Enrico Fermi’s team at Columbia University had been hard at work through 1941 while the government deliberated. Fermi, Leo Szilard, Herbert Anderson and the young physicists who had joined them may never have known how close they came to orphanhood. The isolation of plutonium at Berkeley added a potential military application to their reasons for pursuing a slow-neutron chain reaction in uranium and graphite, but given the necessary resources Fermi at least would certainly have pursued the chain reaction anyway as a physical experiment of fundamental and historic worth. He had missed discovering fission by the thickness of a sheet of aluminum foil; he would not willingly leave to someone else the demonstration of atomic energy’s first sustained release. Thanks largely to Arthur Compton his work found continued support, which may help explain why he admired the pious Woosterite’s intelligence so extravagantly.
Szilard had finally gone on the Columbia payroll on November 1, 1940, when the $40,000 National Defense Research Committee contract came through for physical-constant measurements. To help Fermi without the friction the two men generated when they worked side by side, Szilard undertook to apply his special talent for enlightened cajolery to the problem of procuring supplies of purified uranium and graphite. The record is thick with his correspondence with American graphite manufacturers dismayed to discover that what they thought were the purest of materials were in fact hopelessly contaminated, usually with traces of boron. The cross section for neutron absorption of that light, ubiquitous, silicon-like element, number 5 on the periodic table, was tremendous and poisonous. “Szilard at that time took extremely decisive and strong steps to try to organize the early phases of production of pure materials,” says Fermi. “ . . . He did a marvelous job which later on was taken over by a more powerful organization than was Szilard himself. Although to match Szilard it takes a few able-bodied customers.”1534
In August and September the Columbia team prepared to assemble the largest uranium-graphite lattice yet devised. A slow-neutron chain reaction in natural uranium, like its fast-neutron counterpart U235, requires a critical mass: a volume of uranium and moderator sufficient to sustain neutron multiplication despite the inevitable loss of neutrons from its outer surface. No one yet knew the specifications of that critical volume, but it was obviously vast—on the order of some hundreds of tons. One way to create a self-sustaining chain reaction might be simply to continue stacking uranium and graphite together. But so crude an experiment, if it worked at all, would teach the experimenter very little about controlling the resulting reaction and might culminate in a disastrous and lethal runaway. Fermi proposed to approach the problem by the more circumspect route of a series of subcritical experiments designed to determine the necessary quantities and arrangements and to establish methods of control.
As always, he built directly on previous experience. He and Anderson had calculated the absorption cross section of carbon by measuring the diffusion of neutrons from a neutron source up a column of graphite. The new experiments would enlarge that column to take advantage of the increased stocks of graphite available and to make room for regularly spaced inclusions of uranium oxide: simplicity itself, but in physical form a thick, black, grimy, slippery mass of some thirty tons of extruded bars of graphite confining eight tons of oxide.1535 Fermi named the structure a “pile.” “Much of the standard nomenclature in nuclear science was developed at this time,” Segrè writes.1536 “ . . . I thought for a while that this term was used to refer to a source of nuclear energy in analogy with Volta’s use of the Italian term pila to denote his own great invention of a source of electrical energy [i.e., the Voltaic battery]. I was disillusioned by Fermi himself, who told me that he simply used the common English word pile as synonymous with heap” The Italian laureate was continuing to master the plainsong of American speech.
The exponential pile Fermi proposed to build (so called because an exponent entered into the calculation of its relationship to a full-scale reactor) would be too big for any of the laboratories in Pupin. He sought larger quarters:
We went to Dean Pegram, who was then the man who could carry out magic around the university, and we explained to him that we needed a big room. And when we say big we meant a really big room. Perhaps he made a crack about a church not being the most suited place for a physics laboratory . . . but I think a church would have been just precisely what we wanted. Well, he scouted around the campus and we went with him to dark corridors and under various heating pipes and so on to visit possible sites for this experiment and eventually a big room, not a church, but something that might have been compared in size with a church was discovered in Schermerhorn [Hall].
There, Fermi goes on, they began to build “this structure that at that time looked again in order of magnitude larger than anything that we had seen before. . . . It was a structure of graphite bricks and spread through these graphite bricks in some sort of pattern were big cans, cubic cans, containing uranium oxide.”1537 The cans, 8 by 8 by 8 inches, 288 of them in all, were made of tinned iron sheet; each could hold about 60 pounds of uranium oxide.1538 Each cubic “cell” of the uranium-graphite lattice—a can and its surrounding graphite—was 16 inches on a side. Spheres of uranium in an arrangement of spherical cells would have been more efficient. In these beginning experiments, with materials of doubtful purity, Fermi was pursuing order-of-magnitude estimates, a first rough mapping of new territory. “This structure was chosen because of its constructional simplicity,” the experimenters wrote afterward, “since it could be assembled without cutting our graphite bricks of 4” by 4” by 12”. Although we did not expect that the structure would approach too closely the optimum proportions, we thought it desirable to obtain some preliminary information as soon as possible.”1539 Promising results might also win further NDRC support.
“We were faced with a lot of hard and dirty work,” Herbert Anderson recalls. “The black uranium oxide powder had to be . . . heated to drive off undesired moisture and then packed hot in the containers and soldered shut. To get the required density, the filling was done on a shaking table. Our little group, which by that time included Bernard Feld, George Weil, and Walter Zinn, looked at the heavy task before us with little enthusiasm. It would be exhausting work.”1540 Then Pegram to the rescue in Fermi’s telling:
We were reasonably strong, but I mean we were, after all, thinkers. So Dean Pegram again looked around and said that seems to be a job a little bit beyond your feeble strength, but there is a football squad at Columbia that contains a dozen or so of very husky boys who take jobs by the hour just to carry them through college.1541 Why don’t you hire them?
And it was a marvelous idea; it was really a pleasure for once to direct the work of these husky boys, canning uranium—just shoving it in—handling packs of 50 or 100 pounds with the same ease as another person would have handled three or four pounds.
“Fermi tried to do his share of the work,” Anderson adds; “he donned a lab coat and pitched in to do his stint with the football men, but it was clear that he was out of his class. The rest of us found a lot to keep us busy with measurements and calibrations that suddenly seemed to require exceptional care and precision.”1542
For this first exponential experiment and the many similar experiments to come, Fermi defined a single fundamental magnitude for assessing the chain reaction, “the reproduction factor k.” k was the average number of secondary neutrons produced by one original neutron in a lattice of infinite size—in other words, if the original neutron had all the room in the world in which to drift on its way to encountering a uranium nucleus.1543 One neutron in the zero generation would produce k neutrons in the first generation,k2 neutrons in the second generation, k3 in the third generation and so on. If k was greater than 1.0, the series would diverge, the chain reaction would go, “in which case the production of neutrons is infinite.” If k was less than 1.0, the series would eventually converge to zero: the chain reaction would die out. k would depend on the quantity and quality of materials used in the pile and the efficiency of their arrangement.
The cubical lattice that the Columbia football squad stacked in Schermerhorn Hall in September 1941 extrapolated to a disappointing first k of 0.87. “Now that is by 0.13 less than one,” Fermi comments—13 percent less than the minimum necessary to make a chain reaction go—“and it was bad. However, at the moment we had a firm point to start from, and we had essentially to see whether we could squeeze the extra 0.13 or preferably a little bit more.” The cans were made of iron, and iron absorbs neutrons. “So, out go the cans.” Cubes of uranium were less efficient than spheres; next time the Columbia group would press the oxide into small rounded lumps. The materials were impure. “So, now, what do these impurities do?—-clearly they can do only harm. Maybe they make harm to the tune of 13 percent.” Szilard would continue his quest for materials of higher purity. “There was some considerable gain to be made . . . there.”1544
“Well,” concludes Fermi, “this brings us to Pearl Harbor.”
* * *
Arthur Compton had less than two weeks to throw together a program between his discussion with Vannevar Bush and James Bryant Conant at the Cosmos Club luncheon on December 6 and the first meeting on December 18 of the new leaders of what was now to be called the S-l program. (S-l for Section One of the Office of Scientific Research and Development: Conant would administer S-l, but the National Defense Research Committee was no longer directly involved; the bomb program had advanced from research into development.) On December 18, Conant notes in the secret history of the project he wrote in 1943, “the atmosphere was charged with excitement—the country had been at war nine days, an expansion of the S-l program was now an accomplished matter. Enthusiasm and optimism reigned.”1545 Compton offered his program to Bush, Conant and Briggs the next day and followed up on December 20 with a memorandum.1546 The projects that had come under his authority were scattered across the country at Columbia, Princeton, Chicago and Berkeley. For the time being he proposed leaving them there.
With the arrival of war, not to breathe a word of the mysteries they were exploring, the project leaders had adopted an informal code: plutonium was “copper,” U235 “magnesium,” uranium generically in the nonsensical British coinage “tube alloy.” “On the basis of the present data,” Compton wrote, optimism reigning, “it appears that explosive units of copper need be only half the size of those using magnesium, and that premature explosions can be ruled out.”1547 Because of the difficulty of engineering a remotely controlled chemical plant to extract plutonium, however, he thought that “the production of useful quantities of copper will take longer than the production of magnesium.” For a timetable he offered:
Knowledge of conditions for chain reaction by June 1, 1942.
Production of chain reaction by October 1, 1942.
Pilot plant for using reaction for copper production, October 1, 1943.
Copper in usable quantities by December 31, 1944.
His schedule was designed to show that plutonium might be produced in time to influence the outcome of the war, the standard which Conant was insisting upon after Pearl Harbor even more vehemently than before. But the uranium-graphite work had not yet won even Compton’s full confidence. If graphite proved impractical and “copper production” had to wait for heavy water (of which Harold Urey was urging the extraction at an existing plant in Canada), Compton’s schedule would slip by “from 6 months to 18 months.” And that might be too late to make a difference.
For the next six months, Compton estimated, the pile studies at Columbia, Princeton and Chicago would cost $590,000 for materials and $618,000 for salaries and support. “This figure seemed big to me,” he remembers modestly, “accustomed as I was to work on research that needed not more than a few thousand dollars per year.”1548
He had met with Pegram and Fermi to prepare this part of his proposal and concluded that when metallic uranium became available the project should be concentrated at Columbia. Over Christmas and through the first weeks of January it fell to Herbert Anderson, the native son, to find a building in the New York City area large enough to house a full-scale chain-reacting pile. Not to be outdone in the matter of informal codes, the Columbia team had named that culmination “the egg-boiling experiment.”1549,1550Anderson stumped the wintry boroughs and turned up seven likely locations for boiling uranium eggs. He proposed them to Szilard on January 21; they included a Polo Grounds structure, an aircraft hangar on Long Island that belonged to Curtiss-Wright and the hangar Goodyear used to house its blimps.
But as Compton reviewed the work of the several groups that had come under his authority, bringing their leaders together in Chicago three times during January, their disagreements and duplications made it obvious that all the developmental work on the chain reaction and on plutonium chemistry should be combined at one location. Pegram offered Columbia. They considered Princeton and Berkeley and industrial laboratories in Cleveland and Pittsburgh. Compton offered Chicago. No one wanted to move.
The third meeting of the new year, on Saturday, January 24, Compton conducted from his sickbed in one of the sparsely furnished spare bedrooms on the third floor of his large University Avenue house: he had the flu. Risking infection, Szilard attended, Ernest Lawrence, Luis Alvarez—Lawrence and Alvarez sitting together on the next bed—and several other men. “Each was arguing the merits of his own location,” Compton writes, “and every case was good. I presented the case for Chicago.”1551 He had already won the support of his university’s administration. “We will turn the university inside out if necessary to help win this war,” its vice president had sworn.1552 That was Compton’s first argument: he knew the management and had its support. Second, more scientists were available to staff the operation in the Midwest than on the coasts, where faculties and graduate schools had been “completely drained” for other war work. Third, Chicago was conveniently and centrally located for travel to other sites.
