beyond band termination: spectroscopy at ultra-high spin
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Beyond Band Termination: Spectroscopy at Ultra-High Spin. Sarah Rigby. Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy. Introduction. What is meant by “Ultrahigh Spin”? Why go beyond band termination? Very pure single-particle states - PowerPoint PPT PresentationTRANSCRIPT
Beyond Band Termination: Spectroscopy at Ultra-High Spin
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy
Sarah Rigby
• 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
Introduction
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy
The 12 valence particles move in The 12 valence particles move in equatorial orbits, driving the equatorial orbits, driving the nucleus to an oblate shape!nucleus to an oblate shape!
Simpson et al., Phys. Rev. Lett. (1984)
Up to Band Termination: 158Er by Sharpey-Schafer et al
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy
Valence nucleons relative to 146Gd core
Up to Band Termination: Rigid Rotor plot
Same information as on the previous spectrum represented on a rigid
rotor plot
Band terminating states are highly favoured i.e. much lower in energy on this plot
?What happens
up here?
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy
82
30+
[(h9/2, f7/2)6 (i13/2)2]30+
Up to Band Termination: Tilted Fermi Surface Plot
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy
Work from 1994, Simpson et al
(+,0) triples gate
Feeding 46+
Beyond Band Termination: 158Er
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy
Very weak states observed to feed the 46+ state
Experiment at LBNL using GAMMASPHERE, 2004, by Paul, Simpson and Riley,analysed by A. Evans
Beyond Band Termination: 157Er
• Gammasphere experiment @ LBNL: 114Cd(48Ca, xn)156,157,158,159Er• Discovery of states BEYOND band termination• 2 PRLs: A. O. Evans et al, PRL 92, 252502 (2004) and Paul et al., PRL, 98, 012501 (2008)• 2 PhD theses
Fig. adapted from A. O. Evans et al.
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy
Beyond Band Termination: 157Er
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy
15-
[(h11/2)3(d3/2s1/2)1]15-
61/2+
[(h9/2, f7/2)4 (i13/2)3]61/2+
15-
[(h11/2)3(d3/2s1/2)1]15-
15-
[(h11/2)3(d3/2s1/2)1]15-
15-
[(h11/2)3(d3/2s1/2)1]15-
61/2+
[(h9/2, f7/2)4 (i13/2)3]61/2+
61/2+
[(h9/2, f7/2)4 (i13/2)3]61/2+
15-
[(h11/2)3(d3/2s1/2)1]15-
61/2+
[(h9/2, f7/2)4 (i13/2)3]61/2+
15-
[(h11/2)3(d3/2s1/2)1]15-
15-
[(h11/2)3(d3/2s1/2)1]15-
15-
[(h11/2)3(d3/2s1/2)1]15-
61/2+
[(h9/2, f7/2)4 (i13/2)3]61/2+
61/2+
[(h9/2, f7/2)4 (i13/2)3]61/2+
[(h11/2)3(d3/2s1/2)1]15-
[(h9/2, f7/2)4 (i13/2)3]61/2+
TFSCalcs
91/2- state feeding the 87/2- state via an E2 transition
Beyond Band Termination: 158Er
And there is more!Clear bands seen in the 50-60 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
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
Beyond Band Termination: TSD Bands
I = 69I = 69
Lund PES plot
TRS and PES plots predict a strong triaxial minimumConsistent with other CSM calcs - Ragnarsson
… and onto the present…(almost)
History lesson over….
Warning: Erbium can be intoxicating and poisoning is possible…
• 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 77 021302(R) (2008)), unpaired band crossings (M.A. Riley et al PRL 60 553 (1988))
Also, 2 other Gammasphere (@ LBNL) experiments studying TSDs in neighbouring nuclei: 161Tm and 160Yb (A. Aguilar et al)
New Experiment at Gammasphere: Motivation
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy
Still questions to be answered:
The Experiment at Gammasphere
The experiment: •Fusion-evaporation reaction•116Cd(48Ca, xn)159,160,161Er•215 MeV beam from ATLAS accelerator•fold-7 trigger •coincidence ray data recorded from
Gammasphere•101 HPGe detectors used.
Offline analysis: • Data unfolded into 3 cubes and 4 hypercubes for
use with Radware for coincidence analysis – bulk of level scheme analysis
• Beyond the hypercube – using MTSort to produce 5, 6 and 7 spectra using the Peter Twin Method
• Produce cleaner spectraSarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy
Only record the event if 7 Ge detectors fire simultaneously
Fusion evaporation reaction happens in the centre where the target wheel is mounted
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
Heavy metal collimators and absorbers in front of Ge dets
The Experiment at Gammasphere
Analysis: Going beyond the hypercube
6 analysis → must be in coincidence with at least 5 other ’s as detailed in a gate list.
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy
2 New side bands observed at low spin, with linking transitions
Some evidence of band termination observed with fragmentation at the top of the ground state band
2 Floating bands found
Results: 160Er
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy
1604
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy
Results: TSD candidate band in 160Er
Results: TSD candidate band in 159Er
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy
With thanks to James Ollier for the spectrum
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 i13/2 alignment
And compared to neighbouring bands in 152Dy (SD) and 163Lu (TSD)
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy
TSD bands in the rare-earth region
159
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy
Pattern of TSD type bands all the way to the Hf174 region
“Valley of triaxiality”
Rigid Rotor references (x) taken against 158Er:
156Er – 0.00715I(I+1)157Er – 0.00707I(I+1)158Er – 0.00700I(I+1)159Er – 0.00693I(I+1)160Er – 0.00685I(I+1)161Er – 0.00678I(I+1)
No signs of termination in 161Er
Terminating states in 157Er Termination observed in 159Er, X. Wang – analysis ongoing
“Classic” terminating band in 156Er
Termination observed in 158Er
Will we see termination in 160Er?
Results: 161Er
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy
Results: 161Er
Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy
•161Er – difficult to resolve high energys•Ground state band still yrast at very high spin (>60ħ)•Unlikely to see other structures•Analysis ongoing
Summary of Results from latest data:• Low spin level schemes extended for 159,160Er – probably
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.
Summary
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
Acknowledgements