by Ray Monk
Thus, if you fuse together nuclei of elements lighter than iron, or fission nuclei heavier than iron, the result will be the creation of nuclei that have a greater mass defect than the ones you started with, and thus a tremendous release of energy in accordance with the equation E = mc2. The amount of energy released per fusion of, say, hydrogen is less (by about one-tenth) than the amount of energy released per fission of uranium, but, because the nuclei are so much lighter (by about one-fiftieth) and therefore there are more of them in any given quantity of material, the energy release per kilogram will be far greater in fusion than in fission.
It had been assumed that a fusion bomb was an impossibility because of the tremendous heat that would be required to get the nuclei moving energetically enough to fuse together. To get a fusion reaction going, one would have to reproduce something similar to the conditions that prevail inside the sun. What Fermi mentioned casually to Teller over lunch was the possibility that such heat might, after all, be created: by fission. At Chicago, Teller, together with the young physicist Emil Konopinski, set to work on a report on the possibility of a fusion bomb and concluded that, as Teller later put it, ‘heavy hydrogen [deuterium or tritium] actually could be ignited by an atomic bomb to produce an explosion of tremendous magnitude’.
When he was invited to the meeting organised by Oppenheimer and Serber, Teller asked that Konopinski should also be included, and, when Bethe arrived in Chicago to accompany him to Berkeley, he found that Teller’s mind was racing far ahead of the issue they were being collected together to think about. ‘We had a compartment on the train to California, so we could talk freely,’ Bethe remembered. ‘Teller told me that the fission bomb was all well and good and, essentially, was now a sure thing. In reality, the work had hardly begun. Teller likes to jump to conclusions. He said that what we really should think about was the possibility of igniting deuterium by a fission weapon – the hydrogen bomb.’
Apart from Bethe, Konopinski, Teller and van Vleck, Oppenheimer had also invited Felix Bloch from Stanford and Richard Tolman from Caltech. So, with Serber, Nelson, Frankel and himself, that made ten. According to one account, the meeting began with an attempt by Oppenheimer to bring the contributors face-to-face with the fact that what they were doing was planning to build a bomb of hitherto unimaginable power. To help them to visualise what this might entail (and presumably to overcome any lingering squeamishness there might be about the fact that they were engaged in the design of an explosive), Oppenheimer drew their attention to some details of a large explosion that had occurred in 1917 in the harbour of Halifax, Nova Scotia. The explosion was caused by a collision between two ships, one of which was carrying 5,000 tons of TNT, and resulted in the deaths of up to 2,000 people and the destruction of an area of almost one square mile. No one knew how powerful the atomic bomb would be, but the best guess was that it would be several times more powerful than the Halifax explosion (in fact, the Hiroshima bomb was three times and the Nagasaki bomb four times more powerful, though the number of people killed in each case was more than twenty times the number killed in Halifax).
With everybody’s mind thus focused, Serber explained what had been done so far, both by Breit’s team and, in the preceding few months, by Oppenheimer’s. Nelson and Frankel then gave their critical-mass calculations and, remembers Serber; ‘Everybody agreed that it looked under good control from a theorist’s point of view.’ Bethe’s recollections confirm Serber’s impression. ‘The theory of the fission bomb was well taken care of by Serber and two of his young people,’ he remarked later. They ‘seemed to have it well under control so we felt we didn’t need to do much’.
With all the ‘luminaries’ apparently agreeing with his view that the fission bomb was essentially ‘now a sure thing’, Teller turned the discussion away from fission and towards fusion. As Serber remembers it, what Teller was proposing was ‘a detonation wave in liquid deuterium set off by being heated by the explosion of an atomic bomb’. In his autobiography Serber describes how, when Teller mentioned this idea, ‘everybody forgot about the A-bomb, as if it were old hat, something settled, no problem, and turned with enthusiasm to something new’.
