Inside the Centre: The Life of J. Robert Oppenheimer (57 page)

With Ernest Lawrence (if not with Bush and Conant), Oliphant had succeeded in his aim of using the MAUD Committee’s findings to instil a sense of urgency with regard to the development of an atomic bomb, and, in his desire to hurry the project along, Lawrence had an influential ally in Arthur Compton. On 25 September 1941, somewhat to his annoyance, Conant was subjected to what he described to Bush as an ‘involuntary conference’ on the atomic bomb with Lawrence and Compton. This took place at Compton’s home in Chicago, where Conant was staying as a guest while attending the celebrations commemorating the fiftieth anniversary of Chicago University. Unknown to Conant, Compton had invited Lawrence, who was also in Chicago for the celebrations, to come to his home to present to Conant his case for pressing urgently ahead with the development of the bomb. After taking the opportunity to reprimand Lawrence for allowing the secret of the bomb to be given away to Oppenheimer, Conant listened to Lawrence’s arguments for adopting the MAUD Committee’s findings and working with the British on building the bomb. Then, turning to Lawrence, Conant said: ‘Ernest, you say you are convinced of the importance of these fission bombs. Are you ready to devote the next several years of your life to getting them made?’ After a moment’s hesitation, Lawrence replied: ‘If you tell me this is my job, I’ll do it.’

Though it had been discussed unofficially by American scientists for months, and Lauritsen had supplied officials with a precis, the MAUD report was not officially delivered to Conant until 3 October 1941. Six days later, Bush presented its findings to President Roosevelt, whose response was to set up a high-level policy group – consisting of Bush and
Conant, together with the Vice President, the Secretary of War and the Army Chief of Staff – who would henceforth be responsible for the management of the atomic-bomb project, acting on advice from Arthur Compton’s committee. In response to this development, Compton called a meeting of his committee for 21 October in Schenectady, in upstate New York. A week before the meeting, Lawrence cabled Compton to say: ‘Oppenheimer has important new ideas. Think it desirable he meet with us Tuesday. Can you arrange invitation?’ After a second request, in which Lawrence emphasised that he had ‘a great deal of confidence in Oppenheimer’, Compton capitulated and agreed to allow Lawrence to bring him.

Within a month of his impromptu meeting with Oliphant, therefore, Oppenheimer had gone from being completely ignorant of, and excluded from, the US atomic-bomb programme to being right at the heart of it. This seems to have resulted in a flurry of what the FBI, at least, regarded as extremely suspicious Communist Party activity on Oppenheimer’s part. On 3 October 1941, the agency learned from a ‘reliable confidential informant’ (a wire tap on Folkoff’s phone) that Folkoff had been in touch with Oppenheimer to advise him that he would not be able to meet him at the weekend and had instead arranged for him to meet Steve Nelson. Three days later, from the same ‘informant’ the FBI learned that Nelson had contacted Folkoff to say that he had received $100 from ‘him’. Then, on 14 October, a mere week before the Schenectady meeting, the wire tap revealed that Oppenheimer had contacted Folkoff to ask him to arrange for Rudy Lambert (the head of the California Communist Party labour commission) to contact him and to tell him that ‘Steve’ had contacted him and given him a message for Folkoff.

There is no record of Oppenheimer’s meeting with Lambert – nor even any confirmation that it took place – nor is there any way of knowing what message Steve Nelson wished to pass on to Folkoff via Oppenheimer. Coming at precisely the moment when Lawrence was pressing for Oppenheimer to be invited to a secret meeting to discuss progress on the atomic bomb, it is natural to wonder whether Oppenheimer might have been passing on information about this meeting to people who would then be able to inform Moscow. On the basis of the available evidence, however, it seems more likely that Oppenheimer’s purpose was to let Folkoff know that henceforth his contacts with the Party would be severely reduced.

