# Radioactive decay is a random and spontaneous process. Explain what is meant by the terms 'random' and 'spontaneous' in this context, and describe how the count rate of a radioactive source changes over time.

> Eduqas A-Level Physics — 6.1 Radioactivity · Explain · 5 marks

> A technician monitors a radioactive source over several days and notices that the count rate detected gradually decreases.

## Mark scheme (5 marks)

1. Random means it is impossible to predict which nucleus will decay next (or when any particular nucleus will decay)
2. Spontaneous means the decay is not triggered or affected by external conditions (e.g. temperature, pressure, chemical environment)
3. The count rate decreases over time
4. The count rate decreases because the number of unstable (radioactive) nuclei remaining in the source decreases
5. The count rate never reaches exactly zero / the source always retains some radioactive nuclei (or: the count rate decreases by the same fraction in equal time intervals — halving in each half-life)

## Key terms

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

## 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-0dd9188c) · Published by Druglandscape Ltd.