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Manhattan: The Army and the Atomic Bomb

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Prologue: A History of Atomic Energy to 1939

The concept of the atomic structure of matter first emerged in the fifth century B.C. with the Greek theory of minute particles, or atoms, as the unchangeable and indivisible units comprising all material things.1 This new idea, however, lay dormant for nearly two thousand years because Aristotle’s view that all matter is continuous and composed of four elements – fire, earth, air, and water – prevailed in the minds of men. Following the Renaissance in Europe such philosophers and scientists as Galileo, Descartes, Bacon, Boyle, and Newton supported the early concept, and in the nineteenth century chemists (somewhat later, physicists) transformed this atomic theory into a material reality.

One of the first and important steps was the theory proposed by English chemist John Dalton in 1803 that each element is composed of like atoms, distinguishable from the atoms forming other elements primarily by differences in mass. He thus provided a practical and specific standard for nineteenth century scientists’ descriptions of ninety-two chemical elements (substances that cannot be broken down or transformed by chemical means). By the end of the century, all known elements had been arranged in a table, with similar properties in related positions, in numerical order according to atomic mass; it ranged from element 1, hydrogen, which was the lightest, to element 92, uranium, the heaviest. This “periodic table” not only enabled scientists to predict the properties of undiscovered elements but also became the basis of chemical and physical knowledge of the elements.

Beginning in the last decade of the nineteenth century, scientific discoveries by those European and American physicists who sought to explain the phenomenon of radioactivity opened the way for the modern development of atomic energy. This phenomenon is a property possessed by some elements to spontaneously emit radiation that ionizes gas and

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makes it capable of conducting electricity. Investigating electrical discharges in gases in 1895, German physicist Wilhelm Roentgen observed radiation emissions that penetrated opaque objects and also produced fluorescence. Roentgen’s discovery of these radiations, which he called X-rays, led French physicist Henri Becquerel to test fluorescent salts of uranium to see if they also would produce penetrating rays. In 1896, Becquerel demonstrated that uranium emits penetrating radiations that would ionize gas, proof that it was radioactive.

In England, physicist J. J. Thomson and a young student from New Zealand, Ernest Rutherford, used X-rays to ionize gases, providing further evidence that the penetrating rays were charged particles much smaller than atoms. In 1897, Thomson published data proving the existence of these particles, each having a mass of about one two-thousandth of a hydrogen atom. The following year he suggested that these particles, subsequently designated electrons, formed one of the basic building blocks comprising all atoms.

Rutherford’s succeeding investigations showed that the penetrating streams of emitted particles are composed of at least three different kinds of rays – alpha, beta, and gamma. Alpha ray particles are heavy, high-speed, positively charged bodies, later shown to be nuclei of helium atoms; beta ray particles are electrons; and gamma rays are similar in composition to X-rays. In 1911, Rutherford proposed the theory of the nuclear atom, with its mass and positive charge at the center. The work of Rutherford, Niels Bohr, a Danish physicist, and others led to the concept of the atom as a miniature solar system, with a heavy positive nucleus orbited by much lighter electrons.

Rutherford finally achieved, in 1919, what man had been attempting unsuccessfully for centuries: the artificial transmutation of an element. Since the discovery of natural radiation, scientists had known that disintegration of radioactive elements in nature caused them to change spontaneously into other elements. Bombarding nonradioactive nitrogen with high-energy alpha particles given off by naturally radioactive radium, Rutherford caused the nitrogen to disintegrate and change into what subsequently proved to be a form of oxygen. His achievement, although somewhat removed from the ancient alchemist’s dream of transmuting base metals into gold, was far more valuable and important. It was not only the first artificially induced transmutation; it was also the first controlled artificial disintegration of an atomic nucleus.

