Making of the Atomic Bomb

by Richard Rhodes

  Which Anderson dutifully did, and closed up the squash court and went home to bed.

  The pile as it waited in the dark cold of Chicago winter to be released to the breeding of neutrons and plutonium contained 771,000 pounds of graphite, 80,590 pounds of uranium oxide and 12,400 pounds of uranium metal. It cost about $1 million to produce and build. Its only visible moving parts were its various control rods. If Fermi had planned it for power production he would have shielded it behind concrete or steel and pumped away the heat of fission with helium or water or bismuth to drive turbines to generate electricity. But CP-1 was simply and entirely a physics experiment designed to prove the chain reaction, unshielded and uncooled, and Fermi intended, assuming he could control it, to run it no hotter than half a watt, hardly enough energy to light a flashlight bulb. He had controlled it day by day for the seventeen days of its building as its k approached 1.0, matching its responses with his estimates, and he was confident he could control it when its chain reaction finally diverged. What would he do if he was wrong? one of his young colleagues asked him. He thought of the damping effect of delayed neutrons. “I will walk away—leisurely,” he answered.1691

  “The next morning,” Leona Woods remembers—the beginning of the fateful day, December 2, 1942—“it was terribly cold—below zero. Fermi and I crunched over to the stands in creaking, blue-shadowed snow and repeated Herb’s flux measurement with the standard boron trifluoride counter.” Fermi had plotted a graph of his countdown numbers; the new data point fell exactly on the line he had extrapolated from previous measurements, a little shy of layer 57:1692

  Fermi discussed a schedule for the day with Zinn and Volney Wilson, Woods continues; “then a sleepy Herb Anderson showed up. . . . Herb, Fermi and I went over to the apartment I shared with my sister (it was close to the stands) for something to eat. I made pancakes, mixing the batter so fast that there were bubbles of dry flour in it. When fried, these were somewhat crunchy between the teeth, and Herb thought I had put nuts in the batter.”

  Outside was raw wind. On the second day of gasoline rationing Chicagoans jammed streetcars and elevated trains, leaving almost half their usual traffic of automobiles at home. The State Department had announced that morning that two million Jews had perished in Europe and five million more were in danger. The Germans were preparing counterattack in North Africa; American marines and Japanese soldiers struggled in the hell of Guadalcanal.

  Back we mushed through the cold, creaking snow . . . . Fifty-seventh Street was strangely empty. Inside the hall of the west stands, it was as cold as outside. We put on the usual gray (now black with graphite) laboratory coats and entered the doubles squash court containing the looming pile enclosed in the dirty, grayish-black balloon cloth and then went up on the spectators’ balcony. The balcony was originally meant for people to watch squash players, but now it was filled with control equipment and read-out circuits glowing and winking and radiating some gratefully received heat.1693

  The instrumentation included redundant boron trifluoride counters for lower neutron intensities and ionization chambers for higher. A wooden pier extending out from the face of the pile supported automatic control rods operated by small electric motors that would stand idle that day. ZIP, a weighted safety rod Zinn had designed, rode the same scaffolding. A solenoid-actuated catch controlled by an ionization chamber held ZIP in position withdrawn from the pile; if neutron intensity exceeded the chamber setting the solenoid would trip and gravity would pull the rod into position to stop the chain reaction. Another ZIP-like rod had been tied to the balcony railing with a length of rope; one of the physicists, feeling foolish, would stand by to chop the rope with an ax if all else failed. Allison had even insisted on a suicide squad, three young physicists installed with jugs of cadmium-sulfate solution near the ceiling on the elevator they had used to lift graphite bricks; “several of us,” Wattenberg complains, “were very upset with this since an accidental breakage of the jugs near the pile could have destroyed the usefulness of the material.”1694 George Weil, a young veteran of the Columbia days, took up position on the floor of the squash court to operate one of the cadmium control rods by hand at Fermi’s order. Fermi had scalers that counted off boron trifluoride readings with loud clicks and a cylindrical pen recorder that performed a similar function silently, graphing pile intensities in ink on a roll of slowly rotating graph paper. For calculations he relied on his own trusted six-inch slide rule, the pocket calculator of its day.

