Uranium-238

Uranium-238 is the most common isotope of uranium found. When hit by a neutron, it decays into thorium-234, with a half-life of 1.41 × 10¹⁷ seconds (4.46 × 10⁹ earth years).

Around 99.284% of naturally occurring uranium is uranium-238, which has a half-life of 4.47 billion years. Depleted uranium consists mainly of the 238 isotope, and enriched uranium consists mainly of the uranium-235 isotope.