A further Rutherford achievement was isolation and identification of yet another basic building block of atomic structure. In addition to oxygen, nitrogen transmutation had produced a high-energy particle with characteristics similar to the positively charged nucleus of the hydrogen atom. Later study showed it was a hydrogen nucleus, and scientists gave it the name proton. Such a positively charged particle as a fundamental unit in the structure of all atoms had long been hypothesized; demonstration of its presence in nitrogen and other elements confirmed its identity.

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Discovery of the proton pointed toward the existence of a third particle. In 1932, James Chadwick, Rutherford’s co-worker at Cambridge University, discovered this third particle, the neutron, an uncharged body approximately equal in weight to the proton.

Now the atom was viewed as composed of a positively charged nucleus, containing protons and neutrons, orbited by negative electrons equal in number to the protons. The number of protons determined the atomic number, or numerical position, of the parent element in the periodic table. Thus hydrogen, element 1, has but a single proton; helium, element 2, two protons; and uranium, element 92, ninety-two protons. For each proton there is a balancing electron. The mass, or atomic weight, of an element is the sum of its protons and neutrons; the electrons, with negligible weight, do not materially affect the mass of the atom. The weight of each element is stated in relation to that of hydrogen, the lightest. Hydrogen, with a single proton and no neutrons, has an atomic weight of 1; helium, with 2 protons and 2 neutrons of equal weight, a mass of 4; and uranium, with 92 protons and 146 neutrons, a mass of 238. The chemical symbols for these elements are written 1H1, 2He4 and 92U238.

Thus far, three characteristics of elements had been identified: chemical uniqueness, atomic number, and atomic weight. But scientists also discovered that many elements exist in more than one form, differing solely in the number of neutrons that each contains. For example, there are two forms of helium, each with two protons and two electrons. They are chemically identical but one form has a single neutron, thus an atomic mass of 3, and the other, more prevalent form two neutrons, thus an atomic mass of 4. These substances are called isotopes (from the Greek words iso, meaning alike or same, and topos, meaning place) because they occupy the same place in the periodic table. The chemical symbols for the helium isotopes are written 2He3 and 2He4, or simply He-3 and He-4; or they may be spelled out, helium 3 and helium 4. Many other isotopes exist, either naturally or through scientific transmutations, and they are important in the story of atomic energy.

James Chadwick’s discovery of the neutron was not the only significant development in 1932. That same year British scientist J. D. Cockcroft and Irish scientist E. T. S. Walton, working together at Cambridge University’s Cavendish Laboratory, used a particle accelerator to bombard lithium with a stream of protons, causing the element to disintegrate. Unlike Rutherford, who experimented with alpha particles from natural sources, Cockcroft and Walton, in effect, produced their own protons through artificial means.

This artificially induced nuclear disintegration, however, was only one aspect of Cockcroft and Walton’s accomplishment. As a hydrogen nucleus, or proton, struck a lithium nucleus, the latter body disintegrated into two alpha particles of helium nuclei. The hydrogen atom with a mass of 1 united with a lithium nucleus having a mass of 7, thereby making a total mass of 8, and then this body immediately divided into two helium nuclei, each with a mass of 4. Thus,

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the two scientists were also the first to bring about atomic fission – or, in the popular phrase, to split the atom.2

Still another result of the Cockcroft-Walton experiment, and at the time considered most important, was its confirmation of Einstein’s theory of relativity, proposed in 1905, that matter and energy are merely different forms of the same thing. The atomic weights of the lithium, hydrogen, and helium nuclei expressed by Cockcroft and Walton in their experiment were only approximate. The combined mass of a lithium nucleus and a hydrogen nucleus is, in fact, very slightly more than the combined mass of two helium nuclei. Thus, the formation of two helium nuclei had resulted in a loss of mass. This lost mass was converted into energy in an amount that could be calculated by the Einstein equivalence formula E=mc2 (energy is equal to mass multiplied by the square of the velocity of light) or derived from the speed of the helium nuclei as they flew apart from the lithium. Because the two calculations provided answers in very close agreement, they confirmed Einstein’s theoretical projection and opened the prospect of using atomic fission as a major new source of energy.

