The four types of radiation discussed in this chapter are alpha, beta, gamma, and
DESCRIBE the following types of radiation to include
the definition and interactions with matter.
The alpha particle is a helium nucleus produced from the radioactive decay of heavy metals and
some nuclear reactions.
Alpha decay often occurs among nuclei that have a favorable
neutron/proton ratio, but contain too many nucleons for stability. The alpha particle is a massive
particle consisting of an assembly of two protons and two neutrons and a resultant charge of +2.
Alpha particles are the least penetrating radiation. The major energy loss for alpha particles is
due to electrical excitation and ionization. As an alpha particle passes through air or soft tissue,
it loses, on the average, 35 eV per ion pair created. Due to its highly charged state, large mass,
and low velocity, the specific ionization of an alpha particle is very high.
Figure 1 illustrates the specific ionization of an alpha particle, on the order of tens of thousands
of ion pairs per centimeter in air. An alpha particle travels a relatively straight path over a short