nuclear superdeformation - gsiwolle/telekolleg/kern/pdf/...a~40 superdeformed nuclei • microscopic...
TRANSCRIPT
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Nuclear Superdeformation
Outline
• Introduction• basic physics• the early days• review - what we have learned
• Selected Topics• Decays• C4• Identical Bands• New regions 40Ca• Triaxial SD• Hyperdeformed
- 108Cd ….
• Future
Paul Fallon NS06
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Where it all began ! (revisionist)
TESSA 3 –152Dy
P.J. Twin et al PRL 57 (1986)
A major achievement for ourfield
The discovery of “high-spin” superdeformation was a major motivation and justification for the large 4ππππ arrays Gammasphere and Euroball
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��������������� ��������������������������� ����PHYSICS TODAY December 1991
“Top unexpected physics discoveries of the last five years!”
High temperature superconductivity
Supernova 1987A
Buckyballs
Atom cooling and atom optics
Superdeformed nuclei
Large-scale structure of the universe
J. Garrett“Superdeformation -Nuclear Physics’ Supernova”
B. Mottelson…one of Nuclear Structures finesthours ..
J. Garrett“Superdeformation -Nuclear Physics’ Supernova”
B. Mottelson…one of Nuclear Structures finesthours ..
Nuclear Superdeformation – A Major Discovery
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First Observed 242Am
25yrs later 152Dy(1986)
Since then …
Rapid progress-Large detector arrays
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Deformed Minima/Shell gaps
I II
• Coulomb Energy• Rotational Energy
If gaps due to symmetry - deformation independent of ADeformed analog of spherical gapsSD distinct from normal defs
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Nuclear DeformationsN
orm
aliz
ed Q
uadr
upol
e M
omen
t(D
efor
mat
ion)
ground states
Mass A
Q 2/5ZR2
1/A1/3
208Pb
surface/volume
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Nuclear Deformations
ground states
Mass A
208Pb
c/a~ 2:1
c/a ~3:2
1/A1/3
36Ar
108Cd
152Dy
192Hg
236U
60Zn82Sr 132Ce
40Ca
Nor
mal
ized
Qua
drup
ole
Mom
ent
(Def
orm
atio
n)Q
2/5ZR2
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Deformations
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Deformations Shell Structure and Intruders
Woods Saxon Potential
Quadrupole Deformation
Sin
gle
Pa
rtic
le L
eve
ls (
MeV
)
?
NDND SD SD HDHD
Classify the Structure by the Intruder Occupation
NDND SDSD HDHD
Intruder N+1 N+2 N+3
Z~50 g9/2 h11/2 i13/2
Classify the Intruder by the number of major oscillator shells it has moved
Has some benefits compared with definition based strictly on axis ratio
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The early days ( 1986-1992)
• Observation (A~130,150,190)
• Structure – J(2)
• Identical Bands
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P.Fallon et al. Physics Letters B, 218 (1989)137
Mapping the single-particle (high-j intruder) configurations
Theory by T. Bengsston, et al. PLB 208 (1988) 39,
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192Hg
194Hg
F.S.Stephens et al., PRL 64 (1990) 2626
1990: Identical Superdeformed bandsT.Bryski et al PRL 64(90) 1650
W.Nazarewicz et al PRL 64 (90) 1654
Heroic? New insight? Pseudo-spin alignment (1 Unit Spin Difference !)or
Non-Heroic? : Chance cancellations between pairing & deformation effects?
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Superdeformation and the large arrays
• Data explosion – new regions, multiple bands – new physics
• Precision measurements (Transition energies and rates, deformations, linking the normal and superdeformed minima)
• New phenomena – C4, Triaxial, order-to-chaos
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Shell Structure; Exotic states; Extreme Single-Particle Motion (shell model); Collective Modes; Pairing
Superdeformation – highly polarized systems
Extreme single-particle motion Residual correlations are washed out
Pairing Correlations
142Sm –152Dy
Tool to study many aspects of nuclear structure - Elementary Modes of Excitation
Quasiparticlealignmentππππi13/2 ννννj15/2
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• ~ 250 SD bands – most involve excitations within the second minimum
• Vast majority are single-particle excitations
• limited number of collective excitations (vibrations) — concentrated in heavier systems.