In the experiments conducted so far, however, the total energy required to bombard the atomic nucleus and produce fission was much greater than the energy released. This initially high input of energy enabled the charged particle to approach and penetrate the atom, overcoming the repulsion of their mutual electrical charges. Furthermore, even when high-speed particles were used, only one in a million succeeded in hitting its target. This inefficiency led Rutherford to describe using nuclear fission as an energy source as practical as “moonshine,”3 and so it indeed appeared to many.

But Chadwick’s discovery of the neutron provided the solution. The neutron, because it was an uncharged particle, would not be repelled and therefore could penetrate a nucleus even at relatively slow speeds. Proof was to come from Italy, where in 1934 Enrico Fermi and his co-workers set about systematically bombarding the atoms of all known elements with neutrons. They soon demonstrated that the nuclei of several dozen elements could be penetrated by neutrons and thereby broken down and transmuted into nuclei of other elements. Their best results were obtained when the bombarding neutrons were first slowed down by passing them through such moderators as carbon or hydrogen.

The most important result of Fermi’s work was not fully understood for another four years. Among the substances he had bombarded with slow neutrons was uranium, which was naturally radioactive and the heaviest of all known elements. Theory and chemical analysis seemed to indicate that the substance produced by uranium transmutation was nothing hitherto known, but was in fact a new and heavier element. Uranium is element 92; this new element appeared to be element 93, or possibly

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even element 94. Fermi, so it seemed, had created transuranic elements not present in nature, and the popular press hailed his achievement as a major advance in science.4

Yet many scientists were skeptical, and Fermi himself was uncertain. The properties exhibited by the new substances were not those they had expected to find in transuranic elements. For the next four years, physicists and chemists were hard at work attempting to identify exactly what Fermi had produced. Progress was slow, exacerbated by the uncertainty of the times; fearing the advancing wave of political oppression, many scientists in. Germany, Austria, and Italy fled to havens elsewhere in Europe and in the United States. Nevertheless, out of Nazi Germany, the answer finally came. Just before Christmas of 1938, the radiochemists Otto Hahn and Fritz Strassmann concluded that one of the products of Fermi’s experiment was not a transuranic element at all. It was, rather, the element barium, with an atomic weight approximately half that of uranium.5

When Hahn informed his former co-worker, Lise Meitner, of the conclusions that he and Strassmann had reached, the Austrian physicist – who had recently escaped from Germany to Sweden – quickly comprehended the significance of the findings. Working with her nephew, British (Austrian-born) physicist Otto Frisch, she concluded that the bombardment of uranium by slow neutrons produced two elements of roughly half the weight of uranium. In the splitting process there was a tremendous release of energy, far more than necessary to cause fission. Without delay she passed this exciting information on to Niels Bohr, who was about to leave Denmark for an extended stay at the Institute for Advanced Study at Princeton University. Thus, even as Hahn and Strassmann published the results of their work in Europe, Bohr carried news of their conclusions to the United States.6

Further experiments confirmed the discovery of atomic fission and raised the possibility that a practical means of obtaining atomic energy could at last be realized. Splitting the uranium atom released not only energy but also two or three additional neutrons. Perhaps, under the right conditions, these neutrons might smash other atoms, releasing more neutrons to bombard more atoms while simultaneously generating a continuous emission of energy. This process, or chain reaction, would be self-sustaining and would continue for as long as uranium atoms were present to be split.

