francium, an alkali metal
No. It is not radioactive.
Polonium is a very rare chemical element. It has the atomic number 84. It is produced when uranium decays and is a naturally radioactive metallic element.
Tin is a naturally occurring metallic element. It is only created in supernova explosions. Radioactive tin can be created in nuclear reactors.
Uranium and Plutonium
It is radon that we see formed from the decay of naturally radioactive substances in the earth's crust.
First made in 1950 at the University of California. It is a radioactive metallic chemical element
Radium and polonium
Uranium is a natural chemical element, radioactive, dense, atomic number 92.Uranium is a solid metal.
It is radioactive decay.
Platinum is a metallic, solid, radioactive chemical element; now it is considered a natural element. Plutonium is a member of the actinides group.
Whether an ISOTOPE (not element) is naturally radioactive depends not only on the number of protons, but also on the number of neutrons. For EVERY element, there are radioactive isotopes.There has to be a certain relationship between the number of protons and the number of neutrons, but the relationship isn't a simple one.
Carbon - 14 is the naturally produced right from Nitrogen being bombarded by cosmic rays in the upper atomosphere. Same way Uranium 235, polonium, radium etc are also available naturally. Several dozen radioactive elents at the Link.