  Around midmorning Fermi began the crucial experiment. First he ordered all but the last cadmium rod removed and checked to see if the neutron intensity matched the measurement Anderson had made the night before. With that first comparison Volney Wilson’s team working on the balcony took time to adjust its monitors. Fermi had calculated in advance the intensity he expected the pile to reach at each step of the way as George Weil withdrew the last thirteen-foot cadmium rod by measured increments.

  When Wilson’s team was ready, writes Wattenberg, “Fermi instructed Weil to move the cadmium rod to a position which was about half-way out. [The adjustment brought the pile to] well below critical condition. The intensity rose, the scalers increased their rates of clicking for a short while, and then the rate became steady, as it was supposed to.”1695 Fermi busied himself at his slide rule, calculating the rate of increase, and noted the numbers on the back. He called to Weil to move the rod out another six inches. “Again the neutron intensity increased and leveled off. The pile was still subcritical. Fermi had again been busy with his little slide rule and seemed very pleased with the results of his calculations. Every time the intensity leveled off, it was at the values he had anticipated for the position of the control rod.”1696

  The slow, careful checking continued through the morning. A crowd began to gather on the balcony. Szilard arrived, Wigner, Allison, Spedding whose metal eggs had flattened the pile. Twenty-five or thirty people accumulated on the balcony watching, most of them the young physicists who had done the work. No one photographed the scene but most of the spectators probably wore suits and ties in the genteel tradition of prewar physics and since it was cold in the squash court, near zero, they would have kept warm in coats and hats, scarves and gloves. The room was dingy with graphite dust. Fermi was calm. The pile rising before them, faced with raw 4 by 6-inch pine timbers up to its equator, domed bare graphite above, looked like an ominous black beehive in a bright box. Neutrons were its bees, dancing and hot.

  Fermi called for another six-inch withdrawal. Weil reached up to comply. The neutron intensity leveled off at a rate outside the range of some of the instruments. Time passed, says Wattenberg, the watchers abiding in the cold, while Wilson’s team again adjusted the electronics:

  After the instrumentation was reset, Fermi told Weil to remove the rod another six inches. The pile was still subcritical. The intensity was increasing slowly—when suddenly there was a very loud crash! The safety rod, ZIP, had been automatically released. Its relay had been activated by an ionization chamber because the intensity had exceeded the arbitrary level at which it had been set. It was 11:30 a.m., and Fermi said, “I’m hungry. Let’s go to lunch.” The other rods were put into the pile and locked.1697

  At two in the afternoon they prepared to continue the experiment. Compton joined them. He brought along Crawford Greenewalt, the tall, handsome engineer who was the leader of the Du Pont contingent in Chicago. Forty-two people now occupied the squash court, most of them crowded onto the balcony.

  Fermi ordered all but one of the cadmium rods again unlocked and removed. He asked Weil to set the last rod at one of the earlier morning settings and compared pile intensity to the earlier reading. When the measurements checked he directed Weil to remove the rod to the last setting before lunch, about seven feet out.

  The closer k approached 1.0, the slower the rate of change of pile intensity. Fermi made another calculation. The pile was nearly critical. He asked that ZIP be slid in. That adjustment brought the neutron count
down. “This time,” he told Weil, “take the control rod out twelve inches.” Weil withdrew the cadmium rod. Fermi nodded and ZIP was winched out as well. “This is going to do it,” Fermi told Compton. The director of the plutonium project had found a place for himself at Fermi’s side. “Now it will become self-sustaining. The trace [on the recorder] will climb and continue to climb; it will not level off.”1698

  Herbert Anderson was an eyewitness:

  At first you could hear the sound of the neutron counter, clickety-clack, clickety-clack. Then the clicks came more and more rapidly, and after a while they began to merge into a roar; the counter couldn’t follow anymore. That was the moment to switch to the chart recorder. But when the switch was made, everyone watched in the sudden silence the mounting deflection of the recorder’s pen. It was an awesome silence. Everyone realized the significance of that switch; we were in the high intensity regime and the counters were unable to cope with the situation anymore. Again and again, the scale of the recorder had to be changed to accommodate the neutron intensity which was increasing more and more rapidly. Suddenly Fermi raised his hand. “The pile has gone critical,” he announced. No one present had any doubt about it.1699

  Fermi allowed himself a grin. He would tell the technical council the next day that the pile achieved a k of 1.0006.1700 Its neutron intensity was then doubling every two minutes. Left uncontrolled for an hour and a half, that rate of increase would have carried it to a million kilowatts. Long before so extreme a runaway it would have killed anyone left in the room and melted down.

