Radioactive materials are composed of
atoms that are unstable. An unstable atom gives off excess
energy until it becomes stable. The energy the atom emits
is radiation. The
process by which an atom changes from an unstable state to a
more stable state by emitting radiation is called radioactivity.
Radiation can be classified as either
non-ionizing (low energy) or ionizing (high energy) radiation.
Types of non-ionizing radiation
are ultraviolet light, visible light, infrared radiation, radio
frequency radiation and microwaves. Ionizing
radiation is given off by the sun (cosmic rays),
radioactive materials, and high energy electronic devices (X-ray
There four major types of ionizing
Particles are positively charged particles made up of
two neutrons and two protons. They are relatively heavy
and slower moving than other radioactive emissions. Alpha
particles can be stopped by a piece of paper or the dead
outer layer of our skin.
Particles are negatively charged particles made up of
an electron. A beta particle is lighter and faster than an
alpha particle and can be stopped by a thin piece of aluminium or
a short span of air.
Rays are short wavelength electromagnetic radiation
emitted in the radioactive decay of an unstable
atom. Gamma radiation is highly penetrating and is
stopped by lead.
are similar to gamma rays, but are generally lower in energy and
less penetrating. X-rays are emitted from processes
outside the nucleus, while gamma rays originate inside the
nucleus. A few milimeters of lead can stop