Between his entry and graduation from Columbia, Slack spent a period of study and research with Arnold Sommerfeld at his Institute of Theoretical Physics at the Ludwig Maximilian University of Munich.
[3] In December 1938, the German chemists Otto Hahn and Fritz Strassmann sent a manuscript to Naturwissenschaften reporting they had detected the element barium after bombarding uranium with neutrons;[7] they communicated these results to Lise Meitner.
[10][11][12] Even before it was published, Meitner's and Frisch's interpretation of the work of Hahn and Strassmann crossed the Atlantic Ocean with Niels Bohr, who was to lecture at Princeton University.
It was soon clear to a number of scientists at Columbia that they should try to detect the energy released in the nuclear fission of uranium from neutron bombardment.
On 25 January 1939, Slack was a member of the experimental team at Columbia University which conducted the first nuclear fission experiment in the United States,[13] which was conducted in the basement of Pupin Hall; the other members of the team were Herbert L. Anderson, Eugene T. Booth, John R. Dunning, Enrico Fermi, and G. Norris Glasoe.