Why Is Milk White?: & 200 Other Curious Chemistry Questions (2013)
8. Chemistry in the World
What is the difference between radiation and radioactivity?
Radiation is anything that “radiates” away from something. In chemistry and physics, it refers to light, radio waves, X-rays, and gamma rays, as well as to particles such as neutrons, protons, helium nuclei (alpha particles), and electrons (beta particles).
Most forms of radiation humans encounter are harmless or even necessary for life. Without light and heat, there would be no life. We use radio waves for communication, and they pass through us without harm.
In medicine, radiation usually refers to ionizing radiation. This is radiation that has enough energy to strip electrons away from atoms, forming ions. Since electrons are what form the bonds between molecules in our bodies, ionizing radiation can change those bonds in harmful ways, creating burns or damaging DNA, which can cause cancer.
Radioactivity refers to something that happens to atoms that have too many or too few neutrons in them in proportion to the number of protons. These atoms are unstable and decay into more stable atoms by emitting radiation.
You read in the last question how radioactive carbon-14 decayed into nitrogen; it does so by changing a neutron into a proton and an electron (the latter of which speeds away as a beta particle). More famously, uranium goes through a series of radioactive decays into various elements, eventually turning into lead.
Radioactive elements produce many types of radiation as they decay. They can emit electrons, alpha particles, neutrons, neutrinos, and gamma rays (a form of high-energy X-rays). They can also produce larger atomic nuclei that fly away as the atom splits.