Lawrence and the Bomb

A few months before the Second World War started in Europe, the physics world was shaken by a discovery that would change Ernest Lawrence's life. German scientists reported that the uranium nucleus, when hit by a neutron, splits into two smaller nucleinuclear fission. Unlike the earlier splitting off of small pieces of atoms, fission released some of the huge store of energy bound in the nucleus. When the news reached the United States, staff in Lawrence's Radiation Laboratory bombarded uranium with neutrons and confirmed that they had missed another major discovery. Like many physicists, Lawrence sensed the tremendous possibilities of a nuclear chain reaction.

"We are trying to find out whether neutrons are generally given off in the splitting of uranium; and if so, prospects for useful nuclear energy become very real!"

Lawrence to John Cockcroft; February 9, 1939

Concern about the military potential of fission would lead physicists to hesitate about revealing results of their investigations to the world. But before self-censorship was established, Berkeley physicists announced an important discovery. Edwin McMillan used the large neutron flux from Lawrence's 37-inch-diameter cyclotron to irradiate uranium. In 1940, with the help of Philip Abelson, Glenn Seaborg, and Emilio Segrč, he found that the irradiated uranium decayed to new elements of atomic number 93 and 94, called neptunium and plutonium. Elements with atomic numbers larger than 92, that of uranium, had never been seen in nature, and scientists had been trying for several years to produce them artificially. McMillan and Seaborg would share the Nobel Prize for chemistry in 1951 for their work on transuranics. In 1941 they showed that plutonium was fissionable, like uranium, thus opening a second possible route toward the generation of nuclear energy.

In 1939 refugee Jewish scientists in the U.S., including Albert Einstein, had convinced President F.D. Roosevelt to start a uranium research project. The American effort languished through 1940 into 1941, although Lawrence impatiently urged brisker action. Meanwhile, two refugee scientists in Britain, Otto Frisch and Rudolf Peierls, realized that a nuclear explosion could be created using a relatively small amount of one of the two isotopes present in natural uranium. Only the rare isotope with mass 235 was fissionable, while the much more abundant isotope uranium-238 would only hamper a chain reaction. This secret, brought to the U.S. from Britain, helped to energize the American uranium project. Two of the project leaders, Arthur Compton and James Conant, met with Lawrence in September 1941 and asked him whether he was willing to devote the next several years of his life to a crash program to build an atomic bomb. He was.

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"I can still recall the expression in his eyes as he sat there with his mouth half open...He hesitated only a moment. ‘If you tell me this is my job, I'll do it.'"

Arthur Compton on Lawrence's commitment to a bomb project.

Even before the U.S. entered the war, Lawrence had mobilized the Rad Lab's instruments and staff to help the war effort. In 1940 several Berkeley alumni, including McMillan and Luis Alvarez, helped staff a new laboratory at MIT, where they applied their experience in radio electronics and collaborative research to the development of radar. (The organizers of the radar lab named it the Radiation Laboratory to confuse the enemy.) Now the possibility of atomic bombs gave Lawrence and the original Rad Lab a great enterprise.

A main obstacle to building an atomic bomb was the difficulty of separating the scarce isotope uranium-235 from the much more abundant uranium-238. Since the isotopes were chemically identical, ordinary chemistry could not distinguish them. Lawrence proposed to separate the isotopes by using the minuscule difference in mass between them. Electrically charged ions with different masses would be deflected slightly different amounts by a magnetic field.

To investigate the possibility, Lawrence transformed the 37-inch cyclotron and then the 184-inch magnet into mass spectrographsdevices that separated isotopes electromagnetically. By 1942 he and his staff had developed a successful prototype of a device, called a "calutron" after the University of California.

The uranium project, now code-named the "Manhattan Engineer District" and put under the control of General Leslie Groves of the U.S. Army, rushed to construct calutrons on an industrial scale. Vast "racetracks," each consisting of 96 calutrons, arose at a secret isotope separation plant in Oak Ridge, Tennessee. The hydroelectric power stations of the Tennessee Valley Authority supplied the necessary huge amounts of electric power. The racetracks did not run well at first. Contaminated cooling oil shorted out the giant magnets, and the product often ended up not in the collecting cup but scattered through the interior of the calutrons.