Which convinced no one. Szilard had forty tons of graphite on hand at Columbia and a going concern. The arguments continued. Compton, who was notoriously indecisive, suffered their brunt as long as he could bear it. “Finally, wearied to the point of exhaustion but needing to make a firm decision, I told them that Chicago would be [the project’s] location.”1553
Lawrence scoffed. “You’ll never get a chain reaction going here,” he baited his fellow laureate. “The whole tempo of the University of Chicago is too slow.”
“We’ll have the chain reaction going here by the end of the year,” Compton predicted.
“I’ll bet you a thousand dollars you won’t.”
“I’ll take you on that,” Compton says he answered, “and these men here are the witnesses.”
“I’ll cut the stakes to a five-cent cigar,” Lawrence hedged.
“Agreed,” said Compton, who never smoked a cigar in his life.
After the crowd left, Compton shuffled wearily to his study and called Fermi. “He agreed at once to make the move to Chicago,” Compton writes. Fermi may have agreed, but he found the decision burdensome. He was preparing further experiment. His group was exactly the right size. He owned a pleasant house in a pleasant suburb. He and Laura had buried a cache of Nobel Prize money in a lead pipe under the concrete floor of their basement coal bin against the possibility that as enemy aliens their assets would be frozen. Laura Fermi “had come to consider Leonia as our permanent home,” she writes, “and loathed the idea of moving again.”1554 She says her husband “was unhappy to move. They (I did not know who they were) had decided to concentrate all that work (I did not know what it was) in Chicago and to enlarge it greatly, Enrico grumbled. It was the work he had started at Columbia with a small group of physicists. There is much to be said for a small group. It can work quite efficiently.”1555 But the country was at war. Fermi traveled back and forth by train until the end of April, then camped in Chicago. Laura dug up their buried treasure and followed at the end of June.
To Szilard, the day after the sickbed meeting—he had returned promptly to New York—Compton sent a respectful telegram: THANK YOU FOR COMING TO PRESENT ABLY COLUMBIA’S SITUATION. NOW WE NEED YOUR HELP IN ORGANIZING THE METALLURGICAL LABORATORY OF O.S.R.D. IN CHICAGO. CAN YOU ARRIVE HERE WEDNESDAY MORNING WITH FERMI AND WIGNER . . . TO DISCUSS DETAILS OF MOVING AND ORGANIZATION.1556 Unlike the Radiation Laboratory at MIT, the new Metallurgical Laboratory hardly disguised its purpose in its name. Who would imagine its goal was the transmutation of the elements to make baseball-sized explosive spheres of unearthly metal?
Before Fermi and his team moved to Illinois they built one more exponential pile, this one loaded with cylindrical lumps of pressed uranium oxide three inches long and three inches in diameter that weighed four pounds each, some two thousand in all, set in blind holes drilled directly into graphite.1557 A new recruit, a handsome, dark-haired young experimentalist named John Marshall, located a suitable press for the work in a junkyard in Jersey City and set it up on the seventh floor of Pupin; Walter Zinn designed stainless steel dies; the powdered oxide bound together under pressure as medicinal tablets pressed from powder—aspirin, for example—do.
Fermi was concerned to free the pile as completely as possible of moisture to reduce neutron absorption. He had canned the oxide before; now he decided to can the entire nine-foot graphite cube. “There are no ready-made cans of the needed size,” Laura Fermi says dryly, “so Enrico ordered one.”1558 That, writes Albert Wattenberg, who joined the group in January, “required soldering together many strips of sheet metal. We were very fortunate in getting a sheet metal worker who made excellent solder joints. It was, however, quite a challenge to deal with him, since he could neither read nor speak English. We communicated with pictures, and somehow he did the job.”1559 Laura Fermi picks up the story: “To insure proper assembly, they marked each section with a little figure of a man: if the can were put together as it should be, all men would stand on their feet, otherwise on their heads.”1560 The Columbia men preheated the oxide lumps to 480°F before loading. They heated the contents of the room-sized can to the boiling point of water and pumped down a partial vacuum. Their heroic efforts reduced the pile’s moisture to 0.03 percent. With the same relatively impure uranium and graphite they had used before but with these improved conditions and arrangements they measuredk at the end of April at an encouraging 0.918.
In Chicago in the meantime Samuel Allison had built a smaller seven-foot exponential pile and measured k for his arrangement at 0.94. The University of Chicago had long ago sacrificed football to scholarship; Compton took over the warren of disused rooms under the west stands of Stagg Field, which was conveniently located immediately north of the main campus, and made space available there to Allison. Below solid masonry façades set with Gothic windows and crenellated towers the stands concealed ball courts as well as locker areas. The unheated room Allison had used for his experiment, sixty feet long, thirty feet wide, twenty-six feet high and sunk half below street level, was a doubles squash court.
December 6, 1941, the day of the bomb program expansion, marked another tidal event: Soviet forces under General Georgi Zhukov counterattacked across a two-hundred-mile front against the German Army congealed in snow and –35°F cold only thirty miles outside Moscow. “Like the supreme military genius who had trod this road a century before him,” Churchill writes, evoking Napoleon Bonaparte, “Hitler now discovered what Russian winter meant.”1561 Zhukov’s hundred divisions came as a bitter surprise—“well-fed, warmly clad and fresh Siberians,” a German general describes them, “fully equipped for winter fighting” as the Wehrmacht troops were not—and armies that had advanced half a thousand miles to push within sight of the Kremlin stumbled back toward Germany nearly in rout.1562 For the first time since Hitler began his conquests Blitzkrieg had failed. “The winter had fallen,” Churchill writes. “The long war was certain.”1563 Hitler relieved his Army commander in chief of duty and appropriated that office to himself. By the end of March his casualties in the East, counting not the sick but only the wounded, numbered nearly 1.2 million men.
It was clear in Berlin that the German economy had reached the limits of its expansion. Tradeoffs must follow. The Minister of Munitions installed a rule similar to the rule upon which Conant was insisting in the United States, and the director of Reich military research promulgated it to the physicists studying uranium: “The work . . . is making demands which can be justified in the current recruiting and raw materials crisis only if there is a certainty of getting some benefit from it in the near future.”1564 After considering the question the War Office decided to reduce the priority of uranium research by assigning most of it to the Ministry of Education under Bernhard Rust, the scientifically illiterate SS Obergruppenführer and former provincial schoolteacher who had refused to sanction Lise Meitner’s emigration following the Anschluss. The academic physicists were happy to be out from under the Army but chagrined to be consigned to a backwater ministry run by a party hack. Rust delegated authority to the Reich Research Council. That organization was part of the Reich Bureau of Standards. The KWI physicists considered its physics section head, Abraham Esau, incompetent. In effect, the German uranium program had slipped in status to the level of the old U.S. Uranium Committee and now had its Briggs.
The Research Council decided to appeal directly to the highest levels of the Reich for support. It organized an elaborate presentation and invited such dignitaries as Hermann Göring, Martin Bormann, Heinrich Himmler, Navy commander in chief Admiral Erich Raeder, Field Marshal Wilhelm Keitel and Albert Speer, Hitler’s admired patrician architect who was Minister of Armaments and War Production. Heisenberg, Hahn, Bothe, Geiger, Clusius and Harteck were scheduled to speak at the February 26 meeting, Rust presiding, and an “Experimental Luncheon” would be served offering entrées prepared from frozen foods basted with synthetic shortening and bread made with soy flour.1565
Unfortunately for the council’s ambitious plans, the secretary assigned to send out invitations enclosed the wrong lecture program. A secret scientific conference under the auspices of Army Ordnance had been scheduled at the Kaiser Wilhelm Society’s Harnack House for the same day. Its program listed twenty-five highly technical scientific papers. That was the program the leaders of the Reich mistakenly received. Himmler regretted: he would be away from Berlin that day. Keitel was “too busy at the moment.”1566Raeder would send a representative. None of the leaders chose to attend.
What Heisenberg had to say might have surprised them. He emphasized atomic energy for power but also discussed military uses. “Pure uranium-235 is thus seen to be an explosive of quite unimaginable force,” he told his staff-level auditors. “The Americans seem to be pursuing this line of research with particular urgency.” Inside a uranium reactor “a new element is created [i.e., plutonium] . . . which is in all probability as explosive as pure uranium-235, with the same colossal force.”1567 At the same time at Harnack House, where Leo Szilard once lodged, bags packed, Army Ordnance was learning that “it would suffice to bring together two lumps of this explosive, weighing a total often to a hundred kilograms, for it to detonate.”1568
Basic knowledge of one direct route to an atomic bomb—via plutonium—was at hand. What was lacking was money and materials. The February 26 meeting won over at least the Minister of Education. “The first time large funds were available in Germany,” Heisenberg recalled at the end of the war, “was in the spring of 1942, after that meeting with Rust, when we convinced him that we had absolutely definite proof that it could be done.”1569 Heisenberg’s “large” is relative to the modest funds that had been available before, however. Not Bernhard Rust but Albert Speer needed to be convinced of the military promise of atomic energy to swell the scale of funding anywhere near the billions of reichsmarks that production of even ten kilograms of U235 or plutonium would require.
Speer did not recall the February 26 invitation after the war. Atomic energy first came to his attention, he writes in his memoirs, at one of his regular private luncheons with General Friedrich Fromm, the commander of the Home Army. “In the course of one of these meetings, at the end of April 1942, [Fromm] remarked that our only chance of winning the war lay in developing a weapon with totally new effects. He said he had contacts with a group of scientists who were on the track of a weapon which could annihilate whole cities. . . . Fromm proposed that we pay a joint visit to these men.” Speer also heard that spring from the president of the Kaiser Wilhelm Society, who complained of lack of support for uranium research. “On May 6, 1942, I discussed this situation with Hitler and proposed that Göring be placed at the head of the Reich Research Council—thus emphasizing its importance.”1570
That shift to the obese Reichsmarshal who commanded the Luftwaffe and whom Hitler had designated to be his successor carried only symbolic promotion. More crucial was a June 4 conference at Harnack House that Speer, Fromm, automobile and tank designer Ferdinand Porsche and other military and industrial leaders attended. In February Heisenberg had devoted most of his lecture to nuclear power. This time he emphasized military prospects. The secretary of the Kaiser Wilhelm Society was surprised: “The word ‘bomb’ which was used at this conference was news not only to me but for many others present, as I could see from their reaction.”1571 It was not news to Speer. When Heisenberg took questions from the floor, one of Speer’s deputies asked how large a bomb capable of destroying a city would have to be. Heisenberg cupped his hands as Fermi had done sighting down Manhattan Island from Pupin Hall. “As large as a pineapple,” he said.1572
After the briefings Speer questioned Heisenberg directly. How could nuclear physics be applied to the manufacture of atomic bombs? The German laureate seems to have shied from committing himself. “His answer was by no means encouraging,” Speer remembers. “He declared, to be sure, that the scientific solution had already been found. . . . But the technical prerequisites for production would take years to develop, two years at the earliest, even provided that the program was given maximum support.” They were crippled by an absence of cyclotrons, Heisenberg said. Speer offered to build cyclotrons “as large as or larger than those in the United States.” Heisenberg demurred that German physicists lacked experience building large cyclotrons and would have to start small. Speer “urged the scientists to inform me of the measures, the sums of money and the materials they would need to further nuclear research.” A few weeks later they did, but their requests looked picayune to a Reichsminister accustomed to dealing in billions of marks. They requested “an appropriation of several hundred thousand marks and some small amounts of steel, nickel, and other priority metals. . . . Rather put out by these modest requests in a matter of such crucial importance, I suggested that they take one or two million marks and correspondingly larger quantities of materials. But apparently more could not be utilized for the present, and in any case I had been given the impression that the atom bomb could no longer have any bearing on the course of the war.”1573
Speer saw Hitler regularly and duly reported the findings of the June conferences:
Hitler had sometimes spoken to me about the possibility of an atom bomb, but the idea quite obviously strained his intellectual capacity. He was also unable to grasp the revolutionary nature of nuclear physics.1574 In the twenty-two hundred recorded points of my conferences with Hitler, nuclear fission comes up only once, and then is mentioned with extreme brevity. Hitler did sometimes comment on its prospects, but what I told him of my conferences with the physicists confirmed his view that there was not much profit in the matter. Actually, Professor Heisenberg had not given any final answer to my question whether a successful nuclear fission could be kept under control with absolute certainty or might continue as a chain reaction. Hitler was plainly not delighted with the possibility that the earth under his rule might be transformed into a glowing star. Occasionally, however, he joked that the scientists in their unworldly urge to lay bare all the secrets under heaven might some day set the globe on fire. But undoubtedly a good deal of time would pass before that came about, Hitler said; he would certainly not live to see it.
