Inside the Centre: The Life of J. Robert Oppenheimer (105 page)

Oppenheimer was invited to join Project Vista in July 1951, and from then until its final report was written in the New Year of 1952 he played an increasingly influential role in its thinking. He ended up writing one chapter of the report himself and had a hand in drafting several others, including the introduction. With regard to the defence of Western Europe, the report argued that the annihilation of Russian cities by strategic bombing was something Europeans feared rather than welcomed, because of the danger of provoking retaliatory attacks on
their
cities. ‘On the other hand,’ the report insisted, ‘if we plan also to use our air power (including strategic, tactical, and Naval units) to destroy the march of Russian armies, we can win the confidence of the NATO nations.’

Such thinking was, of course, anathema to the Strategic Air Command and also to the air force generally. When a preliminary version of the report was presented at Caltech towards the end of 1951, it produced an ‘explosion’ from the air force, which saw in it not just ill-considered advice, but dangerous subversion – an attempt to undermine the only arm of the military that stood any hope of defeating, or even of containing, the Soviet Union. Air-force generals became seriously alarmed when
members of the Vista team – DuBridge, Lauritsen and Oppenheimer – went to Europe to discuss their report with NATO top brass, including General Eisenhower, the Supreme Commander, and General Norstad, who was by this time Eisenhower’s Air Deputy and Commander-in-Chief of the Allied Air Forces. Norstad was not as horrified by the report as his air-force colleagues back in the US had been, but he did suggest to DuBridge, Lauritsen and Oppenheimer that they get rid of any suggestion that strategic bombing and the tactical use of atomic weapons were somehow incompatible.

Encouraged by this relatively warm reaction, the authors of the report returned to Caltech to work on the final version, which was finished by February 1952. Because of the horrified reaction of the air force, however, the report was suppressed almost as soon as it was delivered. Thomas Finletter, the Secretary of the air force, ordered all copies to be sent to his office in Washington, where most of them were destroyed and the remaining few hidden under lock and key. Shortly before that, Finletter and General Vandenberg, Chief of Staff of the air force, issued orders that Oppenheimer was no longer to be used as a consultant in any further studies relating to the air force and that classified air-force documents were, despite his security clearance, to be kept away from him. As far as the air force was concerned, what Project Vista showed was that Oppenheimer could not be trusted.

The reason for this was not just the attitude that Oppenheimer, and the report he had helped to write, expressed about strategic bombing. It was also what was said and, perhaps more importantly, what was not said, in the report about the hydrogen bomb. In a report that touched upon (even if it did not concentrate on) the uses of strategic bombing, one might have expected some discussion of the Super. In fact there are only allusions to, and implied rebuffs of, this promised new weapon. ‘We have found no great new weapons – and we believe we can get along with those we have,’ the report says (in the chapter written by Oppenheimer). The report also committed itself to the view that, for strategic bombing, a yield of between one and fifty kilotons was ideal, with no use at all envisaged for bombs in the megaton range. The implication was that even if the H-bomb could be built, it would have no role to play in the defence of Europe.

This was all the more troubling to the air-force leaders because, as they well knew, during the time that Project Vista was being conceived and then carried out (from the end of 1950 to the beginning of 1952), the prospects for overcoming the technical problems in the way of developing the hydrogen bomb improved dramatically. The lowest point for the Super programme was probably the spring and early summer of 1950, when the calculations of Ulam and Everett, and then von Neumann, showed that
Teller’s ‘classical Super’ design would not work. Soon after that, however, Bethe and Fermi arrived at Los Alamos and genuine progress started being made.

