U-235 (Uranium-235)

Uranium-235 (U-235) is a naturally occurring isotope of uranium, a heavy metal found in Earth's crust. It is unique because it can sustain a nuclear chain reaction, making it essential for nuclear power and weapons. When U-235 atoms absorb a neutron, they split through a process called fission, releasing a large amount of energy, additional neutrons, and fission products. This chain reaction can be controlled for electricity generation or uncontrolled for atomic weaponry. U-235 constitutes about 0.7% of natural uranium and typically needs to be enriched to higher concentrations for most nuclear applications.