The Reflection of Atoms from Crystals

Beams of mercury, cadmium, and arsenic incident upon clean cleavage surfaces of rock-salt give rise to specularly reflected beams. Measurement shows that the velocity of the beam of cadmium atoms reflected from rock-salt may be represented by $\lambda =\frac{h}{\mathrm{mv}}=2d{\left(2.26-\frac{\phi }{\frac{1}{2}m{v}^2}-{cos}^2\theta \right)}^{\frac{1}{2}}.$ A beam specularly reflected from a first crystal is specularly reflected at a second if incident upon it at the same angle at which reflection from the first took place. If the angles are nearly equal there is still some specular reflection at the second crystal but the intensity of the specular beam drops off with increasing difference of angles and the incident beam is scattered at random. A beam of cadmium atoms issuing from a boiler at 440°C and striking a rock-salt crystal at an angle of 45° gives rise to a specular beam containing about 17 percent of the incident atoms. The intensity of the beams specularly reflected at 22.5° and 67.5° are in the ratio 1:1.38. These facts indicate that associated with motion of translation of uncharged atoms and molecules there is a wave phenomenon of the type postulated by de Broglie.