two-dimensional hexagonal pyrolitic graphite,   polycrystalline aluminum,   polycrystalline hexagonal p-graphite

7a60.10 Electron diffraction

PURPOSE: To show the diffraction patterns produced by an electron beam passing through crystal targets. One can adjust the accelerating potential to show that the angle of diffraction is proportional to the energy of the electron.

DESCRIPTION: The Welch Scientific 2639 Electron Diffraction Apparatus has three types of targets.  A polycrystalline aluminum sample produces a smooth, continuos ring pattern.  It also has a hexagonal pyrolytic graphite crystal target, which gives a monocrystal dot diffraction pattern, and a polycrystalline graphite crystal sample which gives an intermediate pattern (beaded ring).  The accelerating voltage can be  increased to cause the radius of the circle of diffraction to become smaller.   It can be demonstrated to be inversely proportional to the square root of the kinetic energy by placing a visible measurement ruler onto the screen to measure the radius of diffraction, and simultaneously measuring the potential voltage.

NOTE:

This device is damaged but it is used because it is irreplaceable and cannot be repaired. The crystal targets have many burn holes, like Swiss cheese, from the current of the electron beam.  Please try to keep the intensity adjusted to a low level to limit any further damage when using this apparatus.  The intensity and voltage should be turned off before turning the power supply on. Allow a few minutes for tube filament to warm up, then set anode voltage to about 6 kV but do not exceed 7 kV. Turn intensity up to about 6.5. The current should be held at the 100 uA level.   NEVER EXCEED 100 uA!!!

Use horizontal and vertical controls to steer the beam and locate targets.

http://www.oberlin.edu/physics/catalog/demonstrations/modern/ediffraction.html

http://www.upscale.utoronto.ca/IYearLab/elecdiff.pdf

Due to the poor condition of the crystal targets in the Welch Scientific 2639 Electron Diffraction Apparatus the Tel-Atomic diffraction tube may be used. The Tel-Atomic tube contains only one type of target crystal.   See the photos below:

EQUIPMENT: Electron diffraction apparatus, as photographed.

SETUP NOTES: Stored in modern physics.