GCSE›Edexcel GCSE Physics›Mind mapsRadioactive DecayEdexcel GCSE Physics: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsRandom decayUnstable nuclei emit radiation randomlyCannot predict when one nucleus will decayAlpha, beta and gamma are ionisingTypesAlpha: helium nucleus, 2 protons + 2 neutronsβ−: fast electron from the nucleusβ+: fast positron from the nucleusGamma: electromagnetic radiationNeutron radiation: emitted neutronPenetrationAlpha: stopped by paper or skinBeta: stopped by few mm of aluminiumGamma: reduced by thick lead or concreteMore ionising → less penetratingRadioactive decayunstable nucleiαβγBqNuclear equationsβ−: neutron becomes proton + electronβ+: proton becomes neutron + positronAlpha: mass number −4, atomic number −2β−: atomic number +1, mass unchangedGamma: no change to either number92238U→90234Th+24He^{238}_{92}\text{U} \to {}^{234}_{90}\text{Th} + {}^{4}_{2}\text{He}92238U→90234Th+24HeHalf-lifeActivity = decays per second, measured in Bq1 Bq = 1 decay per secondHalf-life: time for activity to halve800 Bq, half-life 3 h → 400 Bq after 3 hPredicts large numbers, not one nucleusExam tipsAlpha most dangerous inside the body onlyOutside the body alpha is least penetratingBalance mass and atomic numbers both sides