What Is Radon Decay?

Radon occurs in nature and is produced by the decay of uranium. Atoms of radon also decay by releasing atomic particles. The element itself and some of the elements into which it decays are radioactive and can cause disease in humans.

All elements contain protons and neutrons in their nucleus — except hydrogen, which has only a proton. Along with the nucleic particles, an element also has electron particles orbiting the nucleus. Elements are classified by the amount of protons they contain. This number is an element's atomic number. For example, radon always has 86 protons.

Some elements can vary in the numbers of neutrons in their nucleus. These are known as isotopes of an element, and each isotope is known by its mass number, which is the amount of protons added to the amount of neutrons. For example, the most common radon isotope, radon-222, has 86 protons and 136 neutrons in its nucleus. A less common isotope is radon-220.

Elements decay in two ways. They can release two protons and two neutrons, which changes both the atomic number and the mass number. This is known as alpha decay, and the particles released as a bundle are called alpha particles.

Beta decay is when a neutron releases an electron and turns into a proton. The released electron is known as a beta particle. This changes the atomic number because a new proton is present in the element. The mass number does not change.

Radon itself is a decay product of uranium-238. Radon decay happens through a chain of events, with one element turning into another element. Radioactive elements do not all decay at once, so scientists use a half-life measurement to track the concentrations of each element. A half-life is the length of time that half of a quantity of an element takes to change into another element.

As an example, radon-222 has a half-life of 3.8 days. After 3.8 days, half of the radon in an area will have released one alpha particle and will have turned into polonium-238. Polonium-238 has a half-life of just three minutes before it releases an alpha particle and turns into lead-214.

Lead-214, with a 27-minute half-life, turns into bismuth-214 by releasing a beta particle. After 20 minutes, half of the bismuth-214 will have turned into polonium-214 by releasing another beta particle. The polonium, with a mere 180 second half-life, then decays into lead-210 by releasing an alpha particle. The elements in the chain from radon-222 to lead-210 are short-lived and are dangerous because a lot of radioactive particles are released in a short period of time.

Radon decay continues slowly, with lead turning into bismuth-210 over a period of decades. The bismuth then takes a few days to decay into polonium 210. Beta particles are released during these steps in the chain. Finally, the polonium lets an alpha particle go, and the chain ends in a stable, non-radioactive lead-206 isotope.

The reason why radon decay is dangerous to humans is because the particles that are freed from the radioactive elements in the chain can cause cancer if they are ingested or breathed in. Radon is present as a gas in many houses, especially in basements, and it collects where there is no ventilation. Miners also can be exposed to high levels of the gas. Radon itself comes from uranium-238 decaying in the soil. The radon decay chain is therefore only one part of a larger decay chain.