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Ångström (unit)|ɔːŋstrœm|
Also angstrom |ˈæŋstrəm|.
[The name of A. J. Ångström (1814–74), a Swedish physicist.]
A hundred-millionth of a centimetre (10-8 cm.), used in measuring the wavelengths of light, X-rays, etc. (also called absolute Ångström); the same unit used as a measure of the thickness of thin film. Abbrev. Å, Å.U.; also A.U.
The International Ångström (I.Å.) was defined in 1907 in terms of the wavelength of cadmium which in standard conditions is 6438·4696 I.Å. When the metre was defined in terms of the wavelength of krypton in 1960 the Ångström became exactly equal to 10-8 cm.
[1887Phil. Mag. XXIII. 258 As all observers so far seem to accept the measures of Ångström, I have decided that a table of my results would be of value.] 1892Nature 29 Sept. 513/1 This width.. is ·04 of an Ångström or Rowland unit..in the yellow part of the spectrum. 1897Rep. Brit. Assoc. Advancem. Sci. 556 No lines were found to shift more than a fraction..of an Ångström unit. 1906Trans. Internat. Union Solar Research I. viii. 230 Resolutions concerning standards of Wave-length. The wave-length of a suitable spectroscopic line shall be taken as the primary standard of wave-length. The number which defines the wave-length of this line shall be fixed permanently and thereby define the unit in which all wave-lengths are to be measured. This unit shall differ as little as possible from 10-10 metres and be called the Ångström. 1911Kaye & Laby Phys. & Chem. Constants 9, 1 Å.U. = 10-10 metre. 1916Allen & Moore Text-Bk. Pract. Physics iii. vii. 300 Ångström Units (A.U.). 1921Discovery Sept. 226 An X-ray of wave length equal to two-tenths of an Ångström Unit (100-millionth of a centimetre). 1933S. W. Cole Pract. Phys. Chem. (ed. 9) x. 255 Ångström units (Å or A.U.). 1943A. E. Mirsky in Nord & Werkman Advances in Enzymology III. 18 Histone spreads to give a film 7–9 Å thick. 1951Engineering 18 May 589/1 Dr. J. S. Courtney-Pratt has used interferometric methods to study the uniformity and thickness of thin films... He was able to measure the thickness correct to the nearest Ångstrom. 1957Technology July 168/4 Those [fluorescing agents] emitting a visible blue light in the 4,000–4,400 angstrom range are commercially useful in detergents. 1957H. Barrell in Nature 21 Dec. 1388/1 The value λR = 6438·4696 A. was adopted as the spectroscopic reference standard in 1907 and thereby became the means of defining the international angstrom—the unit that has since served for all spectroscopic measurements of wave-length. |