Rn
Noble gas
Radon
Z 86A 222mass 222
Decay curve
Radon-222
half-life
3.82 days
half-lives elapsed1 half-life
0123456
left
50.0%
real time
3.82 days
Sample of 240 nuclei
106 leftEach dot is one nucleus. Decay is random for each one — but the pattern that emerges is the exponential curve on the left.
The numbers
| Half-lives | Time elapsed | Remaining | Of 1000 |
|---|---|---|---|
| 0 | — | 100.0% | 1000 |
| 1 | 3.82 days | 50.0% | 500 |
| 2 | 7.65 days | 25.0% | 250 |
| 3 | 11.5 days | 12.5% | 125 |
| 4 | 15.3 days | 6.25% | 63 |
| 5 | 19.1 days | 3.13% | 31 |
| 6 | 22.9 days | 1.56% | 16 |
N = N₀ × (½)ⁿ — never exactly zero
Real half-lives, for scale
Thorium-23214.05 billion years
Uranium-2384.47 billion years
Potassium-401.25 billion years
Neptunium-2372.14 million years
Plutonium-23924,110 years
Carbon-145,730 years