Uranium-238, the most prevalent
isotope in uranium ore, has a
half-life of about 4.5 billion years; that is, half the atoms in any sample will decay in that amount of time. Uranium-238 decays by alpha emission into thorium-234, which itself decays by beta emission to protactinium-234, which decays by beta emission to uranium-234, and so on. The various decay products, (sometimes referred to as “progeny” or “daughters”) form a series starting at uranium-238. After several more alpha and beta decays, the series ends with the stable
isotope lead-206.
Weapons use “highly enriched uranium” (
HEU) with over 90 percent uranium-235 (which has a half-life of 704 million years).
Uranium: Its Uses and Hazards