Radiation and radioactive materials are a natural part of our environment. Each of us is exposed to radiation from sources that exist in nature. Small traces of radiation are even present in food and water. Radiation from nuclear power plants is made by particles or rays, which come from the centers of atoms. Alpha particles travel about an inch and can be stopped by a sheet of paper.
Beta particles travel a few feet and can be stopped by an inch of wood or heavy clothing.
Gamma rays travel farther and can be stopped by lead or concrete. The length of time of the exposure. How much of the body is exposed. How much radioactive material stays in the body. The general health and age of the exposed person.