GCSE›AQA GCSE Physics›Mind mapsRadioactive DecayAQA GCSE Physics: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsWhy decay?Unstable nuclei emit radiation to become stableDecay is random: one nucleus cannot be predictedActivity = decays per second, measured in Bq1 Bq = 1 decay per secondFour radiationsAlpha: helium nucleus, stopped by paperBeta: fast electron, stopped by few mm aluminiumGamma: EM wave, reduced by thick leadNeutron: stopped by hydrogen-rich water or waxMore ionising → less penetratingNuclear equationsMass and atomic numbers balance both sidesAlpha: mass number −4, atomic number −2Beta: atomic number +1, mass unchangedGamma: no change to either numberU-238 → Th-234: 92 → 90Radioactive decayradiation and nucleiαβγBqContaminationContamination: radioactive atoms on or in a materialHazard lasts as the atoms keep decayingIrradiation: exposure without becoming radioactiveIrradiation stops when source is removedBackgroundNatural: radon in rocks, cosmic rays, foodMan-made: weapons fallout, accidents, medicalDose depends on occupation and locationMedicine: weigh benefits against risksExam tipsAlpha is dangerous inside the body, low-risk outsideWhen evaluating, pair a specific benefit with a specific risk