Everyone present realised that if the ‘Super’ (as they began calling it) could be made to work, it would be many times more powerful than an atomic bomb. In an atomic bomb, one kilogram of uranium would explode with the force of (roughly) 15,000–20,000 tons of TNT; in a thermonuclear, hydrogen bomb, one kilogram of deuterium would explode with the force of 80,000–100,000 tons. Moreover, deuterium is relatively cheap and plentiful. Twenty-six pounds of it would not be difficult to acquire, and that, potentially, could make a bomb equivalent to about one million tons of TNT.
That was startling enough, but, recalls Serber:
At one point Edward [Teller] asked if the fission bomb could ignite the earth’s atmosphere. In view of the difficulties encountered in considering the Super this seemed extremely unlikely, but in view of the importance of the consequences, Hans [Bethe] took a look at it and put numbers to the improbability.
While Bethe was looking at the numbers, Oppenheimer – who took the apocalyptic scenario presented by Teller more seriously than either Serber or Bethe – made a long-distance call to Compton to tell him that his group had ‘found something very disturbing’. Compton asked how soon Oppenheimer could come to Chicago to see him and talk about it. The following day, came Oppenheimer’s reply. And so, early the next morning, Oppenheimer took the train to Chicago, where Compton met him in his car. As they drove back to Compton’s house, Oppenheimer recounted the discussion that his group had been having about fission, fusion and the possibility of global catastrophe, which, as Compton writes, ‘could not be passed over lightly’.
Was there really any chance that an atomic bomb would trigger the explosion of the nitrogen in the atmosphere or of the hydrogen in the ocean? This would be the ultimate catastrophe. Better to accept the slavery of the Nazis than to run a chance of drawing the final curtain on mankind!
With Compton, Oppenheimer agreed there could be only one answer to the crisis, which was, in Compton’s words: ‘Oppenheimer’s team must go ahead with their calculations. Unless they came up with a firm and reliable conclusion that our atomic bombs could not explode the air or the sea, these bombs must never be made.’
By the time Oppenheimer got back, Bethe had done the figures and discovered, as he put it, ‘some unjustified assumptions in Teller’s calculations’. Bethe, in fact, never took seriously the idea that they could destroy the earth’s atmosphere and was surprised that Oppenheimer had thought it worth troubling Compton with, ‘but then Oppie was a more enthusiastic character than I was. I would have waited until we knew more.’
With the apocalyptic worry disposed of, the group got back to discussing bomb physics, again concentrating on the ‘Super’. What came as a pleasant surprise to the members of the group, even to those who knew Oppenheimer well, was what an extraordinarily capable chairman he showed himself to be. Oppenheimer had never previously organised anything – he had never, for example, served as chairman of his department at Berkeley – and yet, here he was, in charge of nine of the country’s most distinguished physicists, revealing himself to be an able leader who commanded the respect of everyone present.
‘The conference didn’t exactly end,’ remembers Serber, ‘it sort of fizzled out. After a week people began to leave, some stayed on a couple of weeks longer.’ For everyone involved, it had been a memorable series of discussions, Oppenheimer’s handling of which had been a revelation. ‘As Chairman, Oppenheimer showed a refined, sure, informal touch,’ Teller later said. ‘I don’t know how he had acquired this facility for handling people. Those who knew him well were really surprised. I suppose it was the kind of knowledge a politician or administrator has to pick up somewhere.’ It was crucial to the success of the meetings, however, that these political and administrative gifts went hand-in-hand with the kind of deep insight into both science and scientists
that was required to get the best out of the participants. ‘A spirit of spontaneity, adventure and surprise prevailed during those weeks in Berkeley,’ Teller remarked, ‘and each member of the group helped move the discussion toward a positive conclusion.’ These sentiments were echoed by Bethe, who recalled: ‘The intellectual experience was unforgettable.’
We were forever inventing new tricks, finding ways to calculate, and rejecting most of the tricks on the basis of the calculations. Now I could see at first-hand the tremendous intellectual power of Oppenheimer, who was the unquestioned leader of our group.
By the time the conference had ‘fizzled’ to an end, Oppenheimer’s own reputation and position within the US bomb project had been transformed from that of a useful, but not essential advisor to that of an indispensable leader and facilitator.
