Chronology of Milestone Events in Particle Physics - LAMB 1947
Chronology of Milestone Events in Particle Physics

  Nobel prize to W. E. Lamb awarded in 1955 "for his discoveries concerning the fine structure of the hydrogen spectrum. Co-winner P. Kusch "for his precision determination of the magnetic moment of the electron''  

LAMB 1947

Lamb, W.E.; Retherford, R.C.;
Fine Structure of the Hydrogen Atom by a Microwave Method
Phys. Rev. 72 (1947) 241;

Reprinted in
The Physical Review - the First Hundred Years, AIP Press (1995) 148, 195.
Selected Papers on Quantum Electrodynamics, editor J. Schwinger, Dover Publications, Inc., New York (1958) 136.

The spectrum of the simplest atom, hydrogen, has a fine structure1 which according to the Dirac wave equation for an electron moving in a Coulomb field is due to the combined effects of relativistic variation of mass with velocity and spin-orbit coupling. It has been considered one of the great triumphs of Dirac's theory that it gave the "right'' fine structure of the energy levels. However, the experimental attempts to obtain a really detailed confirmation through a study of the Balmer lines have been frustrated by the large Doppler effect of the lines in comparison to the small splitting of the lower or n = 2 states. The various spectroscopic workers have alternated between finding confirmations2 of the theory and discrepancies3 of as much as eight percent. More accurate information would clearly provide a delicate test of the form of the correct relativistic wave equation, as well as information on the possibility of line shifts due to coupling of the atom with the radiation field and clues to the nature of any non-Coulombic interaction between the elementary particles: electron and proton... (Extracted from the introductory part of the paper.)
Summary Hydrogen atoms are bombarded by an electron stream. Metastable 22S1/2 atoms are detected by electron ejection from a metal target. The current is reduced if radio-frequency radiation is applied, for which h corresponds to the energy difference between one of the Zeeman components of 22S1/2 and any component of the P levels. The results indicate that the 22S1/2, state is higher than the 22P1/2 by ~ 0.033 cm-1, thereby showing that Dirac's theory is not exact. The method will be extended to measurements of hyperfine structures, etc.

1 (H. E. White, Introduction to Atomic Spectra (McGraw-Hill Book Company, New York, 1934), Chap. 8).
2 (J. W. Drinkwater et al., Proc. Roy. Soc. 174 (1940) 164).
3 (W. V. Houston, Phys. Rev. 51 (1937) 446).
(Science Abstracts, 1947, 3605. L. P.).

Accelerator NONE Detectors OTHER

Related references
More (later) information appears in
W. E. Lamb and R. C. Retherford, Phys. Rev. 79 (1950) 549;
See also
G. Breit and E. Teller, Astr. Jour. 91 (1940) 215;
R. C. Williams, Phys. Rev. 54 (1938) 558;
H. A. Bethe, Handbuch der Phys. XXVI/1 (1933) 495f;
J. W. Drinkwater, O. V. Richardson, and W. E. Williams, Proc. Roy. Soc. A174 (1940) 164;
W. V. Houston, Phys. Rev. 51 (1937) 446;

  H(atom)* H(atom) p

Particles studied
  H(atom) mass

Record comments
First measurements of the fine structure of the hydrogen atom, the Lamb shift.
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