H
Reactive nonmetal
Hydrogen
Z 1A 1mass 1.008
Decay curve
Tritium (hydrogen-3)
half-life
12.32 years
half-lives elapsed1 half-life
0123456
left
50.0%
real time
12.3 years
Sample of 240 nuclei
114 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 | 12.3 years | 50.0% | 500 |
| 2 | 24.6 years | 25.0% | 250 |
| 3 | 37 years | 12.5% | 125 |
| 4 | 49.3 years | 6.25% | 63 |
| 5 | 61.6 years | 3.13% | 31 |
| 6 | 73.9 years | 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