TM-91N
EN-13
8. INTERACTION OF RADIATION WITH
MATTER
The particles and photons that result from
nuclear decay carry most of the energy
released from the original unstable nucleus.
The value of this energy is expressed in
electron Volts, or eV. The energy of beta and
alpha rays is invested in the particles speed. A
typical beta particle from Cesium-137 has an
energy of about 500,000 eV, and a speed that
approaches that of light. Beta energies can
cover a wide range, and many radioisotopes
are known to emit betas at energies in excess
of 10 million eV. The penetration range of
typical beta particles is only a few millimetres in
human skin.
Alpha particles have even shorter penetration
ranges than beta particles. Typical alpha
energies are on the order of 5 million eV, with
ranges so short that they are extremely difficult
to measure. Alphas are stopped by a ~nin sheet
of paper, and in air only travel a few inches at
most before coming to a stop. Therefore, alpha
particles cannot be detected without being in
close contact with the source, and even then
only the alphas coming from the surface of the
source can be detected. Alphas generated
within the source are absorbed before reaching
