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1Paul Fallon GRETA Physics Workshop FSU 2006
Workshop on GRETA Physics
FSU August 17-18, 2006
Paul Fallon – Lawrence Berkeley National Laboratory
2Paul Fallon GRETA Physics Workshop FSU 2006
protons
neutrons
Nuclear LandscapeNuclear Landscape
82
50
28
28
50
82
2082
28
20
126The N/Z Plane
3Paul Fallon GRETA Physics Workshop FSU 2006
protons
neutrons
Nuclear LandscapeNuclear Landscape
82
50
28
28
50
82
2082
28
20
126now add excitation (spin) …beginning to explore thisdimension further from stability- new frontier
GRETA
4Paul Fallon GRETA Physics Workshop FSU 2006
Example 1: 40Ca - nature of np-nh states
• 28Si(20Ne,2α)40Ca • 8p-8h structure identified as π34, ν34 4p-4h
know
n
• New expt 24Mg(24Mg,2α)40Ca
8p-8h
β2 ~0.59
Nature of 0+3 state as 8p8h needed
observation on this band.
E. Ideguchi et al., PRL 87 222501 (2001) C.J. Chiara et al., PRC 67 041303 (2003)
5Paul Fallon GRETA Physics Workshop FSU 2006
Example 2 : 30Na – A 2p2h intruder ground state
30Na ground state observables (mass, spin) in agreement with USD (0p0h) – 30Na a normal nucleus
MCSM predict 30Na to have 100% 2p2h intruder
Measured B(E2) show large Quadrupole moment
Y.Utsuno et al PRC 70 (2004) 044307
Example of importance of knowledge of excited states (transitions strengths)
B(E2) 130 e2fm4
2p2h intruderβ2 ~0.4
B.Pritychenko et. al PRC 63 (2001) 011305R
6Paul Fallon GRETA Physics Workshop FSU 2006
Selected Topics
a) Hyperdeformation – exotic shapes (observation - a major achievement for our field).
b) Elementary excitations in neutron rich nucleirotation/vibration/pairing/s.pinfluence of weak binding
A move from coupled neutron-proton systems to a “decoupled” neutron-proton motion – rotations and neutron skins.
c) Symmetries and Shapes
d) Heavy Elements, Proton–rich …
7Paul Fallon GRETA Physics Workshop FSU 2006
• Prolate axis ratios > 2:1 (3:1 ?)• Large deformations
- on the way to fission- high-spins modify the
microscopic structure.
Hyperdeformed Nuclei
?
NDND SDSD HDHD
Woods Saxon Potential
Quadrupole Deformation
Sing
le P
artic
le L
evel
s (M
eV)
8Paul Fallon GRETA Physics Workshop FSU 2006
Many calculations predict some degree of necking - How pronounced is the necking- When does is develop ?
If it develops well before fission two isolated structures pairingshell structure/symmetries (pseudo SU3 multiplet will breakdown )
Hyperdeformed Nuclei
9Paul Fallon GRETA Physics Workshop FSU 2006
The 108Cd 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)
10Paul Fallon GRETA Physics Workshop FSU 2006
For A~110 the j15/2 state is the neutron “hyper-intruder” (N+3)
108 110 112Cd
N
Esp
j15/2
λ
j15/2 j15/2
Calculations suggest j15/2 occupied at N=64 (close to 108Cd, N=60)
Exciting possibility for Hyperdeformation(both N+3 intruders !)
πi13/2
11Paul Fallon GRETA Physics Workshop FSU 2006
GRETA High spin state from fusion reactions
Simulation GRETA, ε =0.25
4-fold, I=10-54-fold, I=10-5
Simulation GS
Simulation GS, ε =0.09
3-fold, I=10-4
3-fold, I=10-3
64Ni ( 48Ca, 4n) 108Cd, Gammasphere v/c=0.04
12Paul Fallon GRETA Physics Workshop FSU 2006
108Cd
114Sn
48
50
114Cd
94Kr + 26Mg -> 120Cd*“Dream Experiment”
60 62 64 66 68
An example with intense RIBS…
limit with favorable stable-beam reactions
• lmax ~ 62 ħ in 108Cd and 70 ħ in 114Cd• 108Cd produced with stable beams: 48Ca+64Ni at 207 MeV• 114Cd produced with ISOL beams: 94Kr+26Mg at 500 MeV
Hyperdeformation
Also 170-180 region 132Sn + 48Ca –> 180Yb*130-140 region 94Kr + 48Ca -> 142Ba*
13Paul Fallon GRETA Physics Workshop FSU 2006
A New Region – increasing the spin limit
Intense neutron-rich beams
• Fission barrier increases with N/Z: neutron richer nuclei, higher spins
0
2
4
6
8
10
12
14
40 50 60 70 80 90 100 110
Z
Neu
tron
Incr
ease
Gain up to 6-10 more neutrons !
