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.”1593 Providentially 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 m
ile 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 [1942]. 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.
Making of the Atomic Bomb Page 57
