Half-life is a core concept in nuclear chemistry and is essential for understanding radioactive decay, medical imaging, radiocarbon dating, and nuclear energy. This article explains half-life clearly, shows how it works mathematically, and helps you apply it with confidence in exam questions.
What Is Half-Life?
Half-life (t½) is the time required for half of a radioactive substance to decay.
If you start with a certain number of radioactive nuclei, after one half-life:
- Half the nuclei have decayed
- Half remain undecayed
After another half-life, half of the remaining amount decays again.
This process continues in a predictable, exponential pattern.
Why Half-Life Is Important
Half-life tells us:
- How quickly a radioactive substance decays
- How long it remains hazardous
- How long it remains useful (e.g., medical tracers)
- How to calculate how much remains after a given time
- How to determine the age of ancient materials
IB questions often require applying half-life mathematically.
Radioactive Decay Is Exponential
Radioactive decay does not occur linearly.
Instead, the rate of decay is proportional to the number of undecayed nuclei remaining.
This leads to exponential behavior:
- After 1 half-life → 50% remains
- After 2 half-lives → 25% remains
- After 3 half-lives → 12.5% remains
- After n half-lives → (½)ⁿ remains
The pattern is predictable and consistent.
