Elsewhere
In August 1941 Lawrence pulled McMillan from the ether at MIT and dropped him in the water at San Diego. A new laboratory, run jointly by the navy and Jewett's division of NDRC, was being organized there under a contract with the University of California. Its director, Vern Knudsen, professor of physics at UCLA, had built up a small, strong group in applied acoustics with support from the movie industry, for which he had built
[88] Clark, Tizard , 264–70; MIT, Five years , 12, quote; Bowen, Radar days , 157–9, 168–78, quotes; Guerlac, Radar , 248–50.
[89] Anon., Westinghouse eng., 6:2 (Mar 1946), 47.
sound stages. But neither Hollywood nor UCLA had given him work on the scale on which he was now to perform: to study the physics of underwater sound, especially means to measure its spead precisely; to improve or design new methods of underwater detection and evasion appropriate to conditions in the Pacific; and to develop training manuals and devices for operators with very little technical knowledge. Knudsen turned for help to the physicist at the University of California most experienced in big operations. Lawrence "came down [to San Diego], spent time with us . . . , and participated in formulating our research program."[90]
Perhaps most usefully, Lawrence furnished McMillan, much to the irritation of the leaders of the MIT Rad Lab. With the breadth of view and ingenuity that had made him so valuable a member of Lawrence's Laboratory, McMillan contributed to all phases of the work at San Diego. He devised an echo repeater, "Beeping Tom," the first contribution from Knudsen's shop accepted by the navy, which simultaneously freed submarines from service as training targets and sonar operators from the need for practice at sea. He was particularly effective, according to Knudsen's successor, G.P. Harnwell, "in criticizing and directing the program of the laboratory in the fundamental investigations assigned to it."[91]
The first group of cyclotroneers entirely mobilized by NDRC was Tuve's force in the Carnegie Institution. In September 1940 they put aside their Crocker clone for "nights and days with defense work." They had taken on the task of knocking enemy planes from the sky. At the time, conventional wisdom rated very highly an antiaircraft system that could hit one plane in 2,500 shots. Under this mild inhibition, the Luftwaffe could bomb and strafe without much worry about guns on the ground. Following conversations between Lauritsen and Tuve and the navy's Bureau of Ordnance in August, the NDRC contracted with the Carnegie Institution for "preliminary experimental studies on new ordnance
[90] Baxter, Scientists against time , 172–4, 180; Hackman, Seek and strike , 251–2; Knudsen, interview with L. Delsasso and W.J. King, 18 May 1964 (AIP), 24–8, 46–7, quote.
[91] McMillan to Lawrence, 18 June, 4 Jul, and 22 Aug 1941, and Lawrence to McMillan, 8 Jul 1941 (12/30); McMillan to Lawrence, 18 June 1942 (12/31); Harnwell to Bush, 5 Oct 1942 (McMillan P).
devices." Tuve learned about what the British had done from Cockcroft and Fowler and set out to make a fuse activated by radio that would detonate near its target. Everyone working on the Carnegie cyclotron—Tuve himself, L.R. Hafstad, R.B. Roberts, G.K. Green, and Philip Abelson—went to work to make a radio sufficiently small and tough to fit into the space of an ice cream cone and withstand the inspiring forces—some tens of thousands of times greater than the force of gravity—exerted during firing on a five-inch shell. The Carnegie's administration, however, preferred to see its expensive cyclotron brought to completion; and, in a gambit we shall see repeated, requested Tuve's men to return to their machine as a measure of national defense. He rejected the request as selfish and the aim as ineffectual. "Representatives of every Cyclotron Laboratory in the country have individually asked us what they could use their cyclotrons for in defense work and no valid ideas have been forthcoming. . . . It is easy for an enthusiastic entrepreneur to make a casual remark that a cyclotron can be classified as a defense project. If the Institution staff had no other defense work of clearly greater urgency, this would be our position [too] as it was previous to August."[92]
Tuve did find a little war work for his new three-story cyclotron laboratory. He and his associates dropped miniature radio tubes from its roof onto the concrete driveway below as a test of fragility. Enough survived to prompt contracting with their makers. When he declared the worthlessness of cyclotrons for national defense, Tuve had three sorts of tiny tubes that could withstand firing in a five-inch shell. By May 1941, a basic design for a fuse triggered by radio was in hand; but premature firings and duds troubled its tests during the summer. The bombing of Pearl Harbor brought new urgency and manpower to the project and its relocation to a large garage in Maryland. This new facility, dubbed the Applied Physics Laboratory of Johns Hopkins University, which contracted for its operation, improved reliability and invented an ingenious mechanism to prevent unintended explosions. Late in 1942, 4,500 shells, perfectly safe to their users,
[92] Tuve, "Report for September 1940" (MAT, 21/"extra copies"); quotes from, resp., Tuve to Condon, 23 Oct 1940 (MAT, 24/"MIT conf."), and Tuve to Fleming, 25 Jan 1941 (MAT, 25/"cycl. 1940").
