The Intensity of the X-rays Scattered from Rocksalt

Absolute intensity of x-rays scattered from a single rock-salt crystal.—Rays from a Mo target (47.5 kv) filtered through a zirconium phosphate screen were directed onto a thin slab of rock salt at an angle $\theta$ with the normal to the face, and the scattered intensity after transmission was measured with a long ionization chamber at various angles $\varphi$ with incident radiation. Assuming the scattering independent of $\theta$ and eliminating $\mu$ by using Crowther's expression for scattering coefficient when $\theta =\frac{1}{2}\varphi$, scattering in excess of theoretical (Thomson) was observed for $\varphi$ between 9° and 90°, the two maxima at 15° and 30°, about twice theoretical, corresponding respectively to maxima in the incident radiation at about.4 and.7 A, respectively. Similar excess scattering at 20° to 30° had previously been reported for amorphous carbon and liquids but in these cases the excess scattering might have been due to a powdered crystal effect. The scattering drops suddenly to zero at 5°, about the same angle as that for which regular reflection becomes zero. Above 90°, the scattering also departs somewhat from the Thomson curve, showing a minimum for about 100°; it corresponds in shape better with the curve given by the quantum theories of A. H. Compton and Jauncey, the experimental value being, however, greater in the ratio 9/8. The mass scattering coefficient for the primary rays used (.4 to.7A) comes out 0.23±.02 as against Thomson's value of 0.193.