Radioactivity and the three types of decay, half-life and safety, and the structure of the Solar System and the universe.
The nucleus and radioactivity
Some nuclei are unstable and decay, emitting radiation. There are three main types:
| Type | What it is | Charge | Penetration | Stopped by |
|---|---|---|---|---|
| Alpha () | helium nucleus (2p + 2n) | +2 | low | paper/skin |
| Beta () | fast electron | −1 | medium | aluminium |
| Gamma () | EM wave | 0 | high | thick lead/concrete |
Alpha is the most ionising but least penetrating; gamma is the least ionising but most penetrating.
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