reached the Pacific Fleet. In their first engagement they brought down a Japanese bomber in four shots. The project compared in importance, success, and expense with the making of the atomic bomb.[93]
One of Bush's first prizes as chairman of NDRC was the Advisory Committee on Uranium. This body, chaired by Lyman J. Briggs, director of the National Bureau of Standards, had resulted from the famous letter alerting Roosevelt to the possibility of nuclear weapons, signed by Einstein but composed by Szilard and his fellow Hungarian refugees Eugene Wigner and Edward Teller. Briggs was no cyclotroneer. His committee, which had the frequent optimistic advice of Szilard, had not accomplished much by May 1940, after seven months of existence. The delay and the apparent indifference of the armed services to the opportunities opened by fission made the refugees impatient and, perhaps, self-important. "We ought not to try to save the country for the Americans [Wigner wrote Bethe], but to push them to save themselves."[94] Without their pushing, however, a typically American instrument—a body of self-moving private citizens appointed by the president to mobilize scientists within and outside government—had come into being that would vitalize the uranium project.
The citizens, the founders of NDRC, had been drawn into the business of the uranium committee a few months before the creation of their organization. The news from Columbia in March 1940 that, as predicted by Bohr, U235 was the party guilty of fission by slow neutrons, directed attention to the importance of the separation of uranium isotopes. In April, at the meeting of the American Physical Society in Washington, Beams, Fermi, Nier, Tuve, and Urey decided that Beams's ultracentrifuge offered the best hope for separation in kilogram amounts. In May, Beams, Cooksey, Karl Compton, and Lawrence reached a similar conclusion. Compton notified Bush (as head of the rich Carnegie
[93] Baxter, Scientists against time , 221–33, 241–2. Over 130 million proximity fuses were made at an average unit cost of $20; their manufacture eventually monopolized 25 percent of the American electronics industry and 75 percent of the facilities for molding plastic.
[94] Wigner to Bethe, 21 May 1940 (HAB, 14/22/976); Hewlett and Anderson, New world , 19–24.
Institution), who already knew about Beams's work from Tuve, whose department had deliberated purchasing a centrifuge for biological work. Tuve had rated Beams's model, which cost $5,000, as the best available for separating isotopes (he had tracers in mind) and biological materials. Tuve now recommended to Bush that the Carnegie Institution give Beams $10,000 to determine whether U235 could be spun free from U238 . In Tuve's opinion, centrifugation offered "the only hope of separating the isotopes of any but the light elements in quantity." Neither thermal diffusion nor the mass spectrograph (electromagnetic separation) seemed competitive to him.[95]
Bush agreed to provide money and call meetings. The Naval Research Laboratory had been helping Beams with supplies and apparatus at a level estimated by Tuve at $2,000 a year. After Bush's intervention, the army and navy put up $100,000 to study the separation of isotopes, primarily by centrifugation, but also by thermal liquid diffusion, as proposed by Carnegie's Abelson, then recently returned from Berkeley and work on element 93.[96] A possibility that Tuve had not considered explicitly, diffusion of uranium hexafluoride gas through tiny holes in a "barrier," which would slightly enrich the lighter isotope, appealed to Urey and others at Columbia, who obtained money from NDRC in the winter of 1940/41 to follow it up. The runaway favorite in July 1941, as judged by a budget then proposed by Briggs's committee, was Beams's centrifuge ($95,000); Columbia's gaseous diffusion ($25,000) came a poor second. At just this moment, however, the British intervened as decisively as they had in the fall of 1940.[97]
For a year and a half, Chadwick, Cockcroft, Oliphant, Thomson and other leading British physicists knew that a bomb might be made from 10 kg or less of separated U235 . The relevant
[95] Compton to Bush, 9 May 1940 (KTC); Hewlett and Anderson, New world , 23–4; Abelson and Tuve, "The current status of the ultracentrifuge as a research tool," 17 Jan 1940 (MAT, 25/"biophys. 1940"); Tuve to Bush, 13 Apr 1940 (MAT, 19/"Beams"); Beams, RMP, 10 (1938), 248–51; Loofbourow, RMP, 12 (1940), 324–9.
