Film: Matter Waves, sound, 28 min.

Film : Matter Waves Length(min.):28 Color: No Sound: Yes a PSSC Film Alan Holden and Lester Germer, Bell Telephone Laboratories The wave behavior of matter is illustrated by experiments which show that electrons display interference patterns. This film relates to Section 33-8 of the PSSC text. The diffraction pattern at the edge of the 'shadow' of smoke particles as seen with an electron microscope is compared to the diffraction pattern at the edge of an optical shadow cast by a razor blade. This comparison suggests that electrons behave like waves; thus, Professor Holden points out that we should be able to see our interference pattern produced by electrons scattered from a grating. First, he reminds us of the interference pattern of a light beam produced by an ordinary reflection grating. To devise a suitable grating for the diffraction of electrons, he uses the de Broglie relation to estimate the wave length associated with the electrons he will use. This is calculated to be of the order of atomic dimensions. It is pointed out that nature provides a suitable grating with the proper spacing in the regular array of atoms in a crystal. To suggest the type of interference pattern that we might expect from a two-dimensional scattering array as found in a crystal, two optical gratings are placed at right angles to each other. The interference pattern of the scattered light is a two-dimensional, square array of spots. The scene shifts to the Bell Telephone Laboratories in N.J., where Dr. Germer is preparing to perform the experiment with electrons. A beam of electrons is reflected from a crystal onto a fluorescent screen. The pattern is a square array of spots. As the electron energy is increased, the spacing of the spots decreases, indicating a decrease in the electron wave length. Dr. Germer then shows the results and equipment of the original Davisson- Germer experiment which first demonstrated the wave behavior of electrons. Professor Holden continues with a description of the classic experiment of G.P. Thomson in which an interference pattern is produced by a beam of electrons passing through a thin polycrystalline gold foil. The resultant interference pattern is expected to be the same as the optical pattern produced when crossed gratings are rapidly rotated. The rotating spots form bright circles which are compared to a photograph of the circular interference pattern produced by electrons passing through a foil. The patterns produced by electrons and X rays, both of the same wave length and passing through identical foils, are shown to be circles of identical spacing. Finally, evidence for the diffraction of helium atoms and of neutrons is shown indicating that all matter shows wave behavior.