Radioactive Decay and Half-Life
Each nucleus has the same chance of decaying at any moment, but nobody can say which one will go next.
Elapsed time0
Half-lives passed (n)0.00
Parent nuclei left (N)400
Daughter nuclei0
Parent nucleus (not decayed)Daughter nucleus (decayed)
Decay graphred: this sample navy: the exponential curve
Sample100.0% parent
Why is the red line wobbly, and what does half-life mean?
The half-life is the time it takes for half of the parent nuclei in a sample to decay. It is not the time for one nucleus to live half its life. Each nucleus has a 50% chance of decaying in one half-life, but the decays are random, so the red line wobbles around the smooth curve.
With only 100 nuclei the wobble is large. With 1000 it follows the curve closely, which is why the half-life of a real sample, with trillions of nuclei, is so well defined.
The animation always shows each half-life in a few seconds. Pick an isotope to see the real time each half-life represents.
Learn more in the Half-life lesson.