Crucial to the overall success of the project would be the ‘Greenhouse’ series of tests that had been scheduled for May 1951, and which Oppenheimer and many others assumed would fail. Four tests were planned, but the crucial one, scheduled for 9 May 1951, was the third, code-named ‘George’. What George would test was not a bomb, but a device that Teller had designed called the ‘Cylinder’. The idea, in the words of one of its planners, was to use an atomic explosion ‘to send material down a tube and cause a thermonuclear reaction of small magnitude in deuterium’. The design called for the atomic explosion to take the form of a bomb with a yield of 500 kilotons of TNT (about thirty-five times more powerful than the Hiroshima bomb), which would then ignite a fusion reaction in a tiny amount (less than one ounce) of deuterium and tritium. It was, says the Princeton physicist Robert Jastrow, ‘like using a blast furnace to light a match’. Where the Cylinder differed from the classical Super was that the fusion between the deuterium and the tritium was to be initiated not by a flow of high-energy neutrons, but by radiation, in the form of X-rays, travelling from the atomic explosion through a pipe. As it turned out, though no one knew this when the design for the Cylinder was completed in October 1950, this idea of using X-rays was to prove a turning point for the whole programme.

Just after the design of the Cylinder was finalised, Oppenheimer organised a visit of the GAC to Los Alamos to inspect progress. This was mainly for the benefit of new members, the most notable of whom was the chemist Willard Libby, a future Nobel laureate who was an enthusiastic proponent of the H-bomb programme. Also taking part in this visit was Gordon Dean, who, after Lilienthal’s departure, was now chairman of the AEC. In his report of the visit Oppenheimer announced himself to be impressed by the ‘new and elaborate instrumentation’ developed for the Greenhouse tests, particularly with the new information that might be gained through the investigation of ‘the flow of radiation from fission weapons into materials of varying density’. Such information, he acknowledged, ‘will be relevant to many thermonuclear models’. No one, however, believed that the George test would demonstrate the feasibility of a hydrogen bomb.

Thanks primarily to Stanislaw Ulam, this was very soon to change. In December 1950, Ulam had the idea that has since become known as ‘super-compression’, but which Ulam called ‘hydrodynamic lensing’. This was not, initially, anything to do with hydrogen bombs; it was a new atomic-bomb design, motivated by the desire to make more efficient use of fissionable material such as uranium and plutonium. The central idea
was to use the energy from one atomic bomb to compress a small piece of fissionable material, thereby creating a second, more powerful explosion. This sounds less efficient, since two pieces of fissionable material are being used instead of one. However, the energy created by the first explosion is so great that it can be used to implode a much smaller lump of, say, plutonium than would otherwise be needed, making it, in fact, much more efficient.

In the New Year of 1951, it occurred to Ulam how this basic design might be applied to the problem of igniting fusion. His wife, Françoise, has remembered how one day at about noon she found Ulam ‘staring intensely out of a window in our living room with a very strange expression on his face’. ‘Peering unseeing into the garden, he said, “I found a way to make it work.” “What work?” I asked. “The Super,” he replied. “It is a totally different scheme, and it will change the course of history.”’

Ulam’s new H-bomb design called for an atomic ‘primary’ to set off a fusion ‘secondary’, using very high-energy neutrons. When he described it to Teller, however, Teller – perhaps with the Cylinder design in mind – saw that Ulam’s design could be improved by using the
radiation
, rather than the neutron flow, from the primary to compress a piece of fusible material. This is what became known as the ‘Ulam–Teller’ design, which, as both men realised in January 1951, was a very considerable improvement on the ‘classical Super’. ‘From then on,’ Ulam says, ‘pessimism gave way to hope.’ ‘Edward is full of enthusiasm about these possibilities,’ Ulam wrote to von Neumann in February 1951, adding skittishly: ‘This is perhaps an indication they will not work.’ Hans Bethe, meanwhile, was extremely impressed: ‘The new concept was to me, who had been rather closely associated with the program, about as surprising as the discovery of fission had been to physicists in 1939.’

In a series of papers written in February and March 1951, several refinements were added to the Ulam–Teller design, one of which was to place a rod of plutonium – a ‘spark plug’ – inside the fusible material and another of which was to surround the fusible material with a uranium tamper. Together, these two refinements considerably increased the anticipated yield of the bomb, the explosion of which was now a three-stage process: 1. an implosive fission reaction in the ‘primary’ produces radiation of extraordinarily high energy, which compresses the fusible material, causing a fission reaction in the plutonium ‘spark plug’ at its centre; 2. this raises the temperature high enough – and, crucially, quickly enough – to bring about a fusion reaction in the fusible material; 3. this, in turn, causes a fission reaction in the surrounding uranium. As Jeremy Bernstein summarises the process: ‘The sequence is fission-fusion-fission, with most of the energy from a hydrogen bomb actually coming from fission.’

