Neutron Production and Absorption in Uranium in Physical Review Volume 56, Second Series, Number 3, August 1, 1939 pp. 284-286

Lancaster: American Institute of Physics, 1939. 1st Edition. FIRST EDITION IN ORIGINAL WRAPS of an important experiment in early fission research that was also led directly to Albert Einstein's famous letter to President Roosevelt urging his understanding of the potential lethality of chain fission reactions and prompting him to start the Manhattan Project.

It had already been determined that there existed an abundant emission of neutrons from uranium under the action of slow neutrons. While at Columbia, Szilard, Fermi, and Anderson sought to study the production and absorption of neutrons in uranium – working specifically in this paper to “ascertain whether and to what extent the number of neutrons emitted exceeds the number absorbed” (Szilard et al, Physical Review 56, August 1, 1939, 284).

They found that the question could be “investigated by placing a photo-neutron source in the center of a large water tank and comparing, with and without uranium in the water, the number of thermal neutrons present in the water” (ibid). The experiment the physicists designed for a chain reaction device used “water as a "moderator" to slow fast neutrons produced by fissioning nuclei to an energy where they would sustain a chain reaction” (AIP Portal).

Szilard maintained many contacts in the industrial and political spheres and was able to procure a large amount of uranium-235 (200 kg.) “as well as a radium-beryllium neutron source containing more than 2g of radium. The oxide was filled into longish, cylindrical cans, which were arranged in a regular pattern. The source was placed in the centre and the whole assembly put in a tank containing a 10% solution of manganese sulphate in water. The activity of the manganese was a measure for the neutron intensity and was found to be ten percent higher if the uranium was in place” (Brandt, Harvest of a Century, 279).

By this means it was ascertained that more neutrons were emitted by the uranium than absorbed. (See Collected Papers of Enrico Fermi Vol II, p. 11). The experiments had revealed that the hydrogen in water itself absorbs too many neutrons to be an effective moderator”, but the meaning was clear that the chain reaction and with it the use of nuclear energy was within reach” (Brandt, 279; AIP Portal).

While Anderson, Fermi, and Szilard chose to end their paper cautiously, writing “More work is] required before we can conclude that a chain reaction is possible in mixtures of uranium and water”, Szilard thought it time to contact Albert Einstein. (Anderson et al., PR 56, p. 286).

Immediately upon completion of the paper, Szilard contacted Einstein, convincing him to write a letter to President Roosevelt (largely if not wholly drafted by Szilard) that warned of the military implications of the discovery of chain fission and the immensely lethal damage that could be wrought by an atomic bomb. Specifically, the letter warned that Germany was capable of developing atomic bombs and that the United States should develop its own nuclear program. As Slizard had hoped, the letter prompted Roosevelt to action, eventually resulting in the Manhattan Project’s development of the first atomic bombs.

Enrico Fermi was awarded the Nobel Prize in Physics (1938) "for his demonstrations of the existence of new radioactive elements produced by neutron irradiation, and for his related discovery of nuclear reactions brought about by slow neutrons" (Nobel Prize Portal). Item #686

CONDITION & DETAILS: Original wraps. Lancaster: American Institute of Physics. 4to. 10.5 x 7.75 inches (262 x 194mm). Bearing the ownership signature on the front wrap of D. W. Epstein who developed the electron gun in 1934. The wraps remain tight; minor scuffing at the edges; two red stains at the spine. Otherwise bright and clean throughout.

Price: $325.00