Diana Preston - Before the Fallout

On 16 January Frisch at last mailed off his and Meitner’s paper to Nature, together with a supplementary one reporting his experimental findings. To protect their friends, Meitner and Frisch took care to credit Hahn and Strass­mann only for work already in the open literature. However, the articles did not attract the attention the authors deserved. Sadly, they were not finally published until 11 February, by which time the world knew all about fission, not only from Hahn and Strassmann but also from Niels Bohr.

On 7 January 1939 Bohr had sailed for the United States aboard the liner Drottningholm together with the Belgian physicist Leon Rosenfeld, to whom he confided, “I have in my pocket a paper that Frisch has given me which contains a tremendous new discovery, but I don’t yet understand it. We must look at it.” The two men spent the voyage in Bohr’s stateroom going over and over the theory of fission until Bohr was convinced he had “got hold of the solution.” As Rosenfeld observed, “It turned out to be extremely simple.”

A group of scientists was waiting on the quayside to greet Bohr, including the American John Wheeler, who had worked with him in Copenhagen. Wheeler was staggered when, within moments of stepping on dry land, Bohr murmured, in the low voice he used when imparting information of the highest significance, that the uranium atom had been split. That night Wheeler took Rosenfeld off to Princeton, where the latter addressed the physics club. Unaware of Bohr’s promise to keep the news quiet until Frisch and Meitner were in print, Rosenfeld announced the discovery, causing a sensation. A horrified Bohr tried to protect Frisch’s and Meitner’s primacy, but it was too late. All he could do was refrain from public comment himself. However, in late January the first copies of Hahn’s and Strassmann’s paper in Naturwissenschaften arrived in the United States, and Bohr felt free to reveal the physical discovery and theoretical explanation of nuclear fission.

The occasion was a conference at George Washington University on 26 January 1939. Some scientists did not even wait for Bohr to finish before rushing off to try the experiments for themselves. That evening Bohr was invited to watch the Carnegie Institution’s accelerator in action. For the first time he saw the uranium atom splitting before his very eyes, the glowing green pulses on the screen of the oscilloscope leaping each time a uranium nucleus fissured. Leon Rosenfeld, by his side, recalled that “the state of excitement challenged description.” By the end of January 1939 over a dozen laboratories worldwide had produced nuclear fission. At Berkeley, Robert Oppenheimer’s initial reaction to the news of fission had been “that’s impossible,” but within days he changed his mind and was speculating that this “could make bombs.”

The new knowledge could scarcely have been revealed at a worse time. In October 1938 Nazi Germany had been allowed to annex the Sudeten German districts of Czechoslovakia under the Munich Agreement, which an optimistic Neville Chamberlain assured the British people guaranteed “peace in our time.” Hitler promised once again that this was the end of his territorial ambitions, but many, especially those who had suffered personally at the hands of his regime, doubted this.

In the tense political climate, some scientists worried that nuclear fission was far too sensitive to be the subject of cross-border gossip. The old belief in a brotherhood of scientists, openly discussing and publicizing their findings from Cambridge to Columbia to California and from Liverpool to Leipzig to Leningrad, now seemed as naive as it was alarming. Colleagues and comrades would soon be competitors.

One of the first to grasp the danger was the Hungarian physicist Leo Szilard, an eccentric, conceited man but, in the eyes of many contemporaries, “sparkling with intelligence and originality.” Szilard had an uncanny prescience. He had been one of the quickest to grasp the peril facing European Jewry, arriving in England in the early months of 1933. Like his fellow Hungarian Edward Teller, he was the product of a liberal, cultured, middle-class Jewish Budapest family. Szilard had developed an early preoccupation with “saving the world.” After the end of the First World War and the collapse of the Austro-Hungarian Empire, he was swept up in the fervor of Bela Kun’s Soviet Republic, driving trucks draped with socialist slogans around Budapest. When Kun fled in the summer of 1919, Szilard found, like Teller, that the world had changed toward him. When he tried to enroll at the university, other students blocked his way, calling him a Jew. His protestations that he was a Calvinist (he had converted a few weeks earlier, believing it would be prudent) did him no good. They kicked him down the marble stairs.

A shaken Szilard had applied for a visa to study abroad. At first the government refused on the grounds that he had been a socialist agitator, but he applied again and with help from family friends just managed to get out. In Berlin he enrolled at the Technical Institute to study engineering but soon realized that physics was his true interest. In 1920 he boldly sought out Max Planck and announced that he only wanted to know the facts of physics. He would make up the theories himself. Life was hard. Szilard lived in shabby, rented rooms, and his family were too poor to send him food parcels. He survived on the most basic of rations and roamed Berlin’s streets staring in shop windows at food he could not afford to buy.

But at least the intellectual life was satisfying. In 1921 Szilard asked Max von Laue to supervise his thesis, which von Laue suggested should be on relativity theory. That same year, Szilard persuaded Einstein to tutor him and some friends, including fellow Hungarians John von Neumann and Eugene Wigner. Szilard’s particular talent was for intense lateral thinking—teasing out patterns and then seeking ways of uniting them through a theory. His tools were statistics rather than experimental evidence. He applied this approach to a problem in thermodynamics and took his results to Einstein, who listened politely then said, “That’s impossible. This is something that cannot be done.” “Well, yes,” responded Szilard, “but I did it.”

After reaching England, Szilard had worked to get Jewish academics out of Germany, but then, convinced war was coming, he had moved on to the United States. He learned of the discovery of fission at Princeton while visiting Eugene Wigner, who was recovering from jaundice in the university infirmary on what Wigner considered a “miserably” un-Hungarian diet of “potatoes, beans and everything boiled in water.” Szilard came to see him every day, and the two friends “discussed fission problems and this and that.” One morning, Szilard said, “Wigner, now I think there will be a chain reaction.”

As Szilard recognized, the possibility of creating a nuclear bomb depended on whether fission could be used to trigger a self-sustaining chain reaction. In other words, by using neutrons to bombard uranium atoms, was it possible not only to split the uranium nuclei but, in the process, to release enough further neutrons which, if they in turn hit other uranium nuclei, could trigger a self-sustaining chain reaction liberating colossal amounts of energy?

As early as September 1933 he had conceived the idea in theory, sparked by reading a newspaper report of Lord Rutherford’s “moonshine” speech dismissing the idea that energy could be liberated from the atom. Szilard later described the Damascene moment. The article “sort of set me pondering as I was walking the streets of London, and I remember that I stopped for a red light at the intersection of Southampton Row. As I was waiting for the light to change and as the light changed to green and I crossed the street, it suddenly occurred to me that if we could find an element which is split by neutrons and which would emit two neutrons when it absorbed one neutron, such an element, if assembled in sufficiently large mass, could sustain a nuclear chain reaction.”