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Nuclei at the Extremes of Spin: The Superdeformed Bands in 131,132 Ce

Nuclei at the Extremes of Spin: The Superdeformed Bands in 131,132 Ce. Liverpool, Daresbury, Lyon, Grenoble, Strasbourg, Debrecen, Padova, Camerino. Euroball IV. Nuclei at the Extremes of Spin: The Superdeformed Bands in 131,132 Ce. The Nucleus is a Mesoscopic System at the Femtoscale.

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Nuclei at the Extremes of Spin: The Superdeformed Bands in 131,132 Ce

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  1. Nuclei at the Extremes of Spin:The Superdeformed Bands in131,132Ce Liverpool, Daresbury, Lyon, Grenoble, Strasbourg, Debrecen, Padova, Camerino Euroball IV Lund Conference June 2005 : E.S. Paul

  2. Nuclei at the Extremes of Spin:The Superdeformed Bands in131,132Ce Lund Conference June 2005 : E.S. Paul

  3. The Nucleus is a Mesoscopic System at the Femtoscale • Mesoscopic: The atomic nucleus consists of a large, yet finite, number of strongly interacting constituent fermions (nucleons) • Femtoscale: The size of the nucleus is of the order of femtometres (10-15 m) • Similar to nanoscale (10-9 m) mesoscopic systems, e.g. metallic clusters, the properties (shell structure, deformation) are determined by the finite number of constituents Lund Conference June 2005 : E.S. Paul

  4. At the Limits of Angular Momentum: Band Termination • Fundamentally, nuclear angular momentum is generated by the (finite number of) constituent nucleons • Hence there must be a “maximum” value for a given nucleus, or rather nucleonic configuration • Experimentally this is seen as “termination” of a rotational band in nuclei when the nuclear angular momentum is generated entirely from the constituent nucleons rather than collective excitations of the nucleus Lund Conference June 2005 : E.S. Paul

  5. Experimental Band Termination • A band terminates when all valence particles outside a doubly magic (spherical)core are aligned Lund Conference June 2005 : E.S. Paul

  6. Superdeformed Shell Structure • New shell gaps appear when the lengths of the nuclear axes occur in the ratio of small integers: 2:1 (A = 150, dysprosium) 3:2 (A = 130, cerium) 3:1 (“hyperdeformation”) • But they occur at different particle numbers to the spherical case Lund Conference June 2005 : E.S. Paul

  7. To Terminate or Not? • For modest (i.e. small) deformation, solutions of the Harmonic Oscillator suggest that configurations will terminate into a noncollective oblate state where the spin is simply given by the sum of the angular momenta of the ‘pure’ single particle configuration: Imax • For large deformation (e.g. 2:1 superdeformation), however, spin above Imax can be generated • The SD Ce deformation (3:2 axes ratio) occurs at the intersection of these two regimes • The (experimental) question is: will the SD bands in cerium nuclei ‘terminate’ or not? Lund Conference June 2005 : E.S. Paul

  8. Superdeformation in 132Ce • The first SD band was discovered in 132Ce: PJ Nolan et al., J. Phys G 11, L17 (1985) • Its “enhanced” quadrupole moment showed it to correspond to the 3:2 shape AJ Kirwan et al., Phys. Rev. Lett. 58, 467 (1987) The TESSA3 array at Daresbury Lund Conference June 2005 : E.S. Paul

  9. EUROBALL IV Results • A BGO inner ball calorimeter allowed measurement of the total (summed) γray energy and also the number of emitted γrays in an event • Gating on these quantities enhanced the yield of 132Ce (top) Lund Conference June 2005 : E.S. Paul

  10. Yrast SD Band in 132Ce (SD1) • Top: triples (double gated) γ-ray spectrum of SD1 in 132Ce with a high ‘sum-energy/fold’ condition • Bottom: triples γ-ray spectrum from the whole data set Lund Conference June 2005 : E.S. Paul

  11. SD1 in 132Ce • The lowest energy (yrast) superdeformed band in 132Ce spans 50ħ (from 20ħ to 70ħ) of angular momentum (in a finite fermionic system) ! Lund Conference June 2005 : E.S. Paul

  12. SD2 and SD3 in 132Ce Lund Conference June 2005 : E.S. Paul

  13. 132Ce SD1 Rigid-Rotor Plot • The yrast SD band in 132Ce shows similarities to smoothly terminating bands in A ~ 100 nuclei. It is approaching the maximum spin for its configuration (termination at 78ħ) Lund Conference June 2005 : E.S. Paul

  14. Theory: Protons (Z = 58) • Important orbitals (relative to Z = 50): • h11/2‘intruder’ levels (particles) - red • g9/2 ‘extruder’ levels (holes) - blue • Cerium has a 10 particle 2 hole configuration • A ‘finite’ number of valence protons to generate angular momentum Lund Conference June 2005 : E.S. Paul

  15. Theory: Neutrons (N = 74) • Important orbitals (relative to N = 82): • h9/2 and f7/2 intruder orbitals – blue • i13/2 intruder orbitals – green • h11/2 holes – red • Again a finite number of ‘constituents’ to generate the angular momentum Lund Conference June 2005 : E.S. Paul

  16. 132Ce SD1 Theory • Cranked Nilsson Strutinsky calculations have been performed • The yrast SD1 band in 132Ce cannot be described over its whole range by a single configuration • Look at dynamic moment of inertia Lund Conference June 2005 : E.S. Paul

  17. Dynamic Moments of Inertia Lund Conference June 2005 : E.S. Paul

  18. 131Ce SD1 and SD2 Lund Conference June 2005 : E.S. Paul

  19. 131Ce SD1 – SD2 Links 100% 90% 10% Lund Conference June 2005 : E.S. Paul

  20. 131Ce: SD1 & SD2 Extension + Links • The excited band in 131Ce (SD2) has the same configuration as the yrast band in 132Ce (SD1) • 131Ce SD2 becomes favoured (yrast) at high spin • 131Ce SD2 has a larger quadrupole moment (8.2eb) compared to all other bands in 131,132Ce (7.3 eb) Lund Conference June 2005 : E.S. Paul

  21. 131Ce Theory Lund Conference June 2005 : E.S. Paul

  22. Nuclei at the Extremes of Spin:The Superdeformed Bands in131,132Ce The End Lund Conference June 2005 : E.S. Paul

  23. Gammasphere Expt (Nov 2004) (AC Milan) Lund Conference June 2005 : E.S. Paul

  24. 132Ce SD1 Decay & Links Aled Evans Lund Conference June 2005 : E.S. Paul

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