m--the atom radiates
rticles and rays.
Health physicists are concerned with
four emissions from the nucleus of these
atoms. One of these radiations is the alpha
particle which is relatively large and travels
fairly slowly compared to other atomic
particles. Alpha particles are composed of
two protons and two neutrons. They travel
bout one to three inches in the air and are
easily stopped by a sheet of paper.
Another radiation is the beta particle,
basically a very light electron that moves at
less than the speed of light. These particles
are more energetic than alpha particles, but
can be stopped
by a thin sheet of metal or
The third form of nuclear radiation is
the gamma ray. This is a type of electromagnetic
radiation like visible li
- ght, radio waves
and X-rays. They travel at the speed of light.
It takes at least an inch of lead or eight
inches of concrete to stop them.
Finally, neutrons are also emitted by
some radioactive substances. Neutrons are
very penetrating but are not as common in
nature. Neutrons have the capability of
striking the nucleus of another atom and
changing a stable atom into an unstable, and
therefore, radioactive one. Neutrons emitted
in nuclear reactors are contained in the
reactor vessel or shielding and
- cause the
vessel walls to become radioactive.
Radioactive elements emit these radiations
until they have reached a stable state.
For some man-made radioactive materials
this occurs in a few seconds. For
elements a small amount can emit radiation
for thousands of years. As they break down
they turn into other elements.
At ground zero, the elements emitting
gamma rays and alpha and beta particles are
Europium, Cesium, Cobalt, Stron