Radioactivity

1. Radioactivity

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

3. Alpha particles are 4He nuclei. Mass approximately 4 u Charge is +2 Generally 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 Alpha Particles

4. Radon 222 decays into polonium by alpha decay. Find the energy released. The parent nucleus is 222Rn. Get the reaction equation. Look up mass energies The energy released is Q = MRn222-MPo218-MHe4 Q = 12.89 MeV Most of the energy will go to the alpha. Radon Decay

5. Electron decay Nucleus emits an electron and antineutrino Atomic number increases Energy goes to e and n Some 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 Beta Particles

6. Neutrinos are leptons Neutral partners of e, m, t Very light mass Stable particles Produced with lepton partner. Neutrinos rarely interact with matter. Difficult to measure Electron neutrino, ne Mass < 2.8 eV Muon neutrino, nm Mass < 0.19 MeV Dm2 = 0.002 eV2 (m < 3.5 eV) Tau neutrino, nt Mass < 18.2 MeV Neutrinos

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

8. Nuclear decay can leave a nucleus in an excited state. Many possible states may be reached Lifetime typically 10-10 s Excess energy may be lost as a photon or electron. Single gamma Series of gamma emissions Internal conversion beta Excited States 4.785 MeV 94.4%a 5.5%a 0.186 MeV 2.2% 3.3% b 0 MeV

9. Decay Products next