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

DOE-HDBK-1106-97

GLOSSARY (Continued)

Effective Half-Life: See Half-Life, Effective.

External Radiation: Exposure to ionizing radiation when the radiation source is located outside

the body.

Flash Point: The minimum temperature at which a substance gives off flammable vapor that will

ignite if in contact with spark or flame.

Fume Hood: Ventilated containment space, enclosed on five sides, with the sixth side covered by

a movable glass or plastic window to allow access and to maintain sufficient inflow or air and

splash control to protect the worker from the hazardous materials handled inside.

Gamma Ray: Very penetrating electromagnetic radiation of nuclear origin. Except for its origin, it

is identical to an X-ray.

Geiger-Mueller Counter: A radiation detection and measuring instrument. It consists of a gas

filled tube containing electrodes, between which there is an electrical voltage but no current

flowing. When ionizing radiation passes through the tube, a short, intense pulse of current passes

from the negative electrode to the positive electrode and is measured or counted. The number of

pulses per second measures the intensity of radiation. It is sometimes called simply a Geiger

counter, or a G-M counter.

Gray (Gy): The SI unit for absorbed dose. One gray is equivalent to one Joule per kilogram or

100 rad.

Half-Life Biological (Tbio): The time required for the body to eliminate one-half of an

administered dose of any substance by regular processes of elimination. This time is usually the

same for both stable and radioactive isotopes of a particular element. The biological half-life of

tritium is 10 days, whereas the physical half-life is 12.3 years.