Before the Fallout

by Diana Preston

  "It was," Haukelid later wrote, "an anxious job and it took time. The charge and the wire had to be connected; then the detonators had to be connected to the wire and the ignition mechanism. Everything had to be put together and properly laid. It was cramped and uncomfortable down there under the deck, and about a foot of water was standing in the bilge." It was important that the ferry should sink quickly enough; Lake Tinnsjo was so narrow that unless the boat sank within five minutes, the captain might be able to beach her. Haukelid therefore laid the charge, consisting of nineteen pounds of sausage-shaped high explosive, toward the bows. On his reckoning, the blast would punch a hole about eleven feet square in the ship's side, and the ferry would sink rapidly by the bows. The railway trucks holding the heavy water would roll off the deck and go to the bottom first. To be absolutely certain that the explosion occurred where the lake was deepest, Haukelid positioned two alarm clocks on a spar of the hull and wired them to the charge. He timed them to go off at 10:4c a.m. the next morning.

  The saboteurs withdrew, telling the watchman that they had a few things to fetch and would be back on board in good time before the ferry sailed. Haukelid worried about the man who had been so cooperative and whom the Germans would be bound to interrogate after the ferry was sunk. The fate of two Norwegian guards at the Vemork heavy water plant, sent to Grini concentration camp after the February 1943 raid, still weighed on his conscience. Yet if they warned the watchman and he was absent when the ferry sailed, this would raise German suspicions. Haukelid contented himself with "shaking hands with the watchman and thanking him—which obviously puzzled him."

  As the three men ran from the ferry, they heard the rumble of the approaching train bringing the heavy water. Haukelid and Sorlie fled at once, Sorlie up into the mountains and Haukelid to catch a train the next day to Oslo and thence to ski to Sweden. Lier-Hansen was determined to remain behind to check that the ferry actually sailed. If there was any delay, he would defuse the bomb to prevent a premature explosion. The next morning on the train to Oslo Haukelid consulted his watch yet again. It showed 10:4c. a.m. If all had gone according to plan, the ferry should now be sinking. A newspaper headline the next day—"Railway Ferry 'Hydro' Sunk in the Tinnsjo"—told him that the mission had, indeed, succeeded, though at a cost. Of the fifty-three people aboard, only twenty-seven survived. However, the canisters containing more than 1,300 pounds of heavy water lay beyond Nazi reach at the bottom of Lake Tinnsjo.

  Despite an initial wave of arrests, the reprisals the Norwegian resistance had so feared did not materialize. General von Falkenhorst found it less embarrassing to maintain the fiction that the ferry's boilers had exploded than to acknowledge another brilliant act of Allied sabotage and another example of German incompetence and carelessness.

  NINETEEN

  BOON OR DISASTER?

  THE ALLIES HOPED that they had significantly disrupted Germany's bomb project. However, in the spring of 1944 their own experienced a crisis. One of the greatest scientific challenges was how to configure the bombs to ensure an explosion of the right force at the right time. Until then, the assumption had been that the two types of atomic weapon on which they were working concurrently—the uranium-fueled bomb, originally nicknamed "Thin Man" for Roosevelt but renamed "Little Boy" when the proposed gun barrel was shortened, and the plutonium bomb, nicknamed once and for all "Fat Man" for Churchill—would both be detonated by a high-velocity gun. This would fire one subcritical piece of fissile material into another, thereby creating a critical mass, initiating an uncontrolled chain reaction and producing the desired explosion. However, samples of plutonium produced by the Du Pont pilot plant at Oak Ridge, which began reaching Los Alamos at the rate of a gram a day from April 1944, showed an alarming capacity to fission spontaneously. The phenomenon was not entirely unexpected; the possibility of spontaneous fission had been raised in 1939 during discussions about how much material would be required to produce an atomic wreapon. However, what worried the scientists was that these samples appeared five times more likely to fission spontaneously than plutonium hitherto produced for experimental purposes in cyclotrons. It was a rate never observed before.

