Davisson-Germer apparatus

Davisson-Germer apparatus

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Description
This instrument was used by Clinton Davisson [1881-1958] at Bell Telephone Laboratories, likely in the early 1920s. Davisson began to study electron scattering from a nickel target with Charles Kunsman in 1921 and continued in a similar vein with Lester Germer in 1924. The original focus of this work was to investigate electrons scattered at nearly the same energy as the incident beam. A fortuitous accident in 1925 led Davisson and Germer to turn their attention from nickel targets composed of a random assemblage of crystalline structures to a single nickel crystal. They published this work in 1927, showing distinct maxima in the scattered electrons at particular energies positioned in locations that would be expected if the electrons were treated as light waves diffracted from a crystal, providing experimental evidence of the wave nature of the electron—an important aspect of quantum mechanics. Davisson split the 1937 Nobel Prize in physics with George Paget Thomson, who also demonstrated electron diffraction.
Davisson’s basic experimental apparatus consisted of a glass envelope sealed under high vacuum containing an electron gun that was directed at a nickel target and a movable collector which detected the resulting scattered electrons. The 1927 Davisson-Germer apparatus included a feature that allowed for the single crystal target to be rotated. It, however, was lost when the tube imploded on 4 August 1927. The tube presented here contains many of the same features of the 1927 apparatus, including the shielded metal compartment for the electron gun, target, and a collector that can be positioned by tilting the tube. Electrodes controlling the gun, the energy of the electrons used, the energy of electrons admitted into the collector, as well as the signal created by electrons detected by the collector, pass through the glass envelope. The pointed glass tip is likely where the tube was connected to external vacuum pumps and later sealed when most of the air was removed. Two protrusions near the tip contain charcoal (to be cooled) and a bit of misch metal (to be vaporized), which were also used to reduce the internal pressure—an important experimental constraint when working with low energy electrons. This tube does not have a feature to rotate the target, and therefore likely belongs to the scattering work Davisson conducted with either Germer or Kunsman in the early 1920s. Much of this early work was unpublished, so the pairing of this instrument with a particular experiment is difficult.
References:
Gehrenbeck, Richard K., “Electron diffraction: fifty years ago,” Physics Today 31 (1978) p.34-41 http://dx.doi.org/10.1063/1.3001830
“Dr. Lester Germer Dies at 74; Research Physicist at Cornell,” New York Times, 4 Oct 1971, p.42
"The Nobel Prize in Physics 1937," Nobelprize.org, Nobel Media AB 2014. Web. 3 Feb 2017. http://www.nobelprize.org/nobel_prizes/physics/laureates/1937/
"Clinton Davisson – Facts,"Nobelprize.org, Nobel Media AB 2014. Web. 3 Feb 2017. http://www.nobelprize.org/nobel_prizes/physics/laureates/1937/davisson-facts.html
“Clinton Joseph Davisson 1881-1958,” Biographical Memoirs of the National Academy of Sciences [http://www.nasonline.org/publications/biographical-memoirs/memoir-pdfs/davisson-clinton.pdf]
Location
Currently not on view
Object Name
electron diffraction apparatus
Measurements
overall: 22 in x 26 in x 11 in; 55.88 cm x 66.04 cm x 27.94 cm
ID Number
PH.320414
catalog number
320414
accession number
242378
See more items in
Medicine and Science: Physical Sciences
Data Source
National Museum of American History
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