When radioactive atoms decay, energy and subatomic particles are released. Nuclear radiation consists of high-energy particles or electromagnetic waves emitted from atomic nuclei. Here are the three most common types of nuclear radiation, all of which can be harmful to human beings and other living organisms:
- Alpha radiation consists of alpha particles emitted during alpha decay. Alpha particles can do a lot of damage if they collide with a living cell. Fortunately, alpha particles quickly slow down as they travel through air, and they rarely penetrate the outer layers of human skin. So exposure to small amounts of alpha radiation ordinarily isn’t too harmful, so long as the radiation source is outside the body. If radioactive material gets inside your body (e.g. by breathing in radon gas that leaked from the ground into your basement), that’s another story.
- Beta radiation consists of electrons emitted during beta minus decay. Positrons emitted during beta plus decay are also considered beta radiation, but when positrons strike matter they are converted into gamma radiation, which will be discussed below. Beta particles typically travel much faster than alpha particles, and they can penetrate more deeply into the human body. Exposure to large doses of beta radiation can be fatal, and even small doses can damage DNA molecules in living cells, leading to cancer.
Gamma radiation can also be produced when protons or neutrons shift between different energy states, analogous to the way in which electrons emit electromagnetic radiation when they fall from higher-energy orbitals to lower-energy ones, as discussed in chapter 4
- Gamma radiation consists of gamma rays—electromagnetic waves with extremely high energy. (Recall that gamma rays are at the highest-energy end of the electromagnetic spectrum.) Gamma radiation can be produced during alpha decay and during both forms of beta decay; it is also emitted whenever a positron strikes matter. More powerful than x-rays, gamma rays can pass right through you, causing plenty of damage along the way. Since it travels at the speed of light and isn’t easily blocked or absorbed by matter, gamma radiation is in these respects the most dangerous form of nuclear radiation.
Despite its potential harmful effects, nuclear radiation serves many practical purposes in science, technology, and medicine. We’ve already seen how alpha and beta radiation played important roles in scientific discovery, leading to modern atomic theory. Beta radiation is used in radiation therapy to kill cancer cells. (Of course, it destroys healthy cells too, and it can also cause cancer.) Gamma radiation also has applications in medicine. For example, Positron Emission Tomography (PET) scans use the gamma rays emitted when positrons strike matter to see inside a patient’s body.