m--the atom radiates pa

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 a

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 heavy clothing. 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
• other 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