• Identical bands (very stringent test of theory – def. pairing, alignments)
Excitations
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Collective excitations
• A = 240Quadrupole and Octupole240Pu
• A = 190Octupole Vibrations190,194Hg, 196,198Pb
• A = 150Octupole Vibrations152Dy
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Superdeformation Physics and Phenomena
• Identical Bands – Decay out (links)
• Q0’s
• C4
• Triaxiality
• A=40
• 108Cd Towards Hyperdeformation
• ……
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Identical Bands - Spins
G.Hackman et al, PRL 79 (1997) 4100
• Increase in SD Data – identical band systematics in A=150, A190 regions
• Key development – establish spins in 194Hg, an identical band
• Confirm existence of unit spin difference
� What is origin of unit alignment ?
P.Fallon et al, PRC 60 (1999) 04431
Systematic Study• Comparison –Data and Theory
• Suggests –Quasiparticle alignmentand Pairing
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Decays from the second minimum
Distinct States (two minima)
• Tunneling
• Statistical (compound) ?
• Dependence on excitation energy ?(mass region)
• Status• A~40 “All” linked• A~60 (~50% linked)• A~80 (1 linked)• A~130 (~50% linked)• A~150 (149Gd, 152Dy)• A~190 (194Hg, 194Pb, 192Pb)• A~240 (236,238U)
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152Dy Fifteen Years …T.Lauritsen et al., PRL 88 (2002) 042501
4011 keV Determines Ex. EnergyDipole Character (E1)τ ~ 2.9psB(E1) ~ 2x10-6 WU
Other gammas placed > Fixed spins• 2 hbar higher than original estimate• Can test calculations
E1 decays (similar for 194Hg)
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S.Flibotte et al, PRL 71 (93) 4299
D.Haslipet al., PRL 78, (1997) 3447 D.Haslip et al., PRC 58 (98) R2649
C4 Staggering – An unanswered puzzle
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Identical Bands and C4
GS expt by Haslip et al., PRL 78 (1997) 3447
29Si + 124Sn 148Eu + p4n148Gd + 5n
Lots of new bands!
We can useother bands
as a reference!
148Eu(1)
149Gd(1)
148Gd(6)
148Gd(1)
See also Haslip et al.,PRC 58 (1998) R2649for systematic survey
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F.Lerma et al., PRC 67 (2003) 044310; K. Lagergren et al., PRC 68 (2003) 064309
Precision Measurements: Deformation Systematics A~80
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Precision Measurements: A~130 Quadrupole Moments
R.W.Laird et al Phys. Rev. Lett. 88 (2002) 152501
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New regions - new physics
A~170
A~100
A~40
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A~40 Superdeformed Nuclei
• Microscopic understanding of collective motion - Connect deformed intrinsic states (rotational motion) with microscopic wavefunctions (lab system) –20Ne, 24Mg (sd), 48Cr (pf)
• Truncations/approximations (theory) are necessary - must be tested by experiment• Nuclei around A~40 are an ideal place to carry out these studies
- Deformed shell gaps (f7/2 intruder, N=3)
2s1/2
1d3/2
1f7/2
2p3/2
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• 32S, not seen 4p-12h
• 36Ar, 4p-8h (π32, ν32)C.E.Svensson et al., PRL 85 (2000) 2693
• 38Ar, 4p-6h (π32, ν32)D.Rudolph et al., PRC 65 (2002) 034305
• 40Ca, 8p-8h (π34, ν34)E.Ideguchi et al., PRL 85 (2001) 222501
• 44Ti, 8p-4h (π34, ν34)C.O’Leary et al., PRC 61 (2000) 064314
Data on A~40
Determined - Energies, Spins, Parities, B(E2).
Observed to Band head (excited O+)
Allows detailed comparison with theory.
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40CaE. Ideguchi et al., PRL 87 222501 (2001) ; C.J. Chiara et al., PRC 67 041303 (2003)
• 28Si(20Ne,2α)40Ca • 8p-8h structure identified as π34, ν34 4p-4h
kno
wn
• New expt 24Mg(24Mg,2α)40Ca
8p-8h
β2 ~0.59
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Triaxial Shapes and The Wobbling Mode
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Robust triaxial shapes have been sought after for d ecades!
