These objectives are met by sampling various environmental pathways for human exposure and directly measuring radiation levels near the plants and at other locations around the state. Natural radioactivity originates from radioactive elements in the earth's crust as well as extraterrestrial sources, such as cosmic rays. The normal level of natural radiation in Minnesotan ranges from 200 to 400 millirem each year. Most of our natural exposure is due to radon, a gas which emanates from the earth's crust and is present in the air we breathe. Monitoring occurs statewide, where selected locations have milk, air and food samples collected regularly.
More extensive monitoring is performed near each of the two nuclear generating plants.
There are four types of radiation being monitored. Alpha radiation is not considered an external hazard, but is an internal hazard, because the dead layer of skin will absorb all alpha particles with no harmful effect. Beta radiation is considered a slight external hazard and is mainly a skin and internal exposure hazard. They are external hazards, which can penetrate materials and travel much farther in matter than alpha and beta particles. They also penetrate material and are external hazards.