Key Terms

Radiation includes alpha rays, beta rays, gamma rays, X-rays, neutrons, high-speed electrons, high-speed protons, and other atomic particles. It does not include visible light, sound or radio waves, or infrared or ultraviolet light.

Background radiation is radiation that is always in the environment. Most background radiation occurs naturally, but a small fraction comes from man-made elements.

Radioactive decay is the emission of energy in the form of ionizing radiation. Radioactive decay occurs in unbalanced atoms called radionuclides.

Radioactive material refers to any material that emits, by spontaneous nuclear disintegration, corpuscular or electromagnetic emanations.

A restricted area is any area where access is controlled by the employer to protect individuals from exposure to radiation or radioactive materials.

An unrestricted area is any area where access is NOT controlled by the employer to protect individuals from exposure to radiation or radioactive materials.

Dose is the quantity of ionizing radiation absorbed, per unit of mass, by the body or by any portion of the body. There are two types of radiation dose:

• Absorbed dose is the amount of radiation absorbed by an object or person. The unit of measure for absorbed dose is the rad (U.S. unit) or the gray (Gy, international unit). An absorbed dose of 1 rad means that 1 gram of material absorbed 100 ergs of energy from ionizing radiation.
• Effective dose is the amount of radiation absorbed by a person, adjusted to account for the type of radiation received and the effect on organs. The unit of measure for effective dose is rem (U.S. unit) or sievert (Sv, international unit). The dose equivalent is the same as the absorbed dose for beta and gamma radiation. For alpha and neutron radiation, however, the dose equivalent is larger than the absorbed dose because they are more damaging to the human body. Consequently, the following equation is true:

An Erg is a CGS measurement for a unit of energy equal to 10^-7 Joule.

NOTE: More commonly, dose is measured in smaller units called millirem. A millirem (mrem) is one thousandth of a rem.

Exposure refers to the amount of radiation traveling through the air. The unit of measure for exposure is the roentgen (R, U.S. unit) or the coulomb/kilogram (C/kg, international unit)

A radiation area is any area that is accessible to personnel and in which exists levels of radiation that could cause a major portion of the body to receive a dose of more than 5 millirem in any one hour period, or a dose of more than 100 millirem in any five consecutive days.

A high radiation area is any area that is accessible to personnel and in which exists levels of radiation that can cause a major part of the body to receive a dose of more than 100 millirem in any one hour period.

To learn more about Ionizing Radiation visit our Ionizing Radiation Safety Online Training web page.