SOURCES OF IONIZING/NONIONIZING RADIATION
Humans live in a world of radiation--some natural radiation which exists in the
environment and some man-made radiation. This radiation is absorbed by the earth's
inhabitants in varying doses.
a. Natural Background Radiation.
(1) Cosmic rays. These rays are an important source of natural background
radiation. Cosmic rays are particles which enter the earth's atmosphere at such great
speed from outer space that they can penetrate many feet of matter. A single cosmic
ray particle may produce a shower of secondary particles and radiations. Many of these
particles are absorbed in the earth's atmosphere; therefore, the greater the altitude, the
greater the cosmic ray radiation. This means that a person standing in Denver will
receive more cosmic radiation than an individual standing at sea level in Los Angeles.
This also means that people who are in airplanes frequently (pilots, flight attendants,
etc.) are exposed to a great deal of cosmic radiation each year. The aircraft does not
reduce the intensity of the radiation very much. Astronauts who travel through areas of
intense radiation will also be exposed to cosmic radiation.
(2) Terrestrial radiation. Terrestrial means having to do with the earth;
therefore, terrestrial radiation means radiation which comes from the earth. It is
believed that there were radioactive particles in the earth's crust when the earth was
formed. These radioactive particles are a source of radiation for people.
(a) Radiation comes from rocks, soil, and construction materials. At
different geographic locations, there are different levels of radiation in the earth
depending on the mineral composition of the soil and rock. Note the following:
1 Granite rocks have a higher level of radiation than basalt (lava
2 Limestone and sandstone rocks are usually low in radiation.
3 Some shale rocks have a high level of radiation, particularly if
the rocks have potassium salt in the fossil portions.
4 Uranium ore contains radiation in high levels.
(b) Plants may absorb radioactive particles in the soil or those particles
may go from the soil into ground water, enter the food chain, and be eaten by people.
Look at the list of items which come to people from terrestrial or earth radiation:
1 Potassium-40. This is abundant in nature and a large source of
internal radiation in man.