Nuclear (and applied) Physics - PowerPoint Presentation

1. Nuclear (and applied) Physics at the ISOLDE-facility at CERNGerda NeyensUniversity of Leuven, BelgiumandCERN, EP-SME-IS, ISOLDE Physics Group Leadergerda.neyens@cern.ch on behalf of the CERN ISOLDE teamwww.cern.ch/isolde Lecture 1: Nuclear physics

2. Outline This lecture: Introduction to nuclear physicsKey dates and termsForces inside atomic nucleiNuclear landscapeNuclear decayGeneral properties of nucleiNuclear modelsOpen questions in nuclear physicsLecture 2: CERN-ISOLDE facility Elements of a Radioactive Ion Beam FacilityLecture 3: Nuclear Physics and Applications at ISOLDEExamples of experimental setups and results2Aimed at both physics and non-physics students

3. Nuclear scale3protonNuclear physics: studies the properties of nuclei andthe interactions inside them (between protons and neutrons) and between themMatter Crystal Atom Atomic nucleus Nucleon Quark Macroscopic AngstromfemtometerProtonNeutron (similar mass)

4. History4Today: the exact form of the nuclear interaction is still not known, but we are getting to know it better and better with many dedicated experimental facilities and with a matching theoretical effortKnown nuclidesBecquerel, discovery of radioactivitySkłodowska-Curie and Curie, isolation of radiumChadwick, neutron discoveredGoeppert-Meyer, Jensen, Haxel, Suess, nuclear shell modelfirst studies on short-lived nucleiDiscovery of halo nucleiDiscovery of 1-proton decayDiscovery of 2-proton decayCalculations with super computersRutherford Atomic model

5. TerminologyNucleus/nuclide:Nucleons: protons and neutrons inside the nucleusIsotopes: nuclides with the same number of protons, but not neutronsIsotones: nuclides with the same number of neutrons, but not protonsIsobars: nuclides with the same number of nucleons (but different Z and N)5XAZZ protons  element XN neutronsatomic number A = N+ZNIsomers = long-lived excited nuclear statesZ=3Z=4

6. Forces acting in nucleiCoulomb force repels protons 6penν-Strong interaction ("nuclear force") causes binding between nucleons (=attractive).It is stronger for proton-neutron (pn) systems than pp- or nn-systemsNeutrons alone form no bound states (exception: neutron stars (gravitation!)Weak interaction causes β-decay ATTRACTIONProtons charge = +Neutron charge = 0

7. Nuclei and QCDDifferent energy scalesIn nuclei: non-perturbative QCD, so no easy way of calculatingHave to rely on nuclear models (shell model, mean-field approaches)Recent progress: lattice QCD7

8. Properties of nuclear interaction8Nucleon-nucleon interactionHas a very short range (fm = 10-15 m)Consists mostly of attractive central potentialIs charge symmetric Is nearly charge independent (similar p and n)Becomes repulsive at short distancesmodels

9. Chart of elements9Around 100 elementsOrdered by proton number ZMore than 10 of them made only in a labNamed in June 2016

10. Chart of nuclei10Proton drip-lineneutron drip-lineneutronsprotonsMagic numbersstable+/EC decay- decay decayp decayspontaneous fission- About 300 stable isotopes: nuclear models developed for these systems- 3000 radioactive isotopes discovered up to now (many of them made only in labs)- Over 7000 nuclei predicted to exist

11. Nuclear decay11b+b-,eIn nature  systems aim at a minimal energyNUCLEAR MASS = SUM OF NUCLEON MASSES – (binding)energy !Along isobaric chain  decay towards isobar lowest mass (= energy)neutronsprotonsIsobars = same Abut not exactly same massE=mc2Isobars with mass A=25Al is most stable A=25 isotopepnnp

12. β+β-N-ZValley of stability12β+ decay β- decay

13. Nuclear decayb+ decay – emission of positron: p  n + e+ + nee/EC – electron capture: nucleus captures an atomic electron: p + e-  n + neb- decay – emission of electron: n  p + e- + nea decay – emission of alpha particle (4He nucleus)p (or 2p) decay – emission of 1 or 2 protonsin very proton-rich nucleispontaneous fission – spontaneous splitting into two smaller nuclei and some neutronsObserved in heavy nucleiVery long lifetimes13

14. Nuclear de-excitationParticle emission can be followed by emission of gamma radiation (= photon)14 Internal conversion: g-energy of de-exciting nucleus is captured by electron cloudthis causes a deep electron to be emitted from the atoma more energetic electron fills the hole + X-ray is emittedmassless radiation(E=100-3000 keV)massless radiation(E=10-100 keV)

15. Radius15Charge distributionR = 1.25 x A1/3 (fm)A1/3 Density of nucleons almost constant Radius increases with A1/3Volume (~ r3) increases linearly with number of particles radius of nucleus (fm)

