thorium-229

Thorium-229 is a synthetic isotope of thorium, a radioactive chemical element in the actinoid series. Thorium itself is a naturally occurring, silvery-white metal that turns gray or black when exposed to air. It is more abundant in Earth's crust than uranium and is found in minerals like monazite.1

Thorium-229 is formed in the decay chain originating from neptunium. While natural thorium is predominantly thorium-232, with a very long half-life, synthetic isotopes like thorium-229 also exist. Thorium-229 has a half-life of 7,880 years and serves as a tracer for the more common thorium-232. Thorium isotopes, such as thorium-230, are also used in dating methods for marine sediments. Thorium-232 can be converted into the fissionable isotope uranium-233 in breeder reactors, highlighting thorium's potential for nuclear energy production.123