Following that, according to Speer, “on the suggestion of the nuclear physicists we scuttled the project to develop an atom bomb . . . after I had again queried them about deadlines and been told that we could not count on anything for three or four years.” Work on what Speer calls “an energy-producing uranium motor for propelling machinery”—the heavy-water pile—would continue.1575 “In the upshot,” Heisenberg wrote in Nature in 1947, summarizing the war years, German physicists “were spared the decision as to whether or not they should aim at producing atomic bombs.1576 The circumstances shaping policy in the critical year of 1942 guided their work automatically toward the problem of the utilization of nuclear energy in prime movers.” But the Allies had not yet been informed.
* * *
“We may be engaged in a race toward realization,” Vannevar Bush wrote Franklin Roosevelt on March 9, 1942; “but, if so, I have no indication of the status of the enemy program, and have taken no definite steps toward finding out.”1577, 1578 Why Bush was not more curious remains a mystery. Conant, Lawrence and Compton, not to mention the emigrés, fretted continually about the possibility of a German bomb. It was their primary reason for urging an American bomb. It was not Bush’s or Roosevelt’s—to them the bomb offered offensive advantage first of all—but the two leaders were alert to the German danger and surprisingly indifferent to assessing it.
The report that accompanied Bush’s letter stated that five to ten pounds of “active material” would be “fairly certain” to explode with a force equivalent to 2,000 tons of TNT, up from 600 tons in the third National Academy of Sciences report of the previous November 6. It recommended building a centrifuge plant at a cost of $20 million that could produce enough U235 for one bomb a month and estimated that such a plant could be completed by December 1943. A gaseous diffusion plant, its cost unspecified, might deliver by the end of 1944. An electromagnetic separation plant—Ernest Lawrence’s project—won the most attention in the report: it might “offer a short-cut,” wrote Bush, and deliver “fully practicable quantities of material by the summer of 1943, with a time saving of perhaps six months or even more.” In summary, “present opinion indicates that successful use is possible, and that this would be very important and might be determining in the war effort. It is also true that if the enemy arrived at results first it would be an exceedingly serious matter. The best estimate indicates completion in 1944, if every effort is made to expedite.”
Roosevelt responded two days later: “I think the whole thing should be pushed not only in regard to development, but also with due regard to time. This is very much of the essence.”1579 Time, not money, was becoming the limiting factor in atomic bomb development.
A meeting on May 23 brought all the program leaders together with Conant to decide which of several methods of making a bomb should be moved on to the pilot-plant and industrial engineering stages. The centrifuge, gaseous barrier diffusion, electromagnetic and graphite or heavy-water plutonium-pile approaches all looked equally promising. Given wartime scarcities and budget priorities, which should be advanced? Conant used an arms-race argument to identify the point of decision:
While all five methods now appear to be about equally promising, clearly the time of production of a dozen bombs by the five routes will certainly not be the same but might vary by six months or a year because of unforeseen delays. Therefore, if one discards one or two or three of the methods now, one may be betting on the slower horse unconsciously. To my mind the decision as to how “all out” the effort should be might well turn on the military appraisal of what would occur if either side had a dozen or two bombs before the other.1580
To that point Conant reviewed the evidence for a German bomb program, including new indications of espionage activity: information from the British that the Germans had a ton of heavy water; Peter Debye’s report when he arrived in the United States eighteen months earlier that his colleagues at the KWI were hard at work; and “the recently intercepted instruction to their agents in this country [that] shows they are interested in what we are doing.”1581 Conant thought this last evidence the best. “If they are hard at work, they cannot be far behind since they started in 1939 with the same initial facts as the British and ourselves. There are still plenty of competent scientists left in Germany. They may be ahead of us by as much as a year, but hardly more.”
If time, not money, was the crucial issue—in Conant’s words, “if the possession of the new weapon in sufficient quantities would be a determining factor in the war”—then “three months’ delay might be fatal.” It followed that all five methods should be pushed at once, even though “to embark on this Napoleonic approach to the problem would require the commitment of perhaps $500,000,000 and quite a mess of machinery.”1582
* * *
Glenn Seaborg arrived in Chicago aboard the streamliner City of San Francisco at 9:30 A.M. Sunday, April 19, 1942, his thirtieth birthday. As he left the station he noticed first that Chicago was cold compared to Berkeley—forty degrees that spring morning.1583Then headlines at a newsstand caught him up on the developing Pacific war: the Japanese reported American aircraft had bombed Tokyo and three other Honshu cities, a surprise attack that neither Southwest Pacific commander General Douglas MacArthur nor Washington acknowledged (it was Jimmy Doolittle’s morale raid of sixteen B-25 bombers launched one-way across Japan to landing fields in China from the U.S. aircraft carrier Hornet). “This day . . . marks a transition point in my life,” Seaborg writes in his carefully documented diary-style memoir, “for tomorrow I will take on the added responsibility of the 94 chemistry group at the Metallurgical Laboratory on the University of Chicago campus, the central component of the Metallurgical Project.”1584
Transmuting U238 to plutonium in a chain-reacting pile was one thing, extracting the plutonium from the uranium quite another. The massive production piles that Compton’s people were already beginning to plan would create the new element at a maximum concentration in the uranium of about 250 parts per million—a volume, uniformly dispersed through each two tons of mingled uranium and highly radioactive fission products, equal to the volume of one U.S. dime. Seaborg’s work was somehow to pull that dime’s worth out.1585
He had made a good beginning at Berkeley, exploring plutonium’s unusual chemistry. Oxidizing agents are chemicals that strip electrons from the outer shells of atoms. Reducing agents conversely add electrons to the outer shells of atoms. Plutonium, it seemed, precipitated differently when it was treated with oxidizing agents than when it was treated with reducing agents. In a +4 oxidation state, the Berkeley team had found, the manmade element could be precipitated out of solution using a rare-earth compound such as lanthanum fluoride as a carrier. Oxidize the same plutonium to a +6 oxidation state and the precipitation no longer worked; the carrier crystallized but the plutonium remained behind in solution. That gave Seaborg a basic approach to extraction:
We conceived the principle of the oxidation-reduction cycle. . . . This principle applied to any process involving the use of a substance which carried plutonium in one of its oxidation states but not in another. . . . For example, a carrier could be used to carry plutonium in one oxidation state and thus to separate it from uranium and the fission products. Then the carrier and the plutonium [now solid crystals] could be dissolved, the oxidation state of the plutonium changed, and the carrier reprecipitated, leaving the plutonium in solution. The oxidation state of the plutonium could again be changed and the cycles repeated. With this type of procedure, only a contaminating element having a chemistry nearly identical with the plutonium itself would fail to separate if a large number of oxidation-reduction cycles were employed.1586
A two-day chemistry conference began on Wednesday, April 23, with Eugene Wigner, Harold Urey, Princeton theoretician John A. Wheeler and a number of chemists already assigned to the Met Lab on hand. The scientists discussed seven possible ways to extract plutonium from irradiated uranium. They favored four that seemed particularly adaptable to remote control, not including precipitation.1587 Seaborg, the new man, disagreed: “I, however, expressed confidence in the use of precipitation.” They would nevertheless investigate all seven methods proposed. That would require the full-time work of forty men. One of Seaborg’s jobs for months to come was recruiting. It worried him: “Sometimes I feel a little apprehensive about inviting . . . people to give up their secure university positions and come to work at the Met Lab. They must gamble on the future of their careers, and how long they will be diverted from them nobody knows.” But if no one knew how long the work would last, most of them came to believe it transcendently important: “There is a statement of rather common currency around here and Berkeley that goes something like this: ‘No matter what you do with the rest of your life, nothing will be as important to the future of the World as your work on this Project right now.’ ”1588
So far Seaborg had studied plutonium by following the characteristic radioactivity of minute amounts vastly diluted in carrier, the same tracer chemistry that Hahn, Fermi and the Joliot-Curies had used. Chemical reactions often proceed differently at different dilutions, however. To prove that an extraction process would work at industrial scale, Seaborg knew he would have to demonstrate it at industrial-scale concentrations. In peacetime he might have waited until a pile large enough to transmute at least gram quantities of plutonium was built and operating. That normal procedure was a luxury the bomb program could not afford.
Seaborg looked instead for a way to make more plutonium without a pile and a way to work with concentrated solutions of the little he might make. The resources of the OSRD came to his aid in the first instance, his own imagination and ingenuity in the second. He commandeered the 45-inch cyclotron at Washington University in St. Louis, where Compton had once hidden out, and arranged to have 300-pound batches of uranium nitrate hexahydrate bombarded heroically with neutrons for weeks and months at a time. So long and intense a bombardment would give him microgram quantities of plutonium—several hundred millionths of a gram, amounts hardly visible to the naked eye. He then somehow had to devise techniques for mixing, measuring and analyzing them.
Visiting New York earlier that month to deliver a lecture, Seaborg had sought out a quaint soul named Anton Alexander Benedetti-Pichler, a professor at Queens College in Flushing who had pioneered ultramicrochemistry, a technology for manipulating extremely small quantities of chemicals. Benedetti-Pichler had briefed Seaborg thoroughly and promised to send a list of essential equipment. Seaborg hired one of Benedetti-Pichler’s former students and together the two men planned an ultramicrochemistry laboratory. “We looked for a good spot that would be vibration-free for the microbalances and settled on Room 405 (a former darkroom) in Jones Laboratory which has a concrete bench.”1589 The former darkroom, hardly six feet by nine, was scaled to the work.
Another specialist in ultramicrochemistry, Paul Kirk, taught at Berkeley. Seaborg hired a recent Ph.D. whom Kirk had trained, Burris Cunningham, and a graduate student, Louis B. Werner. “I always thought I was tall,” the chemistry laureate comments, but Werner at six feet seven topped him by four inches, “a tight fit” in the small laboratory.1590
With the special tools of ultramicrochemistry the young chemists could work on undiluted quantities of chemicals as slight as tenths of a microgram (a dime weighs about 2.5 grams— 2,500,000 micrograms). They would manage their manipulations on the mechanical stage of a binocular stereoscopic microscope adjusted to 30-power magnification. Fine glass capillary straws substituted for test tubes and beakers; pipettes filled automatically by capillary attraction; small hypodermic syringes mounted on micromanipulators injected and removed reagents from centrifuge microcones; miniature centrifuges separated precipitated solids from liquids. The first balance the chemists used consisted of a single quartz fiber fixed at one end like a fishing pole stuck into a riverbank inside a glass housing that protected it from the least breath of air. To weigh their Lilliputian quantities of material they hung a weighing pan, made of a snippet of platinum foil that was itself almost too small to see, to the free end of the quartz fiber and measured how much the fiber bent, a deflection which was calibrated against standard weights. A more rugged balance developed at Berkeley had double pans suspended from opposite ends of a quartz-fiber beam strung with microscopic struts. “It was said,” notes Seaborg, “that ‘invisible material was being weighed with an invisible balance.’ ”1591
In addition to his new Met Lab responsibilities Seaborg still coordinated basic scientific studies of uranium and plutonium at Berkeley. At the beginning of June he traveled to California to meet with “the fellows on the third floor of Gilman Hall” and to marry Ernest Lawrence’s secretary.1592 On June 6, returning to Chicago through Los Angeles, where Seaborg’s parents lived, bride and groom prepared for a quick Nevada wedding. They got off the train in Caliente, Nevada, stored their bags with the telegraph operator at the station and asked directions to the city hall. “But to our vexation we learned there is no city hall here and in order to get our marriage license we would have to go to the county seat, a town called Pioche, some 25 miles to the north.”1593Providentially the deputy sheriff who served as Caliente’s travel adviser and all-around troubleshooter turned out to be a June graduate of the Berkeley chemistry department. He arranged for the professor and his bride, Helen Griggs, to ride to Pioche in a mail truck. “Our witnesses were a janitor whom we recruited and [a] friendly clerk. We returned to Caliente on the mail truck’s 4:30 run and checked into the local hotel here for our overnight stay.”1594
Arriving in Chicago on June 9 Seaborg delivered his wife to the apartment he had rented before he left for California and proceeded immediately to his office. His mail informed him that Edward Teller was joining the Chicago project to work in the theoretical group under Eugene Wigner.
