The Making of the Atomic Bomb: 25th Anniversary Edition

by Richard Rhodes

Man is not satisfied with a happy idyllic life: he has the need to fight and to encounter danger. And he concluded that what mankind must do to save itself is to launch an enterprise aimed at leaving the earth. On this task he thought the energies of mankind could be concentrated and the need for heroism could be satisfied.

“I took a train from Berlin to Vienna on a certain date, close to the first of April, 1933,” Szilard writes. “The train was empty. The same train the next day was overcrowded, was stopped at the frontier, the people had to get out, and everybody was interrogated by the Nazis.73 This just goes to show that if you want to succeed in this world you don’t have to be much cleverer than other people, you just have to be one day earlier.”

Albert Einstein admired Bohr for “uttering his opinions like one perpetually groping and never like one who [believed himself to be] in the possession of definite truth.”

“Bohr’s different,” Rutherford roared, disguising affection with bluster. “He’s a football player!” Bohr was different in another regard as well; he was easily the most talented of all Rutherford’s many students—and Rutherford trained no fewer than eleven Nobel Prize winners during his life, an unsurpassed record.

In the real world cause and effect sometimes seem to limit our freedom, but at other times we know we choose. In the real world it is meaningless to doubt existence; the doubt itself demonstrates the existence of the doubter. Much of the difficulty was language, that slippery medium in which Bohr saw us inextricably suspended. “It is wrong,” he told his colleagues repeatedly, “to think that the task of physics is to find out how nature is”—which is the territory classical physics had claimed for itself. “Physics concerns what we can say about nature.”

“ ‘God does not throw dice’ was a phrase we often heard from his lips in these discussions,” writes Heisenberg. “And so he refused point-blank to accept the uncertainty principle, and tried to think up cases in which the principle would not hold.” Einstein would produce a challenging thought experiment at breakfast, the debate would go on all day, “and, as a rule, by suppertime we would have reached a point where Niels Bohr could prove to Einstein that even his latest experiment failed to shake the uncertainty principle. Einstein would look a bit worried, but by next morning he was ready with a new imaginary experiment more complicated than the last.”

Bohr, for his part, supple pragmatist and democrat that he was, never an absolutist, heard once too often about Einstein’s personal insight into the gambling habits of the Deity. He scolded his distinguished colleague finally in Einstein’s own terms. God does not throw dice? “Nor is it our business to prescribe to God how He should run the world.”

The difference between the thinking of the paranoid patient and the scientist comes from the latter’s ability and willingness to test out his fantasies or grandiose conceptualizations through the systems of checks and balances science has established—and to give up those schemes that are shown not to be valid on the basis of these scientific checks. It is specifically because science provides such a framework of rules and regulations to control and set bounds to paranoid thinking that a scientist can feel comfortable about taking the paranoid leaps.

The results confirmed the Cavendish’s earlier count. Chadwick then went to Vienna. “He found,” write his biographers, “that the scintillation counting was done by three young women—it was thought that not only did women have better eyes than men but they were less likely to be distracted by thinking while counting!”

Hans Bethe once remarked that he considered everything before 1932 “the prehistory of nuclear physics, and from 1932 on the history of nuclear physics.”603 The difference, he said, was the discovery of the neutron.

“Relativity” was a misnomer. Einstein worked his way to a new physics by demanding consistency and greater objectivity of the old. If the speed of light is a constant, then something else must serve as the elastic between two systems at motion in relation to one another—even if that something else is time.

The Third Reich promulgated its first anti-Jewish ordinance on April 7. The Law for the Restoration of the Professional Civil Service, the harbinger of some four hundred anti-Semitic laws and decrees the Nazis would issue, changed Teller’s life, Pauli’s, Frisch’s, the lives of their colleagues decisively, forever. It announced bluntly that “civil servants of non-Aryan descent must retire.”674 A decree defining “non-Aryan” followed on April 11: anyone “descended from non-Aryan, especially Jewish, parents or grandparents.”675 Universities were state institutions. Members of their faculties were therefore civil servants. The new law abruptly stripped a quarter of the physicists of Germany, including eleven who had earned or would earn Nobel Prizes, of their positions and their livelihood.676 It immediately affected some 1,600 scholars in all.

“Fermi’s thumb was his always ready yardstick,” Laura Fermi writes. “By placing it near his left eye and closing his right, he would measure the distance of a range of mountains, the height of a tree, even the speed at which a bird was flying.”

As Hans Bethe once noted wittily, the efficiency of slow neutrons “might never have been discovered if Italy were not rich in marble. . . . A marble table gave different results from a wooden table.826 If it had been done [in America], it all would have been done on a wooden table and people would never have found out.”

Bohr had won national distinction for his work and the enduring gratitude of refugees for his aid; he had also faced personal pain. In 1932 the Danish Academy offered him lifetime free occupancy of the Danish House of Honor, a palatial estate in Pompeiian style built originally for the founder of Carlsberg Breweries and subsequently reserved for Denmark’s most distinguished citizen (Knud Rasmussen, the polar explorer, was its previous occupant).

“He told me he would be surprised if one could work in Vienna in two years. He said Hitler would be there. And he was”—the Anschluss—“almost to the day.”

During the same period Szilard wrote Michael Polanyi he would “stay in England until one year before the war, at which time I would shift my residence to New York City.”896 The letter provoked comment, Szilard enjoyed recalling; it was “very funny, because how can anyone say what he will do one year before the war?” As it turned out, his prognostication was off by only four months: he arrived in the United States on January 2, 1938.

To a greater extent than any other scientist of the twentieth century Bohr perceived the institution of science to which he dedicated his life to be a profoundly political force in the world. The purpose of science, he believed, was to set men free. Totalitarianism, in Hannah Arendt’s powerful image, drove toward “destroying all space between men and pressing men against each other.”923 It was entirely in character that Bohr, at a time of increasing danger, publicly opposed that drive with the individualistic and enriching discretions of complementarity.

It was also entirely in character, when Fermi came to Copenhagen, that Bohr should lead him aside, take hold of his waistcoat button and whisper the message that his name had been mentioned for the Nobel Prize, a secret traditionally never foretold. Did Fermi wish his name withdrawn temporarily, given the political situation in Italy and the monetary restrictions, or would he like the selection process to go forward? Which was the same as telling Fermi he could have the Prize that year, 1938, if he wanted it and was welcome to use it to escape a homeland that threatened now despite the distinction he brought it to tear his wife from citizenship.

One of Oppenheimer’s students, the American theoretical physicist Philip Morrison, recalls that “when fission was discovered, within perhaps a week there was on the blackboard in Robert Oppenheimer’s office a drawing—a very bad, an execrable drawing—of a bomb.”

“We tried to convince him,” Teller writes, “that we should go ahead with fission research but we should not publish the results. We should keep the results secret, lest the Nazis learn of them and produce nuclear explosions first. Bohr insisted that we would never succeed in producing nuclear energy and he also insisted that secrecy must never be introduced into physics.”

Fermi noted in a later lecture that “it was not very clear [in 1939] that the job of separating large amounts of uranium 235 was one that could be taken seriously.”1126 At the Princeton meeting, Teller remembers, Bohr insisted that “it can never be done unless you turn the United States into one huge factory.”

The next afternoon Fermi turned up at the Navy Department on Constitution Avenue for his appointment with Admiral Hooper. He had probably planned a conservative presentation. The contempt of the desk officer who went in to announce him to the admiral encouraged that approach. “There’s a wop outside,” Fermi overheard the man say.1129 So much for the authority of the Nobel Prize.

Both sides might work from fear of the other. But some on both sides would be working also paradoxically believing they were preparing a new force that would ultimately bring peace to the world.

“How much money do you need?” Commander Hoover wanted to know.1237 Szilard had not planned to ask for money. “The diversion of Government funds for such purposes as ours appears to be hardly possible,” he explained to Pegram the next day, “and I have therefore myself avoided to make any such recommendation.”1238 But Teller answered Hoover promptly, probably speaking for Fermi: “For the first year of this research we need six thousand dollars, mostly in order to buy the graphite.” (“My friends blamed me because the great enterprise of nuclear energy was to start with such a pittance,” Teller reminisces; “they haven’t forgiven me yet.”

Adamson had anticipated just such a raid on the public treasury. “At this point,” says Szilard, “the representative of the Army started a rather longish tirade”: He told us that it was naive to believe that we could make a significant contribution to defense by creating a new weapon. He said that if a new weapon is created, it usually takes two wars before one can know whether the weapon is any good or not.

The possibility of a critical mass is anchored in the fact that the surface area of a sphere increases more slowly with increasing radius than does the volume (as nearly r2 to r3). At some particular volume, depending on the density of the material and on its cross sections for scattering, capture and fission, more neutrons should find nuclei to fission than find surface to escape from; that volume is then the critical mass.

Thus in the first months of 1940 it was already clear to two intelligent observers that nuclear weapons would be weapons of mass destruction against which the only apparent defense would be the deterrent effect of mutual possession.

Enrichment—increasing the proportion of U235 to U238—was also “the only method of producing explosives several orders of magnitude more powerful than the strongest explosives yet known.”1281 (The phrase indicates Heisenberg understood the possibility of fast-neutron fission even before Frisch and Peierls did.)

learning of the War Office’s need it approached the Norwegians with an offer to buy all the heavy water on hand, about fifty gallons worth some $120,000, and to order more at the rate of at least thirty gallons a month. Norsk Hydro was then producing less than three gallons a month, enough in the prewar years to glut the small physics-laboratory market. It wanted to know why Germany needed so vast a quantity. I.G. Farben chose not to say. In February the Norwegian firm refused either to sell its existing stock or to increase production.

Nuclear research in the Soviet Union during this period was limited to skillful laboratory work. Two associates of Soviet physicist Igor Kurchatov reported to the Physical Review in June 1940 that they had observed rare spontaneous fissioning in uranium. “The complete lack of any American response to the publication of the discovery,” writes the American physicist Herbert F. York, “was one of the factors which convinced the Russians that there must be a big secret project under way in the United States.”

The American Embassy quickly passed word that it could guarantee the Bohrs safe passage to the United States. Bohr again chose duty. His immediate concern was to burn the files of the refugee committee that had helped hundreds of emigres to escape to exile. “It was characteristic of Niels Bohr,” his collaborator, Stefan Rozental, writes, “that one of the first things he did was to contact the Chancellor of the University and other Danish authorities in order to protect those of the staff at the Institute whom the Germans might be expected to persecute.”

“Then he started to talk about the role of the scientist,” Teller recalls, “who has been accused of inventing deadly weapons.1324 He concluded: ‘If the scientists in the free countries will not make weapons to defend the freedom of their countries, then freedom will be lost.’ ” Teller believed Roosevelt was not proposing what scientists may do “but something that was our duty and that we must do—to work out the military problems, because without the work of the scientists the war and the world would be lost.”

The Riken began measuring cross sections in December. In April 1941 the official order came through: the Imperial Army Air Force authorized research toward the development of an atomic bomb.

And 94 EkaOs 239, Turner proposed, changing from an odd to an even number of neutrons when it absorbed a neutron preparatory to fissioning (239 nucleons—94 protons = 145 neutrons + 1 = 146) just as U235 changed to U236, ought to be even more fissionable than the lighter uranium isotope:

Consistent with Martin Klaproth’s inspiration in 1789 to link his discovery of a new element with the recent discovery of the planet Uranus and with McMillan’s suggestion to extend the scheme to Neptune, Seaborg would name element 94 for Pluto, the ninth planet outward from the sun, discovered in 1930 and named for the Greek god of the underworld, a god of the earth’s fertility but also the god of the dead: plutonium.

The report began with the statement that the committee was concerned with “the matter of possible military aspects of atomic fission” and listed three of those possibilities: “production of violently radioactive materials . . . carried by airplanes to be scattered as bombs over enemy territory,” “a power source on submarines and other ships” and “violently explosive bombs.” Radioactive dust would need a year’s preparation after “the first successful production of a chain reaction,” which meant “not earlier than 1943.” A power source would need at least three years after a chain reaction. Bombs required concentrating U235 or possibly making plutonium in a chain reaction, so “atomic bombs can hardly be anticipated before 1945.”

He had learned to cooperate for survival in the Soviet Union, where the NKVD—the KGB of its day—had knocked out all his teeth and kept him in solitary confinement for months. But in Germany as in the USSR he withheld as much information as he dared. His private endorsement of 94, to be transmuted by chain reaction from natural uranium, probably contributed to the neglect of isotope separation in Germany. After the summer of 1941 the German bomb program depended entirely on uranium and Vemork heavy water.

Fritz Houtermans

Churchill liked his documents held to half a page.

He thought an isotope-separation plant should be erected not in the United States but in England—despite manpower shortages and the risk of German bombing—or “at worst” in Canada. In that conclusion he differed from the MAUD Committee.1452 “The reasons in favor [of an English location],” he wrote, “are the better chance of maintaining secrecy . . . but above all the fact that whoever possesses such a plant should be able to dictate terms to the rest of the world. However much I may trust my neighbor and depend on him, I am very much averse to putting myself completely at his mercy. I would, therefore, not press the Americans to undertake this work.”

Enrico Fermi and Edward Teller were not, however, the first to conceive of using a nuclear chain reaction to initiate a thermonuclear reaction in hydrogen. That distinction apparently belongs to Japanese physicist Tokutaro Hagiwara of the faculty of science of the University of Kyoto. Hagiwara had followed world fission research and had conducted studies of his own. In May 1941 he lectured on “Super-explosive U235,” reviewing existing knowledge.1468, 1469 He was aware that an explosive chain reaction depended on U235 and understood the necessity of isotope separation: “Because of the potential application of this explosive chain reaction a practical method of achieving this must be found. Immediately, it is very important that a means of manufacturing U-235 on a large scale from natural uranium be found.”

Patriotism contributed to many decisions, but a deeper motive among the physicists, by the measure of their statements, was fear—fear of German triumph, fear of a thousand-year Reich made invulnerable with atomic bombs. And deeper even than fear was fatalism. The bomb was latent in nature as a genome is latent in flesh. Any nation might learn to command its expression. The race was therefore not merely against Germany. As Roosevelt apparently sensed, the race was against time.

The United States was not yet committed to building an atomic bomb. But it was committed to exploring thoroughly whether or not an atomic bomb could be built. One man, Franklin Roosevelt, decided that commitment—secretly, without consulting Congress or courts. It seemed to be a military decision and he was Commander in Chief.

“Jan 19—V.B. OK—returned—I think you had best keep this in your own safe FDR”

Still orphaned was plutonium, which Lawrence and Compton believed so promising. Compton found his chance to speak for it in early December when Bush and Conant called the members of the Uranium Committee to Washington to announce the reorganization of their work. Harold Urey would develop gaseous diffusion at Columbia, Bush and Conant had decided. Lawrence would pursue electromagnetic separation at Berkeley. A young chemical engineer, Eger V. Murphree, the director of research for Standard Oil of New Jersey, would supervise centrifuge development and look into broader questions of engineering. Compton in Chicago would be responsible for theoretical studies and the actual design of the bomb.

When Heisenberg took questions from the floor, one of Speer’s deputies asked how large a bomb capable of destroying a city would have to be. Heisenberg cupped his hands as Fermi had done sighting down Manhattan Island from Pupin Hall. “As large as a pineapple,” he said.

Following that, according to Speer, “on the suggestion of the nuclear physicists we scuttled the project to develop an atom bomb . . . after I had again queried them about deadlines and been told that we could not count on anything for three or four years.” Work on what Speer calls “an energy-producing uranium motor for propelling machinery”—the heavy-water pile—would continue.1575 “In the upshot,” Heisenberg wrote in Nature in 1947, summarizing the war years, German physicists “were spared the decision as to whether or not they should aim at producing atomic bombs.1576 The circumstances shaping policy in the critical year of 1942 guided their work automatically toward the problem of the utilization of nuclear energy in prime movers.” But the Allies had not yet been informed.

Transmuting U238 to plutonium in a chain-reacting pile was one thing, extracting the plutonium from the uranium quite another. The massive production piles that Compton’s people were already beginning to plan would create the new element at a maximum concentration in the uranium of about 250 parts per million—a volume, uniformly dispersed through each two tons of mingled uranium and highly radioactive fission products, equal to the volume of one U.S. dime. Seaborg’s work was somehow to pull that dime’s worth out.

“There is a statement of rather common currency around here and Berkeley that goes something like this: ‘No matter what you do with the rest of your life, nothing will be as important to the future of the World as your work on this Project right now.’ ”

They had not yet bothered to name generic bombs of uranium and plutonium. But from the pre-anthropic darkness where ideas abide in nonexistence until minds imagine them into the light, the new bomb emerged already chased with the technocratic euphemism of art deco slang: the Super, they named it.