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The changing structure of 160 Er from low to ultrahigh spin

The changing structure of 160 Er from low to ultrahigh spin. J. Ollier Daresbury Laboratory. Motivation. Observe nuclear structure up to ultrahigh spin ≈60ħ: understand the influence of single-particle configurations on the collective structures Area of Interest: Rare-earths N≈90

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The changing structure of 160 Er from low to ultrahigh spin

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  1. The changing structure of 160Er from low to ultrahigh spin J. Ollier Daresbury Laboratory

  2. Motivation • Observe nuclear structure up to ultrahigh spin ≈60ħ: • understand the influence of single-particle configurations on the collective structures • Area of Interest: Rare-earths N≈90 • Rich in rotational bands built on many quasi-particle structures • Lies between the classic SD and TSD regions • recent discovery of collective bands – possible TSD structures at high spin • Main aim: • Search for possible TSD structures in 159,160Er - ultrahigh spins? Triaxial Strongly deformed TSD 159 160 Superdeformed SD Our collaboration: 157,158Er: E.S. Paul et al., PRL 98, 0120501 (2007) 160Yb: A. Aguilar et al., PRC 77, 021302(R) (2008) 160,161Tm: C. Teal et al., PRC 78, 017305 (2008)

  3. Reaching ultrahigh spin in 160Er Apparatus: Gammasphere@ ANL USA 110 HPGes – 101 used Trigger: >6 Ge’s fired Experiment: 48Ca+116Cd @ 215 MeV 116Cd(48Ca,4n)160Er Target: 1.3 mg/cm2 • Analysis: • ~1011g-g-g • ~1010g-g-g-g • RadWareg3, g4 • Higher-fold gates

  4. Bands 4 and 5 based on • Vibrational excitations? • Competition between • prolate collective and • oblate shapes at yrast line • Triaxial structures? J. Ollier et al., PRC 80, 064322 (2009) J. Ollier et al., in press PRC (2011)

  5. Band 5: g vibration Duslinget al., PRC 73, 014317 (2006) • Previous work: • Even and odd-spin g-vibrational bands observed; 12+ and (13+) respectively, 159Tb(6Li,5n)160Er. • Present work: From g4 hypercube Odd-spin positive-parity states extended up to (43ħ); Based on g band Yrast band Rare observation! Previous g vibration: collective quadrupole vibrations without radial symmetry Even spin g band states not seen in present work

  6. Band 5: g vibration • Tracks the yrast band, sees both the 1st • n(i13/2)2 alignment • p(h11/2)2 alignment • Based on g vibration at low spin • High spin: Signature partner (p,a)=(+,1) of the (+,0) yrast band Extremely rare observation! Signature (a): rotational quantum number

  7. Band 3  46ħ Band 4: b vibration? • Large alignment • 2 qp + vibrational? Duslinget al., PRC 73, 014317 (2006)  b band to 14+ state Yrast band • b band not seen • in this experiment The (a,p)=(0,+) bands are fed at high spin and depopulate out through yrast band • Band 4: New • +ve parity • even spin In literature: bband or second vacuum?

  8. High spin: The yrast structures Previous work: Yrastbands populated to  (54+), (54-), (47-)* Kondevet al., JPG 25, 897 (1999), * Simpson et al., JPG 13, L235 (1987). Present work: • Lots of new peaks observed at higher spin • No definite ordering • Dramatic drop in intensity

  9. Deciphering the high-spin data CNS calculations for 160Er from I. Ragnarsson, Lund. • 158Er (-2n), prolate bands crossed by terminating bands with very favoured terminating single particle states at: 40+, 46+ • 162Er (+2n), prolate structures observed to highest spins ~(60ħ) and remain yrast • 160Er transitional? competing prolate and oblate configurations? • Competing configurations: • Oblate and prolate at ~50ħ • band terminations • no clear yrast states Band termination: Occurs when all valance nucleons become fully aligned with core (146Gd)

  10. Beyond 50ħ to ultrahigh spin? TSD 3 3 “floating” bands found associated with 160Er Assume in-band stretched E2s  J(2) = DE/DI Similar to the bands found in 157,158Er  bypass terminating states, possible TSD bands J. Ollier et al., PRC 80, 064322 (2009) J. Ollier et al., in press PRC (2011)

  11. Triaxial structures Potential energy surfaces: 160Er (p,a) = (-,+) g = 60o g ~ 20o g = 0o e2cos(g+30o) g ~ -20o Ip = 31- e2cos(g+30o)

  12. Triaxial structures • Take us up to ultrahigh spin region (50  70ħ) • However, can’t prove triaxial configurations • Need lifetime measurements • Qt values measured for 157,158Er and 154Er • See John Revill’s talk on 154Er (Wednesday). • Near future experiments • High-spins states in 162Hf  submitted to ANL • High-spins states and lifetimes around 140Nd  submitted to ANL • 160Er is rich in nuclear structure from low to ultrahigh spin: J. Ollier et al., in press PRC (2011)

  13. Thanks to… J. Simpson1, M.A. Riley2, X. Wang2, E.S. Paul3, A. Aguilar2, C. Teal2, P.J. Nolan3, M. Petri3, J.M. Rees3, S.V. Rigby3, J. Thomson3, C. Unsworth3, M.P. Carpenter4, R.V.F. Janssens4, F.G. Kondev4, T. Lauritsen4, S. Zhu4, D.J. Hartley5, I. Darby6, A. Kardan7and I. Ragnarsson71. STFC Daresbury Laboratory, Warrington, UK2. Florida State University, Florida, USA3. The University of Liverpool, Liverpool, UK4. Argonne National Laboratory, Argonne, USA5. U. S. Naval Academy, Annapolis, USA6. University of Tennessee, Knoxville, USA7. Lund Institute of Technology, Lund, Sweden

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