Portrait of Pierre Curie

Adapted from ⁠an image by Dujardin (public domain), via Wikimedia Commons.

1859–1906

Pierre Curie

Physicist who studied magnetism and crystals before turning to radioactivity with Marie Curie; they shared the 1903 Nobel Prize in Physics with Henri Becquerel.

Elements

The Curies found radium by its radioactivity. Watch radium atoms decay, one at a time.

Radioactive decay

Watching atoms decay

Marie and Pierre Curie discovered radium in 1898, in uranium ore. It is there because radium-226 is one stop on uranium-238’s decay chain, constantly being made and destroyed.

Half of any sample of Ra-226 decays every 1,600 years, turning into Rn-222.

Ra-226 · 100 leftTurned into Rn-222 · 0
100%50%25%12.5%0123456

Half-lives passed (1 half-life = 1,600 years)

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 Rn-222 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.