Fermi, and Lawrence.
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.
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
to John Cockcroft; February 9, 1939
Edwin M. McMillan,
cyclotroneer, recreating the discovery of transuranics at the University
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.
to right: Ernest Orlando Lawrence, Arthur Holly Compton, Vannevar
Bush, J. Bryant Conant, Karl Taylor Compton, and Alfred Lee Loomis.
"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.'"
Compton on Lawrence's commitment to a bomb project.
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.
committee of scientists that oversaw uranium production for the war
effort. From left to right are Harold C. Urey, Ernest O. Lawrence,
James B. Conant, Lyman J. Briggs, E.V. Murphree and A.H. Compton.
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.
Early view of the
Oak Ridge facility.
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.
Women employees at Oak Ridge.
challenged at a checkpoint.
second route to a bomb was based on the element with atomic
number 94 discovered in Berkeleyplutonium.
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.
a heavy toll on Lawrence's health.
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
"We had more
trouble with Ernest Lawrence about personnel than any four other people
of the chief security officer of the Manhattan Project.
exhorting Rad Lab staff.
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
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."
to Karl Darrow and Lewis Akeley, August 1945
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
American Institute of Physics