Absorbed Dose: the amount of energy deposited in a unit of biological tissue. The units of absorbed dose are the rad and gray.

Biological Effective Dose: measured in either rems or sieverts, accounts for the differing effects in tissue of differing types of radiation. It is the absorbed dose multiplied by a Relative Biological Effectiveness (RBE) factor.

Cohort: a group of individuals having a statistical factor ( such as age) in common in a demographic or epidemiological study.

Control Population: a group of people not exposed to the toxic agent under study but otherwise as close in all characteristics to the exposed group as possible.

Dose Limit: regulatory limit set on the amount of radiation that an individual may receive from artificial sources (excluding medical sources). Worker limits are set higher than general population limits.

Dose Reconstruction: estimating exposure by considering emissions, environmental measurements, and routes of exposure.

External Radiation Dose: the dose from sources of radiation outside the body. This is most often from gamma rays, though beta rays can contribute to dose in the skin and other relatively superficial tissues.

Internal Radiation Dose: the dose to the organs of the body from radioactive material that has entered the body through inhalation, ingestion or through cuts and wounds. It may consist of any combination of alpha, beta, and gamma radiation.

Linear Energy Transfer (LET): refers to the rate of energy transfer ( and thus damage) per unit at distance travelled. For example, alpha is high-LET radiation while photons and electrons are low-LET radiation

Lifetime exposure: total amount of exposure to a substance that a person would receive in a lifetime (usually assumed to be 70 years).

Pathway Analysis: an analysis of the ways in which toxic or radioactive substances can reach human beings from the factory, place, or process in which they are made, used, stored or dumped via air, water, soil, the food chain, or some combination of these pathways.

Relative Biological Effectiveness: a factor that measures the relative effectiveness of various kinds of radiation in causing damage. It is complex and organ-specific. Due to its complexity, a simple parameter, called the quality factor, is used in regulatory practice.

Relative Risk: the ratio of disease incidence (or mortality) in an exposed population to that in an unexposed population.

Solubility: the ability to dissolve in water. For instance the less soluble a given amount of material the more difficult it is for the body to remove it. An insoluble material inhaled into the lungs for example would have more time to do damage to the lungs.

Source Term: The amount of a specific pollutant emitted or discharged to a particular medium, such as the air or water, from a particular source.