Why Do We Collide Particles?
Around 100 years ago, Ernest Rutherford was the first
to recognize that much could be learned from having atomic-scale
particles collide with each other, and studying details
of what happened as a result of the collisions. Since
he did not have particle accelerators, he used atoms of
helium (minus their electrons) to bombard atoms from a
wide variety of materials. The helium atoms are produced
at what were then high energies (a few MeV) in radioactive
decays of heavy elements.
He then observed the directions in which
the helium atoms were deflected by the target atoms, and
found, to his surprise, that a few were deflected through
very large angles. He then came to the unexpected conclusion
that almost all of the atom's mass is concentrated in
a region about 1/100,000 of the atom's radius. This region
is what we now call the atomic nucleus.