  Emilio Segre and his team, working in an isolated canyon away from the main Los Alamos site to keep their equipment free of radiation from other work, examined the plutonium samples and discovered that they contained a hitherto unnoticed isotope: Pu-240. This "rogue" isotope—created by the high rate of neutron irradiation of uranium in a reactor pile—spewed forth so many neutrons from spontaneous fission that its presence in the reactor plutonium meant that the gun-assembly technique was useless. It was simply too slow; the spontaneous fission would cause the plutonium to fly apart and vaporize with a modest release of energy before the two parts could combine fully to form a critical mass and produce a full chain reaction. For a while it seemed that the mammoth efforts at Hanford to construct large-scale production plants to ensure a plentiful and timely supply of plutonium had been wasted because the plutonium they would produce would possess the same propensity to fission spontaneously. General Groves seemed to have spent many millions of dollars for nothing.

  Schematic diagrams of Little Boy and Fat Man

  Several solutions were proposed, including a faster gun assembly or purging the plutonium of Pu-240, but none seemed practicable. In July 1944 an anxious Groves convened an emergency meeting in Chicago attended by, among others, Robert Oppenheimer and Enrico Fermi. They discussed an ingenious technique proposed by the physicist Seth Neddermeyer the previous year but not seriously considered until then. Instead of hurling one chunk of fissionable material into another, Neddermeyer's suggestion was to wrap an outer shell of conventional high explosives around an inner core of plutonium. The explosives would be so positioned that, when they detonated, the shock waves would be channeled inwards, squeezing the plutonium into a small, dense, walnut-sized sphere, forcing it into a critical mass, and thus producing a full explosion. The technique was called "implosion." The precise details remain classified to this day.

  Oppenheimer returned to Los Alamos and ordered work on the plutonium gun assembly to cease. Instead, he gave implosion studies top priority. The explosives expert George Kistiakowsky, whom Oppenheimer placed in charge of the work because he thought Neddermeyer lacked the necessary project management skills, brought together a multidisciplinary team, including physicists, machinists, and explosives experts, to work on what had become a highly resourced priority task instead of an interesting theoretical sideline. By the end of 1944 fourteen different groups would be engaged in implosion studies. Philip Morrison was appointed as one of two "G-engineers." (The G stood for gadget, code name for the implosion bomb.) Their work was, as Morrison later recalled, dangerous. It was also arduous. They talked to the heads of all the groups and studied their reports to see where the gaps and problems were, "looking for anything that might go wrong or get in the way." It was also their responsibility "to certify that all problems and issues had been solved."

  The crux of the implosion problem was how to achieve a perfectly symmetrical explosion and thereby produce the perfectly symmetrical pressure waves needed to compress the plutonium into a supercritical sphere. Hans Bethe recalled the first attempts at implosion as "an utter failure." Then James Tuck, a young member of the British team who was thoroughly in love with Los Alamos, believing it embodied the spirit of Plato's ideal republic, suggested using explosive lenses. Just as glass lenses could be used to focus light waves, high explosives—cast into special shapes, or "lenses"—could be used to focus shock waves, driving them inward. This was, according to Bethe, "a most important key."

  Meanwhile, Oppenheimer asked another British physicist, William Penney, to study how waves of highly compressed air radiated outward from an explosion. Penney was one of the few scientists at Los Alamos to have actually witnessed the effects of blast waves on human bodies and buildings, having studied the results of German bombing in Britain. One evening, Penney addressed one of Oppe
nheimer's colloquia on the subject. As Rudolf Peierls recalled, "His presentation was in a scientific matter-of-fact style, with his usual brightly smiling face; many of the Americans had not been exposed to such a detailed and realistic discussion of casualties. . . . he was nicknamed 'the smiling killer.'"