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During 1939, scientists in America, England, France, Germany, the Soviet Union, Japan, and other countries worked intensively to extend both the theoretical and experimental knowledge of atomic fission. By the end of the year, nearly one hundred papers on the subject had been published.7 In the United States, native Americans and a group of European refugees combined their energies and scientific talents to investigate various aspects of the complex problem, carrying on their work at such institutions as Columbia, Johns Hopkins, Princeton, the University of California at Berkeley, and the Carnegie Institution in Washington, D.C.8

Uranium and Fission

Uranium is considered a rare element, although it is a thousand times more prevalent than gold. Uranium is more widely dispersed and occurs infrequently in a relatively concentrated form. Found always with radium, primarily as uranium oxide, it occurs mainly in pitchblende and in carnotite ores. Before World War II the main value of these ores lay in their radium content, although uranium was also used for coloring glassware and ceramics, for tinting photographic film, and for making certain steel alloys. Uranium was rarely produced as a metal; metallurgists had not yet measured its melting point accurately.

Substantial radium-uranium concentrations in the Shinkolobwe mine in Katanga Province of the Belgian Congo were owned by the Union Miniere du Haut Katanga, a Belgian firm that completely dominated the world market. So rich were the Shinkolobwe concentrations that in 1937 the company, having stockpiled sufficient ore to satisfy the anticipated world demand for radium and uranium for the next thirty years, ceased mining operations.

Important but less productive deposits were located in the Eldorado mine at Great Bear Lake in northern Canada, and ores of much lower grade were found in the Colorado Plateau region in the western United States; however, Colorado Plateau radium and uranium producers were forced to close down because they could not compete commercially with those in the Congo and Canada. In addition, other uranium deposits of varying quality were located in Czechoslovakia, Portugal, England, Madagascar, and elsewhere.9

Natural uranium is composed of three isotopes: U-238, about 99.28 percent; U-235, about 0.71 percent;

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and U-234, just a trace. Experimenting with the isotopic properties of uranium, scientists eventually proved that U-235 was fissionable by both slow and fast neutrons, although more controllably so by the former.

When U-235 fissions, it emits fast neutrons, which are captured by the U-238. The U-238 does not fission but becomes radioactive and disintegrates. For a chain reaction to be self-sustaining, at least one neutron emitted by the U-235 has to penetrate another U-235 atom. Because the fast neutrons are most easily absorbed by the U-238, the 140-to-1 ratio of U-238 to U-235 in natural uranium makes it even more improbable that the neutrons can escape the U-238 and be captured by U-235 atoms. Many neutrons, moreover, escape altogether from the uranium and others are absorbed by impurities within it. This is why uranium does not fission in its natural state and why an emission of neutrons does not occur in any ordinary lump of uranium.

Proper conditions for achieving a chain reaction required that the number of neutrons absorbed by impurities in uranium and the number of neutrons lost through its surface or captured by its U-238 isotope be kept to a minimum. Neutron absorption could be decreased by using a careful chemical process to remove the impurities, although the technique was difficult and posed major problems. Because the number of neutrons lost from a piece of uranium depends on the area of the surface and because the number of neutrons captured depends on its mass or volume, neutron escape or capture could be reduced by using a suitable shape and size. The greater the amount of uranium, the smaller would be its surface area relative to volume and thus, proportionately, the fewer neutrons that could be lost through the surface or captured by the U-238. During fission, production of at least one neutron in excess of those lost or captured would cause the uranium to reach its critical mass and possibly trigger a chain reaction.

The dilemma researchers faced in 1939 was ascertaining the exact size of this critical mass. The consensus was that a tremendous amount of uranium – far more than had ever been produced and concentrated – would be necessary. A practical solution to the supposed enormity of the problem therefore was to reduce the size of the critical mass by decreasing the number of neutrons captured by the U-238. The U-235 could be separated from the U-238, or the ratio of U-235 to U-238 could be increased artificially.

