The German and Central European scientists who remained in the lodge, or the family, were those who had left their country and continued their scientific work in America and Britain. Leo Szilard had professed to the American financier Lewis Strauss his disquiet over the possibility that a bomb might be made: ‘All the things that H. G. Wells had predicted appeared suddenly real to me.’ He pestered Edward Teller in Washington, Eugene Wigner in Princeton (both fellow Hungarians), and I. I. Rabi at Columbia University, whom Szilard dispatched to warn Enrico Fermi, then also at Columbia. Despite the Hahn-Strassmann finding and Bohr’s American preview of it in January 1939, Fermi remained skeptical that a neutron chain reaction might be created and ultimately produce a functional atomic bomb. When Szilard quizzed Rabi about Fermi’s response to his warning, Rabi reported dutifully that Fermi had said ‘Nuts!’ Szilard could not believe it, so he and Rabi bearded Fermi in his office.
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 the fission of uranium and then of course that a chain reaction can be made.’
Rabi wanted to know what the man they called ‘The Pope’ meant by ‘remote possibility’. ‘Ten percent,’ said Fermi. Rabi retorted: ‘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 10 per cent, I get excited about it.’ Fermi reconsidered.35
In the aftermath of Szilard and Rabi’s confrontation with Fermi, both Szilard (with Walter Zinn) and Fermi, working in Columbia labs, produced fissions; Szilard called Teller in Washington to report, in Hungarian, that he had ‘found the neutrons’. It was vital, Szilard thought now, to conceal this information from the Nazis, so he urged a ban on publishing accounts of progress toward creating chain reactions. This was too much to ask, at this point, of the scientific republic, members of which insisted, variously, that the Germans had pioneered fission anyway, that publication of data would spur essential research in American labs, that no one had yet actually produced a chain reaction, and that even a chain reaction would not necessarily lead to the creation of an atomic bomb. In France, Frederic Joilot and two collaborators replicated the Szilard and Fermi fissions and refused to withhold publication of their results. The world was not yet officially at war, nor had Werner Heisenberg yet declared to American-based interlocutors that he would stay in Germany. Szilard shifted tactics. He called Albert Einstein in Princeton.36
It was July 1939, and Einstein had gone north to Peconic, Long Island, to sail and think. On Sunday 16 July Szilard and Wigner—the former never learned to drive—drove to the Long Island house. The conversation came quickly to chain reactions, using uranium, of which Einstein had neither heard nor conceived. He was persuaded that there was grave danger should the Nazis find a way to weaponize atomic energy, so he dictated, in German, a letter to a Belgian Cabinet member he knew, with the understanding that it first be cleared by the US State Department. Several days later, Szilard met Dr Alexander Sachs, a Russian-born economist with the Lehman Corporation who was on good terms with President Franklin D. Roosevelt. Sachs knew the physics literature and recognized the urgency of the issue as Szilard presented it to him, along with Einstein’s letter. Sachs wanted Einstein to redraft the letter and address it to the President. He himself would deliver it. Szilard drafted the letter, met Einstein again to discuss it, then rewrote it twice more, with the second redraft receiving Einstein’s signature. The final version, given to Sachs to give to Roosevelt, told of the near certainty of achieving a nuclear chain reaction ‘in the immediate future’. ‘This phenomenon’, Einstein/Szilard went on, ‘would also lead to the construction of bombs, and it is conceivable—though much less certain—that extremely powerful bombs of a new type may thus be constructed.’ (The language is curious here: chain reactions ‘would’, not could, ‘lead to’ an atomic bomb, yet such a thing was by no means ‘certain’.) The letter closed by noting the German embargo on sales of uranium and the presence of Carl Friedrich von Weizsacker, son of the high-ranking German Foreign Office man, at the KWI, ‘where some of the American work on uranium is now being repeated’. The letter was dated 2 August 1939; Szilard gave it to Sachs on the 15th.37