Lawrence and others from the Rad Lab staff frequently visited Oak Ridge to fight the technical difficulties until the racetracks began to operate smoothly. Fifteen of them were eventually built. These served as a first stage of separation, enriching uranium with the fissionable isotope uranium-235. The product was then fed into other devices that relied on other methods (gaseous or thermal diffusion) to produce nearly pure uranium-235. Almost all of the uranium-235 in the atomic bomb that would destroy Hiroshima passed through Lawrence's calutrons in Oak Ridge.

A second route to a bomb was based on the element with atomic number 94 discovered in Berkeley—plutonium. This material was produced in quantity by industrial-scale chain-reacting piles, or reactors, that the Manhattan Project built in Hanford, Washington. Plutonium fueled the first nuclear device tested at the Trinity site in the New Mexico desert and the bomb dropped on Nagasaki.

As Lawrence and his lab made decisive contributions to the Manhattan Project, not least in providing a prototype of the large, multidisciplinary lab combining science and engineering, war work changed the character of Lawrence's lab. Formal hierarchies and organization charts replaced informal collaborations. The Rad Lab staff grew to nearly 1,200 by mid-1944, even as its alumni went forth to staff new sites, including a bomb design laboratory set up at Los Alamos in New Mexico under the leadership of J. Robert Oppenheimer. The cyclotron laboratory on the Berkeley hills became a defense plant, with a force of security guards and checkpoints at the gates.

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Tough security restrictions excluded foreigners from the laboratory and brought an end to Lawrence's generous sharing of cyclotron information with other scientists. Many scientists on the Manhattan Project felt uneasy with military regulations and secrecy, which were alien to the spirit of scientific investigation and a hindrance to research. Lawrence himself felt free to circumvent restrictions when he thought the interests of the project demanded it. When the university ordered that all "enemy aliens" be fired, Lawrence found a way to keep Segrč, an Italian émigré, on the payroll. And without protesting against secrecy, Lawrence said what he wanted to say where it seemed useful.

"We had more trouble with Ernest Lawrence about personnel than any four other people put together."

Testimony of the chief security officer of the Manhattan Project.

The pace and stress of the work taxed even Lawrence's abundant reservoirs of energy and enthusiasm, and plagued him with frequent respiratory infections. The increasing integration of science with military plans added to his responsibilities. As the atomic bomb project neared completion in the spring of 1945, Lawrence was appointed, along with Oppenheimer, Compton, and Enrico Fermi, to a "Scientific Panel." The panel advised the Secretary of War on postwar atomic energy policy and, more immediately, on the military use of atomic bombs. The war against Germany was ending and, to the surprise of Manhattan Project scientists, the Germans had not even come close to developing nuclear weapons. But the war against Japan ground on horribly. Lawrence suggested demonstrating an atomic bomb in front of Japanese representatives before using one against a city. His colleagues raised objections. The demonstration bomb might be a dud; the Japanese might shoot down the delivery plane, or herd American prisoners into the test area; and a demonstration seemed unlikely to convince the Japanese to surrender. Lawrence conceded, and the Panel unanimously recommended that the bomb be dropped without warning upon a war plant surrounded by workers' homes. (This was before the spectacular Trinity test, and the Panel scarcely grasped how a bomb could level an entire city.) The Panel also recommended that the U.S. notify its allies, including the Soviet Union, before using an atomic bomb.

"In view of the fact that two bombs ended the war, I am inclined to feel [the Committee] made the right decision. Surely many more lives were saved by shortening the war than were sacrificed as a result of the bombs."

Lawrence to Karl Darrow and Lewis Akeley, August 1945

Lawrence witnessed the Trinity test of the first atomic bomb on July 16, 1945. Unlike some, Lawrence felt no remorse or dread after the test, but rather relief that the device worked. He suffered no moral anguish after the bombings of Hiroshima and Nagasaki in August. In his view, although one might regret the necessity of its use, the bomb had helped end the war with its bloodshed and suffering, and might help prevent future wars. But Lawrence did join his colleagues on the Scientific Panel that September when they opposed, on moral grounds, the pursuit of a "Superbomb." The hydrogen or fusion bomb, a thousand times mightier than a fission bomb, seemed more destructive than any reason could justify.

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