Nuclear Physics


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Nuclear Physics

  1. 1. 06-20,2005 UH Teacher Workshop What’s New in Nu-clear Physics Ed V Hungerford University of Houston According to Pogo: “Nuclear Physics is not so new, and not so clear either.”
  2. 2. 06-20,2005 UH Teacher Workshop The Answers to our questions are only as good as the questions themselves Why did the tree grow in the notch in the fence ?
  3. 3. 06-20,2005 UH Teacher Workshop 75 years ago Nuclear Physics was New •The neutron had just been discovered •The Proton and Neutron were considered elementary particles •The nuclear force was not understood •Nuclear models were primitive and based on classical liquids Today Nuclear Physics in some sense is Mature •Nucleons are not “elementary” but are composed of other particles called quarks •The nuclear force is understood as an exchange of field quanta called gluons •The nucleus is a VERY complicated interaction of many hadrons whose interaction is described by a theory called Quantum Chromodynamics Nuclear Physics is the Study of the effects of M any-body Hadronic System s interacting via QCD
  4. 4. 06-20,2005 UH Teacher Workshop The Particles and Symmetries of the Standard Model 3 Families
  5. 5. 06-20,2005 UH Teacher Workshop There are 4 known interactions in nature •One of the fundamental driving philosophies of physics is the assumption that these interactions can be “unified” •Two of these are manifestations of the same force (electroweak) •QCD is patterned after the electroweak interaction (gauge theory) •Gravity still lies outside a quantum theory •The new discovery of Dark Energy, if it is real, may imply a 5th force Field QCD
  6. 6. 06-20,2005 UH Teacher Workshop A Field Quanta The interaction of B with A occurs through the absorption of field quanta at B produced by A Particle B Particle A The Interaction through Fields
  7. 7. 06-20,2005 UH Teacher Workshop QCD Features • An interaction that becomes stronger the greater the distance and the lower the energy between interacting particles • A weak interaction at short distances and high energies • A permanently bound quarks and gluons • A self interaction between the field quanta (gluons) • A highly non-linear theory greatly complicating calculations and making intuitive predictions difficult • A symmetry of SU(3) expressed by 3 states of quarks and Gluons (color)
  8. 8. 06-20,2005 UH Teacher Workshop Gluon Field The Quark and Gluon Constituents of the Baryon Valence Quarks Sea Quarks
  9. 9. 06-20,2005 UH Teacher Workshop Quantum ChromoDynamics (QCD) is the Theory of the Strong Interaction (Nuclear Force) Quarks and Gluons Flux Tube Linear Potential vs distance
  10. 10. 06-20,2005 UH Teacher Workshop How do we probe a Nucleon or a Nucleus To determine its Quark Content ? Incident Electron Incident Hadron
  11. 11. 06-20,2005 UH Teacher Workshop Emission of a Quark Stretches the “interaction String” When the string breaks, Quark- anti-quark pairs are produced This is called Hadronization of a Quark Jet Quark Scattering Long Range Nuclear force Collapses to quark-antiquark Exchange (Yukawa Interaction) the “interaction String”
  12. 12. 06-20,2005 UH Teacher Workshop Chiral Symmetry, and Mass Chiral symmetry is the fundamental symmetry of QCD But the particle must not have mass Right HandedVelocity Left HandedVelocity
  13. 13. 06-20,2005 UH Teacher Workshop The QCD Condensate Particles acquire mass through their interaction with the vacuum, i.e. the condensate of quarks and gluons in the vacuum A nucleon in a simple visualization, is a bubble in the vacuum condensate Interaction of these quarks with the condensate at the bubble surface gives an “effective” mass to the system. Chiral Symmetry is then said to be spontaneously broken
