Harold Urey
Post-war years

After the war, Urey became professor of chemistry at the Institute for Nuclear Studies, and then became Ryerson professor of chemistry at the University of Chicago in 1952. He did not continue his pre-war research with isotopes. However, applying the knowledge gained with hydrogen to oxygen, he realized that the fractionation between carbonate and water for oxygen-18 and oxygen-16 would decrease by a factor of 1.04 between 0 and 25 °C (32 and 77 °F). The ratio of the isotopes could then be used to determine average temperatures, assuming that the measurement equipment was sufficiently sensitive. The team included his colleague Ralph Buchsbaum. Examination of a 100-million-year-old belemnite then indicated the summer and winter temperatures that it had lived through over a period of four years. For this pioneering paleoclimatic research, Urey was awarded the Arthur L. Day Medal by the Geological Society of America, and the Goldschmidt Medal of the Geochemical Society. While at the University of Chicago, Urey contributed to the Urey–Bigeleisen–Mayer equation, a model of stable isotope fractionation.

Urey actively campaigned against the 1946 May-Johnson bill because he feared that it would lead to military control of nuclear energy, but supported and fought for the McMahon bill that replaced it, and ultimately created the Atomic Energy Commission. Urey's commitment to the ideal of world government dated from before the war, but the possibility of nuclear war made it only more urgent in his mind. He went on lecture tours against war, and became involved in Congressional debates regarding nuclear issues. He argued publicly on behalf of Ethel and Julius Rosenberg, and was called before the House Un-American Activities Committee.
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