After beginning study at several universities in Germany, he emigrated to the United States in 1937 during the early Holocaust period; though raised as a Lutheran, he had some Jewish ancestry.
[citation needed] He received his Ph.D. from Princeton University in 1940 under the direction of Rudolf Ladenburg; he also worked closely with John A. Wheeler.
After a suggestion by Niels Bohr, he carried out in only a few days with fellow graduate student Morton H. Kanner the first demonstration of fission by fast neutrons and thorium and uranium.
In a paper with John A. Wheeler he reported the discovery of spin-orbit coupling in neutron scattering.
In 1946 he joined the University of Wisconsin–Madison, where he remained for most of his career following a program on determining fast neutron cross-sections, directing the doctoral dissertation research of over forty students.