D O C . 3 1 5 S T E R N - G E R L A C H E X P E R I M E N T 4 4 5 Published in Zeitschrift für Physik 11 (1922): 31–34. Received 21 August 1922. [1]The manuscript was completed before 30 July 1922 (see Docs. 316 and 329). [2]Gerlach and Stern 1922a. [3]Otto Stern (1888–1969) and Walther Gerlach (1889–1979). The proposed experiment was first described in an article by Otto Stern (Stern 1921), published in response to a similar experiment that was being carried out at the same time by Hartmut Kallmann and Fritz Reiche, who used the deflec- tion exerted on electric dipoles in an inhomogeneous electrical field (Kallmann and Reiche 1921). As a first result of their own experiment, Gerlach and Stern reported in a paper received on 18 November 1921 that they did observe a broadening of the silver beam on switching on the inhomogeneous mag- netic field (Gerlach and Stern 1921). Some three months later, they were able to report that the silver beam actually splits up into two distinct beams on passing through the inhomogeneous field (Gerlach and Stern 1922a). Again, a month later, they estimated the magnetic moment of the silver atoms to be about 1 Bohr magneton, in accordance with their theoretical expectations (Gerlach and Stern 1922b). A detailed review of their experiments was published in Gerlach and Stern 1924. The experiments were done with financial support from the Kaiser Wilhelm Institute of Physics (KWIP). On 27 July 1921, Gerlach had applied for funds to the KWIP, with the recommendation of Max Born and James Franck (aVol. 12, 193a). The KWIP awarded Gerlach a lump sum of 10,000 marks (see 20 October, 5 November, and 2 December 1921 in Vol. 12, Calendar). Apparently, Gerlach had used at least part of those funds to buy an electromagnet. In their first joint paper, submitted on 18 November 1921, Gerlach and Stern still expressed their gratitude to the company of Hartmann and Braun for lending them an electromagnet (Gerlach and Stern 1921, note 2). But in their second paper, received on 1 March 1922, Gerlach and Stern thanked Einstein and the KWIP for providing grants for the purchase of the electromagnet (Gerlach and Stern 1922a, p. 352 1924, p. 681). For further historical discussion of the Stern-Gerlach experiment, see Mehra and Rechenberg 1982, pp. 432–445 Weinert 1995 Friedrich and Herschbach 1998, 2003, Trageser 2011 for a biog- raphy of Otto Stern, see Schmidt-Böcking and Reich 2011. [4]The experimental apparatus was placed in a vacuum of mmHg. The vaporized silver left an oven heated to a temperature of 1,000oC through a first diaphragm of cross-sectional area of mm2. At 3.3 cm after this first diaphragm, the silver atoms passed a second slit diaphragm of 0.8 mm in length and between 0.03 and 0.04 mm in width. The beam then passed along 3 cm through the inhomogeneous magnetic field between the poles of an electromagnet and were then collected on a glass plate. Even after exposure times of up to 10 hours, the deposited silver was not yet visible to the naked eye but had to be processed chemically to be made visible (Gerlach and Stern 1922a, 1924). [5]In Stern 1921, p. 250, it is also argued that classical Larmor rotation cannot help explain quantization. [6]On Ehrenfest’s adiabatic hypothesis, see note 12. [7]The theoretical assumptions of Stern and Gerlach are outlined in Stern 1921 as follows. In the quantum theory of magnetism and of the Zeeman effect, it is assumed that the angular momentum vector of an atom can form only certain discrete angles with a magnetic field H. These angles are such that the components of the angular momenta along the magnetic field take only values that are integer multiples of h/2π. (Here, Sommerfeld 1921 is given as reference.) Thus, if we introduce into a mag- netic field a gas of atoms, each of which having total angular momenta of h/2π, then each atom will have only two possible arrangements, with components of +h/2π along the magnetic field. [8]The calculation of the alignment time can be found in Paul Ehrenfest’s diary for 20 May 1922 (entry 5714), as follows, with some change of notation. The radiation rate of a magnetic dipole μ precessing in a magnetic field H is given by c is the velocity of light, i.e., c = μ is the Bohr magneton, γ is the precession frequency , which, for a magnetic field of 10,000 gauss, is (see entry 5698 of the diary, 22 April 1922). The energy, which has to be emitted or absorbed by the atom in order to align or antialign with 10 5– 3 10 3– dE dt ------ - 2 3c3 --------γ4μ2 3 1010------ cm s - μ 10–20------------ erg gauss - γ eH 2mc ---------- γ 0.9 1011-- 1 s - ⋅≈
Previous Page Next Page