Portrait of Marie Curie

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

1867–1934

Marie Curie

Pioneered the study of radioactivity, and remains the only person to win Nobel Prizes in two different sciences.

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.