Friday, July 11, 2014

Samuel Goudsmit and the Electron Spin

George Uhlenbeck, Hendrik Kramers, and
Samuel Goudsmit in 1928
On July 11, 1902, Dutch-born U.S. physicist Samuel Abraham Goudsmit was born. He is best known for the formulation of the concept of electron spin together with George Eugene Uhlenbeck. It led to recognition that spin was a property of protons, neutrons, and most elementary particles and to a fundamental change in the mathematical structure of quantum mechanics.

If you not happen to be a physicist, you probably will never have heard that electrons have a spin. Well, electrons are not literally spinning balls of charge, but they do have intrinsic angular momentum. Spin angular momentum is real angular momentum. The angular momentum of a spin-1/2 particle like an electron is never zero. But, let's go back one more step. In 1891, the Irish physicist, George Stoney, believed that electricity should have a fundamental unit. He called this unit the electron and the electron as the first sub-atomic particle was discovered by J.J. Thomson in 1897. Besides its electric charge and mass, an electron has one more key property, which is called “electron spin".

Two types of experimental evidence which arose in the 1920s suggested this additional property of the electron. One was the closely spaced splitting of the hydrogen spectral lines, called fine structure. The other was the Stern-Gerlach experiment which showed in 1922 that a beam of silver atoms directed through an inhomogeneous magnetic field would be forced into two beams. Both of these experimental situations were consistent with the possession of an intrinsic angular momentum and a magnetic moment by individual electrons. Classically this could occur if the electron were a spinning ball of charge, and this property was called electron spin.

Samuel Goudsmit was born in The Hague, Netherlands, as son of Jewish parents Isaac and Marianne Goudsmit. As he was proud to claim throughout his life, his father his father was a small manufacturer of water closets fixtures while his mother ran a millinery shop. Samuel Goudsmit started his professional life at the University of Leyden during the earliest days of quantum mechanics as a student of Paul Ehrenfest, a theoretical physicist, who made major contributions to the field of statistical mechanics and its relations with quantum mechanics. Ehrenfest was both, an outstanding scientist as well as a gifted pedagogue. Under Ehrenfest's tutelage Goudsmit published his first scientific paper already at age 19 in 1921 in the prestigious journal "Die Naturwissenschaften". In 1925 Goudsmit together with his fellow graduate student George Uhlenbeck were assigned by Ehrenfest to work for a quick update on "what was currently happening in physics". Thus, while being a graduate student, Goudsmit and Uhlenbeck discovered the spin on the electron.

In 1927 after receiving their PhD, Goudsmit and Uhlenbeck together moved to the United States where they continued their physics careers until death. From 1927 to 1946, Goudsmit served as a Professor at the University of Michigan. He was also the scientific head of the Alsos Mission and successfully reached the German group of nuclear physicists around Werner Heisenberg and Otto Hahn at Hechingen (then French zone) in advance of the French physicist Yves Rocard. As part of the Manhattan Project, Alsos was designed to assess the progress of the Nazi atomic bomb project. Goudsmit published in 1947 his conclusion that the Germans did not get close to creating a weapon, which he attributed to the inability of science to function under a totalitarian state. His other conclusion, that the German scientists simply did not understand how to make an atomic bomb, has been disputed by later historians. After the war he was briefly a professor at Northwestern University and from 1948-1970 was a senior scientist at the Brookhaven National Laboratory. In 1974, Goudsmit moved to the faculty of the University of Nevada in Reno, where he remained until his death four years later.

At yovisto, you may learn more about particle physics in the inside tour of the world` biggest supercollider LCH at the CERN research institute, given by physicist Brian Cox.



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