Diana Preston - Before the Fallout

Once in the United States, they briefed American scientists on subjects from the design of the Rolls-Royce Merlin engine—powering the Spitfires currently confronting the Luftwaffe in the skies over southern England in the Battle of Britain and later used in the American P-51 Mustang and the British Lancaster bomber and Mosquito intruder—to the cavity magnetron vital for enhancing radar performance, to the emerging evidence of the feasibility of an atomic bomb. The Tizard mission also attended a meeting of the Uranium Committee—the body set up by President Roosevelt in the aftermath of Albert Einstein’s warning. It was chaired by Lynam J. Briggs, originally a government soil scientist who had become director of the National Bureau of Standards. The other members were experts in military ordnance with little expertise in nuclear physics.

The British mission returned home and reported to the Maud Committee that America was not pursuing nuclear research with any great urgency. It was, however, impressed by the evidence it had seen of the United States’ great productive capacity for costly experimental work. This reinforced the view expressed by Mark Oliphant and shared by many British scientists that “if things go really badly with this country there is a great deal to be said for investigating any possibility which offers a chance of hitting back from the New World.”

Nuclear research was being pushed forward in Britain but under increasingly difficult conditions. In July 1940 Otto Frisch joined Chadwick’s team in Liverpool to work on isotopic separation. Soon after his arrival he heard “the wailing of air-raid sirens” for the first time in his life. Within weeks the city began suffering heavy air raids, and nighttime was dominated by the “popping of anti-aircraft guns” and the “clatter of falling shrapnel.” The bombing intensified when, in November 1940, Hitler ordered a series of bombing raids on British cities.

Liverpool was badly hit, but a worse sufferer was Coventry, where many of the city’s buildings, including the cathedral, were destroyed or badly damaged and _ ;68 people were killed. The Germans invented a new word, Koventrieren —“to Coventrate” or raze to the ground. Some of the fires joined together to produce greater intensity of heat, a fact not lost on the future air marshal Arthur “Bomber” Harris, then working in the Air Ministry. He would later recall that Coventry taught British planners the “principle” of the firestorm, igniting “so many fires at the same time.” It was, nevertheless, the Japanese who a year earlier, in 1939, could be said to have begun strategic bombing of undefended civilian cities and the creation of firestorms by dropping numerous incendiaries on the Chinese provisional capital, Chungking. A Times reporter described how the timber houses “burned like tinder…. the phosphorus kept the fires raging and a breeze extended them, three quarters of a square mile of houses were in flames.”

In the early months of 1941 the German Luftwaffe attacked Liverpool with high explosive bombs, parachute land mines, oil bombs, and incendiary bombs. In March a parachute landmine hit the courtyard of Chadwick’s physics department and blew out all the windows. Scientists hurried to the engineering department to find hammers and nails for makeshift repairs to their labs. Luckily, Chadwick’s cyclotron, deep in the basement, was unharmed. Frisch and the fellow occupants of his boardinghouse spent many nights huddling under the staircase. After one particularly frightening raid, they emerged to find that their landlady had fled. Frisch packed a case and scrambled through inner-city streets littered with debris to seek sanctuary with friends in the suburbs. The Chadwicks, who had sent their daughters to Canada for safety, were sleeping on the ground floor of their house for greater protection. Chadwick was discreetly going out with a Geiger counter and checking bomb craters to reassure himself that the Germans were not mixing radioactive material with the explosive in a kind of “dirty bomb.”

Despite the dangers and difficulties of living in a city under attack, Frisch settled down in Liverpool. As aliens he and Joseph Rotblat were formally subject to restrictions on their movements, but Chadwick persuaded his friend the chief constable of Merseyside to exempt them from what Rotblat called the more “ridiculous” strictures. Frisch was thus allowed to own a bicycle and found himself being fined ten shillings for riding without turning on his lights. He enjoyed working for Chadwick, who encouraged members of the team to discuss their work, “putting no great trust in the bogus security which relies on compartmentalising knowledge, on letting every scientist know only what he needs to know.” Rotblat was lecturing openly on chain reactions.

Frisch’s task was to test the thermal diffusion method for separating isotopes, pioneered by the German scientist Klaus Clusius, and which he and Peierls had recommended in their memorandum. Frisch told Chadwick that to do this he needed uranium hexafluoride, the only gaseous compound of uranium stable enough to be put into a tube. According to Frisch, Chadwick sat for about thirty seconds, “turning his head side to side like a bird,” then said simply, “How much hex do you want?” Frisch set to work with a student assistant, John Holt—the pair were soon nicknamed “Frisch and Chips”—but they discovered that the process would not work with uranium hexafluoride. As Peierls put it, “The effect happens to be practically zero.”

Working with a fellow refugee, the German-born Franz Simon, Peierls thought up another diffusion method for separating isotopes. This involved forcing atoms of uranium hexafluoride gas through fine holes in a porous barrier or membrane made from nickel. Peierls hoped that the lighter U-235. would pass through more quickly than the heavier U-238 and that, by repeating the exercise again and again, a U-235-rich gas would result. The process was difficult because the gas was highly corrosive and broke down on contact with moist air, but it seemed to work. Their research suggested that an industrial separation plant covering forty acres could yield one kilogram of 99 percent pure U-235. a day. The huge complex would take eighteen months to construct.

Chadwick was feeling the pressure. With his overview of all the experimental work, it was becoming ever clearer to him that “a nuclear bomb was not only possible—it was inevitable.” Yet he felt that he had “nobody to talk to.” Although he had a high regard for his chief helpers, Frisch and Rotblat, he was conscious that they “were not citizens of this country” and that the other scientists were “quite young boys.” Isolated and anxious, Chadwick found “the only remedy” was to take sleeping pills—a habit that remained with him for life.

Chadwick also bore the burden of deciding how to prioritize the research. Back in June 1940—on the day after the Germans marched into Paris—a letter, published in the U.S. journal Physical Review by the American scientists Edwin McMillan and Philip Abelson, had reported their results from working with the largest cyclotron yet built, by Ernest Lawrence at Berkeley. It was a giant device with a 60-inch vacuum chamber, compared with the 4.5-inch chamber of Lawrence’s first model. This machine provided a source of high-energy particles that, when they hit a beryllium or similar target, produced a copious stream of neutrons. Using these neutrons, McMillan and Abelson had bombarded uranium and created a hitherto unknown radioactive element. This element, with atomic number 93—named neptunium for the planet next in line to Uranus—decayed into another unnamed element occupying slot 94 in the periodic table. Joseph Rotblat recognized at once that, since the mysterious element shared characteristics with uranium, it would be likely to fission under neutron bombardment. If so, it could be an alternative to U-235 as atomic bomb fuel. He asked Chad­wick to allow him to use the Liverpool cyclotron to produce and explore the new element.