FERMI, Enrico & SZILARD, Leo.

Neutronic reactor. Patent 2,708,656, application filed December 19, 1944, patented May 17, 1955. [Washington, DC]: United States Patent Office, [1955]. [With:] Neutronic reactor. Patent 2,807,581, application filed October 11, 1945, patented September 25, 1957. Ibid., [1957].

[Washington, DC]: United States Patent Office, 1955; 1957.

First edition, incredibly rare, of this “historic patent [2,708,656], covering the first nuclear reactor” (New York Times, May 19, 1955). “No published reference article behind the present Patent exists. Some partial results may be found in several papers of [Fermi], but here very many technical data and some information of historic interest (mainly on the experiments performed in order to obtain the data reported) are given” (Esposito & Pisanti, pp. 218-9). This patent “is the first one on this topic issued by the U.S. Patent Office, and served as a reference for the subsequent Patents on the same subject. In this long Patent, the theory, experimental data and principles of construction and operation of ‘any’ type of nuclear reactor known at that time are discussed in an extremely detailed way” (ibid., p. 217). The second patent is a variant of the first, with a different arrangement of the uranium within the reactor. Fermi emigrated from Italy to the US in January 1939, and immediately accepted a position at Columbia University, New York. “Within weeks of [Fermi’s] arrival, news that uranium could fission astounded the physics community … The implications were both exciting and ominous, and they were recognized widely. When uranium fissioned, some mass was converted to energy, according to Albert Einstein’s famous formula E = mc². Uranium also emitted a few neutrons in addition to the larger fragments. If these neutrons could be slowed to maximize their efficiency, they could participate in a controlled chain reaction to produce energy; that is, a nuclear reactor could be built. The same neutrons traveling at their initial high speed could also participate in an uncontrolled chain reaction, liberating an enormous amount of energy through many generations of fission events, all within a fraction of a second; that is, an atomic bomb could be built … Fermi had built a series of ‘piles,’ as he called them, at Columbia. Now he moved to the University of Chicago, where he continued to construct piles in a space under the stands of the football field. The final structure, a flattened sphere about 7.5 metres (25 feet) in diameter, contained 380 tons of graphite blocks as the moderator and 6 tons of uranium metal and 40 tons of uranium oxide as the fuel, distributed in a careful pattern. The pile went ‘critical’ on Dec. 2, 1942, proving that a nuclear reaction could be initiated, controlled, and stopped” (Britannica). “On December 2, 1942, man first initiated a self-sustaining nuclear chain reaction, and controlled it. Beneath the West Stands of Stagg Field, Chicago, late in the afternoon of that day, a small group of scientists witnessed the advent of a new era in science. History was made in what had been a squash-rackets court. Precisely at 3:25 p.m., Chicago time, scientist George Weil withdrew the cadmium-plated control rod and by his action man unleashed and controlled the energy of the atom. As those who witnessed the experiment became aware of what had happened, smiles spread over their faces and a quiet ripple of applause could be heard. It was a tribute to Enrico Fermi, Nobel Prize winner, to whom, more than to any other person, the success of the experiment was due” (The First Reactor, US Department of Energy, December 1982). Fermi “was the only physicist in the twentieth century who excelled in both theory and experiment, and he was one of the most versatile” (DSB). OCLC lists just one copy of the first patent worldwide (Argonne National Laboratory), and none of the second. There is a copy of both patents in the Enrico Fermi Collection at the University of Chicago (lib.uchicago.edu/e/scrc/findingaids/view.php?eadid=ICU.SPCL.FERMI). We are not aware of any other copy of either patent having appeared in commerce.

Fermi has described the construction of the Chicago Pile, and the events leading up to it, in his autobiography Fermi’s Own Story (in The First Reactor, op. cit.): “The year was 1939. A world war was about to start. The new possibilities appeared likely to be important, not only for peace, but also for war. A group of physicists in the United States—including Leo Szilard, Walter Zinn, now director of Argonne National Laboratory, Herbert Anderson, and myself—agreed privately to delay further publications of findings in this field.

