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This note discusses briefly several methods of describing the width and shape of the resonances characteristic of nuclear paramagnetism. Use of the so-called moments of the shape function is illustrated by an experimental determination of a root mean square line width which is in substantial agreement with a calculation by Van Vleck. The solutions of the Bloch equations, which lead to the Lorentz shape function traditional in the theory of radiation- and collision-broadened lines, are compared with susceptibility curves based on a Gauss absorption curve. A significant difference between the two dispersion curves serves as a criterion for determining whether or not either of these two shapes closely approximates to a given experimental curve, and experimental examples of each are given.For comparison of shape functions, several well-known specializations of the Kronig-Kramers relations are employed. The collection of these formulae may incidentally prove convenient and useful to those engaged in studies of nuclear paramagnetism.
Pake et al. (Mon,) studied this question.