Two days later Robert Oppenheimer turned up in Chicago and dropped by to see Seaborg; they were old friends but “it was more than just a social call.”1595 Gregory Breit, the Wisconsin-based theoretician on the Uranium Committee who had been responsible for fast-neutron studies, had resigned from the bomb project in protest over what he felt were serious violations of security. “I do not believe that secrecy conditions are satisfactory in Dr. Compton’s project,” he had written Briggs on May 18. His litany of examples approached paranoia. “Within the Chicago project there are several individuals strongly opposed to secrecy. One of the men, for example, coaxed my secretary there to give him some official reports out of my safe while I was away on a trip. . . . The same individual talks quite freely within the group. . . . I have heard him advocate the principle that all parts of the work are so closely interrelated that it is desirable to discuss them as a whole.”1596 The dangerous individual Breit chose not to name was Enrico Fermi, pushing to make the chain reaction go. Compton had appointed Oppenheimer to replace Breit and Oppenheimer was visiting Seaborg for a briefing on the fast-neutron studies Seaborg was coordinating at Berkeley. Studying fast-neutron reactions, Seaborg notes, was “a prerequisite to the design of an atomic bomb.”1597 Oppenheimer had found a place for himself on the ground floor.
The Washington University cyclotron crew moved the first 300 pounds of uranium nitrate hexahydrate into position around the machine’s beryllium target on June 17. The UNH was scheduled for a month’s bombardment, 50,000 microampere-hours. Though the chain reaction had not yet been proved and no one had yet seen plutonium, the various Met Lab councils of which Seaborg was a member had already begun debating the design and location of the big 250,000-kilowatt production piles that would create pounds of the strange metal if all went well. Fermi thought plutonium production needed an area a mile wide and two miles long for safety. Compton proposed building piles of increasing power to work up to full-scale production and was considering alternative sites in the Lake Michigan Dunes area and in the Tennessee Valley.
A question that would eventually encompass many other issues, some of them profound, was how to cool the big piles. Early in the organization of the Met Lab Compton had appointed an engineering council to consider such questions; besides an engineer and an industrial chemist the council included Samuel Allison, Fermi, Seaborg, Szilard and John A. Wheeler among its membership. By late June its discussions had progressed to the point of tentative commitment. Helium was one prospective coolant, to be circulated at high pressure inside a sealed steel shell; its zero cross section for neutron absorption was only one of its several advantages. Water was another coolant possibility, the heat-exchange medium most familiar to engineers but corrosive to uranium. An exotic third was bismuth, a metal with a low 520°F melting point that serves as a watchful solid in fuses and automatic fire alarms. Melted to a liquid it would transfer heat far more efficiently than helium or water. Szilard championed a liquid-bismuth cooling system in part because the metal could be circulated through the pile with a scaled-up version of the magnetic pump he and Albert Einstein had invented for refrigerators, a mechanism that had no moving parts to leak or fail.
The engineering council ruled out liquid cooling, Seaborg writes, “because of potential chemical action, danger of leaks and difficulty in transferring heat from oxide. . . . There was general agreement to use helium.”1598 Eugene Wigner had not been invited onto the council despite his interest in its problems and his thorough knowledge of chemical engineering. Wigner strongly favored water cooling, says Szilard, because “a water cooled system could be built in a much shorter time.”1599 Seaborg corroborates Wigner’s continuing desperate concern about a German bomb:
Compton repeated a conversation that ensued between him and Wigner on a possible schedule of the Germans. Like us, they have had three years since the discovery of fission to prepare a bomb. Assuming they know about [plutonium], they could run a heavy water pile for two months at 100,000 kw and produce six kilograms of it; thus it would be possible for them to have six bombs by the end of this year . On the other hand, we don’t plan to have bombs in production until the first part of 1944.1600
Compton encouraged Wigner’s group to design a water-cooled pile but ordered up detailed engineering studies only of a system using helium.
The basic issue behind the technical dispute was control, which Szilard at least understood they were systematically signing away to the U.S. government. A meeting on June 27 intensified the conflict. Bush’s latest status report to Roosevelt on June 17 had proposed dividing the work of development and ultimate production between the OSRD and the U.S. Army Corps of Engineers, bringing in the Army to build and run the factories as Bush had planned to do all along. Roosevelt initialed Bush’s cover letter “OK. FDR.” and returned it immediately. The same day the Chief of Engineers ordered Colonel James C. Marshall of the Syracuse Engineer District, a 1918 West Point graduate with experience building air bases, to report to Washington for duty. Marshall selected the Boston construction engineering corporation of Stone & Webster as principal contractor for the bomb project. To report the reorganization Compton called the June 27 meeting of his group leaders and planning board. Allison, Fermi, Seaborg, Szilard, Teller, Wigner and Zinn attended, among others.1601
“Compton opened the meeting with a pep talk,” Seaborg remembers, “asking us to go ahead with all vigor possible. He said our aim the past half-year has been to investigate the possibilities of producing an atomic bomb—now we have the responsibility to proceed from the military point of view on the assumption it can be done and we can assume we have a project for the entire duration of the war.” Compton was stealthily working his way to the new arrangements. He emphasized the program’s secrecy. “Only about six men in the U.S. Army are permitted to know what is going on,” Seaborg paraphrases him; those privileged few included Secretary of War Henry L. Stimson—heady company for men who had only recently been graduate students or obscure academics—and “two construction experts,” generals whom Compton then named. He described the responsibilities of the “construction experts” and finally broke the news: “It is hoped to have a contractor assume responsibility for the production plant.” A contractor already had.
Compton’s announcement had the effect he seems to have feared, Seaborg goes on: “A number of the people present expressed great concern about working for an industrial contractor because of their fear that this would not be a compatible environment in which to work.” They would not have to work for such a contractor, though they would obviously have to work with one, but to make the reorganization palatable Compton hinted at worse that might be yet to come: “There was considerable talk about our being absorbed into the Army [i.e., commissioned as officers] and what the advantages and disadvantages might be. There were vigorous objections from most of the people present.”
The problem would fester all summer and burst through again in the fall. Szilard would define it precisely in a memorandum: “Stated in abstract form, the trouble at Chicago arises out of the fact that the work is organized along somewhat authoritative[sic:authoritarian] rather than democratic lines.”1602 The visionary Hungarian physicist did not believe science could function by fiat. “In 1939,” he had already written Vannevar Bush passionately in late May, before the cooling-system and contractor debates, “the Government of the United States was given a unique opportunity by Providence; this opportunity was lost. Nobody can tell now whether we shall be ready before German bombs wipe out American cities. Such scanty information as we have about work in Germany is not reassuring and all one can say with certainty is that we could move at least twice as fast if our difficulties were eliminated.”1603
Three hundred pounds of irradiated UNH—yellowish crystals like rock salt—arrived from St. Louis by truck on July 27, a Monday:
The UNH was surrounded by a layer of lead bricks. [Truman] Kohman and [Elwin H.] Covey were detailed to unload the shipment and carry it up to our lab on the fourth floor for extraction of the 94239. The UNH crystals came packaged in small boxes of various sizes, made to fit into the various niches around the cyclotron target. Some of the boxes were made of masonite, but most of them were of quarter inch plywood. Unfortunately, some of the seams and edges had cracked open, allowing crystals of hot [i.e., radioactive] UNH to creep out. We could not get hold of any instrument to measure the radioactivity. I told Kohman and Covey their best protection would be to wear rubber gloves and a lab coat. . . . Although they struggled for half the day to get all the boxes and lead bricks upstairs into the storage area, I think they were conscientious and kept their radiation exposure to a minimum.1604
While Seaborg’s high-spirited crew of young chemists began attempting to extract plutonium 239 from the bulky St. Louis UNH, wrestling with carboys of ether and heavy three-liter separatory funnels held at arm’s length from behind lead shields, Cunningham and Werner in narrow Room 405 started toward isolating plutonium as a pure compound. They first measured out a 15-milliliter solution of UNH irradiated earlier that summer in the 60-inch Berkeley cyclotron. They assumed their solution then contained about one microgram of plutonium 239. (Pu239, that is: Seaborg had chosen the abbreviation Pu rather than P1 partly to avoid confusion with platinum, Pt, but also “facetiously,” he says, “to create attention”—P.U. the old slang for putrid, something that raises a stink.1605) Working with their ultramicrochemical equipment—slow, tedious operations via micromanipulator gearing down large motions to microscopically small—on August 15, a Saturday, they mixed the rare earths cerium and lanthanum into their solution as carriers, partially evaporated it and precipitated the carriers and the Pu as fluorides. They dissolved the precipitated crystals in a few drops of sulfuric acid and evaporated the resulting solution to a volume of about one milliliter, a thousandth of a liter, some twenty drops. They checked the larger volume of solution left behind and found essentially no alpha activity, evidence that the alpha-active Pu had crystallized out with the rare earths. That was a day’s work and they stored the precipitate solution carefully for Monday and went home.
On Monday, August 17, Cunningham and Werner began by oxidizing their small volume of precipitate to change the oxidation state of its Pu. They repeated the oxidation and reduction cycles on the solution several times. At the end of the day their quartz centrifuge microcone contained a minute drop of liquid that radiated some 57,000 alpha particles per minute. They set it in a steam bath to concentrate it.
On Tuesday the two men transferred the concentrated solution to a shallow platinum dish to prepare to concentrate it further. It began creeping over the sides. Rather than lose it they moved it quickly to the only larger dish at hand, which was contaminated with lanthanum. Their misjudgment of volume condemned them to another day of repurifying. Upstairs in the attic and on the roof Seaborg’s bulk UNH crew stirred large-volume extractions of ether and water. It was hot and heavy work.
Room 405 had a purified concentrate again to process Wednesday morning. It was still contaminated with a potassium compound and with silver. Cunningham and Werner diluted it and precipitated out the silver as a chloride. They added five micrograms of lanthanum and precipitated out the Pu along with the lanthanum carrier. They dissolved the precipitate, oxidized it once more to change over the Pu and precipitated out the lanthanum. That left pure plutonium in solution, one more morning’s work to bring down.
Of Thursday, August 20, 1942, Seaborg writes:
Perhaps today was the most exciting and thrilling day I have experienced since coming to the Met Lab. Our microchemists isolated pure element 94 for the first time! This morning Cunningham and Werner set about fuming . . . yesterday’s 94 solution containing about one microgram of 94239, added hydrofluoric acid whereupon the reduced 94 precipitated as the fluoride . . . free of carrier material. . . .1606
This precipitate of 94, which was viewed under the microscope and which was also visible to the naked eye, did not differ visibly from the rare-earth fluorides. . . .