His report from the meeting of the ‘luminaries’ was received and approved by the S-1 committee towards the end of August 1942. Its central message was that an atomic (fission) bomb could indeed be built, but that it ‘would require a major scientific and technical effort’. Such a bomb would need more U-235 than some previous estimates had suggested – about 66 pounds – but its power would be something like 150 times greater than had previously been thought – that is, equivalent to about 100,000 tons of TNT. The report also touched on the possibility of the ‘Super’, saying that a 66-pound fission bomb could, in principle, be used to initiate a fusion explosion in liquid deuterium, two or three tons of which would explode with the force of 100 million tons of TNT, completely destroying an area of 360 square miles.
In the light of the conclusions drawn by Oppenheimer, the S-1 committee submitted a report to Bush, summarising the findings of the ‘luminaries’ and claiming that enough fissionable material for an atomic-bomb test could be obtained by March 1944. ‘We have become convinced,’ the report stated, ‘that success in this program before the enemy can succeed is necessary for victory. We also believe that success of this program will win the war if it has not previously been terminated.’
By the end of August 1942, Bush was giving it as his opinion that ‘nothing should stand in the way of putting this whole affair through to a conclusion’. To him, it was clear that what was now required was strong leadership. The same thought had occurred to General Brehon B. Somervell, who was in charge of the section of the army that included the Engineering Corps, and Somervell knew just the man to provide that strong leadership.
That man was Colonel Leslie Groves, a large and indomitable figure, who stood six feet tall and weighed about eighteen stone (252 pounds). Lieutenant Colonel Kenneth D. Nichols, who served under him for many years, called him ‘the biggest sonovabitch I’ve ever met in my life, but also one of the most capable individuals’. Groves had recently undertaken successfully the demanding task of supervising the construction of the Pentagon, which, impressively, he completed well within the budget he had been allocated. For this, and other reasons, he had a reputation for being a man who got things done. On 17 September 1942, he was in Washington, testifying to the Military Affairs Committee, when he met General Somervell, who told him: ‘The Secretary of War has selected you for a very important assignment.’
Groves was not particularly happy about this appointment, even though Somervell told him that if he did it correctly, ‘it will win the war’. Groves wanted to get out of Washington and into battle, commanding soldiers, not directing civilian scientists. The silver lining offered to him was that, as reward for taking on the job, he would be promoted to brigadier general. The project of which General Groves (as everybody henceforth called him) was now in overall charge had already been christened the ‘Manhattan Project’ by his predecessor, Colonel Marshall, who worked out of an office in Manhattan. Even though Groves had his office in Washington rather than Manhattan, he kept this previous name for the project, its misleading connotations considered by him to be an asset.
From the very beginning, Groves ran the project with a characteristic determination to get the job done and let nothing and nobody stand in his way. With a confidence and speed that inspired both admiration and fear, he took several decisive steps in the first few days of his appointment. On his first day in command, he sent Nichols to buy 1,250 tons of uranium ore from the Belgians, who had been trying to interest the US government in it for the previous six months. The next day, he persuaded (‘bullied’ is probably the word) the civilian head of the War Production Board to give the Manhattan Project a top-priority AAA rating, which meant that he would not have to compete with any other war project for funds and resources. The same day, he acquired for the project a plot of land in Tennessee that extended over 50,000 acres. It was called Oak Ridge and would serve as the site for the industrial plants that would be required to produce the enriched uranium needed for the bomb.
As yet, however, it had not been decided exactly what plants would be built at Oak Ridge. Having been briefed by Bush on the work of the S-1 committee, Groves decided to visit every major site involved in the project. He began with the Westinghouse Research Laboratory in Pittsburgh and the University of Virginia, which were responsible for the development of the centrifuge method of isotope separation. At both places, Groves was horrified to learn how little had been achieved and in what a leisurely manner the work was being conducted. Though it would become in modern times the main method of enriching uranium, the centrifuge method was, on Groves’s orders, abandoned by the Manhattan Project.
