* Uranium-238 (²³⁸U): This is the most abundant isotope, accounting for approximately 99.27% of natural uranium. It's radioactive and decays very slowly, with a half-life of 4.468 billion years.
* Uranium-235 (²³⁵U): This isotope is much less abundant, making up only about 0.72% of natural uranium. It's also radioactive and fissile, meaning it can sustain a nuclear chain reaction. Its half-life is 703.8 million years.
There are other isotopes of uranium present in natural uranium, but their abundance is very low. These include:
* Uranium-234 (²³⁴U): This isotope is formed from the radioactive decay of uranium-238.
* Uranium-236 (²³⁶U): This isotope is produced in nuclear reactors and is not naturally abundant.
Therefore, the natural form of uranium is not a single isotope, but a mixture of isotopes, predominantly uranium-238 and uranium-235.
