Protactinium

Protactinium is a rare, radioactive actinide metal with a silvery-gray appearance. In nature, it forms as uranium decays: nearly all natural protactinium is the isotope protactinium-231, found in tiny amounts in uranium ore and even smaller traces in ordinary soil and water. For scientific research, it is generally recovered from spent nuclear fuel; producing a useful amount requires processing large quantities of material. Protactinium has no uses outside research today. Scientists use measurements of protactinium and thorium isotopes in ocean sediments to help date them and reconstruct past ocean conditions. In thorium-based reactors, protactinium is also an intermediate in the pathway toward uranium-233, so it may be removed during fuel production.