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Lawrence and the Development of the Cyclotron
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Radiological Safety Training For Accelerator Facilities - index
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Synchrotrons cont'd


DOE-HDBK-1108-97
Radiological Training for Accelerator Facilities
Student's Guide
Cyclotrons also serve as tools in producing radionuclides and elements previously unknown to
scientists. This is accomplished by irradiating a target of natural materials with protons,
deuterons, (a nucleus of deuterium or "heavy hydrogen" consisting of one proton and one
neutron") or alpha particles from a cyclotron.
The knowledge gained in these early experiments was significant in the development of the early
atomic weapons. Plutonium, element 94, was first obtained by bombarding Uranium-238 with
deuterons in the University of California cyclotron built by Lawrence.
H.
Synchrotrons
By the late 1930s, still higher energies were needed. Physicists were beginning to think of more
advanced machines to achieve these higher energies. The outbreak of World War II shelved
these plans, as scientists became involved in the Manhattan Project, which built the first atomic
bomb. With the return of peace, scientists began to think again of higher energies.
In 1945, V. Veksler in Moscow and E. M. McMillan in Berkeley independently introduced the
principle of the synchrotron, a fixed-radius circular accelerator. The idea was to vary both the
electric field frequency and the magnetic field at the same time. Veksler and McMillan
demonstrated that the orbits could maintain their stability in this process. Since the magnets of
the synchrotron need be placed only at the fixed radius of the particle orbit, the width of the
magnet pole face is much smaller than for magnets of varying radii machines.
The early synchrotrons had four huge C magnet sections with gaps between them for injecting,
accelerating, and targets. As the particle's energy (and hence its speed) increases, the frequency
of the accelerating field is increased and the magnetic field is made stronger. The choice of the
particle to be accelerated (i.e., electron, proton, positron, heavy ion) depends on the purpose,
such as research isotope production, bremsstrhlung production, or fusion.
The limiting factor with the fixed-frequency synchrotron was its inability to compensate for the
slowing down of the revolution frequency of particles once they had been accelerated to near the
speed of light. To overcome this, scientists hit upon the idea of developing a radio-frequency
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