Theories about what should be done, however, did not quite coincide with what could be done at this stage of the research. Because the two uranium isotopes were chemically identical, their separation by chemical means was impossible. And the about 1-percent difference in mass between U-235 and U-238 meant that separation by physical means would be most difficult. Although producing a sufficient amount of pure U-235 or U-235-enriched natural uranium to maintain a chain reaction in a critical mass of practical proportions appeared only barely possible, there were those who continued to work on the multistage problem of separating what were considered, in Fermi’s

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words, “almost magically inseparable” isotopes.10

All separation methods deemed possible were based on the difference in atomic weight. One process, the electromagnetic method, employed a mass spectrometer or spectrograph. In this process a stream of charged particles of a given element is projected through a magnetic field, which deflects them from their original path. Because the atoms of a heavier isotope will be more strongly affected by the magnetic field than those of a lighter isotope, the stream of particles will be separated into two or more streams, each containing a different isotope, which can then be collected in different receivers. Alfred O. Nier of the University of Minnesota did the initial work on this process. At this time, the electromagnetic method proved to be not only ridiculously slow but also quantitatively insufficient. It would have taken twenty-seven thousand years for each mass spectrometer to produce a single gram of U-235 or 27 million spectrometers a whole year to separate a kilogram of the isotope.

Another process, the gaseous diffusion method, was based on the principle that if two gases of different atomic weights are passed through a porous barrier, the lighter gas will diffuse through more readily. First, uranium would have to be transformed from its naturally solid state into a gas; then, because of the 140-to-1 ratio of U-238 to U-235, the diffusion process would have to be repeated in order to produce any appreciable amount of U-235 or U-235- enriched uranium. Scientists in Great Britain performed most of the early theoretical and experimental work on this method. In the United States, it was not until late 1940 that physicist John R. Dunning and a small group of collaborators at Columbia University began intensive research into the technical problems of gaseous diffusion.11

A third method was the centrifuge process, in which uranium in a gaseous form is rotated rapidly in a cylinder. Because centrifugal force causes the atoms of the heavier isotope to amass along the outer walls and those of the lighter isotope to concentrate around the axis of rotation, the desired isotope can then be drawn off. Jesse W. Beams at the University of Virginia and others in the United States seemed to offer the best initial promise for separating uranium isotopes, but the magnitude of the engineering problem was such that, as with the other separation methods, the centrifuge process offered no quick or easy solution.

The avenues of research were not solely limited to isotope separation methods. At Columbia University, Enrico Fermi and Leo Szilard, a refugee physicist from Hungary, experimented with the possibility of achieving a chain reaction in uranium without separating its isotopes – research that in the not too distant future would culminate in the world’s first chain reaction. Basing their investigations on research that Fermi had carried out five years earlier on

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the use of moderators to slow down neutrons, they explored the likelihood that a moderating substance might be mixed with natural uranium in such a way that the high-speed fission-produced neutrons could be sufficiently slowed before meeting other uranium atoms so as to escape capture by U-238 and remain free to penetrate the U-235.

The two most promising moderators were hydrogen and carbon. Water might make a good moderator; however, because hydrogen exists in two natural isotopes (light hydrogen, the more prevalent, with a mass of 1, and heavy hydrogen, or deuterium with a mass of 2), “heavy water,” containing deuterium, should make an even better one. Scientists in France and England had investigated the use of heavy water, but it was extremely costly to produce and was highly volatile. Feeling that heavy hydrogen was in some ways less efficient as a moderator, Fermi and Szilard turned their attention to carbon, which was readily available in the form of graphite. Proving its feasibility through theoretical investigation and experimentation would take time, energy, and money, but the two scientists were confident they could achieve a chain reaction.12

Because such a chain reaction could provide a tremendous amount of energy in a form that might be converted into power, this uranium-graphite system promised to have ready military application for driving large ships or aircraft but seemed impractical for use as a bomb. A bomb would have to be so large that the sudden release of energy in an uncontrolled nuclear explosion would blow it apart before more than a small amount of energy was freed; that amount was not worth the great effort necessary to detonate it.

