IB›IB Physics SL›Mind mapsE.3 Radioactive decayIB Physics SL: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsBinding energyMass defect: nucleons' mass minus nucleus massBinding energy E=Δmc2E = \Delta mc^2E=Δmc21 u=931.5 MeV c−21\,\text{u} = 931.5\,\text{MeV}\,c^{-2}1u=931.5MeVc−2Per nucleon peaks near iron-56, about 8.8 MeVProducts more bound: energy releasedStrong forceActs between all nucleonsAttractive, beats electrostatic repulsionShort range, about 10⁻¹⁵ mRepulsive at very small separationsDecay typesRandom and spontaneousAlpha: A falls by 4, Z by 2β⁻: neutron → proton, plus antineutrinoβ⁺: proton → neutron, plus neutrinoGamma: excited nucleus, A and Z unchangedDecayradioactive decayα\alphaαβ\betaβγ\gammaγBqPenetrationAlpha: most ionising, stopped by paperBeta: stopped by mm of aluminiumGamma: most penetrating, needs leadMore ionising means shorter rangeHalf-lifeActivity = decays per second, unit BqHalf-life: time for activity to halveAfter n half-lives, fraction is (12)n(\frac{1}{2})^n(21)nCount rate is only a fraction of activityExam tipsBalance A and Z in every equationSubtract background before finding half-lifeBinding energy is energy supplied to split