“We were afraid these findings might help the Nazis. Our action, of course, represented a break with scientific tradition and was not taken lightly. Subsequently, when the government became interested in the atom bomb project, secrecy became compulsory. Here it may be well to define what is meant by the ‘chain reaction,’ which was to constitute our next objective in the search for a method of utilizing atomic energy.

“An atomic chain reaction may be compared to the burning of a rubbish pile from spontaneous combustion. In such a fire, minute parts of the pile start to burn, and in turn ignite other tiny fragments. When sufficient numbers of these fractional parts are heated to the kindling points, the entire heap bursts into flames. A similar process takes place in an atomic pile, such as was constructed under the West Stands of Stagg Field at the University of Chicago in 1942.

“The pile itself was constructed of uranium, a material that is embedded in a matrix of graphite. With sufficient uranium in the pile, the few neutrons emitted in a single fission that may accidentally occur strike neighboring atoms, which in turn undergo fission and produce more neutrons. These bombard other atoms and so on at an increasing rate until the atomic ‘fire’ is going full blast. The atomic pile is controlled and prevented from burning itself to complete destruction by cadmium rods, which absorb neutrons and stop the bombardment process. The same effect might be achieved by running a pipe of cold water through a rubbish heap; by keeping the temperature low, the pipe would prevent the spontaneous burning.

“The first atomic chain reaction experiment was designed to proceed at a slow rate. In this sense, it differed from the atomic bomb, which was designed to proceed at as fast a rate as was possible. Otherwise, the basic process is similar to that of the atomic bomb. The atomic chain reaction was the result of hard work by many hands and many heads. Arthur H. Compton, Walter Zinn, Herbert Anderson, Leo Szilard, Eugene Wigner, and many others worked directly on the problems at the University of Chicago. Very many experiments and calculations had to be performed. Finally, a plan was decided upon. 

“Thirty ‘piles’ of less than the size necessary to establish a chain reaction were built and tested. Then the plans were made for the final test of a full-sized pile. The scene of this test at the University of Chicago would have been confusing to an outsider—if he could have eluded the security guards and gained admittance. He would have seen only what appeared to be a crude pile of black bricks and wooden timbers. All but one side of the pile was obscured by a balloon cloth envelope.

“As the pile grew toward its final shape during the days of preparation, the measurement performed many times a day indicated everything was going, if anything, a little bit better than predicted by calculations. Finally, the day came when we were ready to run the experiment. We gathered on a balcony about 10 feet above the floor of the large room in which the structure had been erected. Beneath us was a young scientist, George Weil, whose duty it was to handle the last control rod that was holding the reaction in check.

“Every precaution had been taken against an accident. There were three sets of control rods in the pile. One set was automatic. Another consisted of a heavily weighted emergency safety held by a rope. Walter Zinn was holding the rope ready to release it at the least sign of trouble. The last rod left in the pile, which acted as starter, accelerator, and brake for the reaction, was the one handled by Weil. Since the experiment had never been tried before, a ‘liquid control squad’ stood ready to flood the pile with cadmium salt solution in case the control rods failed. Before we began, we rehearsed the safety precautions carefully.

“Finally, it was time to remove the control rods. Slowly, Weil started to withdraw the main control rod. On the balcony, we watched the indicators which measured the neutron count and told us how rapidly the disintegration of the uranium atoms under their neutron bombardment was proceeding. At 11:35 a.m., the counters were clicking rapidly. Then, with a loud clap, the automatic control rods slammed home. The safety point had been set too low.

“It seemed a good time to eat lunch. During lunch everyone was thinking about the experiment but nobody talked much about it. At 2:30, Weil pulled out the control rod in a series of measured adjustments. Shortly after, the intensity shown by the indicators began to rise at a slow but ever-increasing rate. At this moment we knew that the self-sustaining reaction was under way. The event was not spectacular, no fuses burned, no lights flashed. But to us it meant that release of atomic energy on a large scale would be only a matter of time. The further development of atomic energy during the next three years of the war was, of course, focused on the main objective of producing an effective weapon.

