Before the Fallout Page 18
Chadwick set Rotblat to work on investigating a very short-lived isotope. The skill, speed, and originality with which the Pole completed the task so impressed him that he offered Rotblat the most prestigious fellowship his department had. It was worth £ i 2o—exactly the sum Rotblat received from his Polish scholarship—and had never before been awarded to a foreigner. A delighted Rotblat exclaimed, "Oh good, this means I shall be able to bring my wife." Chadwick, unaware till now that his protege was married, was aghast at the idea of the couple existing on so little, but Rotblat insisted they would manage. In August 1939, shortly after the Liverpool cyclotron fired its first beam of accelerated particles, Rotblat returned to Warsaw. His thoughts were not only dominated by the chance to bring his wife to England. Like so many others, he had read the article published that summer by the German scientist Siegfried Fliigge, which talked of a uranium device. As he pondered, his ideas crystallized, and he "worked out a rationale for doing research on the feasibility of the bomb." He also concluded that "the only way to stop the Germans from using it against us would be if we too had the bomb and threatened to retaliate," but his scenario "never envisaged that we should use it, not even against the Germans."
Once in Warsaw, Rotblat sought out his former professor, Ludwig Werten-stein, who was Jewish like himself and had been a pupil of Marie Curie in Paris and had also spent a year at the Cavendish, where he had got to know Chadwick. Rotblat told Wertenstein of his conviction that "the only way to stop Hitler was to have the bomb ourselves" and asked his advice. The professor replied that "he couldn't advise. . . . it was a matter of conscience"—a comment Rotblat took deeply to heart and would remember when he became closely involved with the Allied bomb project.* For the present, though, Rotblat's chief worry was his wife. She had been taken ill with appendicitis and was too sick to travel. An anxious Rotblat waited until, in his own words, "the last minute," but finally he left, intending that his wife would come later. As it turned out, he caught almost the last train to leave a free Poland for over fifty years. He reached England on 1 September 1939, the day that the Nazis marched into Poland. He never saw his wife again.
Back in Liverpool, he faced pressing financial problems. His Polish funding had dried up, his fellowship was not due to commence until October, and he had just seven shillings and sixpence in the world. He could not even pay his rent and hitchhiked to London to seek the help of the Polish Embassy, but "there was complete chaos and they asked me, could I help them." However, his hitherto parsimonious landlord proved unexpectedly kind, agreeing he could stay on and pay him back later. Nevertheless, Rotblat was tremendously relieved when Chadwick returned safely to England and immediately threw him a lifeline, appointing him as lecturer in nuclear physics, despite what Rotblat called his "very, very shaky" English. Rotblat spent the next weeks studying English as hard as he could, not only to enable him to lecture but, as he later recalled, to allow him "to go back to the problem which worried me the whole time." Rotblat decided to go to Chadwick and quietly suggest "that we should start work on the bomb."
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Chadwick's reaction to the discovery of uranium fission had initially been low-key. He was not convinced that there would be "any interesting consequences from it" and that "if something could be done with it, it would be a technical development rather than a search for new physical facts." His views were shared by the majority of the scientific community in Britain, despite sensational articles in the press speculating about an awesome and dreadful new weapon.
In October 1939 Edward Appleton, a former colleague of Chadwick's at the Cavendish and newly appointed secretary of the Department of Scientific and Industrial Research, asked Chadwick privately for his views. Chadwick replied that although a device was theoretically possible, the process was complicated and he doubted its feasibility. He had studied Bohr's and Wheeler's conclusions carefully. Their theory that fission by slow neutrons was entirely due to the rare isotope U-235 not only showed that any chain reaction in ordinary uranium would require huge amounts of the metal—perhaps tons—but also implied that this requirement was, in itself, an obstacle. To create a chain reaction, the neutrons would have to travel long distances, seeking out the sparse U-235 atoms and causing the whole process to unfold too slowly. As energy was released, the uranium would heat up and evaporate before the chain reaction had gone very far. Even if a chain reaction was achievable, it was highly unlikely to lead to a bomb. Nevertheless, Chadwick promised Appleton he "would think about it again."
