December 10, 1906–February 14, 2000
BY ALVIN M. WEINBERG
WALTER (“WALLY”) HENRY ZINN was Enrico Fermi’s close associate during the Manhattan Project. After World War II he became the leading U.S. figure in the earliest development of nuclear energy. So pervasive was his stamp on nuclear development that a proper obituary to Walter Zinn must be nothing short of an account of the origins of nuclear energy and how Zinn profoundly affected its development.
Fission was discovered in 1938. By then Zinn had already received his Ph.D. in physics from Columbia (in 1934) and had been on the faculty of City College of New York. He also had a laboratory at Columbia, where he collaborated with Leo Szilard and Enrico Fermi in elucidating the nature of fission. In those exciting days nuclear physicists were asking how many neutrons were emitted by a uranium nucleus undergoing fission induced by a neutron. If the answer were greater than one, a nuclear chain reaction was possible; if less than one, a divergent chain reaction was impossible. Zinn and Szilard found that about two neutrons were emitted by a fissioning uranium nucleus; in this they confirmed the results of Fermi, Anderson, and Hahnstein. Thus was born experimental verification of the Manhattan Project’s purpose: to make an atomic bomb.