Radiation Protection

Radionuclide Basics: Thorium

ThoriumThorium (chemical symbol Th) is a naturally occurring radioactive metal found at trace levels in soil, rocks, water, plants and animals. Thorium is solid under normal conditions. There are natural and man-made forms of thorium, all of which are radioactive. In general, naturally occurring thorium exists as Th-232, Th-230 or Th-228.

Type of Radiation Emitted: Half-lifeHelpHalf-lifeThe time required for half of the radioactive atoms present to decay or transform. Some radionuclides have half-lives of mere seconds, but others have half-lives of hundreds or millions of years.
Alpha Gamma Half-Life
Alpha ParticlesHelpAlpha ParticleA form of particulate ionizing radiation made up of two neutrons and two protons. Alpha particles pose no direct or external radiation threat; however, they can pose a serious health threat if ingested or inhaled. weak Gamma RaysHelpGamma RaysA form of ionizing radiation that is made up of weightless packets of energy called photons. Gamma rays can pass completely through the human body; as they pass through, they can cause damage to tissue and DNA. Thorium-232: 14 billion years
Thorium-230: 77,000 years
Thorium-228: 1.9 years

Natural thorium is present in trace quantities in virtually all rock, soil, water, plants and animals. Where higher concentrations occur in rock or sands, thorium may be mined and refined, producing waste products such as mill tailings. If not properly controlled, wind and water can introduce the tailings into the wider environment. Commercial and federal facilities that have processed thorium may also have released thorium to the air, water or soil. Man-made thorium isotopesHelpisotopeA form of an element that has the same number of protons but a different number of neutrons in the nucleus, giving it a different atomic mass. For example, uranium has thirty-seven different isotopes, including uranium-235 and uranium-238. are rare, and almost never enter the environment.

Thorium is used to make ceramics, welding rods, camera and telescope lenses, fire brick, heat resistant paint and metals used in the aerospace industry, as well as in nuclear reactions. Thorium has the potential be be used as a fuel for generating nuclear energy.

Since thorium is naturally present in the environment, people are exposed to tiny amounts in air, food and water. The amounts are usually very small and pose little health hazard.

Most people are not exposed to dangerous levels of thorium. However, people who live near thorium mining areas or near certain legacy industrial facilities may have increased exposure to thorium.

Occasionally, household items may be found with thorium in them, such as some older ceramic wares in which uranium and thorium were used in the glaze. These generally do not pose serious health risks, but may nevertheless be retired from use as a prudent avoidance measure.

If inhaled as dust, some thorium may remain in the lungs for long periods of time, depending on the chemical form. If ingested, thorium typically leaves the body through feces and urine within several days. The small amount of thorium left in the body will enter the bloodstream and be deposited in the bones where it may remain for many years.

Inhaling thorium dust may cause an increased risk of developing lung or bone cancer.