radon

American  

[rey-don] / ˈreɪ dɒn /

noun

Chemistry.

1. a chemically inert, radioactive gaseous element produced by the decay of radium: emissions produced by outgassing of rock, brick, etc. are a health hazard. Rn; 86; 222.

---

radon British  

/ ˈreɪdɒn /

noun

1. a colourless radioactive element of the rare gas group, the most stable isotope of which, radon-222, is a decay product of radium. It is used as an alpha particle source in radiotherapy. Symbol: Rn; atomic no: 86; half-life of ²²² Rn: 3.82 days; valency: 0; density: 9.73 kg/m³; melting pt: –71°C; boiling pt: –61.7°C

---

radon Scientific  

/ rā′dŏn /

1. A colorless, odorless, radioactive element in the noble gas group. It is produced by the radioactive decay of radium and occurs in minute amounts in soil, rocks, and the air near the ground. Radon is used as a source of radiation for the treatment of cancer and other diseases. Its most stable isotope is Rn 222 with a half-life of 3.82 days. Atomic number 86; melting point −71°C; boiling point −61.8°C; specific gravity (solid) 4.

2. See Periodic Table

---

radon Cultural  

1. A colorless, odorless, radioactive gas that is produced by the decay of radium in the soil.

---

Discover More

Radon seeping through the ground and into buildings is a major source of indoor air pollution and may represent a significant risk for lung cancer.

Etymology

Origin of radon

First recorded in 1915–20; rad(ium) + -on ²

Example Sentences

See Examples For:

radon

“A lot of people don’t know that radon gas is the second-leading cause of lung cancer in the U.S.,”

From The Wall Street Journal ● Jul. 23, 2026

They should avoid secondhand smoke and have their homes tested for radon gas.

From The Wall Street Journal ● Jul. 23, 2026

It contains radium that decays into radon gas, which is radioactive and can cause cancer.

From Barron's ● Oct. 10, 2025

Peak radon levels detected at HMP Dartmoor in 2020 and 2023 were 10 times the recommended workplace limit, according to the response to a Freedom of Information request submitted by the BBC.

From BBC ● Jul. 17, 2024

But a properly functioning coal-burning plant spreads radioactive lead, uranium, radon, polonium, and thorium every day.

From "Meltdown" by Deirdre Langeland