16. Mass and binding energyNuclei are bound systems, i.e. mass of nucleus < mass of constituentsBinding energy – mass excess: Binding energy/nucleon (B/A):16Mnucleus = N Mn + Z Mp – M(N,Z)8 MeV/uMost bound nuclei appear around FeE=mc2

17. Lifetime Some nuclei are stable (i.e. their lifetimes are comparable to that of a proton and we have not seen their decay)E.g. until recently 209Bi was thought to be stableOthers are unstable – they transform into more stable nucleiDecay is a statistical process: exponentiallyHalf-life = time after which half of the initial nuclei have decayed17Examples of half-lives:11Li: 9 ms13Be: 0.5 ns77Ge: 11h173Lu: 74 ms208Pb: stableHalf-life T= T1/2After 6 half-lives: only about 1.5% remains

18. Lifetime18neutronsElements with even Z have more stable isotopes“valley of stability” bends towards N>ZNuclei further away from this valley are more exotic (i.e. shorter-lived)protons

19. Properties of radio-nuclidesExotic nuclei have a different neutron-to-proton ratio than stable nuclei This leads to:New structures (e.g. pear shaped nuclei, halo nuclei)New decay modes (e.g. proton decay)19Example - halo nucleus 11Li (discovered in 1985)Radius of 11Li is similar to that of 208PbExplanation: 9Li core + two loosely bound neutronsWhen taking away 1 neutron, the other is not bound any more (10Li is not bound)11Li = Borromean system Nuclear models derived from properties of ‘stable nuclei’ (50-ies) cannot explain these special features

20. Open questions in nuclear physics202 kinds of interacting fermions(NuPECC long-range plan 2010)Main models:Shell model (magic numbers)Mean-field models (deformations)Ab-initio approaches (light nuclei) Observables:Ground-state properties: mass, radius, momentsHalf-lives and decay modesExcited state properties:energy of discrete (isomeric) excited levels, transition probabilitiesReactions with exotic nuclei

21. Nuclear shell modelCreated in analogy to the atomic shell model (electrons orbiting a nucleus in particular quantum orbits induced by the nuclear field)When electrons ‘fill’ a quantum orbit  element is more stable (higher ionization energy)Explains why noble gasses are more ‘stable’ (less reactive) than other elements21ionization energy =energy to remove one electronAtomic shell modelAlso in chart of nuclei: some nuclei are more stable than their neighboursfilled shell of neutrons or protons results in greater stabilityneutron and proton numbers corresponding to a closed shell are called ‘magic‘He (2)Ne (2+8 =10)Ar (2+8+8=18)

22. Nuclear shell model Differences to atomic shell model:1. The field generating the potential No central potential but a self-created one  needs to be modelled !Two kinds of nucleons Strong spin-orbit coupling changes magic numbers: 8,20,28,50, 82, 126, …2. The interaction between the particlesNucleon-nucleon interaction strong interaction in nuclear medium needs to be modelled !22Quantum orbits in the independent particle shell modelHarmonic Oscillator potentialQuantum levels of the HO potentialChallenge: nuclear shell model was created for stable nuclei, is it valid also for exotic nuclei ?282040

23. Summary Nuclear physics investigates the properties of nuclei and of the underlying nucleon-nucleon interactionRich history and many nuclei discoveredAll 4 fundamental interactions at play details of strong interaction are not knownNuclear landscape – over 3000 known nuclei and even more predictedNuclear decays transform one nucleus into anotherNuclear properties – reveal features of nuclear interactionOpen questions in nuclear physicsHow to describe various nuclear properties with a fundamental strong interactionHow to make predictionsHow do regular patterns emergeNuclear modelsEach is better in one respect and worse in anotherAim: describe known properties and predict new onesWe are getting closer to the answers with radioactive ion beam facilities, such as ISOLDE -> Lecture 2 and 323

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25. Key dates25Today: the exact form of the nuclear interaction is still not known, but we are getting to know it better and better with many dedicated facilitiesKnown nuclides1896: Becquerel, discovery of radioactivity1898: Skłodowska-Curie and Curie, isolation of radium1911: Rutherford, experiments with a particles, discovery of atomic nucleus1932: Chadwick, neutron discovered1934: Fermi, theory of b radioactivity1935: Yukawa, nuclear force mediated via mesons1949: Goeppert-Meyer, Jensen, Haxel, Suess, nuclear shell model1964: Gell-Mann, Zweig, quark model of hadrons1960’ties: first studies on short-lived nucleiSince then:

