IGCSE 0625 · NUCLEAR · 5.2

Radioactivity

Detecting radiation and its background sources, the three emissions and their penetration, decay equations and half-life, and the everyday uses and safety of radioactivity. It builds on the nuclear model of the atom.

TOPIC 5.2: RADIOACTIVITY CAMBRIDGE IGCSE PHYSICS 0625 · PATHWAYS TheLucidSTEM · thelucidstem.com BUILDS ON 5.1 The atom LEADS TO 3.3 Gamma rays Medicine & safety RADIO- ACTIVITY 1 · RADIATION & DETECTION Unstable nuclei give out radiation at random. For a single nucleus the moment of decay cannot be predicted. Background radiation is always present: rocks and soil, cosmic rays, food, and medical scans. A Geiger-Muller tube and counter detect it. 0427 GM tube counter 2 · ALPHA, BETA, GAMMA There are three kinds of nuclear radiation. Alpha (α): a helium nucleus, charge +2, strongly ionising. Beta (β): a fast electron, charge −1, medium range. Gamma (γ): an EM wave, no charge, very penetrating. paper aluminium lead α β γ 3 · DECAY & HALF-LIFE Decay changes one nucleus into another. Alpha decay: nucleon number −4, proton number −2. Beta decay: a neutron becomes a proton (proton number +1) and an electron is emitted. Half-life is the time for half the nuclei, or the activity, to fall away. activity time 1 t½ 2 t½ 3 t½ 4 · SAFETY & USES Radiation is useful, but must be handled with care. Staying safe: Keep your distance and limit the time. Shield sources with lead and store them safely. Everyday uses: Smoke alarms use alpha. Medical tracers and sterilising use gamma. Carbon dating and thickness gauges use beta. Radiotherapy treats cancer with gamma.
TOPIC 5.2: RADIOACTIVITY CAMBRIDGE IGCSE PHYSICS 0625 · PATHWAYS TheLucidSTEM · thelucidstem.com BUILDS ON 5.1 The atom LEADS TO 3.3 Gamma rays Medicine & safety RADIO- ACTIVITY 1 · RADIATION & DETECTION Unstable nuclei give out radiation at random. For a single nucleus the moment of decay cannot be predicted. Background radiation is always present: rocks and soil, cosmic rays, food, and medical scans. A Geiger-Muller tube and counter detect it. 0427 GM tube counter 2 · ALPHA, BETA, GAMMA There are three kinds of nuclear radiation. Alpha (α): a helium nucleus, charge +2, strongly ionising. Beta (β): a fast electron, charge −1, medium range. Gamma (γ): an EM wave, no charge, very penetrating. paper aluminium lead α β γ 3 · DECAY & HALF-LIFE Decay changes one nucleus into another. Alpha decay: nucleon number −4, proton number −2. Beta decay: a neutron becomes a proton (proton number +1) and an electron is emitted. Half-life is the time for half the nuclei, or the activity, to fall away. activity time 1 t½ 2 t½ 3 t½ 4 · SAFETY & USES Radiation is useful, but must be handled with care. Staying safe: Keep your distance and limit the time. Shield sources with lead and store them safely. Everyday uses: Smoke alarms use alpha. Medical tracers and sterilising use gamma. Carbon dating and thickness gauges use beta. Radiotherapy treats cancer with gamma.
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