Before the Fallout

by Diana Preston

  With his hallmark persistence, Szilard continued relentlessly to lobby Fermi with the help of an intermediary: the American-born physicist Isidor I. Rabi, one of the first Jewish physicists appointed at Columbia and selected thanks to glowing references from Werner Heisenberg. As Szilard later recounted, the debate resembled a quick-fire comedy routine rather than a serious debate between scientists.

  I went to see Rabi, and I said to him, "Didyou talk to Fermi?"

  Rabi said, "Yes, I did."

  I said: "What did Fermi say?"Rabi said, "Fermi said 'Nuts!' "

  So I said, "Why did he say 'Nuts!'?"

  And Rabi said, "Well, I don't know, but he is in and we can ask him."

  So we went over to Fermi's office and Rabi said to Fermi, "Look, Fermi, I told you what Szilard thought and you said 'Nuts!' and Szilard wants to know why you said 'Nuts!

  So Fermi said, "Well, there is the remote possibility that neutrons may be emitted in thefssion of uranium and then of course perhaps a chain reaction can be made."

  Rabi said, "What do you mean by remote possibility?"

  And Fermi said: "Well ten per cent."

  Rabi said, "Ten percent is not a remote possibility if it means that we may die of it. If I have pneumonia and the doctor tells me that there is a remote possibility that I might die, and that it's ten per cent, I get excited about it"

  Fermi, who, according to Emilio Segre, abhorred battles, finally gave in. He agreed not to publish any further findings on fission and neutron research and encouraged his colleagues at Columbia to do likewise.

  · · ·

  Leo Szilard also singled out Frederic Joliot-Curie at the College de France as one of those likely to stumble on the chain reaction. The potential of nuclear fission, especially an estimate by Lise Meitner and Otto Frisch that a single fissuring uranium nucleus could release enough energy to make a grain of sand jump visibly, had certainly caught the Frenchman's attention. With two ambitious assistants—the Russian Lew Kowarski and the Austrian Hans von Halban—he was devoting himself to exploring the phenomenon of uranium fission. Kowarski was "a gruff . . . enormous brute of a man . . . with the memory of an elephant." The illegitimate son of a Russian Jewish merchant and a Russian Orthodox opera singer, he had fled to France after the Russian Revolution with his father and had struggled to find enough money to complete his studies. The good-looking von Halban was also partly Jewish but from a much more affluent background in Vienna. He had come to France before Hitler's annexation of Austria and, in contrast to Kowarski, was an urbane, cultured charmer.

  On 2 February 1939 Szilard wrote to Joliot-Curie, begging him to publish nothing openly about neutron research: "Obviously, if more than one neutron were liberated, a sort of chain reaction would be possible. In certain circumstances this might then lead to the construction of bombs which would be extremely dangerous in general and particularly in the hands of certain governments." He asked the Frenchman to exercise "sufficient discretion to prevent a leakage of these ideas" to the press and told him of proposals for a concerted approach to physicists across the United States, Britain, and France seeking a moratorium on publicizing work on fission. He also pointed out that Fermi was holding back from publication results achieved by the Columbia team.

  Szilard's letter arrived at an unfortunate time. The French team was poised to publish a paper reporting the results of an intricate set of experiments proving that uranium fission produced neutrons. They were, as von Halban described, excited by their findings: "We were thoroughly convinced that the conditions for establishing a divergent chain reaction with neutrons could be realized." Their reaction to Szilard's proposal was negative. In the words of Bertrand Goldschmidt, the young French chemist who had promised to be Madame Curie's "slave," "the Szilard proposal was neither completely understood nor accepted at the College de France." Joliot-Curie maintained that self-censorship conflicted with his support for internationalism and the freedom of science, but, according to Goldschmidt, reluctance to forgo the glory was a key factor in his thinking. Joliot-Curie's views were not shared by Paul Langevin, Marie Curie's erstwhile reputed lover. He believed the new discoveries to be more dangerous than Hitler, telling a refugee from Germany, "Hitler? It won't be long before he breaks his neck like all the other tyrants. I'm much more worried about something else. It is something which, if it gets into the wrong hands, can do the world a good deal more damage than that fool who will sooner or later go to the dogs. It is something which—unlike him—we shall never be able to get rid of: I mean the neutron."

