Radioactivity

Unstable  Some nuclei are unstable and give off radiation. Radioactivity - Bequerel 1896Radioactivity - Bequerel 1896 Three types observed: alpha, beta, gammaThree types observed: alpha, beta, gamma

Alpha Particles  Alpha particles are 4 He nuclei. Mass approximately 4 uMass approximately 4 u Charge is +2Charge is +2 Generally from the decay of heavy nucleiGenerally from the decay of heavy nuclei  The energy of the alpha particle is due to the mass difference of the daughter nuclei.  Alpha decay produces an alpha particle. Includes excess energy

Radon Decay  Radon 222 decays into polonium by alpha decay. Find the energy released.  The parent nucleus is 222 Rn.  Get the reaction equation. Look up mass energies  The energy released is Q = M Rn222  M Po218  M He4 Q = MeV  Most of the energy will go to the alpha.

Beta Particles  Electron decay Nucleus emits an electron and antineutrinoNucleus emits an electron and antineutrino Atomic number increasesAtomic number increases Energy goes to e andEnergy goes to e and Some decays include a photon as wellSome decays include a photon as well  Positron decay Nucleus emits a positron and a neutrino Atomic number decreases Kinematics like electron decay Same result as electron capture – no beta out

Neutrinos  Neutrinos are leptons Neutral partners of e, , Neutral partners of e, ,  Very light massVery light mass Stable particlesStable particles  Produced with lepton partner.  Neutrinos rarely interact with matter. Difficult to measureDifficult to measure  Electron neutrino, e Mass < 2.8 eV  Muon neutrino,  Mass < 0.19 MeV  m 2 = eV 2 (m < 3.5 eV)  Tau neutrino,  Mass < 18.2 MeV

Gamma Particles  Nuclei can decay by emitting a gamma ray. High energy photon  Nuclear energy levels are like atomic levels.

Excited States  Nuclear decay can leave a nucleus in an excited state. Many possible states may be reachedMany possible states may be reached Lifetime typically sLifetime typically s  Excess energy may be lost as a photon or electron. Single gammaSingle gamma Series of gamma emissionsSeries of gamma emissions Internal conversion betaInternal conversion beta MeV MeV 0 MeV 94.4%  5.5%  2.2% 3.3% 

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