The qualities that make materials radioactive give them the potential to be incredibly useful sources of energy, but that same radioactivity can be a lethal threat to humans and other living things. Radioactive materials are naturally unstable, and they will tend to release energy while decaying into a more stable isotope. The particles released by this process can be useful when harnessed properly.
The instability of radioactive materials makes them a perfect fuel for a nuclear chain reaction. When a neutron strikes one of these unstable atoms, it splits, forming two more stable atoms and expelling spare neutrons and a large amount of energy. If enough unstable atoms are packed together, these spare neutrons may strike other atoms, creating a fission reaction. The amount of energy released by this process is much greater than that released by any other fuel, with a single inch-long pellet of uranium containing the same amount of energy found in 149 gallons of oil.
The particles and energy released during nuclear fission and natural radioactive decay include alpha particles, beta particles and gamma rays. These radioactive byproducts can damage the DNA inside living cells, causing them to malfunction or die. Exposure to intense radiation can be fatal in a matter of hours, and even a minor exposure can greatly increase the chance of developing cancer or genetic disorders later in life.