Radioactive Decay Simulation — Description
The simulation shows 48 unstable nuclei arranged in a grid, each decaying randomly over time following the exponential decay law N(t) = N₀ · e^(−λt). Students can select five AQA-relevant isotopes from the dropdown — Carbon-14, Polonium-210, Radium-226, Technetium-99m, and Sodium-22 — each with its correct decay type (α, β⁻, β⁺, or γ) and real half-life values.
When a nucleus decays, it flashes and ejects coloured particles outward — gold for alpha, blue for beta, green for gamma — then settles into a darker daughter nucleus with the correct symbol. The live decay curve on the right plots actual simulation data (green-to-purple line) against the theoretical exponential (dashed yellow), building in real time so students can see how random individual events produce smooth exponential statistics across the ensemble. The info card shows the isotope name, decay type, half-life, and daughter product. Counters track undecayed nuclei, decayed nuclei, half-lives elapsed, and approximate activity in Becquerels.
AQA Curriculum Link
Directly covers 4.4.3 — Radioactive decay (Physics Paper 2):
- Random and spontaneous nature of decay
- α, β, γ radiation types and their properties
- Half-life definition and calculation
- Activity and the Becquerel
- Uses of specific isotopes (C-14 in carbon dating, Tc-99m in medical imaging)
Suggested Class Activity — “Half-Life in Real Time” (20 min, KS4)
Starter — 3 min: Ask students: “If I have 100 radioactive atoms right now, how many will have decayed in one half-life?” Take answers. Most will say exactly 50 — press them: “Is it exactly 50, every time?”
Main task — 12 min: Students work in pairs, each pair on a different isotope.
Select Carbon-14. Watch the simulation run. Record in a table:
| Half-lives elapsed | Nuclei remaining (sim) | Predicted N₀·(½)ⁿ |
|---|---|---|
| 0 | 48 | 48 |
| 1 | ? | 24 |
| 2 | ? | 12 |
| 3 | ? | 6 |
Students compare their simulated values to the predicted ones and answer:
- Does the simulation give exactly 24 after one half-life? Why not?
- What does the dashed yellow line represent, and why doesn’t the green line match it perfectly?
- Switch to Technetium-99m. The half-life is 6 hours — why is this useful for medical imaging but Carbon-14 is not?
- Switch to Polonium-210. What type of radiation does it emit? Why would this be dangerous inside the body?
Plenary — 5 min: Return to the starter question. Students revise their answer: “Each atom has a 50% probability of decaying within one half-life — but probability doesn’t guarantee exactly half will go.” This is the key distinction between individual randomness and ensemble statistics — and exactly what Chadwick and Rutherford had to grapple with in their experiments.
Exit card: “A sample starts with 48 atoms of Ra-226. After 3 half-lives, approximately how many remain? Show your working.” Expected: 48 → 24 → 12 → 6.