There are essentially three sources of radioactive elements.Primordial nuclides are radioactive elements whose half-lives are comparable to the age of our solar system and were present at the formation of Earth.
Natural uranium consists of three isotopes: uranium-238, uranium-235, and uranium-234. The nuclei of radioactive elements are unstable, meaning they are transformed into other elements, typically by emitting particles (and sometimes by absorbing particles).
The alkali metals are the elements that make up Group 1 (IA) of the periodic table.
The periodic table is a chart that shows how chemical elements are related to one another.
This process, known as radioactive decay, generally results in the emission of alpha or beta particles from the nucleus.
It is often also accompanied by emission of gamma radiation, which is electromagnetic radiation, like X-rays.
For carbon, there are a lot of C-12, a couple of C-13, and a few C-14 atoms.