“At the same time we all hoped that with the end of the war emphasis would be shifted decidedly from the weapon to the peaceful aspects of atomic energy. We hoped that perhaps the building of power plants, production of radioactive elements for science and medicine would become the paramount objectives. Unfortunately, the end of the war did not bring brotherly love among nations. The fabrication of weapons still is and must be the primary concern of the Atomic Energy Commission.

“Secrecy that we thought was an unwelcome necessity of the war still appears to be an unwelcome necessity. The peaceful objectives must come second, although very considerable progress has been made also along those lines. The problems posed by this world situation are not for the scientist alone but for all people to resolve. Perhaps a time will come when all scientific and technical progress will be hailed for the advantages that it may bring to man, and never feared on account of its destructive possibilities.”

“In this long Patent, the theory, experimental data and principles of construction and operation of ‘any’ type of nuclear reactor known at that time are discussed in an extremely detailed way. Various possible fission fragments produced by the reactor, several forms of the uranium employed (metal, oxide and so on, grouped in different geometrical forms), various materials adopted as moderators, several cooling systems, different geometries of the reactors, etc. are considered accurately.

“The theoretical description, centered around the achievement of a self-sustaining chain reaction, is exhaustive, and great attention is devoted to any possible cause of neutron loss, to the resonance capture of neutrons [the capture of neutrons by ²³⁸U nuclei to form ²³⁹U, which reduces the efficiency of the reactor], and to the effect of the presence of relevant impurities in the reactor. The chain production of neutrons in the pile is described in great detail …

“The problem of the variation of the multiplication factor [the average number of neutrons produced by the impact of a single neutron on a uranium nucleus] due to the production of radioactive elements, such as xenon, is discussed extensively. In particular it is pointed out that, although the initial production of xenon lowers the multiplication factor K due to its relevant neutron absorption, it subsequently increases again due to the decay of xenon into another isotope which absorbs fewer neutrons.

“The building up of reactors with solid (graphite) or liquid (heavy water) moderators is discussed, as well as other possible moderators such as light water or beryllium …

“Procedures for the purification of uranium are described as well. Several methods are reported for testing the purity against neutron absorption of different materials. The effect of the boron and vanadium impurities in the graphite and light water in the heavy water are considered.

“Different cooling systems for the reactors are considered and compared in the Patent, based on the circulation of a gas (typically, air) or a liquid (light or heavy water, diphenyl, etc.).

“The principles and practice for the construction, functioning and control of several kinds of reactors are reported in detail.

“One reactor considered in the present Patent is a low power uranium-graphite one without cooling system, where the active part consists in (small) cylinders of metallic uranium or pseudo-spheres of uranium oxide (or cylinders of U₃O₈). The control rods are made of steel with boron inserts, while limitation and safety rods are made of cadmium.

“In addition, a uranium-graphite pile cooled by air or even by water or diphenyl is considered. It is pointed out that diphenyl should usually be preferred with respect to water, due to its lower absorption of neutrons and to its higher boiling temperature, but the disadvantage related to its use is mainly due to the closed pumping system required and to the possible occurrence of polymerization which makes the fluid viscous.

“Another kind of reactor described in detail is made of uranium (vertical) bars immersed in heavy water. When, during the operation, heavy water is dissociated into D₂ and O₂, these two gaseous elements are carried by an inert gas (helium) into a recombination device. The control and safety rods are made of cadmium.

“Hybrid reactors composed of different lattices in the same neutronic reactor, in order to increase the multiplication factor K, are considered as well.

“A description of the possible uses of nuclear reactors, other than as power supplies, including the production of collimated beams of fast neutrons, the production of plutonium (a fissionable material usable in other reactors), or several other radioactive isotopes (for possible utilization in medicine), are also given” (Esposito & Pisanti, pp. 217-8).

