The First War of Physics (9 page)

McMillan had already devised a name for the new substance –
neptunium
– though he chose to withhold it for the time being. Just as element 93 is one step further along the periodic table from uranium, so Neptune is one planet further along in the solar system from Uranus. Unaware of any reasons for secrecy, on 27 May McMillan and Abelson submitted a paper describing the results of their work to the American journal
Physical Review.
The paper was published on 15 June, and read with great interest by Weizsäcker when the journal reached him in Berlin in July.
³

Of course, this work raised a further question. If element 93 was radioactive, with a characteristic decay time of 2.3 days, what was it decaying into? McMillan had his suspicions. He thought that element 93 might decay through a further emission of a beta particle, turning another neutron into a proton and so forming element 94. He immediately began work to find evidence for it.

Wild enough speculation

Szilard was probably unaware of McMillan and Abelson’s paper until it was published. The physicists had not thought to send it to him to seek his advice on the safety or otherwise of its publication in the open literature. But, by pure coincidence, on the same day that McMillan and Abelson submitted their paper to
Physical Review
, Szilard received a manuscript from Princeton theoretical physicist Louis Turner on precisely the same subject.

In January 1940 Turner had surveyed the literature on uranium fission and published a review in the journal
Reviews of Modern Physics.
This work had set him thinking. While all the attention had so far been diverted towards U-235, Turner now nagged away at the idea of producing atomic energy from the stable, and much more abundant, isotope U-238. The resonant capture of neutrons by U-238 was considered something of a nuisance, to be avoided in a reactor through the use of a suitable moderator. Now Turner followed much the same logic as Weizsäcker, McMillan and Abelson. Neutron capture by U-238 would create an unstable U-239 isotope, which would decay to form element 93. But Turner did not stop there. He had figured from theoretical principles that element 93 would be relatively unstable and would decay quite quickly, creating element 94.

Element 94 opened up an altogether different kind of prospect. It would consist of 94 protons and 145 neutrons, making a total of 239. In this sense it paralleled the pattern in U-235, with 92 protons and 143 neutrons. Some simple calculations suggested that this new element would be even more fissionable than U-235. It would be produced from the abundant isotope U-238 and, because it was a new element with its own distinct chemical properties, it could be chemically separated from its uranium parent. Turner anticipated that element 94 could represent a new source of fissionable material for nuclear chain reactions.

Turner had drafted a paper for submission to
Physical Review
and wanted Szilard’s opinion on whether or not it was safe to publish. ‘It seems as if it was wild enough speculation so that it could do no possible harm, but that is for someone else to say’, he told Szilard.

Speculation it might have been, but Szilard was a master of this game. He was stunned by the implications. ‘With this remark of Turner,’ he later said, ‘a whole landscape of the future of atomic energy rose before our eyes.’ Szilard suspected that achieving self-sustaining chain reactions – and bombs – might be a lot easier with element 94 than with uranium itself.

He recommended that Turner delay publication of his paper ‘indefinitely’.

Undoubtedly a Fascist

Despite these revelations, the Advisory Committee on Uranium still moved at a snail’s pace. Briggs, it seemed, was an innately cautious man. He could move at only one speed – full ahead slow.

Things were about to change, however. Vannevar Bush had vacated his vice presidency of the Massachusetts Institute of Technology (MIT) to
accept the presidency of Washington’s Carnegie Institution in the summer of 1939. Bush had trained as an electrical engineer and had gone on to become a highly pragmatic scientific administrator. During the First World War he had worked on the development of a magnetic device capable of detecting submarines. The device worked well enough, but was never put into operation. This experience had taught him all he needed to know about the importance of proper liaison between military and civilian research in the development of weapons in a time of war.

From his position as president of the Carnegie Institution, Bush lobbied for the establishment of a national organisation for just this kind of liaison. On 12 June 1940 he presented his arguments to Roosevelt, summarised in four short paragraphs in the middle of a sheet of paper. The groundwork had been done for him by Harry Hopkins, a Roosevelt aide, and the National Defense Research Council (NDRC) came into being. Its purpose was to direct all scientific research for military purposes.

One of its first actions was to take over the Advisory Committee on Uranium. The need for censorship was immediately agreed – all research papers on uranium fission would henceforth be subject to strict secrecy. Briggs remained as chairman of the committee, reporting to James Bryant Conant, president of Harvard, who had joined the NDRC at Bush’s invitation. The dependence on sceptical military advisers for funding was now greatly reduced.

Not that this made a great deal of difference, however. Bush and Conant were very aware of the potential threat of a German atomic bomb, but instead of lobbying to secure greatly increased funding for the American nuclear programme they preferred rather to focus research efforts on proving that a bomb was impossible. After all, if it could not be done then there would never be a threat from a German weapon. In a report to the NDRC dated 1 July 1940, Briggs summarised the progress to date and requested $40,000 for further critical research on the nuclear properties of the materials involved and $100,000 for experiments on a large-scale uranium–graphite pile. Briggs got the $40,000.

Szilard was left to wait a while longer.

The creation of the NDRC produced one unlooked-for side-effect. This was an American organisation involved in secret military research projects – only US citizens could be members. Fermi, Szilard, Teller and Wigner were now suddenly excluded from the proceedings. This was obviously absurd, and Sachs argued strenuously that the entire work of the Advisory Committee had depended on the efforts of emigre scientists who were now to be barred from future involvement.

