Thorium-232

Thorium-232 is a naturally occurring radioactive isotope with a half-life of about 14 billion years. Its decay chain passes through radon-220 and ends at stable lead-208.

Thorium-232 decay chain: The sequence of radioactive decays beginning with thorium-232 and ending with stable lead-208. This chain contains radon-220, the defining daughter isotope in this concept’s gloss.
Thorium fuel cycle: A nuclear fuel cycle in which thorium-232 absorbs neutrons and is converted into fissile uranium-233. It describes the principal proposed energy use of thorium-232.
Thorium: A chemical element with atomic number 90 and no stable isotopes. Thorium-232 is thorium’s most abundant naturally occurring isotope.
Naturally occurring radioactive material: Radioactive substances present in the environment without human production. Thorium-232 occurs naturally in rocks, soils, and mineral deposits.
Alpha decay: Radioactive decay in which an atomic nucleus emits a helium-4 nucleus. Thorium-232 begins its decay chain by emitting an alpha particle.
Uranium-233: A fissile uranium isotope formed when thorium-232 captures a neutron and undergoes subsequent beta decays. This is the fissile material bred from thorium-232 in a fuel cycle.
Isotope: One of two or more forms of an element whose atoms have different numbers of neutrons. The number 232 specifies thorium’s total number of protons and neutrons.
Thoron: The common name for radon-220, a short-lived radioactive gas in the thorium decay series. Its rapid decay distinguishes this thorium-series gas from longer-lived radon-222.
Radon-220: A radioactive radon isotope, also called thoron, produced in the thorium-232 decay chain. It is a short-lived daughter product that makes the chain relevant to indoor exposure.
Breeder reactor: A nuclear reactor designed to produce more fissile material than it consumes. Some breeder designs convert thorium-232 into uranium-233 while generating power.

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