  In March 1939, the month that Hitler seized the remnants of Czechoslovakia not ceded to him at Munich, Joliot-Curie and his team rushed their paper to the British journal Nature. Despite further pleas from Szilard and like-minded allies such as his fellow Hungarian Eugene Wigner and the Viennese Victor Weisskopf, on 7 April—the day that Mussolini invaded Albania—they dispatched a second paper to Nature. In it they estimated the number of secondary neutrons produced through the fission of a single uranium nucleus by a single neutron to be 3. c, each of which could fission another uranium nucleus, releasing more and more energy and further neutrons. The figure of 3. c. would prove an overestimate—the true figure was, on average, around 2.5—but from Szilard's perspective, the damage was done. The article appeared in Nature on 22 April 1939.

  Joliot-Curie's team thus became the first to publish results showing that fission produced enough secondary neutrons to have the potential to start a chain reaction. Their principal preoccupation was the ability to use the energy released by fission to produce nuclear power. Anxious to protect France's position, they took out a series of secret patents on the construction and operation of nuclear reactors to contain and exploit chain reactions for the production of nuclear power. However, just as Szilard had feared, their articles in Nature were spotted by German scientists whose interest was in weapons, not nuclear energy. In a letter of 24 April 1939, the Hamburg professor Paul Harteck, a chemical explosives consultant to the German army who had spent a year at the Cavendish Laboratory with Ernest Rutherford, alerted Erich Schumann, the head of weapons research in the German army's weapons office, to the potential military applications of nuclear fission. He wrote that recent developments in nuclear physics might lead to the production of an explosive far more powerful than any yet known and that any country possessing it would have an "unsurpassable advantage."

  In Bertrand Goldschmidt's view Joliot-Curie's team "started the Germans off." After the war, when Lew Kowarski was asked why they had published such sensitive information at such a sensitive time, he replied, "Why not secure priority? Hell, as I always say, it's not vanity—it's bread and butter." The publication of the Joliot-Curie team's work in Nature also blasted Szilard's hopes of a general agreement on self-censorship. He continued to argue fiercely and volubly for restraint, but the Joliot-Curie articles had made his position, for a while, at least, untenable.

  · · ·

  Fermi had meanwhile begun his own experiments into chain reactions at Columbia. They confirmed everything Szilard had warned of. Looking down toward the skyscrapers of lower Manhattan from his high office window and shaping his hands into a large-sized ball, he reflected to a colleague, "A little bomb like that and it would all disappear." By mid-March 1939 Fermi was so concerned that he discussed the need to alert the U.S. government with the head of the Columbia physics department, George Pegram. Pegram wrote to Admiral Stanford C. Hooper, the technical director for naval operations, warning "uranium may be able to liberate its large excess of atomic energy, and this might mean that uranium might be used as an explosive that would liberate a million times as much energy per pound as any known explosive." He added that, in his own view, "the probabilities are against this" but that "the bare possibility should not be disregarded."

  Fermi was invited to Washington to present his findings to a group of senior naval officers. Accounts conflict about the reception Fermi received. According to one, the presentation began unpromisingly
when Fermi overheard himself being announced to Admiral Hooper with the words "There's a wop outside." Having heard "the wop's" careful, measured presentation, the navy gave Columbia a meager fifteen hundred dollars for fission research. As Emilio Segre wryly observed, "Although the sum was puny, it indicated goodwill."