Oppenheimer knew (from Frank’s experience, for example) how damaging it could be to one’s career to be perceived as a communist, and there are many signs that, by the autumn of 1941, what he wanted more than anything was to be involved in government work related to the war – work which, he well knew, was wholly incompatible with close
associations with the Communist Party. In his letter to Willie Fowler in the spring of 1941 mentioned earlier, Oppenheimer had written: ‘I think surely if I were asked to do a job I could do really well and that needed doing I’d not refuse.’ The sense one has from Oppenheimer’s letters of the spring and summer of 1941 is that he felt excluded from what was important, an impression supported by the Berkeley chemist Martin Kamen, who recalls that, though Oppenheimer had previously been the person everybody spoke to about their research, in 1941 this began to change:

Oppenheimer himself said that he was ‘not without envy’ of the men he knew who had gone off to work on radar or other aspects of military research, ‘but it was not until my first connection with the rudimentary atomic-energy enterprise that I began to see any way in which I could be of direct use’.

As usual, Oppenheimer’s behaviour was ambiguous and difficult to interpret. If he had wanted to avoid political controversy in order to ‘be of direct use’, it was rather odd of him, on 13 October 1941, to write a strongly worded letter of protest to Senator F.R. Coudert, who was co-chairman of the committee appointed by the State of New York to investigate communist infiltration of the New York City college system. After making the perfectly reasonable point that the Bill of Rights ‘guarantees not the right to a belief, but the right to express that belief, in speech or in writing’, and that therefore the teachers accused of communism were engaged in ‘practices specifically protected by the Bill of Rights’, Oppenheimer could not help himself ending his letter with some straightforward and, in the context, surely superfluous, abuse: ‘It took your own statement, with its sanctimonious equivocations and its red baiting, to get me to believe that the stories of mixed cajolery, intimidation and arrogance on the part of the committee of which you are the chairman, are in fact true.’ This is not the tone of a man determined to keep a low profile and avoid offending the political establishment. The vitriol in the letter, however, might be seen as further evidence of Oppenheimer’s frustration and anxiety over the possibility that he might
be excluded from war-related work because of his connections with the Communist Party, and his anger at the implied suggestion that he was not entirely loyal to the US.

A week after thus registering his disapproval of those who would deny communists their constitutional rights, Oppenheimer was travelling with Lawrence across the US, from Berkeley to Schenectady, to take part in a meeting that would turn out to be an important milestone in the Allied project to build an atomic bomb. The meeting opened with Lawrence reading Oliphant’s summary of the MAUD report. Compton then reported on various meetings that he had had with leading scientists, at which he received the latest information on key scientific questions relating to the bomb from those most qualified to give it. One assumes that much of this information would have been new to Oppenheimer.

Compton reported that in his meetings with Fermi he had received an estimate of the critical mass of U-235 that put it at about 100 pounds. This was considerably more than the Frisch–Peierls estimate, but still low enough to make the bomb a practical proposition. But, whether one needed two pounds or 100 pounds, the extraction of U-235 from natural uranium remained an extraordinarily difficult task. Compton’s advice on how best to tackle this problem came from the Nobel Prize-winning chemist Harold Urey, who told Compton about the various methods of separating the fissionable isotope, all of which would require a massive investment in time and manpower if they were to produce enough U-235 to make a bomb.

The most promising methods of separation, Urey told Compton (and Compton reported to the Schenectady meeting), were gaseous diffusion and centrifugal separation. The former requires the uranium to be converted from a metal into a gas and then forced through the microscopic holes of a filter, or ‘barrier’. Because the U-235 isotope is slightly lighter than U-238, it will pass through the barrier more readily, so that the barrier will act as a way of ‘enriching’ the uranium – that is, increasing the proportion of U-235. Among the many problems with this method are that the gas is extraordinarily corrosive and the process has to be repeated many times, making it laboriously slow. At the time of Compton’s meeting with Urey, only microscopic amounts of enriched uranium had been produced by this method. The idea that it might furnish the basis for production of the isotope on an industrial scale looked fanciful.

