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1903 A. M. Clerke Probl. Astrophysics 93 A helium-envelope surrounds the sun to a depth of five thousand miles.

1903 A. M. Clerke Probl. Astrophysics 94 Now that the helium-spectrum has been unravelled.

1920 Discovery Apr. 111/1 Helium determinations never can provide data for more than a minimum estimate [of the age of a mineral]. All that the helium-ratio can tell us is that the age of the mineral to which it refers is greater than a certain minimum value.

1926 R. W. Lawson tr. G. von Hevesy & F. A. Paneth Man. Radioactivity xxvi. 216 (heading) Age determination from the helium content.

1938 R. W. Lawson tr. G. von Hevesy & F. A. Paneth Man. Radioactivity (ed. 2) xxv. 267/2 When the ‘helium method’ was first applied to minerals, it gave values for the age which were mostly only about one-half or one-third of the values found by the ‘lead method’.

1940 Chambers's Techn. Dict. 409/1 Helium diving bell, a diving bell in which the nitrogen in the compressed-air is replaced by helium, thus reducing tendency to the bends.

1953 Gloss. Terms Nucl. Sci. (National Res. Council (U.S.)) i. 2/2 If the age is calculated from the relative number of atoms of a stable radiogenic end product and radioactive parent present, the method is designated by the name of the endproduct [sic]. Examples are the lead age and helium age of a uranium-containing and (or) thorium-containing mineral.

1956 A. H. Compton Atomic Quest iii. 163 The only plans for a production plant..were those of Moore's helium-cooled reactor.

1957 Technology Mar. 14/2 In the hydrogen bomb the energy generated is derived from the fusion of hydrogen atoms into helium atoms.

1958 F. E. Zeuner Dating Past (ed. 4) 329 Were there not certain difficulties connected with the gaseous nature of helium, age estimates could be carried out with the helium generated by radioactive substances just as well as with the lead. The amount of helium present is determined and compared with the amount of uranium (and thorium) contained in the mineral, in other words, the helium-ratio is determined.

1958 F. E. Zeuner Dating Past (ed. 4) 427 A sample of magnetite from Larder Lake District..has yielded a helium-age of 2,400 million years.

1960 Nature 24 Sept. 1077/1 At the meeting of the International Committee of Weights and Measures held in Sevres, during September 29–October 3, 1958, the recommendation was adopted that the ‘1958 Helium-4 Vapour Pressure Scale of Temperatures’..should be used as the international standard scale of temperature between 1° and 5·2°K.