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Transcript

Atomic Physics – Part 3 Ongoing Theory Development To accompany Pearson Physics PowerPoint presentation by R. Schultz robert.schulz@ei.educ.ab.ca 17.1 Detecting and Measuring Subatomic Particles Tools Cloud Chamber: supersaturated vapour condenses along track of particle Bubble Chamber: Liquid gas near its boiling point boils along track of particle Recall analysis of alpha, beta, and gamma for charge and relative mass 17.1 Detecting and Measuring Subatomic Particles More tools: Particle accelerators: use high energy particles to probe matter High energy “probe particles” required to overcome the strong nuclear force Types: cyclotron, linear accelerator, synchotron, Van de Graaff, CERN’s LHC 17.1 Detecting and Measuring Subatomic Particles Check and Reflect, page 835, question 5 Note: particle notation uses lines on top for antiparticles, e.g. n = neutron, n = antineutron 17.2 Quantum Theory and the Discovery of New Particles Antimatter Positrons postulated by Dirac, verified by Anderson Matter/anti-matter collision e+ + ephotons? 2γ annihilation Why must there be 2 gamma 17.2 Quantum Theory and the Discovery of New Particles At this point in time, theory has predicted and evidence has supported existence of over 300 subatomic particles Subatomic masses are communicated for convenience in units of eV c 2 Einstein’s equation E mc 2 can be rewritten as E m 2 c 17.2 Quantum Theory and the Discovery of New Particles eV and MeV are units of energy, therefore eV 1 eV c 2 c2 and MeV c2 are units of mass = 1.7827 x 10-36 kg (you don’t need to know this!) Your formula sheet records masses of all first generation “fermions” this way 17.4 Quarks and the Standard Model Moving to the Standard Model: Read Pearson Physics pages 836-8 and 842-3 Read SNAP pages 366-9 17.4 Quarks and the Standard Model Standard Model: (1963 originally with many updates) Fermions (make up matter) leptons e μ τ (+ anti of νe each) νμ ντ Bosons (mediating particles) quarks 1st gen u d s (+ anti of c each) b t make up hadrons baryons (3 quarks) including proton uud neutron udd mesons (2 quarks) 1 reg, 1 anti 17.2 Quantum Theory and the Discovery of New Particles Further: hadrons interact by the strong nuclear force (e.g. protons and neutrons) Leptons do not (e.g. electrons) Bosons are virtual particles that mediate forces W+, W-, Z mediate weak nuclear force existence photons mediate electromagnetic force confirmed gluons mediate strong nuclear force gravitons mediate gravitational force unconfirmed 17.2 Quantum Theory and the Discovery of New Particles Formula sheet chart: Keep this chart in front of you for the next section 17.4 Quarks and the Standard Model Beta decay You already learned that in beta negative decay, a neutron becomes a proton How can we understand this in terms of quarks and mediating particles? 17.4 Quarks and the Standard Model (hadron) (hadron) (lepton) (lepton) neutron → proton + beta negative + antineutrino udd → uud + e+ 1 2 e e 3 1 3 e 3 charge = 0 1 2 e e 3 2 3 e 3 charge = +1e to make this occur, a d quark has turned into a u quark by the following process: d → u + [W-] [W-] → e- + boson mediating weak nuclear force very short lifetime 17.4 Quarks and the Standard Model Beta positive decay: (hadron) (hadron) (lepton) (lepton) proton → neutron + beta positive + neutrino uud → udd + e+ + ν 1 2 e e 3 2 3 e 3 1 2 e e 3 1 3 e 3 charge = +1e charge = 0 to make this occur, a u quark has turned into a d quark by the following process: u → d + [W+] [W+] → e- + ν boson mediating weak nuclear force very short lifetime 17.4 Quantum Theory and the Discovery of New Particles Standard Model Summary: • All matter composed of 12 fundamental particles and their antiparticles …….. • electromagnetic force and weak nuclear force are different aspects of the same force • electromagnetic and nuclear forces mediated by virtual particles called bosons We are done!!! 17.4 Quarks and the Standard Model