Trace radioisotope

From Freepedia

A trace radioisotope is a radioisotope that is naturally occurring. This natural formation can be from the decay of heavier nuclei such as uranium-235 decaying into cesium-135. Natural occurrence of radioisotopes can also be driven by cosmic rays. This is the method that creates hydrogen-3. Isotopes with half-lives greater than about 80 million years also exist in trace amounts. Potassium-40 and vanadium-50 fit into this category.