Uranium 235 2
Uranium 235 2 : Naturally occurring uranium contains 0.72% of Uranium 235 (235U). It is used to fuel nuclear reactors (3-5 % enrichment typically) or to produce nuclear weapons (90% or more enrichment). 235U is the fissile isotope of uranium. It has a half-life of 703.8 million years. See: Fissile Material