Alpha Particles
Certain radioactive materials of high atomic mass
(such as Ra-226, U-238, Pu-239), decay by the
emission of alpha particles. These alpha particles are
tightly bound units of two neutrons and two protons
each (He-4 nucleus) and have a positive charge.
Emission of an alpha particle from the nucleus results
in a decrease of two units of atomic number (Z) and
four units of mass number (A). Alpha particles are
emitted with discrete energies characteristic of the
particular transformation from which they originate.
All alpha particles from a particular radionuclide
transformation will have identical energies.