It is the first time that element 94 . . . has been beheld by the eye of man.
By afternoon “a holiday spirit prevailed in our group.” After several hours’ exposure to air “the precipitated [plutonium] had taken on a pinkish hue.”1607 Someone photographed Cunningham and Werner at their crowded bench in the narrow, tile-walled room—trim, strong-jawed young men looking weary. The crew upstairs that muscled carboys and lead bricks shuffled in like clumsy shepherds to peer through the microscope at the miracle of the tiny pinkish speck.
* * *
In the summer of 1942 Robert Oppenheimer gathered together at Berkeley a small group of theoretical physicists he was amused to call the “luminaries.”1608 Their job was to throw light on the actual design of an atomic bomb.
Hans Bethe, now thirty-six and a highly respected professor of physics at Cornell, had resisted joining the bomb project because he doubted the weapon’s feasibility. “I considered . . . an atomic bomb so remote,” Bethe told a biographer after the war, “that I completely refused to have anything to do with it. . . . Separating isotopes of such a heavy element [as uranium] was clearly a very difficult thing to do, and I thought we would never succeed in any practical way.”1609 But Bethe may well have headed the list of luminaries Oppenheimer wanted to attract. By 1942 the Cornell physicist had established himself as a theoretician of the first rank. His most outstanding contribution, for which he would receive the 1967 Nobel Prize in Physics, was to elucidate the production of energy in stars, identifying a cycle of thermonuclear reactions involving hydrogen, nitrogen and oxygen that is catalyzed by carbon and culminates in the creation of helium. Among other important work during the 1930s Bethe had been principal author of three lengthy review articles on nuclear physics, the first comprehensive survey of the field. Bound together, the three authoritative studies came to be called “Bethe’s Bible.”
He had wanted to help oppose Nazism. “After the fall of France,” he says, “I was desperate to do something—to make some contribution to the war effort.”1610 First he developed a basic theory of armor penetration. On the recommendation of Theodor von Kármán, whom he consulted at Caltech, he and Edward Teller in 1940 extended and clarified shock-wave theory. In 1942 he joined the Radiation Laboratory at MIT to work on radar. That was where Oppenheimer found him.
Oppenheimer cleared his plan with Lee A. DuBridge, the director of the Rad Lab, then set a senior American theoretician, John H. Van Vleck, professor of physics at Harvard, to snare Bethe for the Berkeley summer study. “The essential point,” he counseled Van Vleck, “is to enlist Bethe’s interest, to impress on him the magnitude of the job we have to do . . . and to try to convince him, too, that our present plans . . . are the appropriate machinery.” Oppenheimer felt the weight of the work. “Every time I think about our problem a new headache appears,” he told the Harvard professor. “We shall certainly have our hands full.”1611 Van Vleck arranged to meet Bethe conspiratorially in Harvard Yard and succeeded in convincing him he was needed. The prearranged signal to Oppenheimer was a Western Union Kiddygram, an inexpensive standardized telegram with a message like “Brush your teeth.”1612
Oppenheimer also invited Edward Teller. In 1939 Bethe had married Rose Ewald, the attractive and intelligent daughter of his Stuttgart physics professor Paul Ewald; Edward and Mici Teller, “our best friends in this country,” had attended the New Rochelle wedding.1613 Setting out for Berkeley in early July 1942, the Bethes stopped over in Chicago to pick up the Tellers.1614 Teller showed Bethe Fermi’s latest exponential pile. “He had a setup under one of the stands in Stagg Field,” Bethe remembers—“in a squash court—with tremendous stacks of graphite.” A chain reaction that made plutonium would bypass the problem of isotope separation. “I then,” says Bethe, “became convinced that the atomic-bomb project was real, and that it would probably work.”1615
The other luminaries enlisted for the summer study were Van Vleck, the Swiss-born Stanford theoretician Felix Bloch, Oppenheimer’s former student and close collaborator Robert Serber, a young Indiana theoretician named Emil Konopinski and two postdoctoral assistants. Konopinski and Teller had arrived at the Met Lab at about the same time earlier that year. “We were newcomers in the bustling laboratory,” Teller writes in a memoir, “and for a few days we were given no specific jobs.” Teller proposed that he and Konopinski review his calculations that seemed to prove the impossibility of using an atomic bomb to ignite a thermonuclear reaction in deuterium:
Konopinski agreed, and we tackled the job of writing a report to show, once and for all, that it could not be done. . . . But the more we worked on our report, the more obvious it became that the roadblocks which I had erected for Fermi’s idea were not so high after all. We hurdled them one by one, and concluded that heavy hydrogen actually could be ignited by an atomic bomb to produce an explosion of tremendous magnitude. By the time we were on our way to California . . . we even thought we knew precisely how to do it.1616
That was not news Edward Teller was likely to hide under a bushel, whatever Oppenheimer’s official agenda. Bethe was ushered into the glare as the streamliner clicked west: “We had a compartment on the train to California, so we could talk freely. . . . Teller told me that the fission bomb was all well and good and, essentially, was now a sure thing. In reality, the work had hardly begun. Teller likes to jump to conclusions. He said that what we really should think about was the possibility of igniting deuterium by a fission weapon—the hydrogen bomb.”1617
At Berkeley the luminaries began meeting in Oppenheimer’s office, “in the northwest corner of the fourth floor of old LeConte [Hall],” an older colleague remembers. “Like all those rooms, it had French doors opening out onto a balcony, to which there was easy access from the roof. Accordingly a very strong wire netting was fastened securely over his balcony.” Only Oppenheimer had a key. “If a fire had ever started . . . in Oppenheimer’s absence, it would have been tragic.”1618 But the fires that summer were still only theoretical.
The theoreticians let Teller’s bomb distract them. It was new, important and spectacular and they were men with a compulsion to know. “The theory of the fission bomb was well taken care of by Serber and two of his young people,” Bethe explains. They “seemed to have it well under control so we felt we didn’t need to do much.”1619 The essentials of fast-neutron fission were firm—it needed experiment more than theory. The senior men turned their collective brilliance to fusion. They had not yet bothered to name generic bombs of uranium and plutonium. But from the pre-anthropic darkness where ideas abide in nonexistence until minds imagine them into the light, the new bomb emerged already chased with the technocratic euphemism of art deco slang: the Super, they named it.
Rose Bethe, who was then twenty-four, understood instantly. “My wife knew vaguely what we were talking about,” says Bethe, “and on a walk in the mountains in Yosemite National Park she asked me to consider carefully whether I really wanted to continue to work on this. Finally, I decided to do it.” The Super “was a terrible thing.” But the fission bomb had to come first in any case and “the Germans were presumably doing it.”1620
Teller had examined two thermonuclear reactions that fuse deuterium nuclei to heavier forms and simultaneously release binding energy. Both required that the deuterium nuclei be hot enough when they collided—energetic enough, violently enough in motion—to overcome the nuclear electrical barrier that usually repels them. The minimum necessary energy was thought at the time to come to about 35,000 electron volts, which corresponds to a temperature of about 400 million degrees.1621 Given that temperature—and on earth only an atomic bomb might give it—both thermonuclear reactions should occur with equal probability. In the first, two deuterium nuclei collide and fuse to helium 3 with the ejection of a neutron and the release of 3.2 million electron volts of energy. In the second the same sort of collision produces tritium—hydrogen 3, an isotope of hydrogen with a nucleus of one proton and two neutrons that does not occur naturally on earth—with the ejection of a proton and the release of 4.0 MeV of energy.
The D + D reactions’ release of 3.6 MeV was slightly less by mass than fission’s net of 170 MeV. But fusion was essentially a thermal reaction, not inherently different in its kindling from an ordinary fire; it required no critical mass and was therefore potentially unlimited. Once ignited, its extent depended primarily on the volume of fuel—deuterium—its designers supplied. And deuterium, Harold Urey’s discovery, the essential component of heavy water, was much easier and less expensive to separate from hydrogen than U235 was from U238 and much simpler to acquire than plutonium. Each kilogram of heavy hydrogen equaled about 85,000 tons TNT equivalent.1622 Theoretically, 12 kilograms of liquid heavy hydrogen—26 pounds—ignited by one atomic bomb would explode with a force equivalent to 1 million tons of TNT. So far as Oppenheimer and his group knew at the beginning of the summer, an equivalent fission explosion would require some 500 atomic bombs.1623
That reckoning alone would have been enough to justify devoting the summer to imagining the Super a little way out of the darkness. Teller found something else as well, or thought he did, and with his usual pellmell facility he scattered it before them. There are many other thermonuclear reactions besides the D + D reactions. Bethe had examined a number of them methodically when looking for those that energized massive stars. Now Teller offered several which a fission bomb or a Super might inadvertently trigger. He proposed to the assembled luminaries the possibility that their bombs might ignite the earth’s oceans or its atmosphere and burn up the world, the very result Hitler occasionally joked about with Albert Speer.
“I didn’t believe it from the first minute,” Bethe scoffs. “Oppie took it sufficiently seriously that he went to see Compton. I don’t think I would have done it if I had been Oppie, but then Oppie was a more enthusiastic character than I was.1624 I would have waited until we knew more.” Oppenheimer had other urgent business with Compton in any case: the Super itself. Not to risk their loss, the bomb-project leaders were no longer allowed to fly. Oppenheimer tracked Compton by telephone at the beginning of a July weekend to a country store in northern Michigan where he had stopped to pick up the keys to his lakeside summer cottage, got directions and caught the next train east. In the meantime Bethe applied himself to Teller’s calculations.
The Cornell physicist’s instant skepticism gives perspective to Compton’s melodramatic recollection of his meeting with Oppenheimer:
I’ll never forget that morning. I drove Oppenheimer from the railroad station down to the beach looking out over the peaceful lake. There I listened to his story. . . .1625
Was there really any chance that an atomic bomb would trigger the explosion of the nitrogen in the atmosphere or the hydrogen in the ocean? This would be the ultimate catastrophe. Better to accept the slavery of the Nazis than to run a chance of drawing the final curtain on mankind!
We agreed there could be only one answer. Oppenheimer’s team must go ahead with their calculations.
