A Reply to A. Kostarev

In his letter concerning my article “X-ray Spectra as a Method for Studying the Distribution of Electrons over States” (Uspekhi Fizicheskikh Nauk, vol. XXIX, nos. 1–2), A. Kostarev considers that in that article the Kronig theory of the fine structure of absorption in solids should not have been presented, on the grounds that this theory is incorrect and must be replaced by A. Kostarev’s own theory.

Kronig’s theory, proposed by him in 1932, has since served as the basis for numerous works on the fine structure of absorption spectra. This theory, based on known assumptions, is a theory of “long-range order” and can claim only to explain the region of fine structure sufficiently far removed from the main absorption edge (more than 100 eV). In this region Kronig’s theory explains well a whole series of interesting regularities and for 10 years was undoubtedly a progressive theory. In order to understand the experimental facts accumulated over these years, familiarity with Kronig’s theory is necessary, and this is what led me to set forth this theory—especially since, as far as I know, the only application of A. Kostarev’s theory to the explanation of the fine structure of the absorption of the \(K\)-spectrum of copper was made by A. Kostarev himself at the end of his theoretical work. Nevertheless, in my article I point out that A. Kostarev’s theory, being a theory of “short-range order,” can be expected to explain a whole series of new facts and gives a better approximation than Kronig’s theory. Therefore I am glad to join A. Kostarev in his criticism of Kronig’s theory, but at the same time I believe that, in order to understand the considerable number of experimental works on the fine structure of absorption of X-ray spectra in solids accumulated since 1932, a presentation of Kronig’s theory is necessary.

M. Blokhin