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 θ with the normal to the face, and the scattered intensity after transmission was measured with a long ionization chamber at various angles φ with incident radiation. Assuming the scattering independent of θ and eliminating μ by using Crowther's expression for scattering coefficient when θ=1/2φ, scattering in excess of theoretical (Thomson) was observed for φ 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.