Orientation of Atoms in a Crystal

T. R. Merton. An Experiment relating to atomic orientation. Phil. Mag. 38, p. 463, (1919).

In contemporary theories of the structure of the atom, those of Rutherford–Bohr, it is assumed that the atomic structure is such that one may speak of an axis of the atom, perpendicular to the plane of the electronic orbits. On the other hand, at the present time the regularity of the arrangement of atoms in a crystal has been firmly established. The question arises whether the axes of the atoms of a crystal lattice are also oriented quite definitely, or whether their inclination is distributed according to the law of chance. If one assumes a dependence of the direction of emission of $\alpha$- and $\beta$-particles by radioactive atoms on the direction of their axes, then it becomes possible to decide experimentally the question of the regular or chaotic orientation of atomic axes in the case of radioactive crystals. In the case of regular orientation, the number of $\alpha$- and $\beta$-particles emitted by different faces of a crystal should be different. The author carried out the corresponding experiment with a large crystal of uranyl nitrate. The activity was measured with an electroscope of the Rutherford type. To an accuracy of 3%, the number of $\alpha$-particles emitted by the different faces of the crystal proved to be the same. Thus, either the direction of emission of the $\alpha$ particle by the nucleus of a radioactive atom does not depend on the direction of the axis of the atom, or the atomic axes are arranged in the crystal according to the law of chance. Merton’s experiment is not in a position to give an unambiguous answer to the question posed above.

C. Vavilov.