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

DOE-HDBK-1106-97

GLOSSARY (continued)

Shielding: Any material or obstruction that absorbs radiation and thus tends to protect personnel

or materials from the effects of ionizing radiation.

SI: The International System of Units ("Le Systeme International d'Unites") as defined by the

General Conference of Weights and Measures in 1960. These units are generally based on the

meter/kilogram/second units, with special quantities for radiation including the becquerel, gray,

and sievert.

Sievert (Sv): The SI unit of dose equivalent. It is equivalent to 100 rem.

Specific Activity: The total activity of a given nuclide per gram of material. Specific activity is a

function of half-life and is therefore also unique to each radionuclide. There are approximately

10,000 curies in a gram of tritium and 1 curie in a gram of radium-226.

Survey Meter: An instrument used to monitor the presence of radioactivity by detecting the

radiation emitted during the radioactive decay.

Tenth Value Layer (TVL): Amount of shielding material required to reduce radiation exposure by

a factor of 10. One TVL is equal to 3.3 HVL.

Tissue Equivalent Material: Material made up of the same elements in the same proportions as

they occur in a particular biological tissue.

Thermoluminescent Dosimeters (TLD): Dosimeters made of certain crystalline materials that are

capable of both storing a fraction of absorbed ionizing radiation and releasing this energy in the

form of visible photons when heated. The amount of light released can be used as a measure of

radiation exposure to these crystals.

Tritium: The hydrogen isotope with one proton and two neutrons in the nucleus. Tritium is

radioactive and has a half-life of 12.3 years.