  “Then everyone began to wonder why he didn’t shut the pile off,” Anderson continues.1701 “But Fermi was completely calm. He waited another minute, then another, and then when it seemed that the anxiety was too much to bear, he ordered ‘ZIP in!’ ” It was 3:53 P.M. Fermi had run the pile for 4.5 minutes at one-half watt and brought to fruition all the years of discovery and experiment. Men had controlled the release of energy from the atomic nucleus.

  The chain reaction was moonshine no more.

  Eugene Wigner reports how they felt:

  Nothing very spectacular had happened. Nothing had moved and the pile itself had given no sound. Nevertheless, when the rods were pushed back in and the clicking died down, we suddenly experienced a let-down feeling, for all of us understood the language of the counter. Even though we had anticipated the success of the experiment, its accomplishment had a deep impact on us. For some time we had known that we were about to unlock a giant; still, we could not escape an eerie feeling when we knew we had actually done it. We felt as, I presume, everyone feels who has done something that he knows will have very far-reaching consequences which he cannot foresee.1702

  Months earlier, realizing that the importation of Italian wine had been cut off by the war, Wigner had searched the liquor stores of Chicago for a celebratory fiasca of Chianti. He produced it now in a brown paper bag and presented it to Fermi. “We each had a small amount in a paper cup,” Wattenberg says, “and drank silently, looking at Fermi. Someone told Fermi to sign the [straw] wrapping on the bottle. After he did so, he passed it around, and we all signed it, except Wigner.”1703

  Compton and Greenewalt took their leave as Wilson began shutting down the electronics. Seaborg bumped into the Du Pont engineer in the corridor of Eckhart Hall and found him “bursting with good news.”1704 Back in his office Compton called Conant, who was working in Washington “in my quarters in the dormitory attached to the Dumbarton Oaks Library and Collection of Harvard University.”1705 Compton records their improvised dialogue:

  “Jim,” I said, “you’ll be interested to know that the Italian navigator has just landed in the new world.” Then, half apologetically, because I had led the S-1 Committee to believe that it would be another week or more before the pile could be completed, I added, “the earth was not as large as he had estimated, and he arrived at the new world sooner than he had expected.”1706

  “Is that so,” was Conant’s excited response. “Were the natives friendly?”

  “Everyone landed safe and happy.”

  Except Leo Szilard. Szilard, who was responsible with Fermi for the accomplishment that chill December afternoon of what he had first imagined alone on a gray September morning in another country an age ago—the old world undone by the new—loitered on the balcony, a small round man in an overcoat. He had dreamed that atomic energy might substitute exploration for war, carrying men away from the narrow earth into the cosmos. He knew now that long before it propelled any such exodus it would increase war’s devastation and mire man deeper in fear. He blinked behind his glasses. It was the end of the beginning. It might well be the beginning of the end. “There was a crowd there and then Fermi and I stayed there alone. I shook hands with Fermi and I said I thought this day would go down as a black day in the history of mankind.”1707

  14

  Physics and Desert Country

  Robert Oppenheimer was thirty-eight years old in 1942. He had done by then what Hans Bethe calls “massive scientific work.”1708 He was known and respected as a theoretician throughout the world of physics. Up to the time of the Berkeley summer study, however, few of his peers seem to have thought him capable of decisive leadership. Though he had matured deeply across the decade of the 1930s, his persistent mannerisms, especially his caustic tongue, may have screened his maturity from his colleagues’ eyes. Yet the 1930s shaped Oppenheimer for the work that was now to challenge him.

