U (nat) + Ra-226

Natural uranium is a naturally occurring mixture of uranium isotopes found in the Earth's crust. It primarily consists of uranium-238 (U-238, ~99.3%), uranium-235 (U-235, ~0.7%), and a trace amount of uranium-234 (U-234, ~0.005%). U-238 is the most stable with a half-life of approximately 4.5 billion years, while U-235 is notable for being fissile, meaning it can sustain a nuclear chain reaction. Natural uranium emits alpha particles and contributes to background radiation through its decay chain products, such as radon gas.

In addition to alpha emissions, natural uranium and its decay products emit gamma radiation. Gamma rays are primarily associated with the decay of daughter isotopes in the uranium-238 and uranium-235 decay chains, such as radium-226, lead-214, and bismuth-214. These gamma emissions make natural uranium detectable using gamma spectrometry, which is widely used in environmental monitoring, mining, and radiological safety assessments.

Natural uranium is mainly used as fuel in nuclear reactors, especially in heavy water reactors (e.g., CANDU reactors) that can operate using unenriched uranium. It is also a starting material for enrichment processes to produce uranium-235 for light water reactors and nuclear weapons. Additionally, natural uranium has applications in radiometric dating for geological studies and in research to study nuclear properties and processes.

Natural uranium is found in various minerals, such as uraninite (pitchblende), carnotite, and coffinite. Major deposits are located in countries like Kazakhstan, Canada, Australia, and Namibia. Trace amounts are present in soil, rocks, and water worldwide, making it a common but regulated material due to its radioactive properties and gamma emissions.

In natural uranium, the decay product Radium-226 is always present. However, it is absent in depleted uranium or purified uranium. Radium-226-free uranium was used in uranium glass and various ceramic dyes.