An example of nuclides made by nuclear reactions, are cosmogenic C (radiocarbon) that is made by cosmic ray bombardment of other elements, and nucleogenic Pu which is still being created by neutron bombardment of natural U as a result of natural fission in uranium ores. Cosmogenic nuclides may be either stable or radioactive. If they are stable, their existence must be deduced against a background of stable nuclides, since every known stable nuclide is present on Earth primordially.