  Peierls himself, though based initially in New York, had been advising Edward Teller on the use of Los Alamos's newly arrived IBM punch-card calculators to compute the characteristics of implosion. In the summer of 1944 he and his wife, Genia, moved to Los Alamos, where Hans Bethe, Peierls's old friend, was anxious for him to replace Teller and take charge of implosion theory. Bethe's disagreements with Teller had by then come to a head. Teller was increasingly reluctant to work on implosion calculations or for Bethe—whom he considered "over-organised" as well as overly focused on detail—at all. In June 1944 Oppenheimer transferred Teller out of the Theory Division. Teller's replacement, Peierls, brought Klaus Fuchs with him, and the two men, working closely together, shared an office. Ironically, as Bethe later recalled, Fuchs was "the best of them all in computing just how the implosion wave would proceed." Enrico Fermi joined Los Alamos just a few weeks later, arriving from Chicago in September 1944. Oppenheimer set up a new division for him. Fermi's task was to investigate problems outside the scope of the other more task-specific divisions. Edward Teller, working on the theory of the hydrogen bomb, became one of Fermi's group leaders. With so many different countries of origin represented on site, Oppenheimer often had to remind his colleagues that the project's official language was English.

  Los Alamos was still growing. As Laura Fermi described, "The influx of new families on the mesa never ceased, and building went on at a feverish pace, invariably lagging behind the increase in population. . . . we found the confusion and disorder that always accompany a fast pace of construction." Nevertheless, Genia Peierls was delighted to have exchanged hot, humid New York City for the cooler air of the mountains. Earlier that summer she had taken refuge with the children at Cape Cod at a hotel whose brochure stated that it catered to a "restricted clientele." As her husband later wrote, "We were not yet aware that this phrase means 'No Negroes, Jews, Italians etc' Had we known, she would not have wished to stay there." Genia had already been shocked by the more overt racism of the South. After disembarking from the ship that had brought the British team to Newport News, she had searched for seats for herself and her husband in a crowded train to Washington. She had found an almost empty car containing "two very nice negroes," only to be told that in the South "transport was still segregated."

  The somewhat frenetic atmosphere of Los Alamos exactly suited the exuberant Genia, who, according to Laura Fermi, required "incessant action." She was soon busily organizing picnics to the ruins of old Indian pueblos. On one of these outings Laura found herself being driven by Fuchs. She thought him "an attractive, young man, slim, with a small, round face and dark hair, with a quiet look through round eyeglasses." She tried to make conversation, but he answered her only "sparingly, as if jealous of his words."

  Genia, who had known and fussed over Fuchs since he had first come to work for her husband in Birmingham, laughingly nicknamed him " 'Penny-in-the-slot Fuchs' because talking to him was like putting a coin into a vending machine. You got only one response to each question." Despite this reticence, Fuchs soon became popular at Los Alamos. He was a good dancer, enjoyed a drink, and was ever willing to babysit. He was living a life that, in his later confession, he would describe as "controlled schizophrenia." It allowed him to "establish in my mind two separate compartments. One compartment in which I allowed myself to make friendships . . . the other compartment to establish myself completely independent of the surrounding forces of society." He did this so successfully that Richard Feynman once joked with him about which of the two of them would be the most credible suspect as a spy. They agreed it was Feynman.

  Richard Feynman

  Feynman was an effervescent character, whom C. P. Snow later described as a cross between Groucho Marx and Einstein. He played the bongos and was once commissioned to paint a nude female toreador. He took delight in outwitting the increasingly sophisticated locking devices fitted to the Los Alamos filing cabinets. As he recalled in his memoirs, everybody thought their reports were safe, but, as he repeatedly demonstrated by presenting astonished colleagues with their own papers, the complex arrangements of steel rods, padlocks, and, later, combination wheels "didn't mean a damn thing."

  Feynman's wise-cracking boisterousness and passion for pranks masked a personal tragedy. His wife, Arlene, was dying of tuberculosis in a hospital in Albuquerque. Knowing that the end could come at any time, Feynman asked Fuchs whether he could borrow his car so he could get to Arlene's bedside quickly. Fuchs—always obliging to his friends—readily agreed. When the summons finally came, Feynman tore off in Fuchs's old blue Buick and, despite three flat tires, reached the hospital in time to be with Arlene when she died.

