Deflecting Physics for War
|Lawrence encourages Lab workers during World War II.|
The award of the Nobel prize in physics to Lawrence in 1939 helped his quest for money for the new machine among his usual sources. The Rockefeller Foundation pledged the principal amount, $1.4 million, in April 1940. It was to buy a cyclotron with a magnet face 184 inches in diameter. The machine would open the frontier beyond 100 MeV, where there lurked "discoveries of a totally unexpected character and of tremendous importance." Perhaps, Lawrence guessed, the big accelerator might also induce artificial chain reactions and unlock the "vast storehouse of nuclear energy." A more sinister connection or rather non sequitur appeared in Newsweek's coverage of the pouring in October 1940 of the thousand tons of concrete on which the accelerator would rest. "Japanese and German researchers are already studying the possibility of [using uranium] for military purposes, while nearly twenty American universities have or are now building cyclotrons."
|The Lab blackboard announced Lawrence's Nobel Prize.|
The 184-inch cyclotron could not conveniently be housed on the campus. Its big concrete pad sat on a hill overlooking the University and the bay, a romantic site to which most of the Laboratory ascended after the war. At first, however, it seemed that little more than concrete would be set there. Steel and copper were in short supply. Already in 1940 the nation was preparing for war, stockpiling and rationing strategic material, and surveying its scientific and technical manpower. In the spring of 1941 the Laboratory could not obtain the steel it needed. Lawrence appealed to; the Office of Scientific Research and Development (OSRD), formed in June to guide research and development of "the mechanisms and devices of warfare." By January 1942 the Laboratory had an A-1-a priority for steel. The 184-inch magnet rated as a mechanism of warfare.
The magnet was adapted for use in a huge mass spectrograph to test the feasibility of Lawrence's plan to separate the fissile, or explosive, part of natural uranium, U-235, from its much more plentiful companion isotope, U-238. In 1939 A. O. C. Nier of the University of Minnesota had managed to separate a tiny amount of U-235 by mass spectroscopy, but few if any besides Lawrence thought the process would work on an industrial scale. As usual, he pushed his project hard, to the annoyance of Vannevar Bush, the head of the National Defense Research Committee, the forerunner of OSRD: "I made such a nuisance of myself," Lawrence recalled, "that Bush requested the president of the National Academy to appoint a committee to survey the entire uranium problem." It concluded, in November 1941, that Lawrence's method of separating isotopes should be pursued among others. The disclosure by the British that the calculations of Frisch and Rudolf Peierls indicated that "only" a few kilograms of pure U-235 would be needed for a bomb, convinced him that he had a practical method for making nuclear explosives. Here Lawrence left the merely large, like cyclotrons, for the gargantuan. Using conventional mass spectrographs, it would have taken about 25 million years to make the required kilograms. With Laboratory funds he converted the 37-inch cyclotron for a preliminary demonstration; a team under Segre devised a way to measure the enrichment by its radioactive properties; the OSRD contributed $400,000; and in March 1942 Lawrence had enriched the fissionable isotope in a sample of uranium by a factor of five.
|Lawrence slumps in his chair from fatigue during calutron test.|
During 1942 the Laboratory rushed the design of ion sources, collecting cups and, above all, magnets, to multiply the separation. Many possibilities were tested with the help of the 184-inch magnet. Lawrence called the final product an "alpha calutron," the Greek letter signifying the first stage of the process and the neologism commemorating its origin in California. Ninety-six calutrons were to be combined into each of five production "racetracks." The magnet controlling each racetrack would consume 100 times the power required by the 184-inch cyclotron.
Construction of the huge electromagnetic complex began at Oak Ridge, Tennessee, under the direction of General Leslie R. Groves, commander of the "Manhattan Engineering District" (MED) set up in 1942 to implement the uranium project. Ground was broken on February 18, 1943. So urgent had the project become that no one stopped to build a pilot plant; the Laboratory had managed to make only a small test section of the great magnet proposed. Staff from Berkeley rushed to Oak Ridge to advise the contractor as construction proceeded. In August the first racetrack began to operate, successfully it was thought; but it soon collapsed, its vacuum leaky, its coils shorted, its tanks warped by its mighty magnet. Meanwhile Oppenheimer reported that a bomb would require three times as much U 235 as forecast. Lawrence and others flew in from Berkeley to diagnose the ailing racetrack, which was dismantled and returned to its manufacturers. The pressure overwhelmed even Lawrence. He spent the end of 1943 in a hospital in Chicago.