Patent 2,807,581 “gives a detailed description of a variant of the reactor presented in Patent No. 2,708,656 by the same authors; it makes use of uranium arranged in plates, instead of spheres or rods. Such a different geometry is particularly efficient when a liquid moderator (for example heavy water) is used; in this case the moderator itself serves also as a coolant. In the Patent, however, the use of solid moderators (like graphite or beryllium) is discussed as well. The adoption of the given geometry leads to greater neutron losses in the reactor (due to resonant capture in uranium), but they are compensated by the use of a liquid moderator/coolant. The main subject of this Patent does not appear in any other published paper” (ibid., p. 493).

Enrico Fermi (1901-54) was born in Rome. In 1927, he was elected Professor of Theoretical Physics at the University of Rome (a post which he retained until 1938, when he – immediately after the receipt of the Nobel Prize – emigrated to America, primarily to escape Mussolini’s fascist dictatorship). Following the discovery by Curie and Joliot of artificial radioactivity (1934), he demonstrated that nuclear transformation occurs in almost every element subjected to neutron bombardment. This work resulted in the discovery of slow neutrons that same year, leading to the discovery of nuclear fission and the production of elements lying beyond what was until then the Periodic Table. Fermi won the 1938 Nobel Prize in Physics 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.’  In 1938, Fermi was without doubt the greatest expert on neutrons, and he continued his work on this topic on his arrival in the United States, where he was soon appointed Professor of Physics at Columbia University.

“Soon after his arrival in the United States, Fermi became instrumental in sparking the U. S. government’s interest in developing atomic energy for military purposes. Working with other physicists at the Metallurgical Laboratory in Chicago, which had been established for precisely this reason, he led a team to design and construct an exponential pile (sometimes referred to as Chicago Pile 1) in an empty room (formerly a squash court) under one of the university’s athletics fields. The first-ever controlled self-sustaining nuclear chain reaction took place in that pile on December 2, 1942. During the subsequent two years, Fermi conducted various experiments using the reactor, and assisted in the development of a larger reactor at the nearby Argonne Laboratory” (Britannica).

“In 1940 Szilard (1898-1964) became an American citizen and moved to New York. He began working at Columbia University (Pupin Laboratories) where he collaborated with Enrico Fermi, Walter Zinn, and Herbert Anderson. At Columbia Szilard submitted his nuclear break-through manuscript titled: ‘Divergent Chain Reactions in a System Composed of Uranium and Carbon’ in February of 1940.When World War II started, Szilard became intensely concerned about the possible nuclear weapons development programs that could be initiated. As a result of these concerns, his work on atomic energy intensified. He led an effort to have all nuclear-related research data withheld from publication, to help prevent Germany from obtaining any information, or possibly creating an atomic bomb. These concerns also prompted him, with the assistance of Eugene Wigner and Edward Teller, to contact Albert Einstein. After sharing his fears with Einstein and obtaining his consent, Szilard drafted a letter that Einstein signed. The now-famous Einstein Letter was subsequently delivered by Alexander Sachs to President Franklin D. Roosevelt in October of 1939. This letter outlined the possibility of achieving a nuclear chain reaction and its implications for the development of nuclear weapons for national defense. It also requested government support to conduct a large-scale experiment to prove whether or not a sustained nuclear chain reaction was possible. President Roosevelt approved the funding and the project. Szilard began procuring suitable quality graphite and uranium, the necessary materials for constructing a large-scale chain reaction experiment. This experiment was successfully demonstrated on December 2, 1942 at the University of Chicago. This successful demonstration was partially the result of Szilard’s atomic theories, his uranium lattice design, and the identification and mitigation of a key graphite impurity (boron) through a joint collaboration with graphite suppliers. Szilard was the chief physicist at the Chicago Metallurgical Laboratory from February 1942 to July 1946. He worked for Arthur H. Compton, the head of the Met Lab. Szilard helped build Chicago Pile-1, the first neutronic reactor to achieve a self-sustaining nuclear chain reaction” (atomicheritage.org/profile/leo-szilard).

Esposito & Pisanti (eds.), Neutron Physics for Nuclear Reactors. Unpublished Writings by Enrico Fermi, 2010.

Folio (288 x 197 mm), pp. [31], with 27 pages of plates; pp. [5], with 6 pages of plates.

Item #5926

Price: $45,000.00