Yet, if it were possible to separate U-235 from the naturally more prevalent U-238 or to enrich natural uranium greatly in its U-235 isotope, then a fast-neutron chain reaction might be achieved and extremely powerful bombs, far smaller than any explosive uranium-graphite system, could probably be built. Controlled energy from a fast-neutron chain reaction could, of course, be used as a power source; but, uncontrolled, it would provide a far more powerful explosion than ever before attained by man. Though perhaps too heavy for a conventional bomber, a U-235 bomb could be brought by ship into an enemy port and exploded with devastating effect.

In early 1939, however, the chances of constructing a bomb of U-235 appeared far less certain than those of building a power-producing uranium-graphite system. To use Fermi’s words, there seemed “little likelihood of an atomic bomb, little proof that we were not pursuing a chimera.”13

Nevertheless, possible military application of atomic energy was of increasing interest to a group of foreign-born physicists now living and working in the United States. These men – including Enrico Fermi from Italy; Leo Szilard, Eugene Wigner, and Edward Teller from Hungary;

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and Victor Weisskopf from Austria – knew that government-supported nuclear research was under way at the Kaiser Wilhelm Institute in Berlin, and the likely military consequences of a German breakthrough worried them very much. As most of them had only recently fled their homelands to escape fascist tyranny, they had no wish to see Nazi Germany acquire a means of dominating the whole world. Indeed, if any nations were to exploit atomic energy for military purposes, they believed the democracies would do well to be first.

These physicists therefore directed their energies toward two ends: keeping all advances in nuclear research a secret to discourage an all-out German effort, and obtaining support from the American government for further nuclear research. The group almost achieved one of its goals in early 1939, when leading physicists in the United States and Great Britain pledged not to publish the results of their work in the field. However, in France, Frederic Joliot-Curie refused, and his determination to publish his own research led to continued publication by scientists in other countries. It was not: until late 1940, after a large number of articles had appeared in scientific journals and the popular press, that publication on atomic energy generally ceased.

Efforts To Enlist Support of the U. S. Government

The atomic scientists’ first attempt to gain support from the U.S. government for their atomic energy research came in March of 1939, even as German troops were completing the occupation of Czechoslovakia. Scheduled to give a lecture in Washington, D.C., on the sixteenth, Enrico Fermi arrived in the national capital with a letter of introduction from Dean George B. Pegram of Columbia to Rear Adm. Stanford C. Hooper, director of the Technical Division, Office of the Chief of Naval Operations. On the morning of the seventeenth, Fermi met with Admiral Hooper and other individuals, including Ross Gunn, a physicist and technical adviser of the Naval Research Laboratory. Pegram, who was also a physicist, had explained in his letter what Fermi discussed in his lecture, namely, the importance of atomic energy and its possible uses for mankind, although both men were prudent about making predictions.

Gunn and his associates at the Naval Research Laboratory already were aware of the potentialities of atomic energy; however, they were more interested in the prospects for nuclear ship propulsion than in developing an atomic bomb. Now Fermi’s visit spurred them on to continue their own investigations, but it did not lead to any naval support for the scientists working at the universities.14 A second approach to Gunn, made by Szilard in June, was no more successful. While the Navy pursued its own program of research on uranium isotope separation, Gunn indicated to Szilard in July that “it seems almost impossible, in the light of the restrictions

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which are imposed on Government contracts for services, to carry through any sort of agreement that would be really helpful to you.”15

