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 – 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 159,160 Er - ultrahigh spins? Triaxial Strongly deformed TSD Superdeformed SD Our collaboration: 157,158 Er: E.S. Paul et al., PRL 98, (2007) 160 Yb: A. Aguilar et al., PRC 77, (R) (2008) 160,161 Tm: C. Teal et al., PRC 78, (2008) Our collaboration: 157,158 Er: E.S. Paul et al., PRL 98, (2007) 160 Yb: A. Aguilar et al., PRC 77, (R) (2008) 160,161 Tm: C. Teal et al., PRC 78, (2008)

Reaching ultrahigh spin in 160 Er Experiment: 48 Ca MeV 116 Cd( 48 Ca,4n) 160 Er Target: 1.3 mg/cm 2 Experiment: 48 Ca MeV 116 Cd( 48 Ca,4n) 160 Er Target: 1.3 mg/cm 2 Apparatus: ANL USA 110 HPGes – 101 used Trigger: >6 Ge’s fired Apparatus: ANL USA 110 HPGes – 101 used Trigger: >6 Ge’s fired Analysis: ~10 11  ~10 10  RadWare  3,  4 Higher-fold gates Analysis: ~10 11  ~10 10  RadWare  3,  4 Higher-fold gates

 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, (2009) J. Ollier et al., in press PRC (2011) J. Ollier et al., PRC 80, (2009) J. Ollier et al., in press PRC (2011)

Previous work: – Even and odd-spin  -vibrational bands observed; 12 + and (13 + ) respectively, 159 Tb( 6 Li,5n) 160 Er. Present work: Dusling et al., PRC 73, (2006)  vibration: collective quadrupole vibrations without radial symmetry  vibration: collective quadrupole vibrations without radial symmetry Yrast band Previous Even spin  band states not seen in present work Even spin  band states not seen in present work Odd-spin positive-parity states extended up to (43ħ); Based on  band Odd-spin positive-parity states extended up to (43ħ); Based on  band From  4 hypercube Band 5:  vibration Rare observation!

Tracks the yrast band, sees both the 1st – (i 13/2 ) 2 alignment –  (h 11/2 ) 2 alignment Based on  vibration at low spin High spin: Signature partner ( ,  )=(+,1) of the (+,0) yrast band Band 5:  vibration Signature (  ): rotational quantum number Extremely rare observation!

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

High spin: The yrast structures Previous work: Yrast bands populated to  (54 + ), (54 - ), (47 - )* Kondev et 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 Lots of new peaks observed at higher spin  No definite ordering  Dramatic drop in intensity

Deciphering the high-spin data 158 Er (-2n), prolate bands crossed by terminating bands with very favoured terminating single particle states at: 40 +, Er (+2n), prolate structures observed to highest spins ~(60ħ) and remain yrast 160 Er transitional? competing prolate and oblate configurations? CNS calculations for 160 Er from I. Ragnarsson, Lund. CNS calculations for 160 Er from I. Ragnarsson, Lund. 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 ( 146 Gd) Band termination: Occurs when all valance nucleons become fully aligned with core ( 146 Gd)

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

Triaxial structures  2 cos(  +30 o ) Potential energy surfaces: 160 Er ( ,  ) = (-,+) Potential energy surfaces: 160 Er ( ,  ) = (-,+)  = 0 o  = 60 o  ~ -20 o I  = 31 -  ~ 20 o

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

Thanks to… J. Simpson 1, M.A. Riley 2, X. Wang 2, E.S. Paul 3, A. Aguilar 2, C. Teal 2, P.J. Nolan 3, M. Petri 3, J.M. Rees 3, S.V. Rigby 3, J. Thomson 3, C. Unsworth 3, M.P. Carpenter 4, R.V.F. Janssens 4, F.G. Kondev 4, T. Lauritsen 4, S. Zhu 4, D.J. Hartley 5, I. Darby 6, A. Kardan 7 and I. Ragnarsson 7 1. STFC Daresbury Laboratory, Warrington, UK 2. Florida State University, Florida, USA 3. The University of Liverpool, Liverpool, UK 4. Argonne National Laboratory, Argonne, USA 5. U. S. Naval Academy, Annapolis, USA 6. University of Tennessee, Knoxville, USA 7. Lund Institute of Technology, Lund, Sweden