Ralph Kronig

Ralph Kronig

Ralph de Laer Kronig , born as Ralph Kronig, (born March 10, 1904 in Dresden ; † November 16, 1995 in Zeist ) was a German -US theoretical physicist . He discovered the particle spin before Uhlenbeck and Goudsmit , but did not publish it. Kronig was involved in the early development of quantum mechanics and its application. B. Involved in atomic physics and molecular physics. The Kronig-Penney model and the Kramers-Kronig relation go back to him.

life and work

Ralph Kronig was born in Dresden in 1904. His father, Harold Theodor Kronig, came from Bohemia and was a US citizen. His mother, Augusta de Laer, was of Dutch descent. He attended grammar school in Dresden until the age of 15, before moving to America with his family. He studied at the Columbia University in New York City , where he in 1925 with the work of Change of conductance of Selenium due to Electronic Bombardment Albert Potter Wills doctorate was. With regard to the more recent developments in the physics of atoms, he was largely dependent on the self-study of Arnold Sommerfeld's atomic structure and spectral lines . A year earlier he visited the Centers for the Development of Quantum Mechanics in Germany and Copenhagen, where he among others Niels Bohr , Paul Ehrenfest (whom he knew from New York and who invited him to Leiden ), Werner Heisenberg , Wolfgang Pauli and Hendrik Anthony Kramers met. While still a student, in January 1925 he proposed the introduction of the electron spin to explain the exclusion principle of Pauli in Tübingen, where Kronig was with Alfred Landé after he had written a paper on atomic spectra in Leiden with Goudsmit. Both Heisenberg and Pauli, whom Kronig met in Tübingen, initially disapproved of this, as they had previously banned unobservable quantities in their approach to justify quantum mechanics. In particular, the criticism from Pauli (who nevertheless considered this to be a "funny idea" ) made Kronig hesitate to publish his ideas, so that Uhlenbeck and Goudsmit got ahead of him in 1925 and were recognized as the discoverers of spin. Nevertheless, he remained on friendly terms with Pauli (who published his principle of exclusion after a letter of Kronig's discovery of the spin degree of freedom) and exchanged scientific letters with him. In 1964 he published Pauli's collected works.

Ralph Kronig, 1963 in Copenhagen

After his doctorate, Kronig was an instructor and from 1927 an assistant professor at Columbia University. He was in correspondence with Heisenberg during his development of the matrix form of quantum mechanics. At the suggestion of Isidor Rabi , he solved the Schrödinger equation for the problem of the symmetrical top. In 1927 he was back in Europe in Copenhagen, London and Zurich, where he was Pauli's assistant in the 1928 summer semester. From around 1930 he lived in the Netherlands, where he was Dirk Coster's assistant in Groningen, and from 1931 as associate professor. From 1939 he was a professor of theoretical physics at the Technical Hogeschool van Delft . He stayed there until his retirement in 1969 and was temporarily rector.

In addition to his work on the fundamentals of quantum mechanics, he also dealt with solid-state physics (Kronig-Penney model 1931, a one-dimensional model of electrons in crystals that shows the development of band structures ) and was considered an expert in the theory of molecular spectra. He also developed a model of the fine structure of the X-ray absorption spectra (1931/32), which was well confirmed experimentally at the time.

In 1927 he became a Fellow of the American Physical Society . In 1962 he received the Max Planck Medal .

Fonts

• On the theory of the dispersion of X-rays. In: Journal of the Optical Society of America. Volume 12. 1926, pp. 547-557. (Kramers-Kronig relations)
• Volume spectra and molecular structure. Cambridge University Press 1930.
• with William Penney: In Proc. Roy. Soc. A. , Volume 130. 1931, p. 409. (Kronig-Penney model)
• The Optical Basis of the Theory of Valency. MacMillan, New York 1935.
• Editor: Textbook of Physics. Pergamon Press 1959.
• The turning point. In Markus Fierz, Victor Weisskopf: Theoretical Physics at the Turn of the Century. A Memorial Volume to Wolfgang Pauli. Interscience 1960, pp. 5-39.

literature

• Bartel Leendert van der Waerden (Ed.) Sources of Quantum Mechanics. 1967.
• Abraham Pais : Inward Bound. Clarendon Press 1986.
• Abraham Pais: In Physics Today. December 1989.
• Obituary by Max Dresden . In Physics Today. March 1997.
• Martin J. Klein : In Physics in the Making. North Holland, Amsterdam 1989.
• R. Stumm von Bordwehr: A history of the x ray absorption fine structure. In: Annales de Physique. Vol. 14, 1989, pp. 377-466.
• Ian Duck, ECG Sudarshan: Pauli and the spin statistics theorem. World Scientific 1997, pp. 57f.
• Klaus Hentschel & Renate Tobies : Interview with Friedrich Hund '(on Dec. 15, 1994 in Göttingen), NTM NS 4 [1996], pp. 1-18.

Web links

Commons : Ralph de Laer Kronig  - Album with pictures, videos and audio files

• Photo on page with Pauli's assistant

References and comments

1. ↑ HBG Casismir: Levensbericht R. Kronig. Huygens Institute - Royal Netherlands Academy of Arts and Sciences (KNAW), 1996, accessed February 2, 2020 (Dutch). 
2. ^ ^{A b c} John L. Heilbron: Interview of Ralph Kronig. In: Niels Bohr Library & Archives. American Institute of Physics, November 12, 1962, accessed February 2, 2020 . 
3. ^ Ralph Kronig: Change of conductance of selenium due to electronic bombardment . 1925, OCLC 36606149 (Ph.D. Thesis , Columbia University, 1925).
4. ↑ Ralph de Laer Kronig: Change of Conductance of Selenium due to Electronic Bombardment . In: Physical Review . tape 24 , no. 4 , 1924, pp. 377 , doi : 10.1103 / PhysRev.24.377 .
5. ↑ In the discussion with Kronig during his subsequent visit to Copenhagen, Kramers also expressed himself skeptical there
6. ↑ Kronig himself describes the discovery in the commemorative volume of Wolfgang Pauli, see literature. Van der Waerden also goes into the history of the discovery in detail in Sources of Quantum Mechanics . Uhlenbeck later admitted that Kronig would undoubtedly have anticipated the main point of her ideas , Physics Today June 1976, quoted in Pais Inward bound , p. 280 Kronig himself saw problems for the postulation of an electron spin from nuclear physics at that time. At that time, nuclei were thought to be composed of electrons and protons and a contribution of the electron spin to the nuclear moments would have led to hyperfine structure splitting that was far too high. In a letter to Nature (vol. 117, 1926, p. 550) following Uhlenbeck and Goudsmit's article ( Spinning electrons and the structure of spectra , ibid, p. 264) in the same volume on the introduction of spin, Kronig writes that The problem would only be one floor lower (in the core). See also Pais Inward Bound , p. 299. The saying, handed down in an interview by Friedrich Hund on Dec. 15, 1994, circulated among the physicists of the time: "De Kronig would have discovered spin, had Pauli not deterred it" - see Hentschel & Tobies 1996
7. ^ R. de L. Kronig, II Rabi: The symmetrical top in undulatory mechanics. In: Physical Review. Vol. 29, 1927, pp. 262-269, doi : 10.1103 / PhysRev.29.262 .