# Explain why a sample of a pure beta-minus emitting nuclide shows a continuous energy spectrum for the emitted beta particles rather than a discrete set of energies.

> IB DP Physics Standard Level (2023 syllabus) — E.3 Radioactive decay · Explain · 4 marks

> Beta-minus decay involves the transformation of a neutron into a proton within the nucleus, accompanied by the emission of a beta particle.

## Mark scheme (4 marks)

1. A third particle — the antineutrino — is emitted simultaneously with the beta particle.
2. The total energy released (Q-value) is fixed / constant for each decay.
3. This fixed energy is shared between the beta particle and the antineutrino in varying proportions.
4. Because the sharing can take any value between zero and the maximum, the beta particle can have any kinetic energy from zero up to the Q-value, producing a continuous spectrum.

## Key terms

- [continuous energy spectrum](https://www.gradenine.co.uk/glossary/continuous-energy-spectrum)

## Related

- [Revision notes for IB DP Physics Standard Level (2023 syllabus)](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/explain-why-a-sample-of-a-a0174728) · Published by Druglandscape Ltd.