Glossary cont'd - hdbk110697

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.