# Radioactive decay is a random and spontaneous process. Explain what is meant by the terms 'random' and 'spontaneous' as applied to radioactive decay, and describe how the count rate from a radioactive source changes over time.

> Eduqas A-Level Physics — 1.7 Particles and nuclear structure · Explain · 5 marks

## Mark scheme (5 marks)

1. Random means it is impossible to predict which particular nucleus will decay next
2. Spontaneous means the decay is not triggered or caused by any external factor / conditions
3. The count rate (or activity) decreases over time
4. The count rate decreases in a regular pattern / by the same fraction in equal time intervals (half-life)
5. This is because there are fewer undecayed nuclei remaining over time, so fewer decays occur per second

## Key terms

- [random](https://www.gradenine.co.uk/glossary/random)
- [spontaneous](https://www.gradenine.co.uk/glossary/spontaneous)
- [count rate](https://www.gradenine.co.uk/glossary/count-rate)
- [radioactive decay](https://www.gradenine.co.uk/glossary/radioactive-decay)

## Related

- [Revision notes for Eduqas A-Level Physics](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/radioactive-decay-is-a-random-and-0a0689c8) · Published by Druglandscape Ltd.