Summary:
- Radioactivity involves the spontaneous emission of material and/or energy from the nucleus of an atom.
- The most common radioactive atoms have high atomic numbers and contain a large excess of neutrons.
- Some typical radioactive elements are technetium (atomic number 43), promethium ( atomic number 61), and all elements atomic number 84 (polonium) and higher.
- Some elements considered to be stable do have radioactive isotopes.
- Carbon-14 is radioactive, but this is only a small fraction of the total amount of carbon in existence.
- Hydrogen also has a radioactive isotope known as hydrogen-3 or tritium.