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? ? 1 48
A Brief Status of TSD
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The108Cd Superdeformed Bands
High spin (multiplicity) states selected by a “K” cut
~ 40 - 60 hbar
R.M. Clark et al., PRL 87 (2001) 202502; A. Goergen et al PRC 65 (2002) 027302
Deformation β2 ~ 0.6 (lower limit)
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108Cd: Towards Hyperdeformed Nuclei
?
NDND SDSD HDHD
Woods Saxon Potential
Quadrupole Deformation
Sin
gle
Pa
rtic
le L
eve
ls (
MeV
)
152Dy: “super-intruder”
235U: “normal-intruder”
108Cd: i13/2 “ hyper- intruder”
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For Z~50 and A~110 the ππππi13/2and νννν j15/2 are the “hyper-intruder” (N+3) states
108 110 112Cd
N
Esp
j15/2
λ
j15/2j15/2
Calculations suggest ννννj 15/2 occupied at N=64 (close to 108Cd, N=60)
Exciting possibility for Hyperdeformation(both N+3 intruders !)
ππππi13/2 “hyper-intruder” occupied in 108Cd
108Cd: Towards Hyperdeformed Nuclei
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Future Progress ( example from superto hyper)- Tools (apart from imagination)
• Beams• RIBS
• Detectors• Gamma-ray tracking arrays
• RIB Beams (not usually discussed in this context)
• Extend towards the n-rich (back to the Cd story)• Even a few (6) extra neutrons can make a difference in observedphysics (hyperintruders - need neutron levels)• More neutrons, more spin
• Gamma-ray detectors• Ge Shell (GRETA) – increased efficiency, inverse reactions
Future Prospects “where do we go from here”
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108Cd
114Sn
48
50
114Cd
94Kr + 26Mg -> 120Cd*“Dream Experiment”
60 62 64 66 68An example…
limit with favorable stable-beam reactions
• lmax ~ 62
�
in 108Cd and 70
�
in 114Cd
• 108Cd produced with stable beams: 48Ca+64Ni at 207 MeV
• 114Cd produced with “RIA” beams: 94Kr+26Mg at 500 MeV
HyperdeformationHyperdeformation
A New Region and Increasing the Spin limit
Also 170-180 region 132Sn + 48Ca –> 180Yb*130-140 region 94Kr + 48Ca -> 142Ba*
Hyperdeformation: Production and Population
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121Cd*
112Cd*
Angular Momentum Limit
new spinregime
Gain 1-2 hbarper neutron
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Gamma-ray Detector Development
• Advances in detector technology have resulted in new discoveries.
• Innovations have improved detector performance.— Energy resolution— Efficiency— Peak-to-total ratio— Position resolution— Directional information— Polarization— Auxiliary detectors
• Tracking is feasible, will provide new opportunities and meet the challenges of new facilities.
Central Role in Nuclear Physics
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The 4ππππ Array GRETA
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GRETA High spin state from fusion reactions
Simulation GRETA, ε ε ε ε =0.25
4-fold, I=10-5
Simulation GS
Simulation GS, ε ε ε ε =0.09
3-fold, I=10-3
3-fold, I=10-4
64Ni ( 48Ca, 4n) 108Cd, Gammasphere v/c=0.04
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• Hyperdeformation— location, new physics
• Higher Temperatures (SD unique – shell gap)— feeding, damped nucleonic and rotational motions— GDR
• Decay• Fission Isomers• Connections to cluster states• Periodic orbits (Semi-classical approaches)•
Future Directions
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Just as the discovery of Superdeformation had a major impact, so too has Gammasphere .. built a community, a base for the future
Gammasphere (Euroball) - The best of a kind. Can’t build a better spectrometer using this technology
What’s next - The Ge shell – built on the new technology of highly segmented Ge.
Tools – (i) Beams (stable and RIBS). (ii) Instruments (+ imagination)As we maximize our capabilities, advanced Instrumentation can give the competitive edge
� important today, maybe more so than ever …
• A 4π tracking array (GRETA) is essential for these studies
Concluding observations…
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Thanks….
Still going …
Peter TwinFrank Stephens
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