Uranium metal has three allotropic forms: The major application of uranium in the military sector is in high-density penetrators.
This ammunition consists of depleted uranium (DU) alloyed with 1–2% other elements, such as titanium or molybdenum.
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.
It is malleable, ductile, slightly paramagnetic, strongly electropositive and a poor electrical conductor.
Uranium in ores is extracted chemically and converted into uranium dioxide or other chemical forms usable in industry.
An ensuing arms race during the Cold War between the United States and the Soviet Union produced tens of thousands of nuclear weapons that used uranium metal and uranium-derived plutonium-239.
The security of those weapons and their fissile material following the breakup of the Soviet Union in 1991 is an ongoing concern for public health and safety.
It occurs naturally in low concentrations of a few parts per million in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite. Many contemporary uses of uranium exploit its unique nuclear properties.
Uranium-238 is fissionable by fast neutrons, and is fertile, meaning it can be transmuted to fissile plutonium-239 in a nuclear reactor.