Uranium-238

Uranium-238 (U-238) is one of the isotopes of uranium, which is a naturally occurring element found in the Earth's crust. It is the most abundant isotope of uranium, constituting about 99.3% of natural uranium. U-238 is a heavier isotope, with 146 neutrons and 92 protons in its nucleus, giving it an atomic mass of approximately 238 atomic mass units (amu).