Similar problems attended the centrifuge method, which is today the main method used to enrich uranium, but which in 1941 was a new and relatively untested technique. The basic idea is to place the uranium, again in a gaseous form, in a cylinder, which is then rotated very quickly,
forcing the heavier U-238 to the outer edge and concentrating the lighter U-235 near the centre. Considering both methods fairly promising, Urey gave it as his view that the assembly of a critical mass of U-235 was, though extremely difficult, quite achievable with sufficient resources.

An alternative to the arduous business of collecting together an appreciable amount of U-235 was to make a bomb from the newly discovered element of plutonium, or ‘element 94’, as it was then still known (it did not receive its name or its symbol, Pu, until March 1942). Plutonium does not exist in nature. It is one of the elusive ‘transuranics’ – elements heavier than uranium – that Fermi and others had been looking for, and which they thought would be the result of bombarding uranium with neutrons. That transuranic elements could be created had been believed by physicists for a long time, and that element 94 would be fissionable had been predicted by Bohr and Wheeler in their classic papers on fission in 1939.

In his January 1940 summary paper on the literature of fission Louis Turner had drawn attention to the possibility that there might be alternatives to U-235 as a fissionable material. If, instead of fissioning, an atom of U-238
captures
the neutron fired at it, then it becomes U-239, which, Turner suggested, might fission. But, even if it did not, it would almost certainly be unstable and thus, by beta decay, transmute into the hitherto-unknown element 93 (that is, an element with 93 protons – one more than uranium). And this element would, in turn, decay into element 94, which, Turner predicted, would be even more fissionable than U-235.

Turner was right on all counts, as would eventually be shown by a series of experiments in 1940 and 1941. In the spring of 1940, using the 60-inch cyclotron, Ed McMillan and Phil Abelson produced element 93 – later named neptunium (Neptune being the planet beyond Uranus) – by bombarding uranium with neutrons. Astonishingly, they
published
their results. Their paper announcing the discovery of element 93 appeared in the
Physical Review
of June 1940, much to the disgust of James Chadwick, who persuaded the British embassy to make a formal protest to Berkeley. Though the British were, compared to the US, not particularly vigilant about the protection of their war secrets from Soviet espionage, the open publication of work directly helpful to the Nazi bomb project was something about which they were emphatically not prepared to take a relaxed view.

On 23 February 1941, Glenn Seaborg and his research team at Berkeley, again using the 60-inch cyclotron, made a conclusive identification of element 94 from the decay of element 93, and a month later showed that this element would, indeed, fission like U-235. This time
they did not publish. Instead, Seaborg, together with Eugene Wigner at Princeton, joined Compton’s team of advisors, whom they told that element 94 was indeed more fissionable than U-235 and that it was realistic to believe that a critical mass of it could be produced in a uranium nuclear reactor.

So Compton’s report to the Schenactady meeting concluded that, according to the best scientific advice he had received, an atomic bomb
was
a possibility. The next person to speak was Oppenheimer, who gave his own estimate of the critical mass of U-235, which he put at about 220 pounds – more conservative than Fermi’s estimate, but more or less in the same ballpark (hundreds, rather than thousands, of pounds).

Compton’s biggest disappointment at this meeting was with the engineers who were present (at the express insistence of Bush) in order to provide practical estimates of how long the bomb would take to build and how much it would cost. The reason the meeting was held at Schenectady was that this was the site of the laboratories of General Electric, who provided the engineers. And yet, to Compton’s exasperation, the engineers refused to offer any opinion regarding the likely timescale and/or cost of the project. There was, in their opinion, simply too little data even to hazard a guess. As some kind of answer was needed, Compton himself suggested a time of three and a half years and a cost of ‘some hundreds of millions of dollars’ – an estimate that, at Bush’s suggestion, he played down in his final report, ‘lest the government should be frightened off’.

In his autobiography Compton reported that he had ‘always been rather proud of these forecasts, considering the limited data’. His estimate of the time required to build a bomb was indeed remarkably accurate. Once the project was formally under way, it did indeed take three and a half years to complete. The cost, however, would turn out to be
$2
billion
, largely because of the difficulties of isotope separation.