1. Beyond Band Termination: Spectroscopy at Ultra-High Spin
Sarah Rigby
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

2. What is meant by “Ultrahigh Spin”? Why go beyond band termination?
Introduction
What is meant by “Ultrahigh Spin”?
Why go beyond band termination?
Very pure single-particle states
Keeps the theorists happy
Return to collectivity at higher spins
A further change of phase for the nucleus??
First, a bit of history, then onto the recent experiment
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

4. Up to Band Termination: 158Er by Sharpey-Schafer et al
The 12 valence particles move in equatorial orbits, driving the nucleus to an oblate shape!
Valence nucleons relative to 146Gd core
Simpson et al., Phys. Rev. Lett. (1984)
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

5. Up to Band Termination: Rigid Rotor plot
What happens up here? ?
Band terminating states are highly favoured
i.e. much lower in energy on this plot
Same information as on the previous spectrum represented on a rigid rotor plot
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

6. Up to Band Termination: Tilted Fermi Surface Plot82
Work from 1994, Simpson et al
30+
Szamynski et al, Fast Nuclear Rotation
[(h9/2, f7/2)6 (i13/2)2]30+
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

7. Beyond Band Termination: 158Er
Experiment at LBNL using GAMMASPHERE, 2004, by Paul, Simpson and Riley,
analysed by A. Evans
Very weak states observed to feed the 46+ state
(+,0) triples gate
Feeding 46+
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

8. Beyond Band Termination: 157Er
Gammasphere LBNL: 114Cd(48Ca, xn)156,157,158,159Er
Discovery of states BEYOND band termination
2 PRLs: A. O. Evans et al, PRL 92, (2004) and Paul et al., PRL, 98, (2008)
2 PhD theses
Fig. adapted from A. O. Evans et al.
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

9. Beyond Band Termination: 157Er
[(h11/2)3(d3/2s1/2)1]15-
TFS
Calcs 
[(h9/2, f7/2)4 (i13/2)3]61/2+
91/2- state feeding the 87/2- state via an E2 transition
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

10. Beyond Band Termination: 158Er
And there is more!
Clear bands seen in the ħ spin regime in 158Er
2 such bands seen in 158Er and 2 in 157Er
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

11. Beyond Band Termination: Rigid Rotor plot
So, obvious question is what happens in the neighbouring Er nuclei?
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

12. Beyond Band Termination: TSD Bands
Lund PES plot
I = 69
TRS and PES plots predict a strong triaxial minimum
Consistent with other CSM calcs - Ragnarsson

13. … and onto the present… (almost)
History lesson over….
Warning: Erbium can be intoxicating and poisoning is possible…
… and onto the present… (almost)

14. New Experiment at Gammasphere: Motivation
Still questions to be answered:
Do we still see band termination as we increase neutron number?
Terminating bands predicted in 160Er
What about the predicted stable triaxial minima?
What happens beyond band termination?
Other possibilities: Wobbling modes (D. J. Hartley et al, PLB, 608, 31,(2005)), TSDs (S. W. Odegaard et al, PRL 57, 811 (1986); A. Aguilar et al PRC (R) (2008)), unpaired band crossings (M.A. Riley et al PRL (1988))
Also, 2 other Gammasphere LBNL) experiments studying TSDs in neighbouring nuclei: 161Tm and 160Yb (A. Aguilar et al)
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

15. The Experiment at Gammasphere
Fusion-evaporation reaction
116Cd(48Ca, xn)159,160,161Er
215 MeV beam from ATLAS accelerator
fold-7 trigger
coincidence g ray data recorded from Gammasphere
101 HPGe detectors used.
Offline analysis:
Data unfolded into g3 cubes and g4 hypercubes for use with Radware for coincidence analysis – bulk of level scheme analysis
Beyond the hypercube – using MTSort to produce g5, g6 and g7 spectra using the Peter Twin Method
Produce cleaner spectra
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

16. The Experiment at Gammasphere
Heavy metal collimators and absorbers in front of Ge dets
Only record the event if 7 Ge detectors fire simultaneously
Record energy and detector numbers in the data stream for offline analysis
Use Radware for complete spectroscopy and Prof Twin’s method for looking at very weak structures
Fusion evaporation reaction happens in the centre where the target wheel is mounted
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

17. Analysis: Going beyond the hypercube
g6 analysis → must be in coincidence with at least 5 other g’s as detailed in a gate list.
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

18. Results: 160Er 2 Floating bands found
Some evidence of band termination observed with fragmentation at the top of the ground state band
2 New side bands observed at low spin, with linking transitions
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

19. Results: TSD candidate band in 160Er
1604
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

20. Results: TSD candidate band in 159Er
With thanks to James Ollier for the spectrum
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

21. Results: TSD candidate band in 160Er
A “Family” of erbium TSDs! The candidate band in 160Er compared to bands in 157,158Er. The bump is associated with the ni13/2 alignment
And compared to neighbouring bands in 152Dy (SD) and 163Lu (TSD)
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

22. TSD bands in the rare-earth region
159
Pattern of TSD type bands all the way to the Hf174 region
“Valley of triaxiality”
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

23. Results: 161Er “Classic” terminating band in 156Er
Termination observed in 158Er
Rigid Rotor references (x) taken against 158Er:
156Er – I(I+1)
157Er – I(I+1)
158Er – I(I+1)
159Er – I(I+1)
160Er – I(I+1)
161Er – I(I+1)
Will we see termination in 160Er?
No signs of termination in 161Er
Terminating states in 157Er
Termination observed in 159Er, X. Wang – analysis ongoing
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

24. Results: 161Er 161Er – difficult to resolve high energy gs
Ground state band still yrast at very high spin (>60ħ)
Unlikely to see other structures
Analysis ongoing
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

25. Summary Summary of Results from latest data:
Low spin level schemes extended for 159,160Er – probably b vibrational bands
High spin level schemes extended for 159,160,161Er
Band termination observed in the ground state band of 159Er
Fragmentation seen in 160Er – still under analysis – is it abrupt termination?
TSD candidate bands observed in 159,160Er, 3 new TSD-type bands
161Er appears to be a near-perfect rotor
Analysis and interpretation still ongoing:
Best possible spectra for weak bands being produced
Ingemar Ragnarrson currently working on the theory
Comparisons of the TSDs to neighbouring nuclei still ongoing
Search for feeding transitions to terminating state(s) still ongoing.

26. Acknowledgements
S. V. Rigby1, A. O. Evans1, J. Ollier2, A.Pipidis3, E. S. Paul1, M. A Riley3, J. Simpson2,
X. Wang3, A. Aguilar3, M. Akmali1, D. Appelbe2, M. P. Carpenter4, D.B.Campbell3, P.T.W.Choy1, R. M. Clark7, M. Cromaz7, I. Darby5, P. Fallon7, D. J. Hartley6, A.Gorgen7, D.T.Joss2, F. Kondev4, T. Lauritsen4, I. Y. Lee7A. O. Machieavelli7,
P. J. Nolan1, M. Petri1, N. Rowley2, C. Teal3, J. Thomson1, C.Unsworth1, D.Ward7, S. Zhu4
and
I. Ragnarsson8, F. Saric8
1 University of Liverpool, Liverpool, L69 7ZE, UK
2 STFC Daresbury Laboratory, Warrington, UK
3 Florida State University, Tallahassee, Florida, USA
4 Argonne National Laboratory, Argonne, USA
5 U.S. Naval Academy, Annapolis, USA
6 University of Tennessee, Knoxville, USA
7 LBNL, USA
8 Lund University, Sweden