[96] Bush to Compton, 14 May, and Loomis to Compton, 17 May 1940 (KTC); Tuve to Bush, 13 Apr 1940 (MAT, 19/"Beams"); Hewlett and Anderson, New world , 27, 32.
[97] Hewlett and Anderson, New world , 40–3.
considerations had been put forward in February 1940 by the émigrés O.R. Frisch (Cambridge) and Rudolph Peierls (Birmingham), who assumed, among much else, that fast neutrons as well as slow ones could cause fission in U235 . "From rather simple theoretical arguments," they wrote, without arguing, "it can be concluded that almost every collision produces fission and that neutrons of any energy are effective." This was a capital point: a slow neutron bomb would be more likely to fizzle than to devastate. And where procure the U235 ? Frisch and Peierls suggested gaseous thermal diffusion. Another émigré, Franz Simon (Oxford), showed that diffusion through a barrier could do much better. In his optimistic calculations, completed in December 1940, a plant covering forty acres and employing 1,200 people could turn out 1 kg of 99 percent pure U235 in a day. During the first six months of 1941, these prophecies drew strength from rough measurements by Tuve's group, which confirmed the fundamental hypothesis of fast-neutron fission on a sample of U235 provided by Nier. Peierls exulted: "There is [now] no doubt that the whole scheme is feasible (provided the technical problems of isotope separation are satisfactorily solved)." The official report of the British uranium committee (called the MAUD Committee) of July 1941 endorsed and refined the original Frisch-Peierls memorandum: twenty-five pounds of active material, a gaseous diffusion plant costing £5 million, a bomb deliverable at the end of 1943 equivalent in destructive power to 1,800 tons of TNT.[98]
The MAUD report changed American thinking. Although everybody had known that a chain reaction, if achieved, might make possible a nuclear explosive, Briggs's uranium committee did not have a bomb as its goal. Looking back with the greater wisdom of 1943, Fermi recalled that he knew of no one working with either fission or element 94 in the United States who appreciated their potential as explosives until the spring (or, better, the early summer) of 1941. Ignorance of British thinking was not the reason for this devaluation. Oliphant had written Lawrence in May 1939 that the British defense authorities insisted on looking
[98] Gowing, Britain and atomic energy , 58, 67–8 (quote), 77, 390, 392, 394–8; Smyth, Atomic energy , 66.
into the possibilities of a bomb, however remote, "as there are rumours that great developments have taken place recently along these lines in Germany." Lawrence, conceding the possibility, had asked "Segrè and some of the other boys" to see whether they could fission lead or bismuth. Typically, he saw neither a danger nor the likelihood of imminent success, but an entrepreneurial opportunity. "This sort of thing is another reason why the British government should come forward with generous support of nuclear physics."[99] Nor did disclosure of the Frisch-Peierls report by the Tizard mission inspire Lawrence or other leaders of American nuclear physics to set a high priority on making bombs. Cockcroft thought them overly skeptical about military applications and overly fascinated with the possibilities of nuclear power.[100] But then Britain, not the United States, was at war.
The pace of the Briggs committee exasperated some of its members, particularly Urey, and busy outsiders like Lawrence. In March 1941 Lawrence managed through Karl Compton to have himself assigned by a reluctant Bush—who did not like being pressured—to the post of temporary consultant to Briggs. Lawrence obtained a modest increase ($2,000) in support of the Laboratory's work on elements 93 and 94 and a contract to Nier for 5 mg of U235 . His role was that of gadfly; he did not urge a change of program but greater vigor and less secrecy in pursuing the self-sustaining pile.[101] At the instigation of Briggs, Bush asked Jewett to convene a committee of the National Academy of Sciences to evaluate the uranium program. Jewett appointed A.H. Compton, Coolidge, Lawrence, John Slater of MIT, and John Van Vleck of Harvard. Their report, finished in May, did not emphasize a bomb; it was vague and uplifting, in the style of Lawrence's requests for major funding. The uranium project should be supported for the general significance of achieving a chain reaction and for the importance of even a moderate separation of uranium isotopes; if successful, the project might produce,
[99] Fermi to A.H. Compton, 31 Aug 1943 (Fermi P); Oliphant to Lawrence, 30 May, and reply, 15 June 1939 (14/6).
