Uranium-235

Uranium-235, ²³⁵U

Uranium metal highly enriched in uranium-235
General
Symbol	235U
Names	uranium-235, 235U, U-235
Protons (Z)	92
Neutrons (N)	143
Nuclide data
Natural abundance	0.72%
Half-life (t1/2)	703800000 years
Isotope mass	235.0439299 Da
Spin	7/2−
Excess energy	40914.062±1.970 keV
Binding energy	1783870.285±1.996 keV
Parent isotopes	235Pa 235Np 239Pu
Decay products	231Th
Decay modes
Decay mode	Decay energy (MeV)
Alpha	4.679
Isotopes of uranium Complete table of nuclides

Uranium-235 (²³⁵U or U-235) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, i.e., it can sustain a nuclear chain reaction. It is the only fissile isotope that exists in nature as a primordial nuclide.

Uranium-235 has a half-life of 703.8 million years. It was discovered in 1935 by Arthur Jeffrey Dempster. Its fission cross section for slow thermal neutrons is about 584.3±1 barns.^[1] For fast neutrons it is on the order of 1 barn.^[2] Most neutron absorptions induce fission, though a minority result in the formation of uranium-236.^{[citation needed]}