Atomic Structure & Radioactivity is a core part of GCSE Physics. Revise the key concepts and common mistakes below, then lock them in with the free games.
Key concepts
IrradiationExposed to radiation from a source
ContaminationRadioactive material on/in something
Background radiationAlways present from environment
Half-life useChoose for medical or industrial use
PenetrationAlpha: paper. Beta: aluminium. Gamma: lead
SievertUnit of dose
AlphaHe nucleus (2p, 2n); mass 4, charge +2
Beta-minusElectron from neutron; mass 0, charge -1
GammaEM wave; no mass or charge
ActivityDecays per second; unit Bq
Half-lifeTime for activity to halve
Becquerel1 decay per second
Atom radiusAbout 1 x 10^-10 m
Nucleus radiusAbout 1 x 10^-14 m (1/10000 of atom)
Common mistakes to avoid
Questions where students often pick the tempting wrong answer — make sure you know the right one:
What absorber is needed to stop beta radiation?✗ A sheet of paper — beta is only slightly more penetrating than alpha. ✓ A few millimetres of aluminium (or similar thin metal sheet).
What did Rutherford's alpha-scattering experiment show about the atom?✗ It showed that atoms are solid spheres of positive charge with electrons embedded inside. ✓ Most of the atom is empty space, with a tiny dense positive nucleus.
Which type of nuclear radiation is most ionising?✗ Gamma is most ionising because it can travel furthest and pass through almost anything. ✓ Alpha radiation — large, doubly charged particles cause the most ionisation per unit distance.
Best for medical tracers:✗ alpha, short half-life ✓ gamma, short half-life
After one half-life, what happens to an individual radioactive nucleus?✗ Every nucleus is guaranteed to have half-decayed after one half-life. ✓ It has a 50 percent chance of having decayed — radioactive decay is random for any single nucleus.
Practise Atomic Structure & Radioactivity — free games
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