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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Moseley's law ： ウィキペディア英語版 Moseley's law Moseley's law is an empirical law concerning the characteristic x-rays that are emitted by atoms. The law was discovered and published by the English physicist Henry Moseley in 1913. It is historically important in quantitatively justifying the conception of the nuclear model of the atom, with all, or nearly all, positive charges of the atom located in the nucleus, and associated on an integer basis with atomic number. Until Moseley's work, "atomic number" was merely an element's place in the periodic table, and was not known to be associated with any measureable physical quantity.〔e.g. 〕 Moseley was able to show that the frequencies of certain characteristic X-rays emitted from chemical elements are proportional to the square of a number which was close to the element's atomic number; a finding which supported van den Broek and Bohr's model of the atom in which the atomic number is the same as the number of positive charges in the nucleus of the atom. ==History== Following conversations in 1913 with Niels Bohr, a fellow worker in Ernest Rutherford's Cavendish laboratory, Moseley had become interested in the Bohr model of the atom, in which the spectra of light emitted by atoms is proportional to the square of Z, the charge on their nucleus (which had just been discovered two years before). Bohr's formula had worked well to give the previously known Rydberg formula for the hydrogen atom, but it was not known then if it would also give spectra for other elements with higher Z numbers, or even precisely what the Z numbers (in terms of charge) for heavier elements were. In particular, only two years earlier, Rutherford in 1911 had postulated that Z for gold atoms might be about half of its atomic weight, and only shortly afterward, Antonius van den Broek had made the bold suggestion that Z was not half of the atomic weight for elements, but instead was exactly equal to the element's atomic number, or place in the periodic table. This position in the table was not known to have any physical significance up to that time, except as a way to order elements in a particular sequence so that their chemical properties would match up. The ordering of atoms in the periodic table did tend to be according to atomic ''weights'', but there were a few famous "reversed" cases where the periodic table demanded that an element with a higher atomic weight (such as cobalt at weight 58.9) nevertheless be placed at a lower position (Z = 27), before an element like nickel (with a lower atomic weight of 58.7), which the table demanded take the higher position at Z = 28. Moseley inquired if Bohr thought that the electromagnetic emission spectra of cobalt and nickel would follow their ordering by weight, or by their periodic table position (atomic number, Z), and Bohr said it would certainly be by Z. Moseley's reply was "We shall see!" Since the spectral emissions for high Z elements would be in the soft X-ray range (easily absorbed in air), Moseley was required to use vacuum tube techniques to measure them. Using x-ray diffraction techniques in 1913-1914, Moseley found that the most intense short-wavelength line in the x-ray spectrum of a particular element was indeed related to the element's periodic table atomic number, Z. This line was known as the K-alpha line. Following Bohr's lead, Moseley found that this relationship could be expressed by a simple formula, later called ''Moseley's Law''. :$\backslash sqrt\; f\; =\; k\_1\; \backslash cdot\; \backslash left(Z\; -\; k\_2\backslash right)$ where: :$f\; \backslash$ is the frequency of the main or K x-ray emission line :$k\_1\; \backslash$ and $k\_2\; \backslash$ are constants that depend on the type of line For example, the values for $k\_1\; \backslash$ and $k\_2\; \backslash$ are the same for all $K\_\backslash alpha$ lines (in Siegbahn notation), so the formula can be rewritten thus: :$f\; =\; \backslash left(2.47\; \backslash times\; 10^\backslash right)\; \backslash times\; \backslash left(Z\; -\; 1\backslash right)^2$ (Hz) Moseley himself chose to show this without $k\_1\; \backslash$ per se, which instead was given by Moseley as a pure constant number in the standard Rydberg style, as simply 3/4 (that is, 1 − 1/4) of the fundamental Rydberg frequency (3.29 × 1015 Hz) for K-alpha lines, and (again) for L-alpha lines according to the Rydberg formula, where $k\_1\; \backslash$ must be 1/4 − 1/9 = 5/36 times the Rydberg frequency; this also was the way Moseley chose to write it. Moseley's $k\_2\; \backslash$ was given as a general empiric constant to fit either K-alpha or L-alpha transition lines (the latter being weaker-intensity and lower frequency lines found in all X-ray element spectra, and in which case the additional numerical factor $k\_2\; \backslash$ to modify Z is much higher). Moseley found the entire term was (Z − 7.4)2 for L-alpha transitions, and again his fit to data was good, but not as close as for K-alpha lines where the value of $k\_2\; \backslash$ was found to be 1. Thus, Moseley's two given formulae for K-alpha and L-alpha lines, in his original semi-Rydberg style notion, (squaring both sides for clarity), are: :$f\; \backslash left(K\_\backslash alpha\; \backslash right)\; =\; \backslash left(3.29\; \backslash times\; 10^\backslash right)\; \backslash times\; 3/4\; \backslash times\; \backslash left(Z\; -\; 1\backslash right)^2$ Hz :$f\; \backslash left(L\_\backslash alpha\; \backslash right)\; =\; \backslash left(3.29\; \backslash times\; 10^\backslash right)\; \backslash times\; 5/36\; \backslash times\; \backslash left(Z\; -\; 7.4\backslash right)^2$ Hz 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「Moseley's law」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.