Bethe already had. “I very soon found some unjustified assumptions in Teller’s calculations which made such a result extremely unlikely, to say the least. Teller was very soon persuaded by my arguments.”1626 The arguments—Bethe’s and others’—against a runaway explosion appear most authoritatively in a technical history of the bomb design program prepared under Oppenheimer’s supervision immediately after the war:
It was assumed that only the most energetic of several possible [thermonuclear] reactions would occur, and that the reaction cross sections were at the maximum values theoretically possible. Calculation led to the result that no matter how high the temperature, energy loss would exceed energy production by a reasonable factor. At an assumed temperature of three million electron volts [compare the 35,000 eV known for D + D] the reaction failed to be self-propagating by a factor of 60. This temperature exceeded the calculated initial temperature of the deuterium reaction by a factor of 100, and that of the fission bomb by a larger factor. . . . The impossibility of igniting the atmosphere was thus assured by science and common sense.1627
Oppenheimer returned to that good news and they proceeded with the Super. Teller recaptures the mood: “My theories were strongly criticized by others in the group, but together with new difficulties, new solutions emerged. The discussions became fascinating and intense. Facts were questioned and the questions were answered by still more facts. . . . A spirit of spontaneity, adventure, and surprise prevailed during those weeks in Berkeley, and each member of the group helped move the discussion toward a positive conclusion.”1628
There was serious trouble with Teller’s D + D Super. The reactions would proceed too slowly to reach ignition before the fission trigger blew the assembly apart. Konopinski came to the rescue: “Konopinski suggested that, in addition to deuterium, we should investigate the reactions of the heaviest form of hydrogen, tritium.” This, Teller explains, was at that time “only . . . a conversational guess.”1629 One tritium reaction of obvious interest was the fusion of a deuterium nucleus with a tritium nucleus, D + T, which results in the formation of a helium nucleus with the ejection of a neutron and the release of 17.6 MeV of energy. The D + T reaction kindled at a mere 5,000 eV, which corresponds to a temperature of 40 million degrees. But since tritium does not exist on earth it would have to be created. Neutrons bombarding an isotope of lithium, Li6, would transmute some of that light metal to tritium much as neutrons made plutonium from U235, but the only obvious source of such necessarily copious quantities of neutrons was Fermi’s unproven pile. The luminaries did, however, consider the possibility of making tritium within the Super itself by packing the bomb with a dry form of lithium, lithium deuteride.1630 But lithium in its natural form, like uranium in its natural form, contained too little of the desired isotope; to be effective, the Li6 would have to be separated. But lithium—element number 3 on the periodic table—would be much easier to separate than uranium . . . So the arguments progressed across the pleasant Berkeley summer. “We were forever inventing new tricks,” Bethe says, “finding ways to calculate, and rejecting most of the tricks on the basis of the calculations. Now I could see at first-hand the tremendous intellectual power of Oppenheimer who was the unquestioned leader of our group. . . . The intellectual experience was unforgettable.”1631
At the end of the summer, merging the Serber subgroup’s work with their own, the luminaries concluded that the development of an atomic bomb would require a major scientific and technical effort.1632 Glenn Seaborg heard Oppenheimer’s deduction from that outcome at a meeting of the Met Lab technical council in Chicago on September 29. “Fast neutron work has no home,” Seaborg paraphrases the Berkeley theoretician “[and] may need one.”1633 “Oppenheimer has plans in mind for fast neutron work,” Compton told the council. Oppenheimer was scouting a site where the bomb might be designed and assembled. He thought such an operation might find a home in Cincinnati or with the plutonium production piles in Tennessee.1634
* * *
James Bryant Conant heard the results of the Berkeley summer study at a meeting of the S-l Executive Committee in late August 1942 and jotted down a page of notes under the heading “Status of the Bomb.”1635, 1636 The fission bomb, he wrote, would explode according to the luminaries with “150 times energy of previous calculation” but, bad news, would require a critical mass “6 times the previous [estimated] size[:] 30 kg U235.” Twelve kilograms of U235 were enough to explode, Conant noted, but inefficiently with “only 2% of energy.” News of the Super then startled the NDRC chairman to a slip of the pencil:
To denotate [sic: detonate] 5–10 kg of heavy hydrogen liquid would require 30 kg U235
If you use 2 or 3 Tons of liquid deuterium and 30 kg U235 this would be equivalent 108 [i.e., 100,000,000] tons of TNT.
Estimate devastation area of 1000 sq. km [or] 360 sq miles. Radioactivity lethal over same area for a few days.
Conant then drew a bold line with a steady hand and initialed the file note “JBC.” As an afterthought or at a later time he added: “S-l Executive Committee thinks the above probable. Heavy water is being pushed as hard as it can. [First] 100 kg of D will be available by fall of 1943 before 60 kg of U235 will be ready!”
A formal status report went off immediately from the Executive Committee to Bush. It predicted enough fissionable material for a test in eighteen months—by March 1944. It estimated that a 30-kilogram bomb of U235 “should have a destructive effect equivalent to the explosion of over 100,000 tons of TNT,” much more than the mere 2,000 tons estimated earlier. And it dramatically announced the Super:
If this [U235] unit is used to detonate a surrounding mass of 400 kg of liquid deuterium, the destructiveness should be equivalent to that of more than 10,000,000 tons of TNT. This should devastate an area of more than 100 square miles.
The committee—Briggs, Compton, Lawrence, Urey, Eger Murphree and Conant—concluded by judging the bomb project important beyond all previous estimates: “We have become convinced that success in this program before the enemy can succeed is necessary for victory. We also believe that success of this program will win the war if it has not previously been terminated.”
On August 29 Bush bumped the status report up to the Secretary of War, noting that “the physicists of the Executive Committee are unanimous in believing that this large added factor [i.e., the Super] can be obtained. . . . The ultimate potential possibilities are now considered to be very much greater than at the time of the [last] report.”1637
The hydrogen bomb was thus under development in the United States onward from July 1942.
* * *
The problem that Leo Szilard would call “the trouble at Chicago”—the problem of authority and responsibility for pile-cooling design and much more—erupted in a brief rebellion at the Met Lab in September. Stone & Webster, the construction engineers the Army had hired, had spent the summer studying plutonium production. “Classical engineers,” Leona Woods calls them, “who knew bridges and structures, canals, highways, and the like, but who had a very weak grasp or none at all of what was needed in the new nuclear industry.” The firm sent one of its best engineers to brief Met Lab leaders on production plans. “The scientists sat deadly still with curled lips. The briefer was ignorant; he enraged and frightened everyone.”1638
An exasperated Compton protégé, Volney Wilson, an idealistic young physicist responsible for pile instrumentation, called a confrontation meeting soon afterward on a hot autumn evening. (As a student Wilson had analyzed the motions of swimming fish and invented the competition swimming style known as the Dolphin; with it he had won in Olympics tryouts in 1938 but then suffered disqualification because the style was new and thus unauthorized, a purblindness on the part of the Olympics judges which may have conditioned Wilson’s attitude toward authority.) In his memoirs Compton mixes up the autumn meeting with the similar disagreement in June; Woods, who worked for Wilson, remembers it better:
We (some 60 or 70 scientists) assembled quietly in the commons room at Eckhart Hall, open windows bringing hot, humid air in with an infinitesimal breeze. No one spoke—it was a Quaker meeting. Finally Compton entered carrying a Bible. . . .
Compton thought that the issue of Wilson’s meeting was whether the plutonium production should be undertaken by large-scale industry or should be carried out by the scientists of the Metallurgical Project, keeping control in their hands.1639 Instead, it seemed to me that the primary issue was to get rid of Stone & Webster.1640
Compton vouchsafed a parable. Without introduction he opened his Bible to Judges 7: 5–7 and read to Leo Szilard and Enrico Fermi, to Eugene Wigner, to John Wheeler and threescore serious scientists the story of how the Lord helped Gideon sort among His people to find a few good men to fight the Midianites when there were too many volunteers at hand to demonstrate clearly that the victory would be entirely the work of the Lord. “When Compton finished reading,” Woods remembers, “he sat down.” Not surprisingly, “there was more Quaker-meeting silence.” Or astonishment.1641 Then Volney Wilson stood to direct “well-considered fire and brimstone . . . at the incompetence of Stone & Webster.” Many others in the group spoke as well, all opposing the Boston engineers. “After a while, silence fell and finally everyone got up and disbanded.” Compton had reduced the discussion to a demand that the Met Lab capitulate to his authority. Fortunately the assembly of scientists ignored him. The Army would soon move the responsibility for plutonium production into more experienced hands than Stone & Webster’s. When the change was proposed Compton eagerly endorsed it.
Szilard responded to the struggles at the Met Lab with anger that by now, after four years of frustration, had begun to harden into stoicism. Late in September he drafted a long memorandum to his colleagues that addressed specific Met Lab problems but also considered the deeper issue of the responsibility of scientists for their work. In draft and more moderately in finished form his examination by turns compliments and savages Compton’s leadership: “In talking to Compton I frequently have the feeling that I am overplaying a delicate instrument.”1642, 1643 Beyond personality Szilard pointed to a destructive abdication by those whom Compton led: “I have often thought . . . that things would have been different if Compton’s authority had actually originated with our group, rather than with the OSRD.”1644 He elaborates in the finished memorandum:
The situation might be different if Compton considered himself as our representative in Washington and asked in our name for whatever was necessary to make our project successful. He could then refuse to make a decision on any of the issues which affect our work until he had an opportunity fully to discuss the matter with us.1645
Viewed in this light, it ought to be clear to us that we, and we alone, are to be blamed for the frustration of our work.
An authoritarian organization had moved in—had been allowed to move in—to take over work that had been democratically begun. “There is a sprinkling of democratic spots here and there, but they do not form a coherent network which could be functional.”1646Szilard was convinced that authoritarian organization was no way to do science. So were Wigner and the more detached Fermi. “If we brought the bomb to them all ready-made on a silver platter,” Szilard remembers hearing Fermi say, “there would still be a fifty-fifty chance that they would mess it up.”1647 But beyond debating the virtues of contractors and cooling systems only Szilard continued to rebel:
We may take the stand that the responsibility for the success of this work has been delegated by the President to Dr. Bush. It has been delegated by Dr.1648 Bush to Dr. Conant. Dr. Conant delegates this responsibility (accompanied by only part of the necessary authority) to Compton. Compton delegates to each of us some particular task and we can lead a very pleasant life while we do our duty. We live in a pleasant part of a pleasant city, in the pleasant company of each other, and have in Dr. Compton the most pleasant “boss” we could wish to have. There is every reason why we should be happy and since there is a war on, we are even willing to work overtime.
Alternatively, we may take the stand that those who have originated the work on this terrible weapon and those who have materially contributed to its development have, before God and the World, the duty to see to it that it should be ready to be used at the proper time and in the proper way.
I believe that each of us has now to decide where he feels that his responsibility lies.
The Army had been involved in the bomb project since June, but the Corps of Engineers’ Colonel Marshall had been unable to drive the project ahead of other national military priorities. Divided between the OSRD and the Army it began to look as if it might lose its way. Bush thought he saw a solution in an authoritative new Military Policy Committee that would retain the project under partly civilian control but delegate direction to a dynamic Army officer and back him up. “From my own point of view,” he wrote at the end of August 1942, “faced as I am with the unanimous opinion of a group of men that I consider to be among the greatest scientists in the world, joined by highly competent engineers, I am prepared to recommend that nothing should stand in the way of putting this whole affair through to conclusion . . . even if it does cause moderate interference with other war efforts.”1649
Bush had discussed his problems with the general in charge of the Army Services of Supply, Brehon Somervell. Independently Somervell worked out a solution of his own: assigning entire responsibility to the Corps of Engineers, which was under his command. The program would need a stronger leader. He had a man in mind. In mid-September he sought him out.
“On the day I learned that I was to direct the project which ultimately produced the atomic bomb,” Albany-born Leslie Richard Groves wrote later, “I was probably the angriest officer in the United States Army.”1650 The West Point graduate, forty-six years old in 1942, goes on to explain why:
It was on September 17, 1942, at 10:30 a.m., that I got the news. I had agreed, by noon that day, to telephone my acceptance of a proposed assignment to duty overseas. I was then a colonel in the Army Engineers, with most of the headaches of directing ten billion dollars’ worth of military construction in the country behind me—for good, I hoped. I wanted to get out of Washington, and quickly.
Brehon B. Somervell . . . my top superior, met me in a corridor of the new House of Representatives Office Building when I had finished testifying about a construction project before the Military Affairs Committee.
“About that duty overseas,” General Somervell said, “you can tell them no.”
“Why?” I inquired.
“The Secretary of War has selected you for a very important assignment.”
“I don’t want to stay in Washington.”
“If you do the job right,” General Somervell said carefully, “it will win the war.”
Men like to recall, in later years, what they said at some important or possibly historic moment in their lives. . . . I remember only too well what I said to General Somervell that day.
I said, “Oh.”
