by C. P. Snow
It would require an immense industrial development. It was one thing to talk of separating the isotope on this scale, but a formidable job to do it. Britain might just conceivably have been able to try, in peace-time. But the country was at war, and still had to survive: which meant that an abnormal proportion of its resources had to be spent on radar, a device not only sensible but vital, and on bombing aircraft, which was not so sensible.
America was still not in the war. It took some time for the Peierls-Frisch memorandum to reach American scientists. It was carried over the Atlantic in August 1940 by Cockcroft, who talked in his quiet uninflected manner to American nuclear scientists. A good many were working on uranium projects, but there was not the urgency that was driving British scientists, who, in the good old Johnsonian mood, had their minds concentrated by the prospect of being hanged tomorrow. But it didn’t take long for the Americans to be convinced that the uranium-235 bomb was feasible.
And American physicists had just discovered another isotope which could be used in a fission bomb. This was not an isotope of uranium. Edwin McMillan, with colleagues Philip Abelson and Glenn Seaborg, had achieved what Fermi thought he had done – they had produced trans-uranic elements. Not surprisingly, these had unstable, radioactive nuclei. The new element beyond uranium was called neptunium – because the planet Neptune is beyond Uranus in the solar system. But it was the next element that was bomb material. Called – inevitably – plutonium, element number 94 has an isotope, plutonium-239, which can sustain a chain reaction of disintegrations. Making a plutonium bomb is not so much a question of separating isotopes, but of making sizeable quantities of an element that does not occur in nature. This, however, need not be any more difficult than separating the uranium isotopes; the plutonium bomb had strong advocates, too.
The Einstein letter hadn’t produced much in the way of action. Now the entire US governmental scientific machine began to get to work. American energy was set free in its impressive abundance. The project was codenamed Manhattan. There was, of course, an element of fright communicated by the British. The Peierls–Frisch argument was only too convincing. It now seemed odds on that atomic bombs were makeable. What were the Nazis doing?
The Manhattan project was a feat of technology and scientific administration. As has been said, the essential science had been done earlier. This was application on a gigantic scale. There were, in fact, scientific snags along the way, and plenty of puzzles on the frontiers of science and engineering. A number of the best scientists alive showed considerable versatility in attacking problems utterly different from anything they had met in an academic department. Fermi, who was able to apply his mind to almost anything – on his death-bed he wished that he had given a little thought to politics – was prepared to invent devices of extreme sophistication and occasionally, in an un-American fashion, of childlike simplicity. By common consent, he was the most valuable man around. But many others displayed talents which no one, including themselves, imagined that they possessed. At Los Alamos in New Mexico, which was the brain centre of the project, they lived a life remote but intense, certain that the job was imperative, not worried (such worry is swept away in war) by consequences. It was exciting to be living near a peak of technical achievement.
The chief scientific administrator, Robert Oppenheimer, was one of the most interesting figures in world science. Among a mass of very clever men, he was probably the cleverest. He was highly cultivated in the arts, and had an admirably organized and structured mind. He had genuine scientific talent, and could talk on equal terms with the greatest scientists in the place. Bohr, who was finally evacuated from Denmark via Sweden to London and Los Alamos, at the risk of his life, had a very high opinion of Oppenheimer’s scientific gift. So had Rabi, the least soft of touches.
The curious thing was that Oppenheimer had no great scientific achievement to his name. This is hard to explain. He had lived through a period in which men with a tenth of his talent had made major discoveries. He was scientifically ambitious and would have liked real creative success more than anything in the world. He became a great figure: the achievement of Los Alamos made him famous and he deserved the fame. Nevertheless, one suspects he would have given all that away if he could have exchanged it for one single piece of work of the class, say, of Pauli’s Exclusion Principle. There was his tragedy, probably much more deeply wounding than the political misfortunes which later happened to him.
There were some other strangenesses about the population of Los Alamos. A high proportion were refugees, recent immigrants who had had time to be rapidly naturalized. This was partly, of course, because they included some of the best practitioners on earth: but there was another reason. Most native scientists, in America and even more in Britain, had been swept up in work which appeared, and was, more directly concerned with the Hitler war. For example, Cockcroft, who would have been peculiarly valuable at Los Alamos, was head of an English radar establishment. (He had to be extracted later to lead the British nuclear team in Canada.) Rabi was immersed in similar activities at the Massachusetts Institute of Technology, and so on for dozens of the top American and English nuclear scientists. Refugees were the main source of the available manpower of high class. This may or may not have made a marginal difference when it came to disputes about the long-term political future of what they were doing. Refugees sometimes felt constrained. They wanted to accept the country which they hoped to make their own.
The dominance of refugees had some more farcical concomitants. Security procedures were thrown into a frenzy and at times displayed their dottier aspects. For example, Peierls and Frisch were never given places on Maud, the small British committee responsible for work on the nuclear bomb – and so weren’t able, in official terms, to discuss and explain their own work.
