Similar to non-ionizing radiation, ionizing radiation is energy in the form of particles or waves. However, ionizing radiation is so high in energy it can break chemical bonds -- meaning it can charge (or ionize) an atom that interacts with it. At a lower energy, it may strip off a couple of electrons. At a higher energy, it can destroy the nucleus of an atom. This means that when ionizing radiation passes through the tissues of the body, it actually has enough energy to damage DNA. It's why gamma rays, for example, are good at killing cancer cells through radiation treatment.
Ionizing radiation is given off by radioactive material, very high-voltage equipment, nuclear reactions and stars. It's both natural and man-made. A natural source of ionizing radiation is radon, a radioactive material found underground. X-rays are a good example of man-made ionizing radiation.
The three types of ionizing radiation we're going to discuss here are alpha particles, beta particles and rays.
Particulate radiation involves fast-moving, small particles that have energy and mass. When an unstable atom disintegrates, it produces particulate radiation, including alpha and beta particles. For example, when radioactive elements like uranium, radium and polonium decay, they release radioactive alpha particles. These particles, made up of protons and neutrons, are large and can only travel a short distance -- in fact, they can be stopped with just a piece of paper or even your skin. However, inhalation or ingestion of alpha particles can be very dangerous. Once inside your body, alpha particles expose your tissues to radiation.
Beta particles, on the other hand, are fast-moving electrons. They can travel and penetrate more than alpha particles. Beta particles can be stopped or reduced by a layer of clothing or a substance like aluminum (so think twice the next time you laugh at the guy on the corner wearing a protective tinfoil hat!). However, some beta particles have enough energy to penetrate the skin and cause damage like burns. As with alpha particles, beta particles are quite hazardous if inhaled or ingested.
Gamma rays are a type of electromagnetic radiation, but they still emit ionizing radiation because of their high energy. Gamma rays often accompany alpha and beta particles. Unlike alpha and beta particles, they are extremely penetrating. In fact, several inches of lead or even a few feet of concrete are required to stop gamma rays. They are a radiation hazard for the entire body, meaning that although they will pass through you, your tissue will absorb some rays. Gamma rays occur naturally in minerals like potassium-40. Don't stop taking your vitamins just yet, though. The radioactive isotope of potassium occurs at an extremely low concentration, and potassium is necessary for good health [source: HPS].
X-rays are essentially the same as gamma rays, but their origin is different. Where gamma rays come from inside the nucleus of an atom, X-rays come from processes outside the nucleus. X-rays come from a change in the electron structure of an atom and are mostly machine-produced. They aren't quite as penetrating as gamma rays, and just a few millimeters of lead can stop them. That's why you wear a "lead apron" when receiving medical X-rays.
Overexposure to ionizing radiation can cause mutations in your genes, which causes birth defects, a raised risk of cancer, burns or radiation sickness [source: NLM].
Is this information freaking you out? Then let's get to radiation exposure on the next page.