Glossary cont'd - hdbk110697

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.