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Emission of neutrons by uranium. Offprint
1939.

Szilard, Leo (1898-1964) and Walter H. Zinn (1906-2000). Emission of neutrons by uranium. Offprint from Physical Review 56 (1939). 619-624pp. Text illustrations. 268 x 201 mm. Without wrappers as issued. Light toning but very good. Presentation Copy, inscribed “With Compliments of Leo Szilard” in an unidentified hand on first page. From the library of Theodore von Kármán (1881-1963), docketed and stamped with Kármán’s cataloguing symbols.

First Edition, Offprint Issue. The second of Szilard and Zinn’s two important papers on the experimental production of fast neutrons from uranium—an essential component of the nuclear chain reaction. Hahn and Strassmann had discovered nuclear fission in 1938, and Szilard immediately realized that fission would be the key to releasing nuclear energy. In that year Szilard had emigrated from England to the United States, and he began a series of experiments with Walter Zinn at Columbia University in New York to determine which characteristics of fission would make it possible to establish a chain reaction.

“'All we needed to do,” [Szilard] said later, “was to get a gram of radium, get a block of beryllium, expose a piece of uranium to the neutrons which come from the beryllium, and then see by means of the ionization chamber which Zinn had built whether fast neutrons were emitted in the process . . .'

"He got his radium, two grams sealed in a small brass capsule, early in March, after he arranged admission to the Columbia laboratories for three months as a guest researcher. He and Zinn immediately set up their experiment. They made an ingenious nest, like Chinese boxes, of its various components: a large cake of paraffin wax, the beryllium cylinder set at the bottom of a blind hole in the paraffin, the radium capsule fitted into the beryllium cylinder; resting on the beryllium, inside the paraffin, a box lines with neutron-absorbing cadmium filled with uranium oxide; pushed into that box, but shielded from the radium’s gamma radiation by a lead plug, the ionization tube itself, which connected to an oscilloscope. With this arrangement . . . they could measure the flux of neutrons from the uranium with and without the cadmium shield . . . "(Rhodes, The Making of the Atomic Bomb, pp. 288; 291).

Szilard and Zinn found that about two neutrons were emitted per fission, which matched the results of similar experiments conducted at the same time by Fermi and Anderson at Columbia and by Frédéric Joliot and his colleagues in France. He and Zinn announced their findings in a brief paper (“Instantaneous emission of fast neutrons in the interaction of slow neutrons with uranium,” Physical Review 55 [April 1939]: 799-800), following it in October with the present paper describing their further experiments.

This copy of Szilard and Zinn’s paper is from the library of Hungarian physicist Theodore von Kármán (1881-1963), founder of the Jet Propulsion Laboratory, who made fundamental advances in the fields of aeronautics and astronautics. Wigner, Leo Szilard 1898-1964: A Biographical Memoir (1969). 38913


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Last Found On: 2014-10-02           Check availability:      Biblio    

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