By mid-July, then, Szilard, Teller, and Wigner concluded that another channel had to be found. The results of ongoing nuclear research indicated that a chain reaction could very probably be achieved in a uranium-graphite system, “and that this possibility had to be considered as an imminent danger.”16 There was, moreover, ominous news from Europe of continued German interest and progress in nuclear research. American scientists returning from visits to Germany reported a growing emphasis on the investigation of isotope separation, with the apparent objective of achieving a fast-neutron chain reaction in U-235, the basis of an atomic bomb.17 After moving into Czechoslovakia, the Germans closed the door on the country’s uranium ore exports. Convinced that the need to keep other uranium deposits from falling into German hands required action at the highest level, Szilard, Teller, and Wigner approached Einstein. At first, Szilard thought to have Einstein approach the Department of State and use his acquaintance with the royal family in Belgium as a means for stopping uranium ore shipments to the Germans. But, after further discussion, he decided a direct approach to the White House was necessary. Through a refugee journalist friend, Szilard secured an introduction to Alexander Sachs, a Wall Street economist and student of international affairs who had long been an informal adviser of President Franklin D. Roosevelt. Sachs was familiar with the subject of atomic energy, having read avidly Hahn and Strassmann’s first report and having followed subsequent publications on atomic fission. Also, he had become acutely aware of the possible military applications of atomic energy during Niels Bohr’s visit to the Institute of Advanced Study at Princeton. Indeed, the growing tensions in Europe and Germany’s increasing threat to world peace eventually led him to discuss the Hahn-Strassmann report and its possible effect on the international situation in a brief session with Roosevelt early in March.

Sachs agreed to help, and he and Szilard concluded that a letter from Einstein to Roosevelt would emphasize the importance of their message. The letter, primarily the work of Szilard, was drafted in Sachs’s office. Szilard and Teller took it to Einstein, who was vacationing on Long Island, on 2 August. Sources disagree over whether Einstein rewrote the Sachs-Szilard draft or merely put his name to it; but, in any event, Szilard returned to Sachs with a signed letter from Einstein to the President.18

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This letter, a milestone in the American atomic energy program, states that “it is almost certain that this [a chain reaction in a large mass of uranium] could be achieved in the immediate future” and that this phenomenon could possibly lead to the construction of a new type of an extremely powerful bomb.19

To this letter, Szilard himself added a careful memorandum. In it he explained in more detail the scope and effects of research on atomic fission, the unproved nature of its conclusion, and the need for financial support for further investigation. He pointed out that atomic energy released through a chain reaction achieved with slow neutrons could be utilized for ship or aircraft propulsion, and also raised the possibility that a fast-neutron chain reaction would result in a powerful explosive. Szilard also reemphasized the need for acquiring large stocks of uranium ore from the Belgian Congo and suggested that another attempt to arrange for the withholding of publications on the subject of nuclear research might be necessary.20 Included with the letter and memorandum were reprints of two articles from the Physical Review that provided documentation of the scientific points raised by Einstein and Szilard.

Despite the agreed upon necessity for haste, almost two months passed before Sachs was able to bring Einstein’s letter and its inclosures to the White House. “Mere delivery of memoranda was insufficient,” he felt.21 In the hectic days of August and September 1939, with war in Europe first an imminent danger and then a frightening actuality, there seemed little likelihood that Roosevelt could spare Sachs more than a few moments. Not until early October did Sachs find a time he felt was suitable to approach the President.

The story of Sachs’s visit to the White House has been told frequently and with several variations. Suffice it to say that Sachs met with Roosevelt for over an hour on 11 October. Reading aloud, Sachs prefaced Einstein’s letter and Szilard’s memorandum with a letter of his own in which he summarized and amplified the other material, emphasizing German nuclear research, the danger of German seizure of Belgian uranium, and the “urgent” need to arrange for American access to the uranium ore of the Belgian Congo. He stressed the necessity of enlarging and accelerating experimental work, which could not be done on limited university budgets, and seconded the suggestion made in Einstein’s letter for liaison between the government and the scientists.22

The President’s initial reaction was one of skeptical interest. He was doubtful about the availability of funds to support nuclear research and

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felt, moreover, that there were other aspects of national defense with a higher claim for attention. Nevertheless, he invited Sachs to breakfast the next morning and, at this second meeting, was convinced of the necessity for action.

President Roosevelt’s 12 October decision to explore the potentialities of atomic energy eventually led to complete governmental direction of nuclear research in the United States. And, in the early years of its development, no single government agency was to play a more important role than the United States Army.

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