  · · ·

  With the work at Los Alamos focused on two completely different designs of atom bomb—the uranium device, Little Boy, and the plutonium device, Fat Man—the scientists made their best estimates of how much uranium and plutonium respectively each would require to produce the necessary critical mass. They calculated that Little Boy would need between 87 and 133 pounds of U-235 to cause an explosion equivalent to the detonation of between 10,000 and 20,000 tons of TNT. Estimates of the necessary amount of plutonium for Fat Man were even more uncertain. As everyone knew, having a bomb of either or both types available in time to influence the course of the war depended, above all, on whether sufficient fuel could be produced in time. Groves had always believed this to be the hardest part of the project.

  Manufacturing uranium and plutonium was by then a massive effort. Oak Ridge and Hanford were the heart, but they were supported by factories and laboratories in thirty-nine states. Groves later estimated that by the war's end more than six hundred thousand people had contributed, directly or indirectly, to the Manhattan Project. The Y-12 electromagnetic uranium separation plant at Oak Ridge, where operators sat on high stools six feet apart, produced its first two hundred grams of U-235 in February 1944—barely a year after its construction began. However, production remained worryingly slow until the discovery that feeding the plant with uranium that had already been slightly enriched with U-235 significantly increased the yield. By late 1944, Y-12 was producing more-substantial amounts of U-235. Meanwhile, K-25—the plant using gaseous diffusion to separate U-235 and built in sections by the Chrysler Corporation in Detroit and then assembled at Oak Ridge—was nearing completion. It would not become fully operational in time to make a major contribution. However, the U-235 it began producing in April 194c, by pumping uranium gas against a porous membrane so that the lighter U-235 passed through more rapidly than the heavier U-238, could be used as feed for Y-1 2. *

  The first plutonium-producing plant at Hanford, where workers had labored in nine-hour shifts six days a week, was brought up to full power in late September 1944. Scientists observed the controlled chain reaction with satisfaction. However, after a while the power mysteriously began to drop, and the reactor effectively shut itself down. Soon after, the power level began to rise again, only to be followed once more by a seemingly inexplicable shutdown. Scientists discovered the reason to be a rare isotope—Xenon-135, created during the fission process—which sucked up neutrons, thereby causing the chain reaction to peter out. They solved the problem by increasing the amount of fuel loaded into the reactor. Fortunately, the Du Pont engineers had, with Groves's backing, designed the reactor with a larger number of slots for fuel than the scientists had thought necessary. The first plutonium was extracted from the reactor around Christmas 1944 and dispatched to Los Alamos in early 1945, by which time the second and third plutonium plants at Hanford were also coming online. The plutonium was transported by military convoy. (Air transport was considered too risky in case of a crash, while train connections from Washington State were
too few.)

  The prospect that sufficient plutonium and U-235 would soon be available to build the bombs induced "great pressure to be ready with all the necessary developments for making and detonating them," according to Rudolf Peierls. Oppenheimer drove his teams hard, determined, as he later wrote, "to interpose no day's delay between the arrival of the material and the readiness of the bomb." Scientists worked eighteen-hour days. One of the physicist's wives, Ruth Marshak, recalled how "the Tech Area was a great pit which swallowed our scientist husbands out of sight, almost out of our lives. They worked at night, and often came home at three or four in the morning. Sometimes they set up army cots in the laboratories and did not come home at all."

  Oppenheimer was particularly anxious that everything for Fat Man, the plutonium-fueled implosion bomb, should be in place—that the essential physics research had been completed, that the explosive lenses designed by James Tuck had been made, and that an electric detonator system, developed by Luis Alvarez, was ready. Although the original plan had envisaged using uniform pressure waves to squeeze a thin, hollow shell of plutonium into a sphere, the necessary calculations had proved so complex that the idea had been abandoned for a simpler alternative. Robert Christy, by then working in Hans Bethe's division, had proposed using a solid sphere of plutonium comprising two fused hemispheres, together roughly the size of an apple. Christy calculated that the force of the implosion would at least double the plutonium's density, shortening the neutrons' route between nuclei and thereby swiftly accomplishing the required chain reaction. The device also included an initiator and a natural uranium tamper, or shell. It was vital for achieving the chain reaction that the plutonium sphere remained spherical and did not distort, and the shell's purpose was to compensate for any asymmetrical effects during implosion.