# Radioactive decay

An unstable nucleus randomly gives out radiation to become more stable. It cannot be predicted when a single nucleus will decay, and nothing such as heat or pressure changes the rate.

Physics (school) · Part 08: Atoms and radioactivity · Card 3 of 8 · Last updated 2026-10-19

## Analogy

Popcorn in a pan: you cannot tell which kernel pops next, but the whole pan follows a pattern.

## In practice

Smoke alarms, nuclear power and medical scans use radioactive materials.

## Practice

### Flashcards

- **Is radioactive decay predictable for one nucleus?** No. It is random.

### Interview questions

**A radioactive source has a half-life of 3 hours. A sample starts with 64 g of the isotope. How much is left after 12 hours?**

- 12 hours is 4 half-lives
- Halve four times: 32, 16, 8, 4
- 4 g of the isotope remains

## Questions people ask

### Can you predict when an atom will decay?

No. Decay is random for any single nucleus. You can only say how likely it is over a given time. With millions of atoms, though, the overall pattern is very predictable, which is why half-lives can be measured accurately and used in real sums.

### What is background radiation?

Background radiation is low-level radiation that is always around us. It comes from rocks, the air (radon gas), cosmic rays from space, food, and medical or nuclear sources. When measuring a sample, scientists subtract the background count from the reading to find the sample's true value.

## Related concepts

- [Half-life](https://studyvisually.com/learn/science/physics-school/physics-school-part-8/physics-school-part-8-concept-5)
- [Alpha, beta and gamma](https://studyvisually.com/learn/science/physics-school/physics-school-part-8/physics-school-part-8-concept-4)
- [Ionising radiation and safety](https://studyvisually.com/learn/science/physics-school/physics-school-part-8/physics-school-part-8-concept-6)

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