  · · ·

  Niels Bohr shared Fermi's instinctive distaste for secrecy, believing that "openness is the basic condition necessary for science. It should not be tampered with." However, he also believed, like Szilard, that war was coming. Laura Fermi, who with her husband had been among the group waiting on the New York quayside to welcome Bohr when he stepped off the Drottningholm in January, had noticed how tired and stooped he looked. He had aged since the Fermis had visited him in Copenhagen on their way from Stockholm to the United States. She did not, like John Wheeler, catch his whispered announcement of the discovery of nuclear fission, but she heard him mutter a stream of worried comments: "Europe . . . war . . . Hitler . . . Denmark . . . danger . . . occupation." In the weeks after his arrival she recalled that Bohr spoke constantly of "the doom of Europe in increasingly apocalyptic terms and that his face was that of a man haunted by one idea."

  Almost at once Bohr began working on the consequences of fission at the Institute of Advanced Study at Princeton, helped by John Wheeler. In early February, while puzzling over why the rate of uranium fission he was observing was some one hundred times less than he would have expected, he had a burst of inspiration. Perhaps, he reasoned, the two isotopes present in uranium—the dominant U-238 (so named for its 92 protons and 146 neutrons) and the much rarer U-235 (with 92 protons but 143 neutrons)—behaved differently when bombarded with neutrons. If only U-235 (constituting less than 0.7 percent of natural uraniun) was splitting, and not the U-238 (of which natural uranium was almost entirely composed), this would explain the low rate of fission. It was hard for bombarding neutrons to find a suitable target.

  Pondering why U-235 should be more susceptible to fission than U-238, Bohr deduced that the reason related to the number of neutrons and protons and the effect this had on the binding energy of a nucleus when a neutron was added. Adding a neutron to U-235 resulted in an even number of neutrons and a tightly bound U-236 compound nucleus, whereas adding a neutron to U-238 resulted in an odd number of neutrons and a less tightly bound U-239 compound nucleus. The tighter binding of U-236 meant that its formation released significantly more energy than was the case for the formation of U-239—and this further agitated the neutrons and protons of the U-236 to the point where they elongated into the wasp waist required for fission in Bohr's liquid-drop model. So he concluded that neutrons traveling at any speed would fission U-235. Conversely, in the case of U-238, the energy release was insufficient for fission by slow neutrons.

  As Bohr chalked row after row of formulae on his blackboard, his underlying hope was that, if he was right and the isotope U-235 was the key to fission, this would make an atomic bomb unviable. A massive industrial effort would be required to separate out sufficient quantities of the isotope from natural uranium. According to Edward Teller, Bohr told a group including Szilard, Wigner, and himself, gathered expectantly in his office at Princeton, "You would need to turn the entire country into a factory." On 1 5 March Bohr published his initial conclusions in Physical Review.

  Nevertheless, if sufficient U-23C could, after all, be obtained, an atomic bomb remained a possibility. Bohr conceded as much to a meeting of the American Physical Society in April 1939. Speculating about the results of bombarding a small amount of uranium with neutrons, he admitted it might produce a chain reaction or an atomic explosion. The press picked up his remarks and presented apocalyptic visions to their readers. The science writer of the New York Times, William L. Laurence, portrayed uranium as the "philosopher's stone" and predicted that a tiny quantity could "blow a hole in the earth 100 miles in diameter. It would wipe out the entire City of New York, leaving a deep crater halfway to Philadelphia and a third of the way to Albany and out to Long Island as far as Patchogue."The Washington Post's headline was "Physicists Here Debate Whether Experiments Will Blow Up 2 Miles of the Landscape."

  · · ·

  Scientists in the free world faced decisions not only about whether to publicize their work but about how to respond to old friends and acquaintances still working in totalitarian countries. Some were in no doubt what they should do. In February 1939 the American physicist Percy Bridgman announced in the journal Science: "I have decided from now on not to show my apparatus to or discuss my experiments with the citizens of any totalitarian state. A citizen of such a state is no longer a free individual, but may be compelled to engage in any activity whatever to advance the purposes of that state. . . . Cessation of scientific intercourse with totalitarian states serves the double purpose of making more difficult the issues of scientific information by these states and of giving the individual opportunity to express abhorrence of their practices."

  Yet no such embargoes affected Werner Heisenberg that summer of 1939 when he was invited to lecture at universities across the United States. Some American scientists speculated openly that his real purpose, as he traversed the country, was to gather intelligence on fission. However, his old friends, many of them emigre Jewish scientists like Hans Bethe with whom personal bonds of trust and affection were still strong, welcomed him. They also urged him again and again to leave Germany. At Ann Arbor, where Heisenberg stayed with Sam Goudsmit, a Dutchman of Jewish extraction who had emigrated to the United States in the 1920s, he met Enrico Fermi, who was attending the annual physics summer school at the University of Michigan. Their friendship too went back a long way—both had attended Max Born's lively seminars in Gottingen—but while bonds remained, their discussions revealed how much their lives and opinions had diverged.

  Heisenberg's view was that "Italy's leading physicist" had chosen to "ride out the coming storm" in the United States. He did not seem to recognize that choice had had little to do with it, if Fermi was to protect his wife and children. According to Heisenberg, the two men discussed whether Heisenberg should also emigrate. It would certainly have been easy for him to find a post. George Pegram at Columbia University was one of several only too eager to offer the German Nobel laureate a professorship. Fermi queried why Heisenberg did not stay in America and play his part "in the great advance of science." "Why renounce so much happiness?" Fermi asked. Heisenberg's reply was that he had gathered around him a small circle of young people anxious to ensure that "uncontaminated science" could make a comeback in postwar Germany and that "if I abandoned them now, I would feel like a traitor."

  According to a young graduate hired as a bartender at a party attended by Fermi and Heisenberg and who overheard them, Fermi tried to convince Heisenberg that his belief that he "could influence, even guide the [Nazi] government in more rational channels" was a naive illusion. He argued that the fascists had "no principles; they will kill anybody who might be a threat. . . . You only have the influence they grant you." Heisenberg's reply was that "Germany needed him." According to his own account, Heisenberg also argued, "Every one of us is born into a certain environment, has a native language and specific thought patterns, and if he has not cut himself off from his environment very early in life, he will feel most at home and do his best work in that environment." He added, with characteristic insouciance, that "people must learn to prevent catastrophes, not to run away from them."

  Heisenberg also recorded how Fermi pressed him on the issue of fission—a subject which, according to Heisenberg, he himself was never the first to raise during his visit. Fermi warned that "there is now a real chance that atom bombs may be built. Once war is declared, both sides will perhaps do their utmost to hasten this development, and atomic scientists will be expected by their respective governments to devote all their energies to building the new weapons." Heisenberg, however, recalled assuring him that "the war will be over long before the first atom bomb is built."

  Announcing cheerfull
y to his friends in America that he had to get back for machine-gun practice with the Mountain Rifle Brigade to which he had been assigned for annual military service, Heisenberg sailed home in a nearly empty ship, the Europa, arriving back in Germany in mid-August 1939. He spent the next few weeks helping his wife furnish and prepare the country house he had bought in Urfeld, high in the Bavarian mountains, so that, as he later wrote, she and the children could take refuge from the coming disaster.

  · · ·

  In Japan, with the long war against China prospering, ordinary citizens had little sense of impending catastrophe. Down by the Aioi Bridge in the central Hiroshima district of Salugakucho—the name means "music" or "Noh theater" and was bestowed because many Noh artistes lived there—life was, as one inhabitant recalled, "lively and busy." In 1939 the Aioi Bridge itself had been rebuilt into a T shape ingeniously connecting three tongues of land. The area was "a calm, cosy place with many traditional homes and stores." In the Kimatsu family's rice shop, rice-polishing machines with their funneled hoppers stood in a neat line. Behind the storeroom, where bags of rice and sacks of charcoal and firewood were piled, lay the garden and living area. There in the summer months, while crickets clicked noisily, the Kimatsus chilled watermelons and beer to ward off the heat. In the autumn they burned olive wood, scenting their lattice-doored house with its pungent aroma.