Alpha Radiation – α
Alpha particles (denoted by the first letter in the Greek alphabet) (α) consist of two protons and two neutrons bound together into a particle identical to a helium nucleus, which is produced in the process of alpha decay. During radioactive decay of an alpha particle, the nucleus loses two protons and two neutrons. For example, an alpha particle is released when radon-222 decays to polonium-218. These particles can be shielded by a sheet of paper or by human skin. However, radionuclides that emit alpha particles can be very harmful if inhaled, ingested, or enter the body through an open wound.
|Alpha Particles…. |
– Large in mass
– Low penetrating power
– Slow moving
– RBE 20 times greater than Beta/Gamma
– Cancer causing RDP
Alpha particles are the heaviest and most highly charged of the nuclear radiations. Without additional energy input, these characteristics make alpha particles less penetrating than beta particles and gamma rays. Alpha particles cannot travel more than four to seven inches (10 to 18 cm) in air and are completely stopped by an ordinary sheet of paper. These particles are more massive than beta or gamma but have a low penetration power due to their relatively slow-moving nature. The effect of Alpha radiation is the most damaging to the bronchial epithelium (lung tissue). Its Relative Biological Effect (RBE) is 20 times greater than Beta or Gamma radiation. In other words, the Alphas emitted from radon atoms are the bad guys that can cause lung cancer!
Beta Radiation – β
Beta particles are high-energy, high-speed electrons emitted by certain types of radioactive nuclei. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay. They are designated by the Greek letter beta (β). There are two forms of beta decay, β− and β+, which respectively give rise to the electron and the positron. A sheet of paper cannot stop this type of radiation. Some beta particles can be stopped by human skin, but some need a thicker shield (like wood) to stop them. Just like alpha particles, beta particles can also cause serious damage to your health if they enter your body. For example, if ingested, some radionuclides that emit beta particles might be absorbed into your bones and cause damage.
|Beta Particles…. |
– Very small
– Relatively fast moving
– Total charge of -1
– More penetrating than alpha particles
– Stopped by a thin sheet of aluminum
– Can cause skin burns.
Beta particles are smaller and travel much faster than alpha particles. They are physically similar to the electrons discussed earlier in this unit, but they are not in orbit around an atom. Since beta particles travel faster and have less charge than alpha particles, they penetrate further into any material or tissue.
Gamma Radiation – γ
Gamma rays are the most penetrating of the three types of radiation listed here. Gamma rays usually accompany beta, and some alpha rays. Gamma rays will penetrate paper, skin, wood, and other substances. To protect yourself from gamma rays, you need a shield at least as thick as a concrete wall. This type of radiation causes severe damage to your internal organs. (X-rays fall into this category, but they are less penetrating than gamma rays.) While gamma radiation, designated by the Greek letter gamma (γ) can penetrate all the way through your body, the amount emitted by radon and its RDPs are not nearly as detrimental to the lungs as alpha particles. Gamma rays are high-frequency electromagnetic radiation similar to medical x-rays. Other types of electromagnetic radiation include television and radio waves, microwaves and visible light. The only differences between gamma rays and these more familiar forms of electromagnetic radiation are that gamma rays are generally higher in energy and that gamma rays originate in the nuclei of atoms.
|Gamma Particles…. |
– Pure energy
– Released from nucleus whenever an alpha or beta is emitted
– High penetrating power
– Move at the speed of light
– Same as X-rays but with much more energy
– Gamma rays have no mass and no charge
Additional types of radiation unrelated to radon and not covered in this context include microwaves, ultraviolet waves, radio waves, and medical x-rays, which are artificially produced rather than coming directly from the atom’s nucleus. (Figure 2-5) shows the penetrating power of these types of radiation. Almost all the health risk of radon comes from inhaling the alpha-emitting decay products.