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Physics at the extremes with large gamma-ray arrays Lecture 1

Physics at the extremes with large gamma-ray arrays Lecture 1. Robert V. F. Janssens. The 14 th CNS International Summer School CNSSS15 Tokyo, August 26 – September 1, 2015. Outline:. Lecture 1: - Introduction to Gamma-ray Arrays - At the limits of spin

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Physics at the extremes with large gamma-ray arrays Lecture 1

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  1. Physics at the extremes with large gamma-ray arraysLecture 1 Robert V. F. Janssens The 14th CNS International Summer School CNSSS15 Tokyo, August 26 – September 1, 2015

  2. Outline: Lecture 1: - Introduction to Gamma-ray Arrays - At the limits of spin Lecture 2: - Spectroscopy at the proton drip line - Spectroscopy of the heaviest nuclei Lecture 3: - Spectroscopy of neutron-rich nuclei Lecture 4: - Spectroscopy of neutron-rich nuclei continued Robert V. F. Janssens CNSSS15

  3. Outline: Lecture 1:- Introduction to Gamma-ray Arrays - At the limits of spin Lecture 2: - Spectroscopy at the proton drip line - Spectroscopy of the heaviest nuclei Lecture 3: - Spectroscopy of neutron-rich nuclei Lecture 4: - Spectroscopy of neutron-rich nuclei continued Robert V. F. Janssens CNSSS15

  4. A bit of History: Gammasphere Euroball NaI(Tl) Ge(Li) Robert V. F. Janssens CNSSS15 Small Compton-suppressed array

  5. Robert V. F. Janssens CNSSS15

  6. Gamma-Ray Spectroscopy: Times are Changing • A new generation of gamma-ray arrays with tracking capability is (almost) here: AGATA and GRETA . GRETINA AGATA Demonstrator Robert V. F. Janssens CNSSS15

  7. Two decades of large arrays: Motivation: “One area where enormous gains can be made is in RESOLVING POWER (R)” R: The ability to isolate a given sequence of g rays from a very complex spectrum. . . Robert V. F. Janssens CNSSS15

  8. Two decades of large arrays: Robert V. F. Janssens CNSSS15

  9. Euroball Array: 15 seven-fold Cluster detectors 30 coaxial detectors 26 four-fold Clover detectors Robert V. F. Janssens CNSSS15

  10. Gammasphere at the ATLAS facility at Argonne National Laboratory Robert V. F. Janssens CNSSS15

  11. Gammasphere: Basic Components Robert V. F. Janssens CNSSS15

  12. Gammasphere: Basic Principle Robert V. F. Janssens CNSSS15

  13. Nuclear Structure at the limits: First Case Limit in Angular Momentum Robert V. F. Janssens CNSSS15

  14. Basic Nuclear Structure from g – ray Spectra Collective Rotation Single-Particle Excitation Deformed nucleus rotating about an axis perpendicular to the symmetry axis. Excitation energy and angular momentum are generated by single- particle excitations from continually changing configurations. Robert V. F. Janssens CNSSS15

  15. vibrations Robert V. F. Janssens CNSSS15

  16. Basics of Rotation axial symmetry: rotational axis  symmetry axis for K1/2: I+14 kinematic moment of inertia I+12 dynamic moment of inertia I+10 I+8 E J (2) measures the variation of J (1) rigid rotor: J (2) = J (1) I+6 rotational frequency J (2) [ħ2MeV-1] I+4 superdeformed 152Dy I+2 I ħ [keV] j single-particle angular momentum  projection of j on symmetry axis R collective angular momentum J total angular momentum K projection of J on symmetry axis Robert V. F. Janssens CNSSS15

  17. Superdeformation: Shell Effects at Large Deformation Single-particle levels for an Harmonic Oscillator potential as a function of elongation  Shell gaps at large deformation (2:1, 3:1) Single-particle levels for a Woods-Saxon potential (high level density regions are shaded)  Shell gaps remain, but not necessarily at 2:1 or 3:1 exactly Role of Rotation: deepening of the SD minimum  yrast at high spin use fusion-evaporation with heavy ions to generate high spin Robert V. F. Janssens CNSSS15

  18. Superdeformation: Shell Effects at Large Deformation Robert V. F. Janssens CNSSS15

  19. Superdeformation: The Spectrum that helped make the case for the large arrays: 152Dy P. Twin et al., PRL 57, 811 In this presentation: answers to SOME of the questions about physics at 2:1 deformation: - E*(SD), Ip -Nature of Excitations in SD well Robert V. F. Janssens CNSSS15