  14. 14. 06-20,2005 UH Teacher Workshop The Vacuum is NOT Empty This Computer simulation shows the instantaneous gluon field that might be Present in a vacuum. Red Indicates bending (winding) in the field lines perhaps a precursor to quark condensates
  15. 15. 06-20,2005 UH Teacher Workshop We Live Here Phase Diagram of Matter Each of the 4 interactions is has its own impact on the existence of our Universe The Strong (nuclear) force is responsible for the creation and stability nuclear matter
  16. 16. 06-20,2005 UH Teacher Workshop Studying the Vacuum and QCD Relativistic Colliding Nuclei Quark Gluon plasma Hadronization
  17. 17. 06-20,2005 UH Teacher Workshop Connecting the very large to the very small One of the more recent advances in physics has been to connect microscopic theory to macroscopic (cosmology) For example, stellar burning and supernovae produce the nuclei of which the Universe is composed We can use this information to look back in time, as well as discuss the present features in our universe
  18. 18. 06-20,2005 UH Teacher Workshop Mesons and baryons are composed of quarks Flavor SU(3) Symmetry Allows Placement of lowest Mesons And Baryons in Symmetry Octets
  19. 19. 06-20,2005 UH Teacher Workshop The Nuclear Equation of State Neutron Star Nuclear Matter
  20. 20. 06-20,2005 UH Teacher Workshop A modern cut-away view of a Neutron Star
  21. 21. 06-20,2005 UH Teacher Workshop Measuring Matter Creation in the Galaxy
  22. 22. 06-20,2005 UH Teacher Workshop Proton number vs Neutron Number Stability
  23. 23. 06-20,2005 UH Teacher Workshop The Present Model of a Supernovae
  24. 24. 06-20,2005 UH Teacher Workshop Inside a SupernovaInside a Supernova ν ν ν ν ν Dense core 100 km M . 3x107 km 3000 km ν ν ν ν ν n* 10 km M . >8 M evolves ~107 yr Extreme temp: photodissociates nuclei back to protons, neutrons and alphas. Neutronisation: p+e-  n+νe e+ +e- → γ+γ ; γ+γ → νx + νx (all flavours equally) ρ ~ few x ρnuclear Huge thermal emission of neutrinos ~5-10 seconds Core bounces
  25. 25. 06-20,2005 UH Teacher Workshop Supernovae: Facts and FiguresSupernovae: Facts and Figures  Energy release ~3x10Energy release ~3x104646 J (theJ (the gravitational binding energy of thegravitational binding energy of the core), in about 10 secondscore), in about 10 seconds  Equivalent to 1000 times the energyEquivalent to 1000 times the energy emitted by the Sun in its entireemitted by the Sun in its entire lifetime.lifetime.  Energy density of the core isEnergy density of the core is equivalent to 1MT TNT per cubicequivalent to 1MT TNT per cubic micron.micron.  99% of energy released is in the99% of energy released is in the form of neutrinosform of neutrinos  ~1% is in the KE of the exploding~1% is in the KE of the exploding mattermatter  ~0.01% is in light – and that’s~0.01% is in light – and that’s enough to make it as bright as anenough to make it as bright as an entire galaxy.entire galaxy.  Probably site of the r-processProbably site of the r-process .. ¼ MT test (Dominic Truckee, 1962)
  26. 26. 06-20,2005 UH Teacher Workshop A Computer model of a Supernovae
  27. 27. 06-20,2005 UH Teacher Workshop A Brief Summary Nuclear Science has tremendous breadth and complexity After 75 years we have found some to the “right” questions to ask but others remain I have purposely avoided discussion of the more traditional nuclear studies There are impressive new results and insights into nuclear matter. But these require detailed exposition and are difficult to develop to grasp without some prior knowledge. As a mature, advanced science, there are significant applications in Including the fields of Medicine, Computing, Industrial Products, Energy, Finance, etc. More than 50% of the Phd graduates in Nuclear Physics are employed in industry, medicine, and national defense. N uclear P hysics is a vibrant, exciting Field
  28. 28. 06-20,2005 UH Teacher Workshop