"X-ray scattering patterns have given considerable information concerning atomic distributions in matter, both crystalline and amorphous. Work on the diffraction of x-rays by crystals was begun in 1912 by Friedrich, Knipping, and Laue, and much valuable information concerning the arrangement of atoms in crystals has been supplied by this method. Diffraction of x-rays by gases was studied as early as 1911, and work in this field has given information concerning the arrangement of atoms in molecules and electron distribution in atoms. Work on the diffraction of x-rays by liquids was begun by Friedrich who obtained diffraction patterns of Canada Balsam, paraffin, and amber. More investigations gave theories concerning the determination of atomic distributions in liquids and gave quantitative means of describing the structure of liquids.
Considerable work has been done on elements in the liquid state since fewer assumptions need be made and the theory is more exact for monoatomic elements as compared to polyatomic elements. The theories by which the atomic distribution function is computed from experimental evidence is more simply applied to a group of many atoms of one kind than to polyatomic liquids. Following a method given by Zernike and Prins and later expounded by Gingrich, an average atomic density at a distance r in angstroms from any atom in the element can be round by means or a Fourier inversion or the x-ray scattering pattern.
The effects or temperature and pressure upon the x-ray scattering from argon has been studied by Eisenstein and Gingrich, using 26 different combinations of temperature and pressure, and measuring the scattering at various angles from the incident ray. One of the observations requiring clarification was that of the unusually large scattering at small angles, particularly large as the specimen approached the critical temperature and pressure. There are several explanations for this small angle scattering, perhaps the most common being that which compares this type or scattering to the diffraction of light. In other words, the explanation would be that this seemingly homogenous material would actually be made up of many areas or inhomogenieties. Thus, though there would be an overall average density for the material, there are or may be regions of higher or lower densities existing within the boundaries of the material under examination. Accepting this assumption, then, it would be reasonable to assume also that the incident x-ray would be scattered at the boundaries of these regions in a similar manner to light being diffracted at the boundary of a substance such as glass. The problem involved in attempting to prove or disprove this or similar theories would be to compute the extent of these areas of inhomogeniety and then to determine whether the volume occupied could contain a sufficient number of atoms to cause the abnormally large scattering observed at the small angles"--Introduction, pages 1-3.
Lund, Louis H., 1919-1998
M.S. in Physics
Missouri School of Mines and Metallurgy
v, 35 pages
© 1951 Walter Graham, All rights reserved.
Thesis - Open Access
X-rays -- Diffraction
X-rays -- Scattering
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Graham, Walter, "A correlation function for liquid argon" (1951). Masters Theses. 4152.