It was Fermi who took the first step into the nuclear age. Although no one now had any doubt that the bomb was possible, it was important to test that chain reactions could take place. Physicists needed to monitor, to measure, a nuclear chain reaction that went leisurely. Fermi achieved this with naturally occurring uranium, where the overwhelming amount of stable uranium-238 would prevent an explosion. His earlier intuition that slow neutrons were best at instigating nuclear fission was vital. This time he used blocks of graphite to slow them. In a disused squash court at the University of Chicago he built an edifice from six tons of uranium, fifty tons of uranium oxide and four hundred tons of graphite blocks: he called it a ‘pile’, because it was literally that. But in present-day terms it was the first nuclear reactor.
On 2 December 1942, Fermi withdrew the neutron-absorbing ‘control rods’. The chain reaction began. Neutrons split the minority of uranium-235 nuclei; heat and more neutrons streamed from the disintegration. These neutrons shot out of the uranium block, but were slowed by the graphite, and so split more uranium-235 nuclei as they entered the next uranium block. Fermi’s pile was not designed to produce nuclear power as such. It was a test. After making his measurements, Fermi took it apart again. Theoretically, at least, the path to the bomb was now clear.
Scientists at Los Alamos were certainly all confident that it would not be long before a bomb was ready. They had the euphoria of all concerned in an extraordinary enterprise. That was the overmastering emotion. Apprehensions about the putative Nazi performance were lessening slightly – though in official London the word still went round that the war was going well if we are safe from that which we mustn’t talk about.
It would have horrified General Leslie Groves, the supreme administrator of the Manhattan project, to discover how badly his security system actually worked. It was nothing like so effective as security about the decoding techniques (the English called this process Ultra). Groves’ iron rules certainly made communication between the people doing the job at times bizarrely complicated. Another result was to prevent any news of the operation reaching the Vice President of the United States and the Deputy Prime Minister of the United Kingdom: but a good deal of
news reached hundreds of other people. This wasn’t because of treachery or even gossip. Men like Groves underestimate the intelligence of their fellow citizens. Why were well-known scientists disappearing to unknown destinations? Why should Niels Bohr arrive in London and shortly afterwards get swallowed up in America? To scientists, it was all too obvious.
Niels Bohr was both unusually busy and unusually worried. After inspecting the diffusion plants where the uranium isotopes were separated, he had no doubt that the nuclear bomb was a certainty: and, what was more, not just a certainty for this war, but a feature of the world scene for ever. He was one of the most far-sighted of men, and he belonged to the world. He went to Los Alamos, anxious to help where he could, but deliberately not attaching himself formally to either the American or British contingents. He knew another certainty. It was taking America about four years to make the bomb: it wouldn’t take long for the Soviet Union, or other industrialized societies with a strong enough purpose, to do the same. Nearly all scientists agreed. There are no secrets in science: and very few, and those short-lived, in technology.
From the moment it became known that the Americans were moving towards a fission bomb, the general guess was that it would take the Soviet Union perhaps five years to catch up – some, more in touch with Soviet engineering physics, thought that was an overestimate. General Groves gave contemptuous snorts. He told his political masters that the United States had at least a twenty-year lead, probably much more. That was believed by those who wanted to believe, and produced some political dangers. General Groves was a singularly bad choice for his job.
Bohr, after characteristic reflection, decided that it was worth trying to avert or minimize the post-war perils which any sentient person could imagine. It would do no harm, and might do some good, to give the Soviet government an indication about the bomb. (We now know they were already informed. Bohr didn’t know this, but he assumed that their scientists had made their own predictions from 1939 onwards, as had duly happened.) Even a tentative disclosure, Bohr thought, might make for international confidence.
Bohr revealed his thoughts to Halifax, the British Ambassador in Washington, and received considerable sympathy, as he did from Felix Frankfurter. He was despatched to have a talk, with Churchill.
That encounter was one of the black comedies of the war. For some obscure reason, Churchill was strongly averse to seeing Bohr. It wasn’t that he didn’t come with the highest recommendations. Sir John Anderson, whom no one could think had pro-Soviet leanings, had already heard Bohr’s case, and thought there was a lot in it. It perhaps wasn’t irrelevant that Anderson had had a scientific education, had even done some research, and found it easy to believe the temporary nature of the Western lead. He also had great respect for Bohr. So presumably did Cherwell, who couldn’t have been well disposed to the actual proposal, but knew all about Bohr and helped force the interview on Churchill. The President of the Royal Society had also insisted. After all, Bohr was one of the greatest men of the century.
After very long and discourteous delays, Bohr was granted a discourteous half-hour. It bore a resemblance, seen through a distorting mirror, to the meeting with Rutherford which got Bohr launched on his career. No doubt Bohr whispered conscientiously alone. This time, however, the other party wasn’t prepared to listen, or apparently didn’t trouble to understand what was being said. On the stroke of the half-hour Bohr was dismissed.
Bohr didn’t suffer from offended dignity. But he was miserable. He had failed in what he believed to be his most important public mission.
Would Einstein have done better? Probably not, so far as the outcome went. There would have been a difference of tone. Einstein was not outfaced by any man alive, and there would have been some Jehovianic words spoken from his side of the table.