The final report explaining this device, credited to both Teller and
Ulam, was entitled ‘On Heterocatalytic Detonations I: Hydrodynamic Lenses and Radiation Mirrors’, and dated 9 March 1951. In the light of this new design, the George test, held on 9 May, acquired a new significance, promising as it did to provide experimental data on radiation implosion. The location chosen for the Greenhouse tests was the Eniwetok Atoll, on the north-west end of the Marshall Islands in the Pacific: 8,500 men were flown out there to carry out the extensive and elaborate preparations for the tests. The scientific observers included, apart from Teller, Ernest Lawrence and Gordon Dean.

The explosion of the Cylinder certainly produced an impressive blast. The yield was measured at 225 kilotons – not quite the 500 kilotons originally envisaged, but, even so, at least fifteen times more powerful than the Hiroshima bomb – and the fireball it produced was estimated to be 1,800 feet high. Whether fusion had taken place, however, could not be known until certain measurements had been carried out. While waiting for the results of those measurements, Teller went swimming with Lawrence. ‘When I came out of the water to stand on the white sands of the beach,’ Teller later remembered, ‘I told Lawrence that I thought the experiment had been a failure. He thought otherwise, and bet me five dollars.’ The next day, the results showed that Lawrence had won the bet. The world’s first man-made fusion reaction had taken place. That tiny amount of deuterium and tritium – less than one ounce – had yielded twenty-five kilotons of explosive energy, twice the force that had destroyed Hiroshima.

Oppenheimer’s prediction that the test would be a disaster and would mark the point at which the hydrogen-bomb project was abandoned could not have been more wrong. As urged by Gordon Dean, Oppenheimer convened a meeting of the GAC to discuss the improved prospects for the Super at Princeton on 16–17 June. Teller, naturally, was invited. The agenda for the meeting envisaged a discussion first of the results obtained from the Greenhouse tests, moving on to theoretical results concerning the classical Super, before finally considering the Ulam–Teller design. Teller, however, had no patience for that, and interrupted the first presentation to talk about the promise of this novel design. As he explained the new concept, all the scientists present, including Oppenheimer, could see its potential and it immediately won the backing of the GAC. ‘The outcome of the meeting,’ Oppenheimer later said, ‘was an agreed program and a fixing of priorities and effort both for Los Alamos and for other aspects of the Commission’s work. This program has been an outstanding success.’

When asked to explain why his reaction to the Ulam–Teller design differed so markedly from his 1949 reaction to the classical Super, Oppenheimer said:

This is not entirely convincing. The technical problems of the classical Super certainly played a part in the GAC’s recommendation in 1949 not to pursue a crash programme, but what seemed more decisive were the moral considerations raised and urged by Conant. The moral issues raised by this new design were exactly the same as those raised by the old design. If anything, the fact that the new design stood a better chance of working would seem to make those moral issues more pressing. Moreover, as Oppenheimer later said, though from a technical point of view he could consider the hydrogen-bomb design ‘a sweet and lovely and beautiful job’, he ‘still thought it was a dreadful weapon’.

As even Teller acknowledged, however, the attitude of Oppenheimer, the GAC and the AEC changed after this meeting of June 1951. Now the AEC got fully behind the programme and gave it all the resources it needed. In September 1951, with the AEC’s backing, the thermonuclear division at Los Alamos began making preparations for a full test of the Ulam–Teller bomb, and on 1 November 1952, scarcely more than a year later, that test (code-named ‘Mike’) was duly carried out and was a stunning success, the bomb exploding with an awe-inspiring yield of ten megatons (about 700 Hiroshima bombs).

Thus, less than three years after President Truman’s announcement of its existence, the AEC had brought the crash programme to build a hydrogen bomb to a successful conclusion. Why then had Teller and others complained so bitterly that Oppenheimer was delaying the development of the bomb? There simply was no delay. The bomb was, on the contrary, developed with remarkable speed and the programme to construct it managed with exactly the kind of scientific and administrative skill that had been so admired in the Manhattan Project. It all went surprisingly smoothly.