In late November Rotblat summoned up sufficient courage and grasp of English to present in detail to Chadwick his plans for research on the feasibility of an atom bomb. Recognizing that slow neutrons would not cause the immediate and catastrophic conditions required for an explosion, he argued that the chain reaction must be triggered by fast neutrons instead. At the end of his presentation his mentor, who had remained silent, gave a response that was typically Chadwickian. As Rotblat recalled, "He just grunted," leaving Rotblat discouraged by his reaction. In fact, his views had melded with Chadwick's own evolving opinions. As Chadwick later wrote: "It was only the direct impact of war which made me put my mind to such questions. I then saw how simple the problem of producing a violent explosion really was, provided that a suitable material existed . . . which would support a chain reaction with fast, not slow neutrons, so that a substantial part would react, and release large amounts of energy, before the system had time to fly apart."
Chadwick came back to Rotblat and asked, "What sort of experiments do you want to do?" Rotblat told him and began exploring such critical but unknown areas as the energies of neutrons generated by fission and the proportion of neutrons that would be absorbed by other nuclei without producing fission. By then half of Chadwick's team had been diverted to classified radar work, from which Rotblat, as a foreigner, was barred, and research assistants were thin on the ground. Rotblat was assigned a young Quaker called Flanders to help him. As a conscientious objector, Flanders had been sent to the university instead of being drafted into the army. Rotblat wondered whether he should tell his assistant that he was working on research with possible military applications, but Chadwick had ordered him to divulge nothing of the work's true purpose and Rotblat reasoned that the experiments had independent scientific validity. After the war he discovered that Flanders had "guessed something was going on," so in a sense "we were both deceiving each other."
Chadwick meanwhile reported to Appleton his revised conclusions that "it seems likely" that fission "could be developed to an explosive process under appropriate conditions." These disturbing views prompted the government to unite all uranium and fission research under the Air Ministry. This included not only Chadwick's work but also experimental work conducted by George Thomson at Imperial College in London and at Birmingham University under Rutherford's former pupil, the Australian Mark Oliphant. All information would be reviewed by the Air Defence Research Committee, chaired by Sir Henry Tizard, the rector of Imperial College. By the spring of 1940 Tizard and his commitee were still uncertain whether nuclear research would be valuable to the war effort. However, a note forwarded by Mark Oliphant, from two emigre scientists in his department, changed everything. One of them was Otto Frisch. The other was the Berlin-born mathematical physicist Rudolf Peierls. Just like Rotblat, they believed an atom bomb was possible. Also like him, they had arrived at the idea of nuclear deterrence.
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Rudolf Peierls had originally come to England in 1933 to spend the second half of a Rockefeller scholarship at the Cavendish Laboratory in Cambridge, having spent the first half with Enrico Fermi in Rome. He and his ebullient Russian physicist wife, Genia, had adapted quickly to English life, pleased that the rules of polite behavior were "much less rigid" than in Germany, although the food was rather a shock. With characterisic humor, Peierls devised "a theory of the typical English boarding-house food: it would be undemocratic for the cook to impose his or her taste on the guests, so things a
re boiled until only a neutral matrix remains, to which the guest can give any flavor by adding salt, pepper, horseradish, mustard, ketchup, and so on."
As Peierls's fellowship drew to an end, he had looked anxiously for a job in England. As he was learning from every letter mailed to him from Germany, Jewish academics were being thrown out of their jobs, and, as a Jew himself, Peierls knew he no longer had a future there. His wife's pregnancy added to his personal worries, but he still did what he could for others. When he saw a junior post at Cambridge advertised, he applied himself but generously sent a telegram to Hans Bethe in Germany, suggesting he also apply. As it turned out, neither man was appointed. However, Lawrence Bragg, a professor at Manchester University, came to Peierls's rescue with a two-year grant from a fund similar to that set up by the Academic Assistance Council, which Rutherford was then spearheading. The grateful Peierlses moved north with their new baby daughter and were soon joined by Hans Bethe when he came to England, and they offered him a room in their "damp and icy" house.
