Glossary cont'd - doe-hdbk-1106-97

DOE-HDBK-1106-97

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 x 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.)