Military security checks were duly carried out. The security report on Fermi labelled him ‘undoubtedly a Fascist’ (he was not) and recommended that he should not be employed on secret work. The report on Szilard suggested that he was ‘very pro-German’ and had ‘remarked on many occasions that he thinks the Germans will win the war’. The report recommended that Szilard, too, be barred from employment on secret work. Both reports quoted ‘highly reliable sources’. The irony was lost on them. The only secrets worth protecting were in the minds of the very scientists the authorities wanted to exclude.

The reports were sent to J. Edgar Hoover in August 1940 with a request for further FBI security checks. The FBI merely repeated what the military authorities had already claimed. It appeared not to matter. Sachs’ arguments won the day. All four émigré’ physicists were allowed to continue to make their contributions to the project, but now as advisers to the NDRC rather than full members.

Despite its now greatly raised profile, the work still proceeded slowly. In fairness, the results obtained thus far painted a rather confused picture. U-235 was clearly responsible for slow-neutron fission in uranium but separation of this isotope from U-238 was going to be an incredibly difficult feat. The early signs pointing to the feasibility of a uranium reactor were both encouraging and discouraging. Graphite in a suitably pure form would serve as a suitable moderator, but it was still not yet known if a self-sustaining chain reaction would develop in a uranium reactor without considerable enrichment of the minor U-235 isotope. Nier and Dunning’s conclusions in this regard had not been very promising. If a working reactor could be built, resonant absorption of neutrons by U-238 in such a
reactor might produce element 94, which could be more easily separated from uranium and which might prove to be fissionable in its own right.

To cap it all, Teller had carried out some calculations which suggested that a uranium bomb would require a mass of more than 30 tons. Even if it could be made to explode, it was difficult to see how such a bomb could be delivered to its target.

Bush remained sceptical of the science. It was difficult to see all this as anything other than a wild goose chase.

Thousands of times more powerful

The reckless, naked aggression that had been unleashed in Europe by Nazi Germany shaped the attitudes of all who observed it from across the Atlantic, but its effect on European émigrés was particularly profound. In the spring of 1940 Teller had been playing out an internal moral debate. He was at once uneasy with the prospect of working on weapons of such potentially massive destructive power, but at the same time understood enough about German military and technical superiority to develop real fear of a Nazi victory. ‘At that time,’ he later said, ‘I believed that Hitler would conquer the world unless a miracle happened.’

Teller had not seen fit to involve himself in politics or pay any attention to the pronouncements of politicians. He had initially thought not to accept an invitation to attend a Pan American Science Congress in Washington, which was to be addressed by Roosevelt, but Hitler’s rape of Europe in May 1940 caused him to change his mind. In the event, Roosevelt’s speech helped determine his moral position and gave him a resolve that was to remain unshakeable for the rest of his life.

Of course Teller was well aware of Einstein’s letter to Roosevelt and its consequences in terms of America’s stuttering nuclear programme. He had never met Roosevelt but, sitting in the audience listening to his speech, Teller was overcome by the eerie sensation that the president was talking to him directly. After pointing out how small the world had now become, Roosevelt cautioned that America could not depend on its ‘mystic immunity’ from a European war that threatened the very kind of civilisation so
valued by Americans. He then turned to the role of the scientists themselves:

You who are scientists may have been told that you are in part responsible for the debacle of today … but I assure you that it is not the scientists of the world who are responsible … What has come about has been caused solely by those who would use, and are using, the progress that you have made along lines of peace in an entirely different cause.

For Teller this was both rallying-cry and moral absolution. He had been fortunate to have escaped the tyranny that was now overrunning Europe and threatening to engulf the whole world. ‘I had the obligation to do whatever I could to protect freedom’, he said.

His mind was now firmly made up.

The news from Europe became ever more depressing. After unleashing his blitzkrieg on continental Europe, Hitler had anticipated negotiating a peace with Britain before turning his attention to Russia, his notional ally. Churchill had become prime minister of a new coalition government in early May. Unlike his predecessor Neville Chamberlain, who after the fall of France wanted to sue for peace, Churchill was not minded to negotiate. Hitler was left with no choice but to subdue Britain first, and this meant gaining air superiority over the south-east of England and the English Channel.

The Luftwaffe launched air assaults from their newly-acquired bases in northern France, harrying British convoys crossing the Channel, their purpose being not only to sink ships but also to lure British fighters out over the sea. In August Hermann Göring, head of the Luftwaffe, ordered assaults on coastal airfields and radar stations, and then inland airfields and aircraft production centres. The Battle of Britain had begun.

On 7 September Göring launched a series of massive air raids against London, partly in reprisal for a British bombing raid on Berlin and as a prelude to Operation Sealion, the full-scale invasion of Britain. Göring dispatched nearly 400 bombers and more than 600 fighters in two waves
against London’s East End. When 200 German bombers returned later that night in a further wave of attacks, London was still burning.

As news of the bombing reached Szilard, he remarked quietly: ‘Before this war is over there will be bombs thousands of times more powerful than those in the blitz.’

¹
The longer of these papers cites H.G. Wells’s
The World Set Free
, which was published in 1913 and which first introduced the idea of ‘atomic bombs’.

²
The term ‘pile’ crept into common usage over the course of several years’ experimental effort on the first nuclear reactor. Readers suspecting some deep scientific significance in this term should know that Fermi used it because the first reactor was literally a pile of graphite and uranium blocks.

³
British physicists strongly protested at the publication of the McMillan-Abelson paper and Lawrence received a formal dressing-down by an attache from the British embassy for giving away secrets to the Germans.