By
the mid 1930s, the understanding of the fundamental structure
of matter seemed almost complete. Decades before, Rutherford
had shown that atoms have relatively tiny but massive nuclei.
The quantum theory had made sense of atomic spectra and electron
orbitals. The discovery of the neutron
had explained nuclear isotopes. So protons,
neutrons,
and electrons
provided the building blocks of all matter.
Some puzzles remained, however:
What holds the protons and neutrons together to form the nucleus?
What are the forces involved in the radioactive decays of nuclei
that make alpha, beta, and gamma rays?
Enter the Accelerator
To study the nucleus and the interactions of neutrons and protons
that form it, physicists needed a tool that could probe within
the tiny nucleus, as earlier scattering experiments had probed
within the atom. The accelerator
is a tool that allows physicists to resolve very small structures
by producing particles with very high momentum and thus short
wavelength. The wavelength ()
of the associated wave is inversely proportional to the momentum
(p) of the particle (=
h/p), where h = Planck's constant. The greater the momentum,
the shorter the wavelength, and the smaller the particle that
can be studied.
Particle experiments study collisions of high energy particles
produced at accelerators. In modern experiments, large multi-layered
detectors surround the collision point. Each layer of the detector
serves a separate function in tracking and identifying each
of the many particles that may be produced in a single collision.
)
of the associated wave is inversely proportional to the momentum
(p) of the particle (