Biomedical Engineering Reference
In-Depth Information
Figures 1.3 through 1.5 show how the complexity and size of particle accelerators
have grown. Lawrence's first cyclotron (1930) measured just 4 in. in diameter. With
it he produced an 80-keV beam of protons. The Fermi National Accelerator Labora-
tory (Fermilab) is large enough to accommodate a herd of buffalo and other wildlife
on its grounds. The LEP (large electron-positron) storage ring at the European Or-
ganization for Nuclear Research (CERN) on the border between Switzerland and
France, near Geneva, has a diameter of 8.6 km. The ring allowed electrons and
positrons, circulating in opposite directions, to collide at very high energies for the
study of elementary particles and forces in nature. The large size of the ring was
needed to reduce the energy emitted as synchrotron radiation by the charged par-
ticles as they followed the circular trajectory. The energy loss per turn was made
up by an accelerator system in the ring structure. The LEP was recently retired,
and the tunnel is being used for the construction of the Large Hadron Collider
(LHC), scheduled for completion in 2007. The LHC will collide head-on two beams
of 7-TeV protons or other heavy ions.
In Lawrence's day experimental equipment was usually put together by the in-
dividual researcher, possibly with the help of one or two associates. The huge ma-
chines of today require hundreds of technically trained persons to operate. Ear-
lier radiation-protection practices were much less formalized than today, with little
public involvement.
Fig. 1.3
E. O. Lawrence with his first cyclotron. (Photo by
Watson Davis, Science Service; figure courtesy of American
Institute of Physics Niels Bohr Library. Reprinted with
permission from
Physics Today
, November 1981, p. 15.
Copyright 1981 by the American Institute of Physics.)
