Atomic and Nuclear Physics
INTERACTION OF RADIATION WITH MATTER
Interaction of Radiation with Matter Summary
An alpha particle deposits a large amount of energy in a short distance of travel
due to its large mass and charge.
Beta-minus particles interact with the electrons orbiting the nucleus of atoms,
causing ionization by displacing the electrons. The beta particle loses energy with
each interaction. After the beta particle loses enough energy, it is captured in the
orbital shells of an atom.
Positrons interact with matter much the same way as beta minus particles. After
the positron has lost most of its energy by ionizing atoms, it is annihilated by
interaction with an electron. The electron-positron pair disappear and are replaced
by two gammas, each with the energy equivalent of the mass of an electron (0.51
Neutrons interact with matter by elastic scattering, inelastic scattering, or
Photoelectric effect is where a gamma interacts with an electron orbiting an atom.
The entire energy of the gamma is transferred to the electron, and the electron is
ejected from its orbit.
In Compton scattering a gamma interacts with an orbital electron, but only part of
the gamma energy is transferred to the electron. The electron is ejected from its
orbit, and the gamma is scattered off at a lower energy.
In pair-production, a gamma interacts with the electric field of a nucleus and is
converted into an electron-positron pair. The gamma must have an energy greater
than 1.02 MeV for this to occur.
The important information in this chapter is summarized below.