During 1944 the alpha calutrons improved and a second generation, called beta, were introduced. The beta calutrons refined further the yield from the alpha type. Nonetheless the total output stayed below expectation. To increase it to usable amounts, the alpha plants were adapted to accept/enriched feed from other separation processes. Ultimately nine alpha tracks and six beta tracks operated at Oak Ridge. Through the beta type passed the uranium for the bomb that destroyed Hiroshima. (See Episode beginning page 36.)
|The alpha calutrons required constant attention to keep the ion beam current at a maximum.|
Electromagnetic separation of U-235 was not the only road to nuclear explosives that began in Berkeley. There, in 1939 and 1940, studies of fission products brought to light a new element, heavier than uranium, that promised to be as susceptible to a chain reaction as U-235. It happened this way. McMillan directed neutrons created by deuterons from the 37-inch cyclotron through a layer of uranium oxide spread on paper. He was interested to find that two radioactive substances, with half lives of 23 minutes and 2.3 days, remained embedded in the target; since fission fragments should have recoiled out of the paper, he inferred that the new activities came from elements about as heavy as uranium. The 23-minute activity belonged to U-239, which Otto Hahn, Lise Meitner, and Fritz Strassmann had synthesized in 1936. The longer activity was the product of the beta decay of U-239; it turned out to be an isotope of the first transuranium element, number 93. At first, however, it appeared to have the chemical properties of the rare earths, which are common fission fragments, and not those of the homologue of rhenium that 93 was expected to be.
McMillan returned to the problem early in 1940 when he used the 16-MeV deuteron beam of the 60-inch cyclotron to produce the 2.3-day activity. It still did not behave as a fission product, nor, as close inspection disclosed, as a typical rare earth. Philip Abelson, who had been searching for the same activity in uranium samples at the Carnegie Institution of Washington, where he had gone to set-up a cyclotron, came on a visit to Berkeley and joined forces with McMillan. They showed that the activity grew from U-239 and that its chemistry resembled uranium's. The resemblance had protected it from detection by investigators who expected something similar to rhenium. No one had suspected, as McMillan and Abelson now did, that there existed a "second 'rare earth' group of similar elements." McMillan named the new element neptunium after the planet next beyond Uranus, and noticed (after Abelson's return to Washington) that it has a descendent that emits alpha particles. Before he could determine its chemistry, however, he went to MIT to help develop radar, the war technology then most pressing. With McMillan's consent, Seaborg picked up the work on the alpha emitter, element 94. They were to share the Nobel prize in chemistry in 1951 for their discoveries of the first transuranic elements.
The new element, called plutonium on McMillan's principle of nomenclature, proved elusive. The first isotope identified was not McMillan's alpha emitter but Pu-238, a shorter-lived decay product of neptunium made by irradiating uranium-238 with deuterium in the cyclotron. The discoverers, Seaborg, McMillan, J. W. Kennedy, and A. C. Wahl, learned enough about plutonium chemistry to know how to concentrate McMillan's alpha emitter (Pu-239). In May 1941 Kennedy, Seaborg, Segre, and Wahl succeeded in doing so and also established the new isotope's fissionability. It appeared that in sufficient quantities plutonium-239 might sustain an explosive chain reaction. After Pearl Harbor, the OSRD authorized Lawrence to continue plutonium studies at Berkeley and Arthur Compton to supervise the work toward a controlled, self-sustaining, plutonium-producing chain reaction that had been started by Fermi at Columbia and moved to Chicago. In March 1942 Seaborg was asked to join Compton and Fermi to develop chemical processes to separate plutonium after production. On April 17 he boarded the train for Chicago with the world's supply of plutonium in his briefcase.
|First plutonium sample used to determine its fission properties in March, 1941.|
Seaborg's move did not put an end to work on plutonium in Berkeley. Wahl, for example, worked on the lanthanum-fluoride process, that Seaborg used to isolate the first weighable amount of plutonium in the summer of 1942. The Dean of the College of Chemistry, Wendell Latimer, supervised the work and began investigations of the effects of heat upon materials to be used in the plutonium production piles. In work parallel to Latimer's, Hamilton's group at the 60-inch cyclotron examined the effects of fast neutrons on the graphite moderator provided for the reactor. The 60-inch also prepared plutonium for the research in Chicago. In July 1944 it shut down after 20,000 continuous hours of operation for decontamination and overhaul. The machine designed to serve Asclepius had exhausted itself for Mars.
