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

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

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

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

Up to Band Termination: Tilted Fermi Surface Plot 82 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

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

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 [(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

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 Lund PES plot I = 69 TRS and PES plots predict a strong triaxial minimum Consistent with other CSM calcs - Ragnarsson

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

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 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) Sarah Rigby:: Nuclear Structure Seminar:: Beyond Band Termination: Ultra-High Spin Spectroscopy

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

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

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

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

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

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

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

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

Results: 161Er “Classic” terminating band in 156Er Termination observed in 158Er 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) 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

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

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.

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