The Electron Diffraction Tube

The electron diffraction experiment where we sent a beam of electrons through a graphite crystal, can be viewed either as an experiment to demonstrate the wave nature of electrons or as an experiment to study the structure of a graphite crystal. Perhaps both.
The apparatus, shown in Figure (1), consists of an evacuated tube with an electron gun at one end, a graphite target in the middle, and a phosphor screen at the other end. A finely collimated electron beam can be aimed to strike an individual flake of graphite, producing a single crystal diffraction pattern on the phosphor screen. Usually you hit more than one crystal and get a multiple image on the screen, but with some adjustment you can usually obtain a single crystal image.

Figure 1: Electron diffraction apparatus. An electron beam, produced by an electron gun, strikes a graphite crystal located near the center of the evacuated tube. The original beam and the scattered electrons strike a phosphor screen located at the end of the tube.