# Explain why the products of a uranium-235 fission reaction are radioactive and why this radioactivity presents a long-term challenge for nuclear waste management.

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

> When uranium-235 absorbs a slow-moving neutron it undergoes fission, splitting into two smaller nuclei (fission fragments) along with several fast neutrons and gamma radiation.

## Mark scheme (4 marks)

1. Fission fragments have a high neutron-to-proton ratio because they originate from a heavy nucleus (U-235) which requires proportionally more neutrons for stability than lighter nuclei do.
2. These neutron-rich fission fragments therefore undergo beta-minus decay (and may also emit gamma radiation) to reach a stable configuration.
3. The waste contains a mixture of isotopes with a very wide range of half-lives, including some radioisotopes with half-lives of thousands to millions of years.
4. Safe containment must therefore be maintained for extremely long periods, making geological storage / deep underground repositories necessary to protect living organisms from ionising radiation over these timescales.

## Key terms

- [nuclear waste](https://www.gradenine.co.uk/glossary/nuclear-waste)

## 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)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-the-products-of-a-b6f4ce9b) · Published by Druglandscape Ltd.