Table 2 - Some Common Radioactive Isotopes
3H = Tritium = Luminous watch dials
14C = Carbon 14 = Radioactive dating
60Co = Cobalt 60 = Food irradiation
40K = Potassium 40 = Biological tracer
99Tc = Technetium 99 = Medical diagnosis
131I = Iodine 131 = Thyroid-function diagnosis and treatment
238Pu = Plutonium 238 = Spacecraft power supplies, pacemakers
241Am = Americium 241 = Smoke alarms
All of the elements heavier than lead in the periodic table have multiple isotopes, and all are naturally radioactive; most of them decay into one of the stable lead isotopes. Uranium and thorium have the greatest number of isotopes - uranium with 22 isotopes and thorium with 28 - though most of these are not naturally occurring. As a rule of thumb, elements are happiest when they have about the same number of protons and neutrons. When there is a sizable difference, they tend to decay until there isn't.
So, what about this radioactive business? How does it work? How dangerous is it? And for how long?
A very interesting subject: Don't miss the next chapter.