Radon

Radon is a radioactive noble gas produced by the decay of radium in rocks and soil. It seeps up through the ground and can accumulate in buildings, particularly in basements, to levels where it is the second leading cause of lung cancer after smoking. It is colourless, odourless and completely undetectable without special equipment.

  • Atomic Number8686 protons, 86 electrons
  • Atomic Mass222.01758 u86× heavier than hydrogen
  • State at Room TempGasGas
  • Density0.00973 g/cm³
  • Melting / Boiling-71.1°C / -61.7°C
  • Discovered1900

What is Radon?

Radon has 86 protons and is the heaviest naturally occurring noble gas. All of its isotopes are radioactive. The most stable, radon-222, has a half-life of 3.8 days. Radon decays to polonium, which deposits in the lungs and emits alpha particles that damage DNA. Like all noble gases, radon does not react chemically with anything under normal conditions.

Discovered in 1900 by Friedrich Ernst Dorn in Germany, who identified a radioactive gas emanating from radium compounds. Ernest Rutherford also worked on it extensively. Named radon in 1923 from radium (from which it decays).

Fact The UK has designated "radon affected areas" where indoor radon levels are elevated and homes should be tested. Radon comes up through cracks in floors and walls from granite and other radon-producing rock. It is responsible for approx. 1,100 lung cancer deaths per year in the UK alone. Simple measures, sealing floor cracks, improving underfloor ventilation, can dramatically reduce levels.

Where you find Radon

On Earth

Naturally produced from radium-226 decay in rocks and soils worldwide. Concentrations vary enormously depending on local geology, granite-rich areas have highest levels.

How we use Radon

  • Radiotherapy (historical).. Radon gas was once used in cancer radiotherapy by trapping it in tiny gold seeds placed near tumours. Now replaced by safer sources.
  • Risk measurement.. Radon detectors are sold to homeowners to measure indoor radon levels. Areas with high-radon geology may require building ventilation to reduce levels below safe thresholds.

How it was discovered

Discovered in 1900 by Friedrich Ernst Dorn in Germany, who identified a radioactive gas emanating from radium compounds. Ernest Rutherford also worked on it extensively. Named radon in 1923 from radium (from which it decays).

Deeper dive: radon properties

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Moving to 87 protons on the periodic table takes us to the next element.