As deputy chief of construction for the entire U.S. Army, Groves knew enough about the bomb project to recognize its dubious claim to decisive effect and be thoroughly disappointed. He had just finished building the Pentagon, the most visible work of his career. He had seen the S-l budget; it amounted in total to less than he had been spending in a week. He wanted assignment commanding troops. But he was career Army and understood he hardly had a choice. He crossed the Potomac to the Pentagon office of Somervell’s chief of staff, Brigadier General Wilhelm D. Styer, for a briefing. Styer implied the job was well along and ought to be easy. The two officers worked up an order for Somervell to sign authorizing Groves “to take complete charge of the entire . . . project.”1651 Groves discovered he would be promoted to brigadier—for authority and in compensation—in a matter of days. He proposed to delay official appointment until the promotion came through. “I thought that there might be some problems in dealing with the many academic scientists involved in the project,” he remembers of his initial innocence, “and I felt that my position would be stronger if they thought of me from the first as a general instead of as a promoted colonel.”1652 Styer agreed.
Groves was one inch short of six feet tall, jowly, with curly chestnut hair, blue eyes, a sparse mustache and sufficient girth to balloon over his webbing belt above and below its brass military buckle.1653 Leona Woods thought he might weigh as much as 300 pounds; he was probably nearer 250 then, though he continued to expand. He had graduated from the University of Washington in 1914, studied engineering intensely for two years at MIT and gone on to West Point, where he graduated fourth in his class in 1918. Years at the Army Engineer School, the Command and General Staff College and the Army War College in the 1920s and 1930s completed his extensive education. He had seen duty in Hawaii, Europe and Central America. His father was a lawyer who left the law for the ministry and served in a country parish and an urban, working-class church before Grover Cleveland’s Secretary of War convinced him to enlist as an Army chaplain on the Western frontier. “Entering West Point fulfilled my greatest ambition,” Groves testifies. “I had been brought up in the Army, and in the main had lived on Army posts all my life. I was deeply impressed with the character and outstanding devotion to duty of the officers I knew.”1654 The dynamic engineer was married, with a thirteen-year-old daughter and a plebe son at West Point.
“A tremendous lone wolf,” one of his subordinates describes Groves.1655 Another, whose immediate superior Groves was about to become, distills their years together into grudgingly admiring vitriol. Lieutenant Colonel Kenneth D. Nichols—balding, bespectacled, thirty-four in 1942, West Point, Ph.D. in hydraulic engineering at Iowa State—remembers Groves as
the biggest sonovabitch I’ve ever met in my life, but also one of the most capable individuals. He had an ego second to none, he had tireless energy—he was a big man, a heavy man but he never seemed to tire. He had absolute confidence in his decisions and he was absolutely ruthless in how he approached a problem to get it done. But that was the beauty of working for him—that you never had to worry about the decisions being made or what it meant. In fact I’ve often thought that if I were to have to do my part all over again, I would select Groves as boss. I hated his guts and so did everybody else but we had our form of understanding.1656
Nichols’ previous boss, Colonel Marshall, had worked out of an office in Manhattan (where in August he had disguised the project to build an atomic bomb behind the name Manhattan Engineer District). But decisions of priority and supply were made in wartime in hurly-burly Washington offices, not in Manhattan, and to fight those battles the colonel had chosen the capable Nichols. Groves therefore sought out Nichols next after Styer. And found the project in even worse condition than he had feared: “I was not happy with the information I received; in fact, I was horrified.”1657
He took Nichols with him to the Carnegie Institution on P Street to confront Vannevar Bush. Somervell had overlooked clearing Groves’ appointment with Bush and the OSRD director was infuriated. He evaded Groves’ questions brusquely, which puzzled Groves. Controlling his anger until Groves and Nichols left, Bush then paid Styer a visit, which he describes in a contemporary memorandum:
I told him (1) that I still felt, as I had told him and General Somervell previously, that the best move was to get the military commission first, and then the man to carry out their policies second; (2) that having seen General Groves briefly, I doubted whether he had sufficient tact for such a job.1658
Styer disagreed on (1) and I simply said I wanted to be sure he understood my recommendation. On (2) he agreed the man is blunt, etc., but thought his other qualities would overbalance. . . . I fear we are in the soup.
Bush changed his mind within days. Groves immediately tackled his worst problems and solved them.
One of the first issues the heavyweight colonel had raised with Nichols was ore supply: was there sufficient uranium on hand? Nichols told him about a recent and fortuitous discovery: some 1,250 tons of extraordinarily rich pitchblende—it was 65 percent uranium oxide—that the Union Minière had shipped to the United States in 1940 from its Shinkolobwe mine in the Belgian Congo to remove it beyond German reach. Frédéric Joliot and Henry Tizard had independently warned the Belgians of the German danger in 1939. The ore was stored in the open in two thousand steel drums at Port Richmond on Staten Island. The Belgians had been trying for six months to alert the U.S. government to its presence. On Friday, September 18, Groves sent Nichols to New York to buy it.
On Saturday Groves drafted a letter in the name of Donald Nelson, the civilian head of the War Production Board, assigning a first-priority AAA rating to the Manhattan Engineer District. Groves personally carried the letter to Nelson. “His reaction was completely negative; however, he quickly reversed himself when I said that I would have to recommend to the President that the project should be abandoned because the War Production Board was unwilling to co-operate with his wishes.”1659 Groves was bluffing but it was not the bluster that swayed Nelson; he had probably heard by then from Bush and Henry Stimson. He signed the letter. “We had no major priority difficulties,” notes Groves, “for nearly a year.”1660
The same day Groves approved a directive that had been languishing on his predecessor’s desk throughout the summer for the acquisition of 52,000 acres of land along the Clinch River in eastern Tennessee. Site X, the Met Lab called it. District Engineer Marshall had thought to wait to buy the land at least until the chain reaction was proved.
On September 23, the following Wednesday, Groves’ promotion to brigadier came through. He hardly had time to pin on his stars before attending a command performance in the office of the Secretary of War called to assemble Bush’s outmaneuvered Military Policy Committee with Stimson, Army Chief of Staff George Marshall, Bush, Conant, Somervell, Styer and an admiral on hand. Groves described how he intended to operate. Stimson proposed a nine-man committee to supervise. Groves held out for a more workable three and won his point. Discussion continued. Abruptly Groves asked to be excused: he needed to catch a train to Tennessee, he explained, to inspect Site X. The startled Secretary of War agreed and Leslie Richard Groves, the new broom that would sweep the Manhattan Engineer District clean, departed for Union Station. “You made me look like a million dollars,” Somervell praised Groves when he got back to Washington. “I’d told them that if you were put in charge, things would really start moving.”1661They did.
* * *
Enrico Fermi began planning a full-scale chain-reacting pile in May 1942 when one of the exponential piles his team built in the west stands of Stagg Field indicated its k at infinity would muster 0.995.1662 The Met Lab was searching out higher-quality graphite and sponsoring production of pure uranium metal, denser than oxide; those and other improvements should push k above 1.0. “I remember I talked about the experiment on the Indiana dunes,” Fermi told his wife after the war, “and it was the first time I saw the dunes. . . . I liked the dunes: it was a clear day, with no fog to dim colors. . . . We came out of the water, and we walked along the beach.”1663
As they began preparations that summer Leona Woods remembers swimming “in frigid Lake Michigan every afternoon at five o’clock, off the huge breakwater rocks at the 55th street promontory”—she, Herbert Anderson, Fermi.1664 She was still a graduate student, twenty-two and shy. “One evening, Enrico gave a party, inviting Edward and [Mici] Teller, Helen and Robert Mulliken (my research professor), and Herb Anderson, John Marshall, and me.”1665 They played Murder, the parlor game then in fashion. “The second the lights went out on this particular evening, I shrank into a corner and listened with astonishment to these brilliant, accomplished, famous sophisticated people shrieking and poking and kissing each other in the dark like little kids.” All nice people are shy, Fermi consoled her when he knew her better; he had always been dominated by shyness. She records his sly self-mockery: “As he frequently said, he was amazed when he thought how modest he was.”1666
Woods was finishing her thesis work during the summer but sometimes helped Anderson scour Chicago for lumber. CP-1—Chicago Pile Number One—Fermi planned to build in the form of a sphere, the most efficient shape to maximize k. Since the pile’s layers of graphite bricks would enlarge concentrically up to its equator, they would need external support, and wood framing was light and easy to shape and assemble. “I was the buyer for a lot of lumber,” Anderson says. “I remember the Sterling Lumber Company, how amazed they were by the orders I gave them, all with double X priority. But they delivered the lumber with no questions asked. There was almost no constraint on money and priority to get what we wanted.”1667
Horseback riding one Saturday afternoon in the Cook County Forest Preserve twenty miles southwest of Chicago, Arthur and Betty Compton found an isolated, scenic site for the pile building, a terminal moraine forested with hawthorne and scrub oak known as the Argonne Forest. The Army’s Nichols negotiated with the county to use the land; Stone & Webster began planning construction.
The Fermis rented a house from a businessman moving to Washington for war work; since they were enemy aliens and not allowed to own a shortwave radio the man had to have his big all-band Capehart temporarily disabled of its long-distance frequencies, though it continued to supply dance music to the party room on the third floor. Fermi was angry to find his mail being opened and complained indignantly until the practice was stopped (or managed more surreptitiously). The Comptons gave a series of parties to welcome newcomers to the Met Lab. “At each of these parties,” Laura Fermi writes, “the English film Next of Kin was shown. It depicted in dark tones the consequences of negligence and carelessness. A briefcase laid down on the floor in a public place is stolen by a spy. English military plans become known to the enemy. Bombardments, destruction of civilian homes, and an unnecessarily high toll of lives on the fighting front are the result. . . . Willingly we accepted the hint and confined our social activities to the group of ‘metallurgists.’ ”1668 Compton, who describes himself as “one of those who must talk over important problems with his wife,” arranged uniquely to have Betty Compton cleared.1669 None of the other wives was supposed to know about her husband’s work. Laura Fermi found out, like many others, only at the end of the war.
In mid-August Fermi’s group could report a probable k for a graphite-uranium oxide pile of “close to 1.04.”1670 They were working on control-rod design and testing the vacuum properties of both metal sheet and balloon cloth. The cloth was Anderson’s idea, a possible alternative to canning the pile to exclude neutron-absorbing air. It proved serviceable and Anderson followed up: “For the balloon cloth enclosure I went to the Goodyear Rubber Company in Akron, Ohio. The company had a good deal of experience in building blimps and rubber rafts but a square balloon 25’ on a side seemed a bit odd to them.” They made it anyway, “with no questions asked.”1671 It should be good for a 1 percent improvement in k.1672
Between September 15 and November 15 Anderson, Walter Zinn and their crews also built sixteen successive exponential piles in the Stagg Field west stands to measure the purity of the various shipments of graphite, uranium oxide and metal they had begun to receive in quantity. Not all the uranium was acceptable. But Mallinckrodt Chemical Works in St. Louis, specialists at handling the ether necessary for oxide extraction, began producing highly purified brown oxide at the rate of thirty tons a month, and the National Carbon Company and a smaller supplier, by using purified petroleum coke for raw material and doubling furnace time, significantly improved graphite supplies (graphite is molded as coke, then baked in a high-temperature electric-arc oven for long hours until it crystallizes and its impurities vaporize away). By September regular deliveries began to arrive in covered trucks. Physicists doubled as laborers to unload the bricks and cans and pass them into the west stands for finishing.
Walter Zinn took charge of preparing the materials for the pile. The graphite came in from various manufacturers as rough 4¼ by 4¼-inch bars in 17- to 50-inch lengths. So that the bars would fit closely together they had to be smoothed and cut to standard 16½-inch lengths. About a fourth of them also had to be drilled for the lumps of uranium they would hold. A few required slots machined through to make channels for control rods. The uranium oxide needed to be compressed into what the physicists called “pseudospheres”—stubby cylinders with round-shouldered ends—for which purpose the press from the Jersey City junkyard had been shipped to Chicago the previous winter.1673
For crew Zinn had half a dozen young physicists, a thoroughly able carpenter and some thirty high school dropouts earning pocket money until their draft notices came through. They were Back of the Yards boys from the tough neighborhood beyond the Chicago stockyards and Zinn improved the fluency of his swearing keeping them in line.