In 1935 Rudolf Peierls was offered an appointment at the Mond Laboratory in Cambridge, originally built for Peter Kapitza to conduct his magnetism and low-temperature experiments. The money allocated for Kapitza's salary was unused, and Ernest Rutherford had persuaded the Royal Society to award Peierls a research fellowship. Then, in the spring of 1937, Mark Oliphant suggested he apply for a mathematics professorship at Birmingham University. He was successful and at last had the security of a permanent appointment. The Peierlses celebrated by buying an old car for twenty-five pounds and learning to drive. Their peripatetic life appeared to have ended.
In 1939 Otto Frisch turned up in Birmingham. The Nazi invasion of what remained of Czechoslovakia in March 1939 had made him uneasy about remaining in Copenhagen and, in his own words, "in a state of complete doldrums," believing war was coming and fearing that nothing he did would be any good. He was also depressed, fighting "a pretty strong presentiment" that he had only a few months left to live. This prompted him for "the only time in my life" to take "some initiative." When Mark Oliphant visited Copenhagen, Frisch appealed to him, confessing his fears that Denmark "would soon be overrun by Hitler" and asking "would there be a chance for me to go to England in time, because I'd rather work for England than do nothing or be compelled in some way or other to work for Hitler or be sent to a concentration camp." A "very sympathetic" Oliphant said, "You just come over in the summer. We'll find you something to do. You can give a few lectures or something." Frisch arrived in July 1939 with two small suitcases, and the Peierlses took him under their wing. Rudolf Peierls particularly admired Frisch's talent "to ponder until he could present a problem in a form that admitted of a solution, the mark of a real physicist." Their mutual talents were about to combine.
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By then most of Mark Oliphant's work at Birmingham was concerned with radar development. Security regulations did not allow aliens born in enemy countries like Otto Frisch and recently naturalized British citizens like Rudolf Peierls to be employed on sensitive war work, and thus both men were excluded from taking part. Indeed, neither was supposed to know anything about the project. However, the secrecy was "a bit of a charade." As Frisch recalled, Oliphant would sidle up to Peierls and pose him a "hypothetical" question, to which Peierls would furnish an answer, knowing full well what it would be used for. "Oliphant knew that Peierls knew, and I think Peierls knew that Oliphant knew that he knew. But neither of them let on." However, their formal exclusion from the radar work freed the two men to think about uranium fission.
While Frisch had been at Niels Bohr's institute, there had been little belief in a "superweapon" as a practical possibility. Frisch assumed that to be correct until in early 1940 in Birmingham he was invited to contribute an article on fission to the annual report of the British Chemical Society. He was then living in a freezing apartment, where in winter, even with the gas fire on, the daytime temperature did not rise above 43 degrees Fahrenheit and where at night "the water froze in the tumbler at my bedside." Huddled in his overcoat and with his typewriter balanced on his knees, he typed out his article, writing in unfamiliar English, "There are now a number of strong arguments to the effect that the construction of a super bomb would be, if not impossible, prohibitively expensive and that furthermore the bomb would not be so effective as was thought at first." He sent off his article, but writing it had raised nagging doubts about whether he was right.
Frisch also brooded about the possibilities suggested by some studies he had recently begun into a method for separating isotopes known as "thermal diffusion." Invented by the German scientist Klaus Clusius, it consisted of filling a tube with a gas mixture. If this mixture was heated at one end and cooled at the other, experiments had shown that the lighter isotopes would migrate to the hotter end and the heavier ones to the cooler region, thus suggesting the possibility of separating the lighter, fissionable U-235 from the heavier U-238.
Frisch sought out Peierls and startled him with the question "Suppose someone gave you a quantity of pure 235 isotope of uranium—what would happen?" They began to calculate the consequences, using a formula worked out by Peierls for calculating the "critical mass"—the amount of fissionable material needed to be brought together to release sufficient neutrons to start a self-sustaining chain reaction. As Peierls recalled, "The work of Bohr and Wheeler seemed to suggest that every neutron that hit a 235 nucleus should produce fission. Since the number of secondary neutrons per fission had been measured approximately, we had all the data to insert in my formula for the critical size." The result amazed them. Others who had tried to calculate the critical mass "had tended to come out with tons"; the Joliot-Curie team, for example, had estimated it at around forty tons. Frisch and Peierls's first estimate was "about a pound," which as Frisch observed was not, after all, "such a lot." Frisch calculated that using the Clusius thermal diffusion method of isotopic separation, he could produce a pound of reasonably pure U-235 in a matter of weeks.