  His distinctive appearance sharpens the memory of an admiring new friend of that decade, a Berkeley professor and translator of French literature named Haakon Chevalier:

  [Oppenheimer] was tall, nervous and intent, and he moved with an odd gait, a kind of jog, with a great deal of swinging of his limbs, his head always a little to one side, one shoulder higher than the other. But it was the head that was the most striking: the halo of wispy black curly hair, the fine, sharp nose, and especially the eyes, surprisingly blue, having a strange depth and intensity, and yet expressive of a candor that was altogether disarming. He looked like a young Einstein, and at the same time like an overgrown choir boy.1709

  Chevalier’s portrait identifies Oppenheimer’s youthfulness and sensitivity but misses the self-destructiveness: the chain-smoking, the persistent cough persistently ignored, the ravaged teeth, the usually empty stomach assaulted by highly praised martinis and highly spiced food. Oppenheimer’s emaciation suggests he had an aversion to incorporating the world. His body embarrassed him and he seldom allowed himself to appear, as at the beach, undressed. At school he wore gray suits, blue shirts and well-polished black shoes. At home (a small spare apartment at first; later, after his marriage, the elegant house in the Berkeley hills he bought with a check the day he first toured it) he preferred jeans and blue chambray work shirts, the jeans hung on his narrow hips with a wide Western silver-buckled belt. It was not a common look in the 1930s—he had picked it up in New Mexico—and it was another detail that made him seem different.

  Women thought him handsome and dashing. Before a party he might send gardenias not only to his own date but to his friends’ dates as well. “He was great at a party,” a female acquaintance of his later adulthood comments, “and women simply loved him.”1710 His unfailing attentiveness probably elicited that admiration: “He was always,” writes Chevalier, “without seeming effort, aware of, and responsive to, everyone in the room, and was constantly anticipating unspoken wishes.”1711

  Men he could antagonize or amuse. Edward Teller first met Oppenheimer in 1937. The meeting, Teller says, was “painful but characteristic. On the evening I was to talk at a Berkeley colloquium, he took me out to a Mexican restaurant for dinner. I didn’t have the practice in speaking that I’ve had since, and I was already a little nervous. The plates were so hot, and the spices were so hot—as you might suspect if you knew Oppenheimer—and his personality was so overpowering, that I lost my voice.”1712 Emilio Segrè notes that Oppenheimer “sometimes appeared amateurish and snobbish.�
� Out of curiosity in 1940, while visiting Berkeley to deliver a lecture, Enrico Fermi attended a seminar one of Oppenheimer’s protégés led in the master’s style. “Emilio,” Fermi joked afterward with Segrè, “I am getting rusty and old. I cannot follow the highbrow theory developed by Oppenheimer’s pupils anymore. I went to their seminar and was depressed by my inability to understand them. Only the last sentence cheered me up; it was: ‘and this is Fermi’s theory of beta decay.’ ” Although Segrè found Oppenheimer “the fastest thinker I’ve ever met,” with “an iron memory . . . brilliance and solid merits,” he also saw “grave defects” including “occasional arrogance . . . [that] stung scientific colleagues where they were most sensitive.” “Robert could make people feel they were fools,” Bethe says simply.1713 “He made me, but I didn’t mind. Lawrence did. The two disagreed while they were both still at Berkeley.1714 I think Robert would give Lawrence a feeling that he didn’t know physics, and since that is what cyclotrons are for, Lawrence didn’t like it.” Oppenheimer recognized the habit without diagnosing it in a letter to his younger brother Frank: “But it is not easy—at least it is not easy for me—to be quite free of the desire to browbeat somebody or something.”1715 He called the behavior “beastliness.” It did not win him friends.

  Oppenheimer’s mother died after a long battle with leukemia in late 1931; that was when he announced himself to Herbert Smith, his former Ethical Culture teacher, to be “the loneliest man in the world.”1716 His father died suddenly of a heart attack in 1937. The two deaths frame the beginning years of the unworldly physicist’s discovery of the suffering in the world. Later he testified to the surprise of that discovery: