GCSE Physics: Different half-lives of radioactive isotopes

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1. How much do the half-lives of different radioactive isotopes vary?

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   Over a very wide range — from fractions of a second to billions of years.

2. Why is an isotope with a short half-life an intense hazard at first?

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   Its activity is high — many decays per second — so it emits a lot of radiation initially, although this dies away quickly.

3. Why is an isotope with a long half-life hazardous for a long time?

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   Its activity is low, but it keeps decaying for a very long time, so it remains radioactive (and contaminating) for years or centuries.

4. How does half-life affect how quickly a source's activity falls?

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   The shorter the half-life, the faster the activity falls — it halves every half-life.

5. A radioactive source with a ? half-life has a high initial activity that falls quickly.

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   short

6. For the same number of nuclei, which has the higher activity: a short or a long half-life isotope?

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   The short half-life isotope — its nuclei decay more often per second.

7. Why are half-life values often written in standard form?

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   Because they span many orders of magnitude (e.g. 10⁻³ s to 10⁹ years), standard form keeps very large and very small values readable and comparable.

8. Write a half-life of 4,500,000,000 years in standard form.

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   4.5 × 10⁹ years.