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

The changing structure of 160Er from low to ultrahigh spin

J. OllierDaresbury 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 159,160Er - ultrahigh spins?

Triaxial Strongly deformed TSD

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)

159 160

Reaching ultrahigh spin in 160Er

Experiment:48Ca+116Cd @ 215 MeV116Cd(48Ca,4n)160ErTarget: 1.3 mg/cm2

Experiment:48Ca+116Cd @ 215 MeV116Cd(48Ca,4n)160ErTarget: 1.3 mg/cm2

Apparatus:Gammasphere @ ANL USA110 HPGes – 101 usedTrigger: >6 Ge’s fired

Apparatus:Gammasphere @ ANL USA110 HPGes – 101 usedTrigger: >6 Ge’s fired

Analysis:• ~1011 - - g g g• ~1010 - - -g g g g• RadWare g3, g4

• Higher-fold gates

Analysis:• ~1011 - - g g g• ~1010 - - -g g g g• RadWare g3, g4

• 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, 064322 (2009)J. Ollier et al., in press PRC (2011)

• Previous work:– Even and odd-spin g-vibrational bands observed;

12+ and (13+) respectively, 159Tb(6Li,5n)160Er.

• Present work:

Dusling et al., PRC 73, 014317 (2006)

g vibration:collective quadrupolevibrations withoutradial symmetry

Yras

t ban

d

Previous

Even spin g bandstates not seen inpresent work

Odd-spin positive-parity states extended up to(43ħ); Based on g band

From g4 hypercube

Band 5: g vibration

Rare observation!

• 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

Band 5: g vibration

Signature (a): rotational quantum number

Extremely rare observation!

Band 4: b vibration?Yr

ast b

and

Band 3 46ħ

Band 4: New• +ve parity• even spin In literature: b band or second vacuum?

• Large alignment 2 qp + vibrational?

Dusling et al., PRC 73, 014317 (2006)

b band to 14+ state

• b band not seen in this experiment

The (a,p)=(0,+)bands are fed at highspin and depopulate out through yrast band

High spin: The yrast structuresPrevious 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

Deciphering the high-spin data• 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?

CNS calculations for 160Erfrom 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 (146Gd)

Band termination:Occurs when all valance nucleons

become fully aligned with core (146Gd)

Beyond 50ħ to ultrahigh spin?

3 “floating”bands foundassociatedwith 160Er

Assume in-bandstretched E2s J(2) = DE/DI

Similar to the bandsfound in 157,158Er bypass terminatingstates, possible TSD bands

TSD 3

J. Ollier et al., PRC 80, 064322 (2009)J. Ollier et al., in press PRC (2011)

Triaxial structures

e2cos(g+30o)

e2c

os(g

+30o )

Potential energysurfaces: 160Er(p,a) = (-,+)

g = 0o

g =

60o

g ~ -20o

Ip = 31-

g ~ 20o

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)

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. Kardan7 and I. Ragnarsson7

1. 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