A large conference on nuclear physics was held in London and Cambridge from October 1–6, 1934. Six German refugee physicists were present, but Werner Heisenberg was not. Czech theoretical physicists Guido Beck and Kurt Sitte had proposed a theory of beta decay that challenged Fermi’s, which Beck presented but apparently gained no support for. On October 22, Fermi serendipitously discovered the efficaciousness of slow neutrons in producing nuclear reactions. Niels Bohr would be the greatest beneficiary of Fermi’s discovery. In 1935 Bohr, with the assistance of refugee Otto Robert Frisch, began to develop experimental nuclear physics at his institute, which after its inauguration in 1920 became a mecca for young physicists. On September 29, 1943, Bohr and his family were among the 7220 Danish and other Jews who were transported to Sweden in the greatest mass rescue operation of the war.