Machining the graphite was like sharpening thousands of giant pencils. Zinn used power woodworking tools. A jointer first made two sides of each graphite brick perpendicular and smooth; a planer finished the other two surfaces; a swing saw cut the bricks to length. That processing produced 14 tons of bricks a day; each brick weighed 19 pounds.
To drill the blind, round-bottomed 3¼-inch holes for the uranium pseudospheres, two to a brick, Zinn adapted a heavy lathe. He mounted a 3¼-inch spade bit in the headstock of the lathe, where the material to be turned would normally be mounted, and forced the graphite up against the tool with the lathe carriage. Dull bits caused problems. Zinn tried tough carballoy bits first, but they were tedious to resharpen. He began making bits from old steel files, sharpening them by hand whenever they dulled. One sharpening was good for 60 holes, about an hour’s work. Before they were through they would shape and finish 45,000 graphite bricks and drill 19,000 holes.
General Groves made his first appearance at the Met Lab on October 5 and delivered his first pronouncement. The technical council was debating cooling systems again. “The War Department considers the project important,” Seaborg paraphrases Groves’ formula, which they would all learn by heart. “There is no objection to a wrong decision with quick results. If there is a choice between two methods, one of which is good and the other looks promising, then build both.”1674 Get the cooling-system decision into Compton’s hands by Saturday night, Groves demanded. It was Monday. They had been debating for months.
Groves moved on to Berkeley more impressed with their work than his Met Lab auditors realized. “I left Chicago feeling that the plutonium process seemed to offer us the greatest chances for success in producing bomb material,” he recalls. “Every other process . . . depended upon the physical separation of materials having almost infinitesimal differences in their physical properties.” Transmutation by chain reaction was entirely new, but the rest of the plutonium process, chemical separation, “while extremely difficult and completely unprecedented, did not seem to be impossible.”1675
At the beginning of the month, to Compton’s great relief, the brigadier had convinced E. I. du Pont de Nemours, the Delaware chemical and explosives manufacturers, to take over building and running the plutonium production piles under subcontract to Stone & Webster. He meant to involve the industrial chemists more extensively than that—meant for them to take over the plutonium project in its entirety. Du Pont resisted the increasing encroachment. “Its reasons were sound,” writes Groves: “the evident physical operating hazards, the company’s inexperience in the field of nuclear physics, the many doubts about the feasibility of the process, the paucity of proven theory, and the complete lack of essential technical design data.”1676 Du Pont also suspected, once it had sent an eight-man review team to Chicago at the beginning of November, that the plutonium project was the least promising of the several then under development and might even fail, tarnishing the company’s reputation. Nor was it happy at the prospect of identifying itself with a secret weapon of mass destruction; it still remembered the general condemnation it had received for selling munitions to Britain and France before the United States entered the First World War. Groves told the Du Pont executive committee that the Germans were probably hard at work and the only defense against a Nazi atomic bomb would be an American bomb. And added what he took to be a clinching argument: “If we were successful in time, we would shorten the war and thus save tens of thousands of American casualties.”1677 The second week in November Du Pont admitted the possibility of regular production by 1945 and accepted the assignment (limiting itself to a profit of one dollar to avoid arms-merchant stigma), but made its skepticism and reluctance clear.
By then Stone & Webster’s construction workers had gone on strike. The pile building scheduled for completion by October 20 would be indefinitely delayed. Fermi lived with the problem only long enough to recalculate the risks of pile control. In early November he cornered Compton in his office and proposed an alternative site: the doubles squash court where his team had built its series of exponential piles. A k greater than 1.0 presented an entirely different order of risk from a k of less than 1.0, however; Compton had, in Seaborg’s words, a “dreadful decision” to make.1678 “We did not see how a true nuclear explosion, such as that of an atomic bomb, could possibly occur,” Compton writes with more calm than he probably felt at the time. “But the amount of potentially radioactive material present in the pile would be enormous and anything that would cause excessive ionizing radiation in such a location would be intolerable.”1679 He asked for Fermi’s analysis of the probability of control.
No doubt Fermi discussed the various hand and automatic control rods he planned for the pile. But even slow-neutron fission generations had been calculated to multiply in thousandths of a second, which might flash the pile to dangerous levels of heat and radiation before any merely mechanical control system could move into position. The “most significant fact assuring us that the chain reaction could be controlled,” says Compton, was one of the Richard Roberts team’s earliest discoveries at the Carnegie Institution’s Department of Terrestrial Magnetism following Bohr’s announcement of the discovery of fission in 1939—in Compton’s words, that “a certain small fraction of the neutrons associated with the fission process are not emitted at once but come off a few seconds after fission occurs.”1680 With a pile operating at k only marginally above 1.0, such delayed neutrons would slow the response sufficiently to allow time for adjustment.1681
For once Compton made a quick decision: with control seemingly assured, he allowed Fermi to build CP-1 in the west stands. He chose not to inform the president of the University of Chicago, Robert Maynard Hutchins, reasoning that he should not ask a lawyer to judge a matter of nuclear physics. “The only answer he could have given would have been—no. And this answer would have been wrong. So I assumed the responsibility myself.”1682 The word meltdown had not yet entered the reactor engineer’s vocabulary—Fermi was only then inventing that specialty—but that is what Compton was risking, a small Chernobyl in the midst of a crowded city. Except that Fermi, as he knew, was a formidably competent engineer.
* * *
In mid-November Fermi reorganized his team into two twelve-hour shifts, a day crew under Walter Zinn (who continued to supervise materials production as well), a night crew under Herbert Anderson. Construction began on Monday morning, November 16, 1942. From the balcony of the doubles squash court in the west stands of Stagg Field Fermi directed the hanging of the cubical dark-gray Goodyear balloon as his men hauled it into place with block and tackle. It dominated the room: bottom panel smoothed on the floor, top and three sides secured to the ceiling and the walls, the fourth side facing the balcony furled up out of the way like an awning. Someone drew a circle on the floor panel to locate the first layer of graphite and without ceremony the crew began positioning the dark, slippery bricks. The first layer was “dead” graphite that carried no load of uranium: solid crystalline carbon to diffuse and slow the neutrons that fission would generate. Up the pile as it stacked, the crews would alternate one layer of dead graphite with two layers of bricks each drilled and loaded with two five-pound uranium pseudospheres. That created a cubic cell of neutron-diffusing graphite around every lump of uranium.
To build the wooden framing, Herbert Anderson recalls, “Gus Knuth, the millwright, would be called in.1683 We would show him . . . what we wanted, he would take a few measurements, and soon the timbers would be in place. There were no detailed plans or blueprints for the frame or the pile.” Since they had batches of graphite, oxide and metal of varying purity, they improvised the placement of materials as they went along. Fermi, says Anderson, “spent a good deal of time calculating the most effective location for the various grades of [material] on hand.”1684
They were soon averaging not quite two layers a shift, handing the bricks along from their delivery skids, sliding them to the workers on the pile, singing together to pass the time.1685 The bricks in the dead graphite layers alternated direction, three running east and west and the next three north and south. That gave support to the oxide layers, which all ran together from front to back except at the outer edges, where dead graphite formed an outer shell. The physicist bricklayers had to be careful to line up the slots for the ten control-rod channels that passed at widely distributed points completely through the pile. “A simple design for a control rod was developed,” says Anderson, “which could be made on the spot: cadmium sheet nailed to a flat wood strip. . . . The [thirteen-foot] strips had to be inserted and removed by hand. Except when the reactivity of the pile was being measured, they were kept inside the pile and locked using a simple hasp and padlock, the only keys to which were kept by Zinn and myself.”1686 Cadmium, which has a gargantuan absorption cross section for slow neutrons, held the pile quiescent.
As it grew they assembled wooden scaffolding to stand on and ran loads of bricks up to the working face on a portable materials elevator. Before the arrival of the elevator, during the period when they were building large exponential piles, they had simply leaned over from the precarious 2 by 12-inch scaffolding and reached the bricks up from the men on the floor below. Groves walked in on them one day and dressed them down for risking their necks. The elevator appeared unbidden soon after.
When they achieved the fifteenth layer Zinn and Anderson began measuring neutron intensity at the end of each shift at a fixed point near the center of the pile with the control rods removed. They used a boron trifluoride counter Leona Woods had devised that worked much like a Geiger counter, clicking off the neutron count. Standard indium foils bombarded to radioactivity by pile neutrons gave daily checks on the boron counter’s calibration. Fermi had complained to Segrè in October that he was doing physics by telephone; now he moved a little closer to the work. “Each day we would report on the progress of the construction to Fermi,” Anderson notes, “usually in his office in Eckhart Hall. Then we would present our sketch of the layers that we had assembled and reach some agreement on what would be added during the following shifts.”1687 Fermi took the raw boron-counter and indium measurements and calculated a countdown. As the pile approached its slow-neutron critical mass the neutrons generated within it by spontaneous fission multiplied through more and more generations before they were absorbed. At k= 0.99, for example, each neutron would multiply through an average one hundred generations before its chain of generations died out. Fermi divided the square of the radius of the pile by a measure of the intensity of radioactivity the pile induced in indium and got a number that would decrease to zero as the pile approached criticality. At layer 15 the countdown stood at 390; at layer 19 it dropped to 320.1688 It was 270 at layer 25 and down to 149 at layer 36.
As winter locked down, the unheated west stands turned bitterly cold. Graphite dust blackened walls, floors, hallways, lab coats, faces, hands. A black haze dispersed light in the floodlit air. White teeth shone. Every surface was slippery, hands and feet routine casualties of dropped blocks. The men building the pile, lifting tons of materials every shift, stayed warm enough, but the unlucky security guards stationed at doors and entrances froze. Zinn scavenged rakish makeshift to thaw them out:
We tried charcoal fires in empty oil drums—too much smoke. Then we secured a number of ornamental, imitation log, gas-fired fireplaces. These were hooked up to the gas mains, but they gobbled up the oxygen and replaced it with fumes which burned the eyes. . . .1689 The University of Chicago came to the rescue. Years before, big league football had been banned from the campus; we found in an old locker a supply of raccoon fur coats. Thus, for a time we had the best dressed collegiate-style guards in the business.
Fermi had originally designed his first full-scale pile as a 76-layer sphere. Some 250 tons of better graphite from National Carbon now promised to reduce neutron absorption below previous estimates; more than 6 tons of high-purity uranium metal in the form of 2¼-inch cylinders began arriving from Iowa State College at Ames, where one of the Met Lab’s chemistry group leaders, Frank Spedding, had converted a laboratory to backyard mass production. “Spedding’s eggs,” dropped in place of oxide pseudospheres into drilled graphite blocks that were then stacked in spherical configuration close to the center of the CP-1 lattice, significantly increased the value of k. Adjusting for the improvements, Fermi saw that they would not need to seal the Goodyear balloon and evacuate the air from the pile and could eliminate some 20 layers: his countdown should converge to zero, k = 1.0, between layers 56 and 57. Instead of a sphere the pile would take the form of a doorknob as big as a two-car garage, a flattened rotational ellipsoid 25 feet wide at the equator and 20 feet high from pole to pole:
Anderson’s crew assembled this final configuration on the night of December 1:
That night the construction proceeded as usual, with all cadmium covered wood in place. When the 57th layer was completed, I called a halt to the work, in accordance with the agreement we had reached in the meeting with Fermi that afternoon. All the cadmium rods but one were removed and the neutron count taken following the standard procedure which had been followed on the previous days. It was clear from the count that once the only remaining cadmium rod was removed, the pile would go critical. I resisted great temptation to pull the final cadmium strip and be the first to make a pile chain react. However, Fermi had foreseen this temptation and extracted a promise from me to make the measurement, record the result, insert all cadmium rods, and lock them all in place.1690
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