Glossary cont'd - hdbk110697

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GLOSSARY (continued)

Half-Life, Effective (Teff): The time required for the amount of a radioactive nuclide deposited in a living

organism to be diminished 50 percent as a result of the combined action of radioactive decay T and

biological elimination Tbio.

Teff = Tbio @ T / Tbio + T

Half-Life, Physical (T): The time in which half the atoms of a particular radioactive substance

disintegrate to another nuclear form. Measured half-lives vary from millionths of a second to billions of

years.

Half-Value Layer (HVL): Thickness of a specified substance which, when introduced into the path of a

given beam of radiation, reduces the exposure rate by one half.

Health Physicist: A person trained to advise on operating procedures for minimizing radiation exposures,

perform radiation surveys, oversee radiation monitoring, and estimate the degree of radiation hazard.

Health Physics: The science concerned with recognition, evaluation, and control of health hazards from

ionizing radiation.

Health, Radiological: The art and science of protecting human beings from injury by radiation, as well as

promoting better health through beneficial applications of radiation.

High Efficiency Particulate Air (HEPA): An air filter generally rated as being capable of removing at

least 99.97 percent of the particulate material in an air stream.

Indirect Bioassay: The assessment of radioactive material deposited in the body by detection of

radioactivity in material excreted or removed from the body.

Intake: The quantity of material (activity or mass) initially taken into the body. (For example, in the case

of inhalation, the intake includes the quantity of material immediately exhaled.)