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.
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.” 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.”
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. 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
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.
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 man-made 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 plu-tonium 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.
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. 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.’”
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.” 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.
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 micro-cones; 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.’”
