A chemical impurity that absorbed neutrons would prevent the chain reaction from developing. ![]() This was one of two possible materials needed as a “moderator” to slow down the neutrons emitted in fission so they could be absorbed by other uranium atoms to produce a chain reaction. One of the elements Rubby was investigating was carbon in the form of graphite. He was told to keep his discovery secret, and published his nuclear studies after the war, with only a hint of his discovery. In the course of his second measurement, Rubby made an accidental discovery that was significant for the war effort to control nuclear fission to make a bomb. Rubby was the sole author of the paper “Collision Cross Sections for 25-MeV Neutrons.” He did the measurements while he was at Harvard, sometime between 19, but submitted the paper for publication a few years later, on September 27, 1945, six weeks after the end of WWII when Japan surrendered on August 15, 1945. In the second study, the 25-MeV neutron beam was used to measure the sizes of nuclei of several elements ranging from carbon to mercury. While the nuclear reaction did produce a small number of gold atoms, the gold isotopes were radioactive and decayed back to mercury within a few days. Their results were published in 1941 and attracted considerable attention. (By contrast, three quarters of a century later, the energy of the beam in the Large Hadron Collider in Geneva is 500,000 times greater.)įor the first study, Rubby directed the neutrons onto a mercury target causing nuclear reactions that converted some of the mercury into gold. At that time, this was the highest energy beam that had been produced. The neutrons came out of the target with a wide range of energies up to a maximum of 25 MeV. He did two studies of nuclear reactions with high-energy neutrons that were produced when 11 MeV deuterons from the cyclotron struck a lithium-7 target. In 1939 Rubby left Princeton to join the faculty at Harvard where he continued nuclear research with the recently constructed Harvard cyclotron. This was a time when little was know about many of these nuclei. Rubby and White did a study of short-lived radioactive isotopes produced by bombarding various targets with the cyclotron beam. In 1935 Professor Milton White had constructed a cyclotron in the basement of Palmer Hall (now the Frist Student Center). Rubby’s first nuclear physics experiment was done at Princeton shortly after he received his doctorate. These sudden changes propelled Rubby into a career in nuclear physics that eventually took him to Los Alamos and the development of the first atomic bomb. Later that year, Germany invaded Poland and set off World War II. The discovery meant the possibility of a new beneficial source of power, and also, the prospect of powerful bombs. ![]() The Hahn-Strassmann data on the breakup uranium by slow neutrons in late 1938, followed by the theoretical interpretation by Meitner and Frisch in early 1939, implied a huge release of energy by slow-neutron fission of uranium. at a time when new developments in physics and international affairs had far reaching consequences. ![]() Rubby (pronounced “Ruby”) completed his Ph.D. It was a testament to his experimental talent. thesis, “The Separation of Isotopes by Diffusion” was a daunting experimental challenge involving twenty-nine glass mercury diffusion pumps with hundreds of vacuum seals. degree in physics in 1934, then entered graduate school at Princeton University and completed his Ph.D. He attended New York University, where he received his B.A. Rubby Sherr was born Septemin Long Branch, New Jersey, of immigrant parents form Lithuania. Princeton Center for Theoretical Physics.The Center for the Physics of Biological Function.Institute for Research and Innovation in Software for High Energy Physics.
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