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When refined, uranium is a silvery white, weakly radioactive metal.It has a Mohs hardness of 6, sufficient to scratch glass and approximately equal to that of titanium, rhodium, manganese and niobium.Uranium is a chemical element with symbol U and atomic number 92.It is a silvery-white metal in the actinide series of the periodic table.Research by Otto Hahn, Lise Meitner, Enrico Fermi and others, such as J.Robert Oppenheimer starting in 1934 led to its use as a fuel in the nuclear power industry and in Little Boy, the first nuclear weapon used in war.Uranium-238 is fissionable by fast neutrons, and is fertile, meaning it can be transmuted to fissile plutonium-239 in a nuclear reactor.

Depleted uranium ( Uranium is used as a colorant in uranium glass, producing lemon yellow to green colors.As little as 15 lb (7 kg) of uranium-235 can be used to make an atomic bomb.The first nuclear bomb used in war, Little Boy, relied on uranium fission, but the very first nuclear explosive (the Gadget used at Trinity) and the bomb that destroyed Nagasaki (Fat Man) were both plutonium bombs.Uranium-235 was the first isotope that was found to be fissile.

Other naturally occurring isotopes are fissionable, but not fissile.

A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons.