1 / 24

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.

mcoates
Download Presentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related