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.”1566 Raeder 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 ma
terials 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.
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“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.1583 Then 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 beginn
ing 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
Making of the Atomic Bomb Page 56