26. Nuclear models26Nucleus = N nucleons interacting with strong forceNucleon-Nucleon forceunknown No complete derivation from the QCDThe many-body problem(the behavior of each nucleoninfluences the others)Can be solved exactly for N < 10For N > 10 : approximationsShell model only a small number of particles are activeApproaches based on the mean field no inert core but not all the correlations between particles are takeninto accountDifferent forces used depending on the method chosen to solve themany-body problem

27. Nuclear force and experiments27After http://web-docs.gsi.de/~wolle/TELEKOLLEG/KERN/LECTURE/Fraser/L5.pdf

28. Creation of nuclidesH, He, and some Li were created during the Big Bang28Heavier nuclei were produced in stars = stellar nucleosynthesisUp to Fe – via fusion (see binding energy/A)Above: via proton or neutron captureStellar environment not yet knownSeveral locations suggested by models (e.g. supernovae explosions, neutron star mergers)Need nuclear physics data to constrain models

29. Binding energyBinding energy = mechanical energy required to disassemble a whole into separate partsBound system = interaction energy is less than the total energy of each separate particleEnergy is needed to separate the constituentsMass of constituents = mass of bound system + binding energy (positive)Atoms:Mass of electrons + mass of nucleus > mass of the atomNuclei:Mass of protons + mass of neutrons > mass of the nucleusE.g for 12C: 11.18 GeV > 11.27 GeV (difference of 90 MeV = binding energy)Nucleons:It looks like mass of quarks < mass of nucleon (ca 10MeV < 1GeV)But quarks don’t exist as separate particles, thus 10MeV is a rest mass of quarks inside a nucleon. It would take an enormous energy to isolate quarks, so as separate particles they would be much heavier, so:mass of constituents > mass of nucleon29

30. Mass parabola30Pairing energy

31. Atomic vs nuclear structure31AtomsNuclei calculated by solving Schrödinger equation with central potential dominated by nuclear Coulomb fieldnot easily calculated; nucleons move and interact within a self-created potentialEnergy levelsshell model: e- fill quantized energy levels shell model (but not only): p and n separately fill quantized energy levels Descriptionn, l, ml, s, parity (-1)l n, l, ml, s, parity (-1)l Quantum numbersmax. S possible (due to Coulomb force):J= L+S= Sli + Ssi or J= Sji = S(li +si)min. S possible (due to strong force pairing):J = Sji = S(li +si)Lowest en. levelsweakstrongSpin-orbit couplingfor 3 electrons in a d orbitalfor 3 nucleons in a d orbitald3/2d5/2

32. Does di-neutron exist?If nuclear force is charge independent, why does system with 1n and 1p exist (deuteron), but that with 2n and 2p, etc don’t? And what binds neutrons in neutron stars?Nuclear force is charge independent, but it depends on the spin, i.e.Spin-up to spin-up (↑ ↑) interaction of 2 protons is the same as for 2 neutronsBut ↑↓ interaction of 2p is different than ↑ ↑ for 2p or 2nAnd there is Pauli principleAs a result => A system of n and p can form either a singlet or triplet state. The triplet state is bound, but not the singlet (we know it from deuteron). A system of 2n or 2p can only form a singlet (due to Pauli principle), so no bound state of 2p or 2n, etc, exists.Neutron stars exist thanks to gravity32See more details in http://web-docs.gsi.de/~wolle/TELEKOLLEG/KERN/LECTURE/Fraser/L5.pdf ↑pn↑↑pn↓↑pp↓↑nn↓↑pp↑↑nn↑boundNot allowedunbound

33. Discovery of nucleiDiscovery Project at MSU – documenting discoveries of nuclei33http://www.nscl.msu.edu/~thoennes/isotopes/criteria.html

34. Modelling nuclear interaction34

35. NN potential from QCD35Aoki, Ishii, Matsuda

36. Liquid drop model36

37. Liquid drop modelBased on the experimental binding energy per nucleon Nuclei have nearly constant density => they behave like a drop of uniform (incompressible) liquidForces on the nucleons on the surface are different from those insideDescribes general features of nuclei, but not detailsTerms:37Additional terms -> shell model

38. Mean-field modelsEach particle interacts with an average field generated by all other particles: mean fieldMean field is built from individual excitations between nucleonsNo inert core Very good at describing deformationsCan predict properties of very exotic nucleiNot so good at closed shells38

39. Halo nuclei3911Li:3p,8n208Pb:82p,126nHalo: nucleus built from a core and at least one neutron/proton with spatial distribution much larger than that of the corediscussed88811111985: first halo system identified: 11Li2013: half-dozen other halos knownNuclear structure and core-halo interaction still not well understoodRecent achievements: charge radii of 11Li (Uni Mainz/GSI), 6He (Argonne)=> Crucial information:Mass/binding energySpin-parityMagnetic momentMass and charge radiusQuadrupole momentEnergy level scheme

40. Examples of nuclear decays40