Groves next went to New York to visit Columbia, where Harold Urey and his colleague John Dunning were working on the gaseous-diffusion method. There, Groves discovered that the theory of gaseous diffusion was developing nicely, but it had not been used to produce even a speck of U-235, nor did it look at all likely that it could be used on an industrial scale for a long time.
On 5 October, Groves went to Chicago, where he was shown the pile of graphite that was being amassed for the nuclear reactor, and where he attended a meeting of the scientists working at the Met Lab. It was an impressive group that included no fewer than three Nobel laureates (Compton, Fermi and Franck), as well as Szilard, Wigner and about a dozen others. However, the meeting was tense; the scientists, especially Szilard, were suspicious of the military, and Groves was contemptuous of what he regarded as the arrogance and impracticality of the theorists. At the end of the meeting, Groves told the scientists that, though he did not have a PhD, he had ten years of formal education after he left college, so ‘That would be the equivalent of about two PhDs, wouldn’t it?’ There was an embarrassed silence, and then Groves left. ‘You see what I told you?’ Szilard exclaimed after Groves had gone. ‘How can you work with people like that?’
After Chicago, Groves travelled to Berkeley to meet Lawrence and see the Calutron, which Lawrence demonstrated with all the winning, boyish enthusiasm that had served him so well and landed him so many prizes and so much research funding in the past. Groves, however, was not especially impressed with the machinery or especially charmed by Lawrence’s breezy optimism. Rather, he saw in Lawrence the same frustrating failure to see the project in industrial, rather than academic, terms that he had seen everywhere else. Groves wanted someone to start talking about getting pounds, not micrograms, of enriched uranium. Instead of which, Lawrence, having shown Groves the magnificence of the 184-inch Calutron, was forced to admit, when asked how much uranium he had separated so far: ‘Well, actually, we don’t get any sizeable separation at all. I mean, not yet. This is still experimental, you see . . .’
Oppenheimer’s first meeting with Groves took place on 8 October 1942 at a lunch hosted by Robert Sproul, President of Berkeley. In some ways, the meeting is reminiscent of the moment in 1926 when, as an unknown, twenty-two-year-old graduate student at Cambridge, Oppenheimer had been introduced to Max Born, then the leading theorist in the emerging field of quantum mechanics. At that meeting Oppenheimer had seemed to cast a spell over Born, a spell that resulted in an invitation to come to Göttingen, the very centre of research into q
uantum mechanics, where he was treated as if he in some way had superiority over Born. Similarly, when he met Groves, Oppenheimer was, compared to the people Groves had already met, a relatively junior member of the project. He was not, like Compton, Fermi, Franck and Lawrence, a Nobel Prize-winner; nor was he, like Szilard, Teller and Wigner, an originator of the atomic-bomb project. Moreover, he seemed, in his love of French poetry, his absorption in the literature of Hinduism and his resolutely theoretical approach to physics, the very personification of the remote academic whom Groves had come to despise.
And yet, on meeting the thirty-eight-year-old Oppenheimer, Groves was immediately won over, feeling that here, at last, was someone who could see and understand the real problems that the project faced. A clue to Oppenheimer’s success with both Born and Groves perhaps lies in a remark Haakon Chevalier once made about him: ‘He was always, without seeming effort, aware of, and responsive to, everyone in the room, and was constantly anticipating unspoken wishes.’
Certainly, Oppenheimer seems to have had an unerring sense of what Groves wished to hear. In his own account of the history of the Manhattan Project, Now It Can Be Told, Groves says remarkably little about his first meeting with Oppenheimer, and nothing at all about his own first impressions. He says only that at this first meeting they ‘discussed at some length the results of his study and the methods by which he had reached his conclusions’. From this, it is impossible to say why Groves took such a liking to Oppenheimer, but in the autobiographical statement that Oppenheimer prepared for his security case in 1954, one begins to realise what Groves might have seen in him. Remembering the period immediately after the meeting of ‘luminaries’ at Berkeley in July 1942, Oppenheimer writes: