Types of Ionizing Radiation

Ionizing radiations are of three types:

  • α Alpha particles. They are helium nuclei (consisting of two protons and two neutrons). Alpha particles are the ionizing radiation with the greatest mass, so their ability to penetrate matter is limited, and they cannot pass through a sheet of paper or the skin of our body. Alpha particles are very energetic.
  • β Beta particles. They are electrons or positrons and have a much lower mass than alpha particles, so they have a greater capacity to penetrate matter. A beta particle can pass through a sheet of paper, but it will be stopped by a thin sheet of metal or methacrylate and by clothing. They are less energetic than alpha particles.
  • γ Gamma ray. They are electromagnetic radiation, so they have no mass or charge, which makes them have great penetrating power in matter. To stop them you need a thick layer of lead or a concrete wall. Gamma rays and X-rays have the same properties, differing only in their origin. While gamma rays are produced in the nucleus of the atom, X-rays come from the outer layers of the atom, where the electrons are found.

There is a fourth type of ionizing radiation, neutrons, although it must be known that these are not ionizing by themselves, that is, when they interact with matter they do not remove electrons. However, when they collide with an atomic nucleus they can activate it or cause it to emit a charged particle or a gamma ray, so they are indirectly ionizing. Neutrons are the ionizing radiation with the greatest penetrating capacity, so to stop them you need a thick concrete wall, light and/or heavy water, graphite, beryllium and/or boron-10.

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