Radiation Terms

absorbed dose: Absorbed dose is used for purposes of radiation protection and assessing dose or risk to humans in general terms. Absorbed dose is the amount of radiation absorbed in an organ or tissue (i.e., the amount of radiation energy that has been left in cells, tissues, or organs). Absorbed dose is usually defined as energy deposited (joule) per unit of mass (kilogram). See gray and rad.

Becquerel (Bq) is the unit in the International System of Units to replace the curie. It is based upon the radioactive decay rate of the radionuclide. One Bq is equal to one disintegration per second (dps). The most common activity level used in laboratories is the megabecquerel (MBq). A megabecquerel is one million becquerel and is equal to 22 microcuries (┬ÁCi). Thirty seven (37) gigabecquerel (GBq) is equal to one curie.

curie: Curie (Ci) is the traditional unit used to describe the amount of radioactive material present or strength of the source. See becquerel.

dose: Dose is a general term used to express how much radiation energy is deposited in something (a person or other material). The energy deposited can subsequently be expressed in terms of the absorbed, equivalent, committed, and/or effective dose based on the amount of energy absorbed and in what tissues.

effective dose: Radiation exposures to the human body, whether from external or internal sources, can involve all or a portion of the body. The health effects of one unit of dose to the entire body are more harmful than the same dose to only a portion of the body. To enable radiation protection specialists to express partial-body exposures (and the accompanying doses) to portions of the body in terms of an equal dose to the whole body, the concept of effective dose was developed. Effective dose, then, is the dose to the whole body that would carry with it the same risk as a higher dose to only a portion of the body. As an example, 80 millisievert to the lungs is roughly the same potential detriment as 10 millisievert to the whole body based on this idea.

equivalent dose: Equivalent dose is a dose quantity used for radiation protection purposes that takes into account the chance that a type of radiation will cause an effect. Different types of radiation (alpha, beta, gamma) interact with human tissues differently, with some leaving a lot of energy in the tissue and others leaving very little energy in the tissue, and the energy that is left is what partially determines whether an effect will occur. Because of this, different types of radiation are assigned numbers based on how effective that type of radiation is at leaving its energy in the tissue, thus having more potential to cause an effect. By using equivalent dose we are provided an indication of the potential for biological effects. From this, risk comparisons can be made between different types of radiation.

exposure: Exposure is commonly used in reference to being around a radiation source, e.g., if you have a chest x ray, you are exposed to radiation. By definition, exposure is a measure of the amount of ionizations produced in air by photon radiation.

gray: Gray (Gy) is the unit in the International System of Units used to describe absorbed radiation dose. It describes a specific amount of energy absorbed in a medium (human tissue, for example). In the traditional units, the rad describes absorbed radiation dose. One gray is equal to 100 rad.

observable health effect: An observable health effect is a change in physical health that can be detected medically. Observable health effects may include changes in blood cell counts, skin reddening, cataracts, etc.

rad: Rad is the traditional unit used to describe the absorbed dose. See gray.

radiation weighting factor: Radiation weighting factors are dimensionless factors developed for radiation protection to assess health risks from radiation doses, taking into account the biological effectiveness of different types of radiation.

rem: Rem is the traditional unit used to describe equivalent or effective radiation dose. See sievert.

roentgen (R):
Roentgen (R) is used to describe radiation exposure. This term describes the amount of ionization in air. In the International System of Units, the coulomb per kilogram (C kg-1) describes radiation exposure. One roentgen is equal to 2.58 x 10-4 C kg-1.

sievert: Sievert (Sv) is the unit in the International System of Units to describe equivalent or effective radiation dose. One sievert is equal to 100 rem. It is a unit that is the product of energy absorbed in human tissues and the quality of the radiation being absorbed (the ability of the radiation to cause damage).

tissue weighting factor:
A number assigned to various tissues, taking into account the tissue's sensitivity to radiation, i.e., how likely it is that the tissue will be affected by the radiation dose it receives.