  20. Superdeformation: Some fundamentals Experimental Signature of Rotational Bands: Why a picket fence? E(I) ~ I(I+1) ~ I2 + I Eg~ 4I + 6 E(I+2) ~ (I+2)(I+3) ~ I2 + 5I +6 Eg~ 4I + 14 Eg ~ 4I E(I+4) ~ (I+4)(I+5) ~ I2 + 9I +20 Eg~ 4I + 22 E(I+6) ~ (I+6)(I+7) ~ I2 + 13I + 42 Robert V. F. Janssens CNSSS15

  21. Superdeformation: Shell Effects at Large Deformation Robert V. F. Janssens CNSSS15

  22. Superdeformation: Magic SD Nuclei Lower Frequency at A~190 SD trapping to lower spin Robert V. F. Janssens CNSSS15

  23. Superdeformation: 20 Years Later: SD band is linked 400000 300000 200000 100000 108Pd(48Ca,4n)152Dy 38 shifts (12 days) Isomer tagging (87 nsec isomer) T. Lauritsen et al. PRL 88, 42501 Robert V. F. Janssens CNSSS15

  24. Superdeformation: 20 Years Later: SD band is linked Robert V. F. Janssens CNSSS15

  25. Superdeformation: 20 Years Later: SD band is linked Highest spin established with certainty thus far To 68+ E* and Ipestablished Decay mechanism understood T. Lauritsen et al. PRL 88, 42501 Isomer Robert V. F. Janssens CNSSS15

  26. Superdeformation: The Strength of the Shell Effects Experiment: Lowest State in SD band: Ip = 24+ E(0+) = 7.5 MeV Calculations: Nilsson – Strutinsky26+ 8.8 MeV I. Ragnarsson NP A557, 167 Woods – Saxon 22+ 8.4 MeV J. Dudek et al., PR C38, 940 Relativistic Mean Field 24+ 8.3 MeV A.V. Afanasjev et al., NP A634, 395 HartreeFockBogoliubov24+ 7.1 MeV J.L. Egido et al., PRL 85, 26 Robert V. F. Janssens CNSSS15

  27. Superdeformation: Transition Rates & Quadrupole Moments y x z x quadrupole moment and deformation parameter: spectroscopic quadrupole moment observed in the laboratory frame Qs=0 for I=0) reduced transition probability unit: 1 e2b2 = 104e2fm4 lifetime or transition rate  [ps], B(E2) [e2b2], E [MeV],  conversion coefficient ellipsoid with symmetry axis z electric quadrupole moment with respect to z electric charge distribution unit: 1b = 10-28 m2 = 100fm2 intrinsic quadrupole moment in the body-fixed frame Robert V. F. Janssens CNSSS15

  28. Superdeformation: Lifetimes Doppler shift attenuation method target with backing gamma rays are emitted • with full recoil velocity • slowed down • stopped Lineshape profile characteristic of lifetime Robert V. F. Janssens CNSSS15

  29. Superdeformation: Lifetimes 192Hg • =0.184 (40) ps, • B(E2) ~2310W.u. • =0.083 (24) ps, • B(E2) ~2590W.u b2 ~ 0.5 • =0.049 (13) ps, • B(E2) ~1930 W.u E.F. Moore et al. PRL 64, 3127 Robert V. F. Janssens CNSSS15

  30. Superdeformation: Lifetimes E [keV] cos  cos  cos  fit average recoil velocity for each transition 6.6 eb 5.9 eb 5.6 eb 8.0 eb 6.7 eb 5.9 eb 3.5 eb 3.5 eb  average recoil velocity 0 average initial recoil velocity Fractional Doppler shifts – F() method thin target data forward detectors (50º) no Doppler correction backward detectors (130º) no Doppler correction very fast transitions at the top of the SD band have almost the full initial recoil velocity: F()1 not quite as fast transitions are emitted still within the thin target, but after the recoils have been slightly slowed down, F()0.9 slower transitions at the bottom of the band and ND transitions are emitted after the recoils have left the target, F()0.8 • Extract quadrupole moment by comparing with simulation, including stopping powers. • Gives quadrupole moment of the band, not individual lifetimes. Robert V. F. Janssens CNSSS15

  31. Superdeformation: Lifetimes 152Dy B(E2) ~2660 W.u. b2 ~ 0.6 M.A. Bentley et al. PRL 59, 2141 Robert V. F. Janssens CNSSS15

  32. Superdeformation: P. Dagnal et al., PLB 335, 313 More SD Bands  the SD well sustain many excitations Robert V. F. Janssens CNSSS15

  33. Superdeformation: Nature of the excitations in the SD well P. Dagnal et al., PLB 335, 313 Most excitations are understood as quasi-particle excitations  dominant role of high-j intruder orbitals W. Nazarewicz et al., NP A503, 285 “The picture of extreme single particle motion applies, the best example of the application of the shell model at extremes of angular momentum and deformation” Robert V. F. Janssens CNSSS15

