**Abstract:** A closed-form equation was derived that describes the powder-ring distribution factor as a function of 2*θ*, soller slit collimation, and *σ**, which is defined as the standard deviation of an axially symmetrical Gaussian orientation function. Methods were developed for measuring *σ** in the reflection mode by means of a *θ*/2*θ* diffractometer. Six experimental arrangements for a sedimentary chlorite showed widely different intensity ratios of the 001/005 reflections and gave a standard deviation of ±5.8% when corrected by the theory. The absolute integrated intensities of the 003 reflection from eleven illite samples provided an eight-fold maximum range which, when corrected, yielded a standard deviation of ±7.7%.

The intensity distributions within each of two X-ray powder diffraction patterns obtained from instruments with different soller-slit configurations could not be directly compared at low diffraction angles unless corrections, based on *σ**, were introduced to allow for the differences in axial divergence.

*Clays and Clay Minerals*; August 1986 v. 34; no. 4; p. 359-367; DOI: 10.1346/CCMN.1986.0340402

© 1986, The Clay Minerals Society

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