oceans was at least equal to that of the land flora, and might be several times greater. 1963G. M. B. Dobson Exploring Atmosphere i. 12 The radio⁓carbon formed in the upper atmosphere becomes radio⁓carbon dioxide and is gradually mixed throughout the whole atmosphere. 1970Nature 4 Apr. 45/1 The chronology of several glacial stages has been recognized in the microfossils and dated by radiocarbon. 1976P. L. Brown Planet Earth iii. 77 Radiocarbon then combines with oxygen to form C14O2 which is diffused through the atmosphere and then is absorbed by plants via photosynthesis and ultimately by all living things.
2. attrib. and Comb. (usu. with reference to radio-carbon dating), as radio-carbon age, radio-carbon content, radio-carbon method, radio-carbon year, etc.; radio-carbon dating, a method of isotopic dating which is applicable to dead organic matter and in which the proportion of carbon 14 (which has decreased at a known rate since the death of the sample material), is measured and compared with the known natural abundance of the isotope; hence radio-carbon date; radio-carbon-dated ppl. adj.
1949Antiquity XXIII. 113 A method of dating dead pieces of formerly living substances (such as wood and bone) by means of their radiocarbon content. 1949Science 23 Dec. 679/2 These results indicate that the two basic assumptions of the radiocarbon age determination method—namely, the constancy of the cosmic radiation intensity and the possibility of obtaining unaltered samples—are probably justified for wood up to 4600 years. 1950Arnold & Libby (title) Radiocarbon dates. 1951Amer. Jrnl. Sci. CCXLIX. 257 (heading) Radiocarbon dating of Late-Pleistocene events. Ibid., All of the dates are of the right order of magnitude, with a few exceptions where it seems likely that the stratigraphic position of the sample, and not the radio⁓carbon age, has been incorrectly given. Ibid. 268 The radio⁓carbon date, 12,148 {pm} 700 years. 1956M. Wheeler in A. Pryce-Jones New Outl. Mod. Knowl. 399 A radio-carbon dating gives 7538 b.c. (with a possible error {pm} of 350 years) for the settlement. 1957G. E. Hutchinson Treat. Limnol. I. i. 8 The dating of the events, based primarily on the varve chronology, is in fair accord with the radio-carbon chronology. 1963D. W. & E. E. Humphries tr. Termier's Erosion & Sedimentation iii. 55 (caption) Old peat deposits (radio⁓carbon-dated to the Early Holocene) dot the area ‘drowned’ by the Flandrian transgression. 1966Radiocarbon VIII. 534 The result of a radiocarbon determination is commonly expressed as an age given in radiocarbon years. Ibid., The conversion of a radiocarbon age..to a true calendar year makes necessary certain assumptions with respect to: (1) the half-life of C14, (2) the production rate of C14 by cosmic rays, (3) the size of reservoirs into which C14 is distributed and the exchange rate of this distribution. 1973Nature 1 June 266/1 Three radiocarbon laboratories, at La Jolla, Philadelphia and Tucson, have obtained radiocarbon dates over the past decade for specimens of bristlecone pine already dated dendrochronologically, thereby allowing the ‘correction’ of the radiocarbon scale. 1973Nation Rev. (Melbourne) 31 Aug. (Suppl.) 2/3 Until 1972 only two radio⁓carbon-dated remains of Chinese origin were known. 1978New Scientist 2 Mar. 599/2 The dating of carbon in glacier varves would extend the calibration of the radiocarbon dating curve. |