  34. Superdeformation: Collective excitation in the SD well Linking transitions competing with fast E2 in-band transitions  Collective E1 transitions T. Lauritsen et al., PRL 89, 282501 0.07% Calc.: Nakatsukasa et al. PLB 343, 19 (1995) 1.8% The presence of intruder orbitals (j15/2 neutrons and i13/2 protons) near the Fermi surface, close to levels of opposite parity with Dl = 3 (g9/2 neutrons and f7/2 protons) results in octupole vibration as favored collective mode Robert V. F. Janssens CNSSS15

  35. 152Dy: A laboratory to study generation of angular momentum Robert V. F. Janssens CNSSS15

  36. Octupole Correlations: Traditional View Octupole correlations originate from the long-range interactions between valence nucleons occupying states with Δj = Δl = 3 In actinide nuclei: j15/2g9/2 i13/2f7/2 Robert V. F. Janssens CNSSS15

  37. Octupole Correlations: Vibrations • Signatures: • Negative-parity states higher than ground-state band positive-parity states • Strong E1 linking transitions • E1 transitions only from negative-parity states to ground-state band positive-parity states • Negative-parity states not necessarily the lowest excitation • Note; Coulomb excitation gets to I ~ 30-35  not a spin limit Robert V. F. Janssens CNSSS15

  38. Octupole Rotation: signatures Signature 1: 1- energy & hindrance in a decay Robert V. F. Janssens CNSSS15

  39. Octupole Rotation: signatures Signature 2: E1 “zig-zag” transitions Robert V. F. Janssens CNSSS15

  40. Octupole Rotation: signatures Signature 3: Parity Doublets Robert V. F. Janssens CNSSS15

  41. Octupole Rotation: signatures (I+5)- (I+6)+ (I+3)- (I+5)- (I+1)- (I+4)+ (I+3)- S(I) (I+2)+ (I+1)- I+ Octupole Vibration Octupole Deformed Signature 4: Energy Staggering Robert V. F. Janssens CNSSS15

  42. Octupole Correlations: Not everything is understood (240Pu) Experiment: “Unsafe” Coulomb Excitation of 240Pu with a 208Pb beam ~ 15% above the barrier Observations: (1) “zig-zag” pattern of E1 transitions between states of bands 1 (+ parity) and 2 (- parity) at high spin just like in octupole deformed rotors (2) strong E1 transitions between band 3 (+ parity) and band 2 (- parity). To the best of our knowledge this is a “first”! 240Pu X. Wang et al., PRL 102, 122501 Robert V. F. Janssens CNSSS15

  43. From collective rotation to band termination ? J. Simpson et al., Phys. Lett. B 327, 187 (1994) Robert V. F. Janssens CNSSS15

  44. 93/2+ 89/2- 87/2- Feeding of the terminating states The very weak feeding transitions originate from the levels of weakly-deformed, core-breaking configurations. 157Er Evans et. al., Phys. Rev. Lett. 92, 252502 Robert V. F. Janssens CNSSS15

  45. Evidence for return to collectivity E.S. Paul et al., PRL 98, 012501 158Er 157Er No links to known structure(s)  guess on spins  I ~ 60?? Robert V. F. Janssens CNSSS15

  46. Return to collectivity E.S. Paul et al., PRL 98, 012501 Robert V. F. Janssens CNSSS15

  47. TRIAXIAL (positive-gamma) TSD NEAR-AXIAL (Enhanced Deformation) TRIAXIAL (negative-gamma) TSD What deformation? Robert V. F. Janssens CNSSS15

  48. FW 90O BW Doppler Shift (DSAM) Measurement X. Wang et al., PLB 702, 127 Robert V. F. Janssens CNSSS15

  49. M E A S U R E D M E A S U R E D Z O N E Z O N E Theory vs Experiment TSD1 ED THEORY NEEDS WORK STAY TUNED TSD2 TSD3 Qt = Q0 * cos(+30O)/cos(30O); Q0 = [2*(1+ 2/2)+25/33* 42- 2* 4]*[4/5*(1.2)2*Z*A(2/3)]/100; Qt is transitional quadrupole moment; Q0 is intrinsic quadrupole moment; 4 is set to be 0 here; Z is proton number; A is mass number. X. Wang et al., PLB 702, 127 Robert V. F. Janssens CNSSS15

  50. Take-away Message • Large, modern arrays are powerful tools for high-precision nuclear structure studies up to the very limit in spin that nuclei can sustain • Many interesting phenomena occur at high spin: a few examples were given here  Superdeformation •  Octupole vibrations & rotations •  The demise & return of collectivity Robert V. F. Janssens CNSSS15

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