[100] Hewlett and Anderson, New world , 28–9; Hartcup and Allibone, Cockcroft , 124.
[101] Hewlett and Anderson, New world , 35–9; Bush, Pieces , 60; Compton, Atomic quest , 47.
in order of military importance, radioelements in sufficient quantities to poison enemy territory, power plant for submarines, and a bomb, the last unlikely before 1945.[102]
Bush and Conant then knew about British hopes for a bomb, which Conant had learned of during a sojourn in London in the early spring as liaison between NDRC and British defense authorities. He and Bush dismissed the NAS report as too vague on bombs and too fanciful on power. They asked for another. Jewett added two engineers to the committee. Its report, of 11 July, did not differ significantly from its predecessor's. Conant inclined to squelch the project. No one seemed to know much of the MAUD report or to take it seriously. Lawrence heard about it in September 1941, not from Briggs, who appears to have kept the report secret even from himself, but from Oliphant, on tour of American laboratories engaged in radar and other war work. What had been missed in the United States, judging from a letter from Coolidge, who had chaired the NAS committees, was the connection between fast-neutron fission, ten-kilogram explosives, and practical gaseous diffusion. Oliphant raised Lawrence's enthusiasm for nuclear bombs. Oliphant thought that 10 kg of pure U235 might be within reach, perhaps by cyclotronics. And there was also element 94, which the Laboratory had shown to be fissionable and MAUD had mentioned as an alternative, if unlikely, explosive.[103] At the end of September 1941, just after meeting with Oliphant, Lawrence attended the fiftieth anniversary celebrations of the University of Chicago. There he met with Compton and Conant and urged that a new NAS committee be empanelled to consider the uranium project in the light of the MAUD report.[104]
[102] Smyth, Atomic energy , 50–2; Hewlett and Anderson, New world , 36.
[103] Cockburn and Ellyard, Oliphant , 102–6; Coolidge to Jewett, 11 Sep 1941, ibid., 106; Gowing, Britain and atomic energy , 433. According to Cockburn and Ellyard, Oliphant , 104, Fermi doubted the possibility of a fast-neutron explosive.
[104] Compton, Atomic quest , 8; Smyth, Atomic energy , 51–2; Lawrence, "Historical notes," 26 Mar 1945. Compton misdates the meeting in Chicago to early or mid September, before Oliphant reached Berkeley; Lawrence arrived in Chicago on 25 Sep, according to Lawrence to Compton, 5 Sep 1941 (4/10).
The illumination from London came just after Bush had reorganized and extended his empire. On June 28, 1941, he took over the directorship of a new agency, the Office of Scientific Research and Development (OSRD), which gave him responsibility for development of instruments of war as well as for research of military interest, authority to coordinate the efforts of various agencies, and immediate access to the president. Conant took the chairmanship of NDRC and Briggs remained as chairman of the uranium committee, which Bush raised to an independent unit, "S-1," of OSRD. He and Conant followed Lawrence's and others' promptings and returned to the NAS to ask for a new review with emphasis on the U235 bomb and the gaseous-diffusion plant. While the new committee deliberated under the chairmanship of A.H. Compton, Bush conferred with the president. He left the White House on October 9 with authority to expedite research on nuclear weapons in every way possible short of the construction of production plants. Compton's committee, which included Lawrence and Oppenheimer, endorsed the British findings, with some qualifications that proved wrong. Oppenheimer expected that 100 kg of U235 would be needed for a bomb. The committee thought that centrifugation might work. They raised the cost of separation to $100 million.[105]
On December 18, less than two weeks after Pearl Harbor, the complete S-1 section met at the National Bureau of Standards. It was time for a crash program. And to let contracts. Lawrence spoke up, immediately and eloquently, for study of electromagnetic separation on a large scale. The committee immediately recommended a sum of $400,000. It was easier than dealing with the Rockefeller Foundation.[106]
[105] Hewlett and Anderson, New world , 44–50.
[106] Ibid., 52.