That meeting, if one can use an inappropriate word, took place in the summer of 1944, just before the invasion of Europe. As soon as the Anglo-American forces got a foothold in Germany, a mission was despatched to investigate what the German nuclear physicists had really been doing. The mission consisted of two excellent physicists, both originally Dutch, now American, Goudsmit and Uhlenbeck. Their report was pleasing but surprising. The German nuclear physicists had done remarkably little. As had been thought, Heisenberg had been in charge of a group, small but high-powered. The members were to be interrogated in England as soon as they could be tracked down. Anyway, that specific war-long anxiety was now wiped away.
So only the Americans, with their British affiliates, had been making the bomb. Bohr, nothing if not pertinacious, continued with his resolve. Brushed off by Churchill, he went back to American confidants, Frankfurter, Vannevar Bush (the first of presidential scientific advisers), J B Conant. They, too, had been trying to read the future, and were ready to support Bohr. It was arranged for him to explain his thoughts to Roosevelt.
There he got a very different response from Churchill’s. It was warm, cordial, amiably sympathetic. With knowledge of what followed within three months, this now seems puzzling. It may have been just a politician’s professional technique, but it appears more likely that the President was at least half impressed. He would, of course, have been carefully briefed by Bush and the others, and he had picked up more about Bohr himself than Churchill had. Churchill seems to have taken a violent personal dislike to Bohr – about the only human being who ever did so.
It would be false to give the impression that the scientists at Los Alamos had any knowledge of these attempts to cope with the future. Bohr was much too punctilious and honourable to let slip any word of those discussions, though two or three of his senior colleagues, Fermi and Oppenheimer among them, had an intimation of what was being tried and agreed with it, though without much hope. Most of the Los Alamos population wouldn’t have felt it as a personal concern. They knew that the project was soon going to succeed or fail. Failure was unthinkable, and yet some couldn’t suppress the thought as the gigantic enterprise approached its climax.
The Manhattan project was now employing 500,000 people, directly and indirectly, and spending a billion dollars per year. The uranium isotopes were separated by two different processes – at the beginning, no one knew which would be the more efficient. The first was a diffusion process. When the metal uranium reacts with fluorine, the compound formed – uranium hexafluoride – is a gas. A molecule containing uranium-238 is very slightly heavier than a molecule of uranium-235 hexafluoride, and as a result is slightly more sluggish. If uranium hexafluoride gas made from natural uranium – which contains only 0.7 per cent uranium-235 – is forced through a filter, the lighter uranium-235 will find it slightly easier to get through. So the gas on the far side is marginally enriched in the required isotope. Repeat the process, and the proportion of uranium-235 will rise a little more. To get ‘weapons-grade’ uranium – containing 90 per cent of the rare isotope – needed thousands of passes through the filters. But, slow though it was, it was gradually accumulating the fissile material.
Running in parallel was separation by means of electric and magnetic fields. Uranium atoms were stripped of electrons in a vacuum. Now they were electrically charged, and they were susceptible to outside fields. Again the heavier uranium-238 was more sluggish, and uranium-235 could gradually be separated out.
And plutonium was now in ‘commercial scale’ production – kilograms of a new element were being created. In huge reactors, uranium was bombarded by neutrons. The important isotope this time was the common uranium-238, which absorbed a neutron, then emitted two electrons from the nucleus and ended up as plutonium-239. With large quantities of plutonium to investigate, the scientists had found that it was indeed fissile – something they had had to take on trust from the theoreticians at the beginning of the Manhattan project.
The bomb, or more exactly one uranium bomb and one plutonium bomb, should be ready by the late summer of 1945, a year ahead. There would be a test just before the bombs were despatched.
Thus very few at Los Alam
os had any glimmer of the first results of Bohr’s diplomacy. This was another piece of black comedy. Roosevelt and Churchill met at the second Quebec conference. Roosevelt surrendered without a struggle to Churchill’s view of Bohr. He was on the verge of ‘mortal crimes’ – an extraordinary Churchillian phrase. Churchill drew up his and Roosevelt’s understanding. Nothing whatever about the project was to be communicated to anyone outside the circle of secrecy, certainly not to the French, above all not to the Russians. Bohr, and anyone under his influence, was to be kept under surveillance.
At one point Churchill was demanding that Bohr should be arrested. That was, however, too much for the President’s advisers and Churchill’s own, many of them shaken by this singular display. Possibly the only person who wasn’t shaken was Admiral Leahy, who, with his habitual lack of judgement, was certain that the bomb would be a fiasco and wouldn’t go off at all.
Why did Roosevelt and Churchill behave like that? Roosevelt was a sick man, and may not have felt capable of resisting Churchill in one of his obsessive nagging phases, prepared to go on grinding away in perpetuity. But Churchill? There has never been much of an explanation. He had always had a naive faith in ‘secrets’. He had been told by the best authorities that this ‘secret’ wasn’t keepable and that the Soviets would soon have the bomb themselves. Perhaps, with one of his surges of romantic optimism, he deluded himself into not believing it. He was only too conscious that British power, and his own, was now just a vestige. So long as the Americans and British had the bomb in sole possession, he could feel that that power hadn’t altogether slipped away.