Delay set in. Sachs admitted to Szilard that he was ‘still sitting’ on the letter. In the realm of nuclear research, Szilard complained, ‘things were not moving at all’. Sachs finally moved on 11 October, over a month after the outbreak of war in Europe. Given to prolixity and indirection, Sachs nevertheless managed to hold Roosevelt’s attention for nearly an hour, reading to the President from a recent book describing some of the history of nuclear exploration, from his own lengthy memorandum, detailing (as Peter Wyden has described it) ‘the roles of Hahn and Meitner and Szilard and Fermi and Wigner and Teller’, and finally from a portion of the Einstein/Szilard letter dated more than two months earlier. Roosevelt began to flag, so Sachs cadged an invitation for the following morning. He spent the night rethinking his approach, and, though he still could not avoid rambling, he managed at breakfast to make his point: if the Germans built a bomb first, it would be disastrous for the world. Turning to his aide, General Edwin ‘Pa’ Watson, Roosevelt said, ‘Pa, this requires action.’ Action of a sort ensued. Watson set up an Advisory Committee on Uranium, constituted of representatives from the Bureau of Standards, the Army, and the Navy. The committee held its first meeting ten days after Sachs had first met the President. On hand, along with the government representatives, were Sachs, Szilard, Wigner, and Teller. The men sparred about the urgency of nuclear research. In the end, the officials offered the scientists $6,000 to buy graphite. Roosevelt took note of the committee’s report coming out of the meeting, and, to Szilard’s enormous frustration, matters once more receded into the shadows.38
In Great Britain, there was also growing interest in an atomic bomb. Unlike the United States, Britain was from the beginning of the Second World War on the front line, and its refugee scientists had in their new government an ally in their urgency to beat the Germans in the nuclear weapons race. Otto Frisch, the nephew of Lise Meitner who had, with his aunt, worked through the implications of the Hahn-Strassmann fission research in late 1938, was in Birmingham when war broke out, and, rather than return to Copenhagen where he was now based, he decided to remain in Birmingham to work with his fellow refugee Rudolf Peierls. Initially skeptical that a chain reaction could be harnessed for a bomb—it would be ‘prohibitively expensive’ and probably ineffective, they thought—the scientists changed their minds as they contemplated using not a compound of uranium 235 and 238 but pure 235 at the core of the bomb. Early in 1940 Frisch and Peierls produced a three-page memorandum that laid out, more logically and bluntly than any single document previously written, how to go about building what they called a ‘Super-Bomb’. Using U-235 exclusively would mean not having to slow down neutrons, allowing fission to take, as it were, its natural course, and rapidly releasing an enormous amount of energy. They suggested fabricating a bifurcated uranium sphere, its halves to be thrown together at great speed to produce an explosion. In three paragraphs, Frisch and Peierls indicated that thermal diffusion, filtering a gaseous uranium compound through a long series of ‘separating units’, should produce enough U-235 for an atomic bomb.
The memo ended with a remarkably prescient warning concerning the dispersal of radiation from the bomb:
Most of it will probably be blown into the air and carried away by the wind. This cloud of radioactive material will kill everybody within a strip estimated to be several miles long. If it rained the danger would become even worse because active material would be carried down to the ground and stick to it, and persons entering the contaminated area would be subjected to dangerous radiations even after days. If 1% of the active material sticks to the debris in the vicinity of the explosion and if the debris is spread over an area of, say, a square mile, any person entering this area would be in serious danger, even several days after the explosion.
Frisch and Peierls added that radiation exposure would not be felt immediately by those subject to it. Like poison gas, it was an insidious killer.39
The Frisch-Peierls memorandum, as Margaret Gowing has pointed out, asked (and answered) the right questions. The Japanese and Germans never properly asked them. The Americans had not yet asked them, though the Hungarians in the United States, backed by Einstein, had started to do so. The memorandum made its way through the physics community in Britain during early 1940, as the blitzkrieg paused, ominously; ‘interest about the uranium bomb which had been waning now waxed rapidly,’ according to Gowing. As in the United States, a committee was formed to consider the feasibility of building a bomb. It included, among others, G. P. Thomson (its chair), whose request for a ton of uranium oxide the year before had stirred the curiosity of Henry Tizard, the chemist and chair of the Committee on the Scientific Survey of Air Defence, who now also joined the group. The committee met first on 10 April to hear from Jacques Allier of the French Ministry of Armament, who reported the Germans’ sudden craving for heavy water. At its second meeting two weeks later, the Thomson group discussed the Frisch-Peierls findings concerning the prospect of an atomic bomb. ‘The Committee generally was electrified by the possibility,’ wrote participant Marcus Oliphant some years later. Across England, the pace of experimentation now picked up. The Americans dithered. The war resumed its fury.40