The scattering of electrons by metal vapours. II.―Zinc

Abstract

In a previous paper the importance of experimental investigations of the scattering of electrons by metal vapours was pointed out. It appears probable that the diffraction effects which occur in the elastic collisions of electrons with gas atoms are mainly determined by the ratio of the wave-length of the incident electrons to a certain atomic distance r 0 . The distance is such that the potential energy of the electron in the atomic held at the distance is comparable in magnitude with its initial kinetic energy. If this be correct the determination of atomic and molecular fields by scattering experiments can be readily carried out by comparative methods and it is therefore important to test the validity of such an interpretation of the diffraction process. This can only be done by a wide series of investigations of electron scattering by atoms with a great variety of electron structures. As only the rare gases can be investigated in the gaseous state it is essential to develop methods of measuring the scattering from metal vapours. In paper I a technique suitable for such measurements was described. With its use cadmium vapour was investigated and the comparison of the results with those obtained in mercury vapour combined the idea outlined above. With the election energies used (4-48 volts) the scattering should be due to the outermost shells of the atoms. These are of very similar dimensions and electron density for mercury and cadmium and hence very similar angular distributions are expected and were in fact observed. In the present paper the investigations are extended to zinc vapour for a range of electron energies from 4-143 volts, and the results obtained throw further light on tbs applicability of the general method of viewing the phenomena outlined above. 1. Description of Apparutus and Experimental Procedure .—The apparatus used was identical in essentials with that described in paper I. A homogeneous beam of electrons >was bred through a cloud of metal vapour issuing from a circular aperture in an oven and tire scattering was measured by a rotating the source about an axis coincident with that of the oven. Owing to the smallness of the scattering volume the vapour pressure of the metal may be taken as constant over the volume.