The Intensity of Reflection of X-Rays by Powdered Crystals, I. Sodium Chloride and Sodium, Lithium and Calcium Fluorides

Through measurements by the ionization method of the relative intensities of reflection of x-rays by the different planes of powdered crystals, the author has obtained data which are free from the errors inherent in the work with large single crystals. Darwin's formula for the intensity of reflection from an ideally imperfect crystal may be applied to these results without correction for primary or secondary extinction. In order to get reflected radiation of sufficient intensity to permit accurate measurement, a focussing method has been used, in which a primary beam of wide divergence strikes the surface of a briquet of the powder under investigation and the reflected beam is focussed sharply at the ionization chamber slit. Measurements were made out to angles slightly larger than $\theta =45\mathrm{}°$. The absolute values of the intensity of reflection were determined by comparison with reflections from powdered sodium chloride, the results of Bragg, James and Bosanquet on the latter crystal, after allowance for secondary extinction, being taken as correct.