The two men also calculated whether the chain reaction would last long enough to cause a catastrophic explosion. Scribbling literally on the back of an envelope, they worked out that a substantial amount of the uranium would fissure, releasing energy equivalent to "thousands of tons of ordinary explosive." As Peierls remembered, "We were quite staggered by these results: an atomic bomb was possible at least in principle! As a weapon it would be so devastating that, from a military point of view, it would be worth setting up a plant to separate the isotopes. In a classic understatement, we said to ourselves, 'Even if this plant costs as much as a battleship, it would be worth having.'" With further understatement, Frisch said thoughtfully to Peierls, "Look, shouldn't somebody know about that?"
Rudolf Peierls
Together they composed the famous Frisch-Peierls memorandum titled "On the Construction of a 'Superbomb'; Based on a Nuclear Chain Reaction in Uranium." The compelling three-page, two-part document dealt with scientific, strategic, and ethical issues. It suggested that "one might think of about i kg [of uranium] as a suitable size for the bomb." Their estimates of the critical mass were, in fact, an underestimate. They were unaware that some of the neutrons colliding with U-23C would simply be absorbed, or "captured," rather than causing fission, but, as Peierls later wrote, "the order of magnitude was right." They also described how to explode a bomb with a mechanism that would force two pieces of uranium together at tremendous speed to constitute the critical mass.
The memorandum addressed the human consequences not only of the blast, which could probably destroy "the centre of a big city," but of the subsequent effect of radiation, "fatal to living beings even a long time after the explosion." "Most of it," the note predicted, "will probably be blown into the air and carried away by the wind. This cloud of radioactive material will kill everybody within a strip estimated to be several miles long. If it rained the danger would be even worse because active material would be carried down to the ground and stick to it." Frisch and Peierls sugg
ested that the probably very high number of civilian casualties "may make it unsuitable as a weapon for use by this country," but pointed out that as there was no effective defense, other than the threat of retaliation with the same weapon, it would be worth developing as a deterrent, "even if it is not intended to use the bomb as a means of attack." They also warned that although "we have no information that the same idea has also occurred to other scientists . . . all the theoretical data bearing on this problem are published, [so] it is quite conceivable that Germany is, in fact, developing this weapon."
The Frisch-Peierls memorandum—with its origins in a cold room in Birmingham where a refugee muffled in an overcoat tapped with chilly fingers on a typewriter balanced on his knees—was the first document to demonstrate scientifically the real possibility of creating an atomic weapon and the first to describe its shocking effects. For security reasons the two scientists typed the note themselves, making only one carbon copy, and gave it to Oliphant, who in March 1940 sent it to a startled Sir Henry Tizard. The depiction of a weapon that would be "practically irresistible" was about to kick-start the faltering British atomic program.
*Despite Niels Bohr's efforts to save him, Wertenstein would be killed by flying shrapnel as he tried to flee to Hungary across the Danube in 1944.
TEN
MAUD RAY KENT
ON THE MORNING OF 21 June 1940, the British collier Broompark docked at Falmouth after a nerve-racking thirty-six-hour crossing from Bordeaux during which an accompanying vessel had been sunk by a German mine. On board was a motley cargo of twenty-six drums of heavy water, 4 million pounds' worth of industrial diamonds, and piles of machine tools. The passengers included a bedraggled group of French scientists and their families. This was the conclusion of a mission entrusted to the eccentric, thirty-three-year-old earl of Suffolk—Charles Henry George Howard but known to all as "Jack." Barred by his limp from the armed forces, he had been appointed scientific liaison officer at the British Embassy in Paris, where he lived at the Ritz and, according to his contemporaries, "spent a lot of time drinking kirsch" and carousing with pretty women. With France about to fall, his bosses ordered him to gather some fifty eminent French scientists and engineers they had identified as useful and whisk them to safety in Britain. In the time available Suffolk had been able to find only about half of them, and the disappointed reaction of the government official meeting the train bringing the party to London was "Oh, is that the lot?" However, the little group included Frederic Joliot-Curie's two right-hand men, Hans von Halban and Lew Kowarski, though Joliot-Curie himself had opted to remain in occupied France.