Particle Accelerator
Why build a particle accelerator?
Introduction
Particle accelerators do exactly what the name says; they are machines
which accelerate (thereby increasing the energy) charged particles (usually
electrons or protons, but sometimes heavy ions). Since accelerators are
large and expensive, people must want those high energy particles or they
wouldn't bother. High energy particles, or else the radiation they produce,
are used for many kinds of research, medical applications, and by industry.
There are sources of charged particles in nature, they can be
emitted through the radioactive decay of certain elements. However, these
particles are of low energy, not sufficient for most present day research.
Some of the first important experiments determining the structure
of the atom used the products of radioactive decay. In about 1910, Rutherford
bombarded gold foil with alpha particles (2 protons + 2 neutrons) emitted
from radium via radioactive decay, and discovered that an atom has a well
defined positive central core, the nucleus, surrounded by a lot of empty
space.
There is a source of higher energy charged particles than those emitted from
atoms via radioactive decay. Cosmic rays are particles coming from space,
and hit the Earth from all directions. The typical energy range
for particles from cosmic rays is between 100 MeV and 10 GeV, although much
higher energies have been occasionally observed. However, their exact
arrival times are not predictable, and fewer by far hit an intercepting
area than can be made to do so by an accelerator. Accelerators can make
directed beams, with many more particles per cross-sectional area per time
(this is called particle flux for convenience) than ever come from cosmic
rays.