U238

Uranium-238 (U-238) is a radioactive isotope of the element uranium. It has atomic number 92 and mass number 238. In nature it is the most abundant uranium isotope, accounting for about 99.3% of natural uranium. It occurs together with smaller amounts of U-235 and trace U-236 in uranium ore.

U-238 decays by alpha emission with a half-life of 4.468 billion years, producing thorium-234, which subsequently decays by beta emission through a long decay series to stable lead-206. The long half-life means that U-238 is a persistent source of radioactivity in minerals and rocks.

Although not fissile, U-238 is fertile: it readily captures neutrons to form uranium-239, which beta decays to neptunium-239 and then to plutonium-239. Pu-239 is fissile and can sustain a nuclear chain reaction, making U-238 an important component of reactor fuel cycles and of plutonium production for weapons in certain contexts. In civilian power generation, many reactors use U-238 as the principal source of fuel via neutron capture and breeding of plutonium-239 or other actinides.

Industrial uses of U-238 include depleted uranium, which due to its high density is used for shielding, ballast, and armor-penetrating projectiles; its chemical toxicity and radiological hazards require careful handling and regulatory controls.

U-238's long half-life and prevalence also make it useful in radiometric dating, particularly for determining ages of geological materials by the uranium-lead dating technique. Safety considerations center on its alpha radiation, chemical toxicity, and potential radiological exposure through inhalation or ingestion.