Diana Preston - Before the Fallout

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.”