Uranium-235

<p>Uranium-235 (235U or U-235) is an <a href="/facts/Isotope_of_uranium/zWIQ6MVL">isotope of uranium</a> making up about 0.72% of <a href="/facts/Natural_uranium/lgFulQYb">natural uranium</a>. Unlike the predominant isotope <a href="/facts/Uranium-238/QhcHm6q8">uranium-238</a>, it is <a href="/facts/Fissile/XJR9qoxW">fissile</a>, i.e., it can sustain a <a href="/facts/Nuclear_chain_reaction/3l0lHBM4">nuclear chain reaction</a>. It is the only fissile isotope that exists in nature as a <a href="/facts/Primordial_nuclide/lFAUqHDv">primordial nuclide</a>.
</p><p>Uranium-235 has a <a href="/facts/Half-life/kGVH8BAB">half-life</a> of 703.8 million years.  It was discovered in 1935 by <a href="/facts/Arthur_Jeffrey_Dempster/Ts6YYDM6">Arthur Jeffrey Dempster</a>. Its <a href="/facts/Fission_cross_section/AtghNytD">fission cross section</a> for slow <a href="/facts/Thermal_neutron/UMKR4XgJ">thermal neutrons</a> is about 584.3±1 <a href="/facts/Barn_(unit)/0yCEtKJ9">barns</a>. For <a href="/facts/Fast_neutron/UMKR4XgJ">fast neutrons</a> it is on the order of 1 barn.
Most <a href="/facts/Neutron_absorption/elsFpM12">neutron absorptions</a> induce fission, though a minority (about 15%) result in the formation of <a href="/facts/Uranium-236/1JepNWSb">uranium-236</a>.
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Uranium-235 open-in-new

Uranium-235