Natural vs. Man-made Radiation

Humans are primarily exposed to natural radiation from the sun, cosmic rays, and naturally occurring radioactive elements found in Earth's crust. Cosmic rays from space include the following:

• Energetic protons
• Electrons
• Gamma rays
• X-rays

The primary radioactive elements found in Earth's crust are uranium, thorium, and potassium, and their radioactive decay products. These elements emit alpha particles, beta particles, and gamma rays. The decay of naturally occurring radium produces radon gas, which emanates from the ground.

Man-made radiation is produced by devices, such as X-ray machines, and artificially produced radioisotopes made in a reactor or accelerator. This type of radiation is used in both medicine and industry. Main users of man-made radiation include the following:

• Medical facilities (for example, hospitals and pharmaceutical facilities)
• Research and teaching institutions
• Nuclear reactors and their supporting facilities (for example, uranium mills and fuel preparation plants)
• Federal facilities involved in nuclear weapons production

Many of these facilities generate some radioactive waste, and some release a limited amount of radiation into the environment. Radioactive materials are also used in consumer products, such as smoke detectors and self-illuminating exit signs.

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