Portrait of Friedrich Ernst Dorn

Adapted from ⁠an image (CC BY-SA 3.0), via Wikimedia Commons. This version is shared under the same licence.

1848–1916

Friedrich Ernst Dorn

Discovered radon in 1900.

Element

86RnRadon
1900

In 1900 Friedrich Ernst Dorn, in Halle, found that radium gives off a radioactive gas, now called radon. Rutherford and the Curies had seen related gases the year before.

Explore radon

Dorn found radon given off by radium. Watch how quickly radon itself decays.

Radioactive decay

Watching atoms decay

Radon is a gas made in rocks and soil wherever uranium decays. Being a gas, it can seep into buildings, where it builds up in poorly ventilated basements.

Half of any sample of Rn-222 decays every 3.82 days, turning into Po-218.

Rn-222 · 100 leftTurned into Po-218 · 0
100%50%25%12.5%0123456

Half-lives passed (1 half-life = 3.82 days)

No time passed · 0 half-lives · 100 of 100 atoms left

Each atom decays at a random moment, so no one can say which will go next, but about half of whatever is left goes in every half-life. The dashed curve is the prediction; the solid line is this sample. The new Po-218 atoms decay too, on their own schedule, which the chain below follows.

From U-238 to stable Pb-206: 14 steps

  1. U-238Uranium4.5 billion yearsαdecays by alpha
  2. Th-234Thorium24 daysβdecays by beta
  3. Pa-234mProtactinium1.2 minutesβdecays by beta
  4. U-234Uranium250,000 yearsαdecays by alpha
  5. Th-230Thorium75,000 yearsαdecays by alpha
  6. Ra-226Radium1,600 yearsαdecays by alpha
  7. Rn-222Radon3.8 daysαdecays by alpha
  8. Po-218Polonium3.1 minutesαdecays by alpha
  9. Pb-214Lead27 minutesβdecays by beta
  10. Bi-214Bismuth20 minutesβdecays by beta
  11. Po-214Polonium160 microsecondsαdecays by alpha
  12. Pb-210Lead22 yearsβdecays by beta
  13. Bi-210Bismuth5 daysβdecays by beta
  14. Po-210Polonium140 daysαdecays by alpha
  15. Pb-206Leadstable

Arrows show how each atom decays: α gives off an alpha particle (2 protons and 2 neutrons), β turns a neutron into a proton, γ gives off a gamma ray.

Half-lives and decay modes from the IAEA Live Chart of Nuclides (evaluated ENSDF data). The chain follows each atom’s most common decay; a few steps have rare side branches.

Keep exploring

Where the dates and stories on this page come from; each event on the timeline links to its own source. The Deutsche Biographie gives years only.