Groves decided to build a production plant for plutonium shortly after Fermi ignited and controlled a chain reaction in December 1942. Like the alpha racetracks and the diffusion plants at Oak Ridge, the manufacturing piles and chemical treatment facilities at Hanford, Washington, were built without benefit of a full-scale pilot plant. And, again like the Oak Ridge complex, Hanford delivered enough fissile product to fill a nuclear bomb by June 1945. Two practical designs for a weapon then existed, one of which--using U-235 as ingredient--seemed secure enough not to require expenditure of the precious material in a test. The other, using plutonium, had a complex and problematic explosive trigger. No fault could be found with it when the first nuclear explosion released by man lit up the sky above New Mexico on July 16, 1945. A similar performance demolished Nagasaki a few weeks later.
|The Trinity test, first man- made nuclear explosion, Alamagordo, New Mexico, July 16, 1945.|
Lawrence attended the desert test, code named Trinity, at which he felt no sin, remorse, or dread, as others since have thought they did, but rather relief that the thing worked. A few weeks before Trinity he, Fermi, Oppenheimer, and Compton had advised the Secretary of War, Henry Stimson, on the use of the new weapon. Lawrence preferred a demonstration before Japanese representatives to immediate use against a populated center. After further consideration, he changed his mind to agree with his fellow advisers that only application without advertisement would guarantee prompt surrender and a great saving in American lives. When the Emperor of Japan surrendered unconditionally on August 15, 1945, the Laboratory could rejoice that it had helped to end the war in the Pacific.
The mobilization had extended throughout the Laboratory, to nuclear medicine as well as to nuclear physics and chemistry. Hamilton and his colleagues had studied the physiological effects of fission products for the OSRD. John Lawrence and his associates in the new Donner Laboratory had examined biological consequences of high-altitude flying. Using radioactive isotopes of inert gases, they had penetrated the secrets of decompression sickness and other maladies, and tested 1500 persons in a low-pressure chamber simulating high altitudes. Tracer studies at the Laboratory had brought fundamental contributions to the understanding of the circulation and diffusion of gases and practical devices like oxygen equipment, a parachute-opener, and methods to measure the rate of circulation and perfusion of the blood by capillaries.
|Lawrence challenged by Laboratory security guard at wartime Laboratory.|
Before the war Lawrence's associates had learned to work together to keep their machines producing radioisotopes, therapeutic rays, and beams for biological, physical, and chemical research. During the war formality and hierarchy entered, apparently for the first time on paper in an organization chart composed in June 1942. Three committees advised Lawrence on planning, production, and operation of calutrons. Wallace Reynolds managed the Laboratory, a job now spun off from Donald Cooksey's office. Brobeck ran an engineering department. Laboratory shops became the production section. Thornton headed research and development. Purchasing, auditing, and personnel divisions appeared. To coordinate the newly specialized functions of the Laboratory, Lawrence set up a process engineering committee in November 1942 and charged its members with the "responsibility for seeing that the ball is carried in the right direction and with all speed." They divided responsibility for design of calutron components from the central magnet (Brobeck) to peripheral "gunk catching, cleaning and recovery" assigned to E. J. Lofgren, who interrupted his graduate studies to come to the Laboratory during the war.
The charts grew larger and the committees proliferated as the Laboratory and the war effort expanded. By May 1, 1943 the staff numbered 826 plus 65 guards. The total rose to nearly 1200 in June 1944, including a small British force led by M. L. E. Oliphant. Before the war the staff of the Laboratory could be photographed within the yoke of the 60-inch magnet. Now their individual photos filled books of pass records maintained by an increasingly obtrusive security service. Organization of another kind also came to the Laboratory during the war. Oppenheimer tried to set up a local of the Association of Scientific Workers; Lawrence counseled physicists not to join it. A more telling recruitment, conducted by the Federation of Architects, Engineers, and Technicians, prospered when forced transfers to Oak Ridge began in 1943. Known communists led the Federation. Security officers arranged to draft some organizers and to fire others.
|Newspaper headlines on August 7, 1945, revealed to the Bay Area public for the first time that the laboratory had played a crucial role in the war effort.|
Bomb design demanded a higher order of security. A remote and isolated laboratory was set up at Los Alamos under Oppenheimer. Groves hoped to compartmentalize the study of the weapon as he had its production facilities. As if physics had been declared a crime and its leading perpetrators imprisoned, Los Alamos grew until in 1945 it held more than 2000 of the nation's physicists. They included many from the Laboratory, among others Alvarez, Lofgren, McMillan, Segre, Serber, and Wilson.
The surrender of Japan ended the emergency that had created Los Alamos but not the large organization and tight security that had come to characterize nuclear science. Elaborate classification schemes, supervision by government bureaucracies, and depersonalized administrative hierarchies remained at the Laboratory as at Los Alamos, Argonne, Oak Ridge, and Hanford. Otherwise the terms of parole were most generous. The methods and resources of big science, enlarged by the war, were to dominate the study of nuclear physics in the peace.