Theoretical Physics Conference, 1937

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REPORT OF THE THIRD WASHINGTON CONFERENCE ON THEORETICAL PHYSICS [March 12, 1937]

The Third Washington Conference on Theoretical Physics was devoted to the problems of the properties and interactions of elementary particles and the related questions of nuclear structure.

The general plan of the Washington Conferences has been to evolve in the United States something similar to the Copenhagen Conferences, in which a small number of theoretical physicists working on related problems assemble to discuss in an informal way difficulties met in their researches. This year we were privileged to have Professor Bohr with us at the Conference, thus strengthening the tie between Washington and Copenhagen. Most of the members are former students of Bohr who had spent some time in Copenhagen and worked under his direction.

One of the most important events of the Conference was the report of Professor Bohr on his recent ideas on the general treatment of nuclear problems. According to his views many of the calculations made in this country and in Europe about nuclei are based on unjustified analogy between atomic and nuclear structures. He proposed instead a much simpler picture of the nucleus comparing it to a liquid droplet. Nuclear processes should be calculated, according to Bohr and to his collaborator, Dr. Kalckar, in the same way as the vibrations and evaporation of a droplet can be treated in classical theory. These ideas are closely related to previous discussions at George Washington University. Professor Bohr’s talk has given the theoreticians in this country a more definite picture and has encouraged all of us to go on in this general direction. One of the results of the discussions following Professor Bohr's talk was to clarify the basis of the calculations made by Wheeler on the generalized alpha-particle model of the nucleus.

Other investigations concerning the general structure of nuclei were reported by Wigner, who applied group-theory to the systematics of isotopes and the understanding of their binding energies, and by Breit, who treated the relativistic invariance of nuclear forces and the connected problem of fine structure of nuclear levels actually observed at the Department of Terrestrial Magnetism of the Carnegie Institution of Washington. In all the above discussions important contributions were made by Thomas, which clarified the mathematical assumptions and indicated various uncertainties in present calculations.

An interesting discussion took place between Bethe, Bohr, and Kalckar concerning the radii of radioactive nuclei. The question of the magnetic moment of neutrons was particularly discussed by Bloch and by Rabi. The former has proposed a method to determine this moment by neutron-scattering in ferromagnetic substances; the latter showed that by the method of rotating fields one can determine the sign of the magnetic moment. Bloch, Bethe, and Teller discussed the possibility of detecting an asymmetry in the alpha-particle emission induced by the capture of neutrons from a “polarized” neutron-beam (spins oriented chiefly in one direction by previous scattering). It was concluded that with the usual assumption of a neutron-spin of 1/2 no effect is to be expected, but with a neutron-spin of 3/2 such an effect will occur.

One of the subjects discussed was the generalization of the beta-decay theory and its application to the problem of nuclear forces, recently proposed by Gamow and Teller. This theory also establishes a connection between electric and gravitational forces, which problem was discussed by the authors and by Bohr three years ago during a Copenhagen Conference. It was found that the easiest way to obtain an experimental test of this theory would be to scatter protons of more than 2,000,000 volts in hydrogen. Such experiments are already planned as part of the program by Tuve and Hafstad for the new high-tension laboratory at the Department of Terrestrial Magnetism. A special conclusion of Gamow and Teller, namely, that a new type of saturation should be effective in nuclei, was generally discussed. This led to a more definite formulation of the problems involved, of which Critchfield (student at George Washington University) will attempt a further theoretical analysis.

One significant feature was the initial meeting at which Crane of the University of Michigan outlined his present experimental indications that the beta-particles of continuous spectra behave differently in their passage through matter from the secondary beta-rays arising as recoil electrons. Crane agrees that the evidence at present is insufficient to indicate a necessity for changing our fundamental conceptions of the beta-ray process. Rumors of these experiments had recently disturbed all theoreticians, lest the physical basis for all their calculations might be erroneous. The discussion of these experiments encouraged Crane to carry out the decisive Bücherer experiment and encouraged the theoreticians to continue their calculations on the old basis at least until further evidence against these conceptions is brought forward.

It was again the unanimous opinion of the members of the Conference that this type of “working” meeting is much more effective in furthering their investigations than any other scientific meetings for physicists now organized in this country. Letters so far received from members of the Conference emphasize this; extracts from these letters are attached to this report as Appendix A.

This Conference, as in previous years, was held under the joint auspices of the George Washington University and the Carnegie Institution of Washington, from February 15-20, 1937, with formal sessions on the afternoons of February 15 (at the Department of Terrestrial Magnetism, Carnegie Institution of Washington) and February 17 (at George Washington University). Besides the informal sessions, meetings were held also at the Department of Terrestrial Magnetism February 18, 19, and 20 and at George Washington University on the other days. The invited members of the Conference were:

Professor Niels Bohr, Institute for Theoretical Physics, University of Copenhagen Professor, Frits Kalckar, Institute for Theoretical Physics, University of Copenhagen, Professor James H. Bartlett, Jr., University of Illinois, now at Institute for Advanced Study, Princeton University, Professor H. A. Bethe, Cornell University Professor, Felix Bloch, Stanford University, Professor G. Breit, University of Wisconsin (also Research Associate of the Carnegie Institution of Washington), Professor W. H. Furry, Harvard University, Professor G. Gamow, George Washington University (also Research Associate of the Carnegie Institution of Washington), Professor M.S. Plesset, University of Rochester, Professor I. I. Rabi, Columbia University, Professor E. Teller, George Washington University, Professor L. H. Thomas, Ohio State University, Professor John A. Wheeler, University of North Carolina, now at Institute for Advanced Study, Princeton University, Professor Eugene P. Signer, University of Wisconsin,

The following investigators also were present informally:

Professor J. Franck, Johns Hopkins University, Professor K. F. Herzfeld, Catholic University of America, Dr. H. R. Crane, University of Michigan, Professor K. J. Seegar, George Washington University, Dr. F. B. Silsbee, National Bureau of Standards, Dr. M. A. Tuve, Dr. L. R. Hafstad, and Dr. I. F. Heydenburg, Department of Terrestrial Magnetism, Carnegie Institution of Washington, Dr. S. A. Korff and Dr. R. D. Roberts, guest investigators, Department of Terrestrial Magnetism, Carnegie Institution of Washington, Charles Critchfield, Graduate Student, George Washington University,

The total cost of this Conference, chiefly for the travel and living expenses of its invited members, was $973.87 which was shared equally by George Washington University and the Carnegie Institution of Washington.

Attached is a photograph of the members of the Conference taken at the Department of Terrestrial Magnetism, Carnegie Institution of Washington, February 18.

NOTE: Charles Critchfield [1], who was a GW student at the time of this conference, went on to work on the Manhattan Project.

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Author or Source: President's Papers/RG0002; Office of Public Relations
Document Location: University Archives
Date Added to Encyclopedia: January 11, 2007
Prepared by: Lyle Slovick, Assistant University Archivist

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