Uranium-235

Highly enriched uranium

Diagram of a nuclear fission reaction

Uranium-235 (U

) is an isotope of uranium making up about 0.72% of natural uranium. Unlike the predominant isotope uranium-238, it is fissile, meaning it can sustain a nuclear chain reaction.

Properties

Uranium-235 has a half-life of approximately 703.8 million years. It decays into thorium-231 through alpha decay. The isotope is notable for its ability to undergo nuclear fission when it absorbs a neutron.

Nuclear Fission

When uranium-235 absorbs a neutron, it can undergo fission, splitting into two smaller nuclei, along with a few neutrons and a large amount of energy. This process is the basis for both nuclear power and nuclear weapons. The fission of uranium-235 releases about 200 MeV of energy per atom, which is harnessed in nuclear reactors to produce electricity.

Enrichment

Natural uranium contains only about 0.72% uranium-235, with the rest being mostly uranium-238. For many applications, such as in nuclear reactors and weapons, uranium must be enriched to increase the concentration of uranium-235. Enriched uranium contains a higher percentage of uranium-235, while depleted uranium has a lower percentage.

Applications

Uranium-235 is used as a fuel in nuclear reactors and as a material in nuclear weapons. In reactors, it is used to sustain a controlled chain reaction, providing a steady source of energy. In weapons, it is used to create an uncontrolled chain reaction, resulting in a powerful explosion.

History

The discovery of uranium-235's fissile properties was a key development in the Manhattan Project, which led to the creation of the first nuclear weapons during World War II. The first atomic bomb used in warfare, dropped on Hiroshima, was a uranium-based bomb known as "Little Boy."

Related pages

• Uranium-238
• Nuclear reactor
• Nuclear weapon
• Nuclear power