Major Category
Physical/Radiation
Synonyms
Thorium-232; [HSDB]
Description
Gray-white lustrous metal; [Merck Index]
Sources/Uses
Thorium is a fairly abundant naturally-occurring element, about as common as lead and three times as common as uranium. Almost all of naturally-occurring thorium is Th-232. Th-230 and Th-228 are present in trace amounts and have half-lives of 75,400 and 1.9 years, respectively. Thorium is chiefly found in monazite sands. It is also found in the minerals thorite and thorianite. Used to make mantles for gas lanterns; Also used in crucibles, tungsten wire coating for electronic components, camera lenses, welding rods, and light bulb filaments; [Argonne]
Comments
"Thorium-232 and its decay products, administered intravenously as a colloidal dispersion of ThO2, are carcinogenic to humans." [IARC]
Most Important Radionuclide: Thorium-232
Source: Monazite sand
Half-Life: 14 billion years
Effective Half-Life: 200 years
Specific Activity: 0.00000011 Ci/g
Decay Mode: Alpha
GI Absorption: 0.02-0.05%
Lung Clearance Half-Time: Years for oxides and hydroxides; Weeks for all other compounds;
Critical Organ: Bone
Internal Toxicity: Very High
Annual Limit on Intake: 0.000001 mCi
Average Radiation Energy (MeV): Alpha 4.0; Beta 0.012; Gamma 0.0013; [Argonne]
Radiation Accidents (1945-2000): 3 incidents of "Meltings of Radioactive Materials";
[See Glossary for references.] See "Radiation, ionizing."
Restricted
No longer used in diagnostic radiology as a medical contrast agent (Thorotrast);
Explanatory Notes
Water soluble compounds: chloride, fluoride, nitrate, and sulfate salts; Insoluble compounds: dioxide, carbonate, hydroxide, oxalate, and phosphate salts; [ATSDR ToxProfiles]
Processes
Industrial Processes with risk of exposure: