- Person
- Otto Stern
- Lived
- 1888–1969
- Field
- Experimental physics
- From
- German-American
The story
Before Otto Stern, the properties of atoms were mostly inferred from the behaviour of huge numbers of them in gases, liquids and solids. In 1911 the French physicist Louis Dunoyer had shown that sodium atoms travel through a vacuum in straight lines, like light, but no one had yet turned such beams into a precise measuring tool.
After the First World War, during which a spell in Walther Nernst's Berlin laboratory had converted him from a theorist into an experimenter, Stern returned to Frankfurt as assistant to Max Born. His idea was to measure the properties of single atoms and molecules by sending a thin beam of them through a vacuum, where they travel without colliding. Born was so taken with the idea that he put his whole laboratory, workshop and skilled mechanic, Adolf Schmidt, at Stern's disposal.
Stern's first apparatus was simple and ingenious. A heated platinum wire coated with silver released silver atoms, which passed through narrow slits and condensed on a cold plate. The whole arrangement could rotate at up to 2,400 turns a minute, and the shift in the position of the silver spot revealed how fast the atoms were moving. In April 1920 he reported the atoms' average speed. At first his result was noticeably higher than the kinetic theory of gases predicted, until Einstein pointed out a correction for the fact that atoms of different speeds pass through a slit at different rates. With it, theory and experiment agreed. Stern noted that his apparatus made it possible, for the first time, to prepare molecules with a uniform velocity.
That made the molecular beam a precision instrument. Stern used it for the Stern–Gerlach experiment, for showing that atoms behave as waves and for measuring the magnetism of the proton. At Hamburg from 1926 he published a series of 30 papers titled Investigations by the molecular-beam method, and his 1943 Nobel Prize in Physics cited his contribution to the development of the molecular ray method.
Historians have called him the founding father of experimental atomic physics. About 20 Nobel Prizes have since been awarded for work based on the method, including those for the maser, nuclear magnetic resonance and the atomic clock.
Why it matters
Molecular beams became a basic tool of physics and chemistry, used in atomic clocks, magnetic resonance and molecular beam epitaxy, a technique for growing materials for electronics.
About Otto Stern
Physicist whose molecular-beam method proved space quantisation in the Stern–Gerlach experiment and measured the proton’s magnetic moment; Nobel Prize in Physics 1943.
More about Otto Stern
- Otto Stern showed whole atoms behave like wavesAround 1930 Otto Stern's Hamburg laboratory diffracted beams of helium atoms and hydrogen molecules off crystals, proving that entire atoms, not just electrons, travel as waves.
- Otto Stern proved atoms obey quantum rules in 1922In February 1922 the Stern–Gerlach experiment split a beam of silver atoms cleanly in two, the first direct proof that quantum rules govern how atoms behave in a magnetic field.
- Otto Stern's lab trained Rabi, opening a path to MRIIsidor Rabi learned the molecular-beam technique in Otto Stern's Hamburg lab, and built on it the magnetic resonance method behind NMR, MRI and atomic clocks.
- Otto Stern found the proton is not a simple particleIn 1933 Otto Stern, Otto Frisch and Immanuel Estermann measured the proton's magnetism and found it unexpectedly large, the first sign that the proton has inner structure.
Sources
- Otto Stern (1888–1969): The founding father of experimental atomic physics Annalen der Physik / arXiv
- Otto Stern Wikipedia
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