95Kr97Rb90Br129In132Sn133Sb136Te139I142Xe142Cs144Ba145La148Ce
95Kr + 26Mg,48Ca…76Ge
132Sn, 136Te,142Xe +48Ca…76Ge
A new regime for very high spin Increase spin limit near stability using intense n-rich beams fusion reactions10 ħ more in many systems - a new unexplored regime.
A new regime for very high spin Increase spin limit near stability using intense n-rich beams fusion reactions10 ħ more in many systems - a new unexplored regime.
Gain 1-2 hbarper neutron !
~ 8-10 hbar !!
Gain 1-2 hbarper neutron !
~ 8-10 hbar !!
14Paul Fallon GRETA Physics Workshop FSU 2006
Hyperdeformations
• Many studies done – high sensitivity.
• Future Progress— Detectors
• Gamma-ray tracking— Beams
• Stable and RIBS
• Fusion reactions— 48Ca+64Ni, 48Ca+80Se (Stable)— 94Kr+ 26Mg, 94Kr+ 48Ca (ISOL)
• GRETA – 100 x Gammasphere— Discrete structures 10-5 of channel— weaker beams
• ISOL beams— neutron rich , higher spins
15Paul Fallon GRETA Physics Workshop FSU 2006
Neutron Rich – accessing excited states
• excitation modes are a “largely” unexplored area (certainly when compared to proton-rich and near stability, even high-Z)
• Limited available reactions (fast-beams have been the dominant way,but also fission fragments)
• Physics we want to access – towards drip-lines – weak binding.
> light nuclei – tough to reach
• This is a challenge for future facilities – promises new physics that we cannot do with today's facilities
• We will need more than 1st excitedstate
Neutron skins (Xe, Zn) ?
Large deformations (32Mg, 34Mg) – rotations ? - pairing ?
ShapesymmetriesMo,Zr
16Paul Fallon GRETA Physics Workshop FSU 2006
Shapes and Symmetries
From RIABrochure
17Paul Fallon GRETA Physics Workshop FSU 2006
Shapes and Symmetries
stablep-dripline
n-dripline
NpNnNp+Nn
~ 5
A~110 Zr, Mo
• Critical point• Tetrahedral• SD
Stable Beams• Deep Inelastic
RIBS• Coulex
18Paul Fallon GRETA Physics Workshop FSU 2006
Neutron-rich Zr Isotopes
N. Schunck, J. Dudek, A. Góźdź, P. ReganPhys. Rev. C69 061305(R) (2004) Tetrahedral Shape
simplest case Y32 non-zeroTetrahedral Shapesimplest case Y32 non-zero
19Paul Fallon GRETA Physics Workshop FSU 2006
Example of a multinucleon-Transfer Experiment
238U + 170Er 5.7 MeV/uGS + CHICO3 ·109 p/s (0.5 pna), 0.5 mg/cm2
3 days, γ−γ−γ
1n transfer 169Er
SimulationGS + CHICO
Simulation 170Er + 238U 5.7 MeV/u
GRETINA + SuperCHICO1n 3 ·109
GRETINA + SuperCHICO3n 3 ·109
GRETA + SuperCHICO6n 3 ·109
C.Y. Wu et al., PRC 70, 014313 (2004)
104Zr, 106Mo104Zr, 106Mo
20Paul Fallon GRETA Physics Workshop FSU 2006
“Low-Energy” Coulex~104 pps with milligram targets
112Mo (108Zr)
GRETA + super Chico
Measure B(E2)
Coulex with re-accelerated (RIBS) beams
21Paul Fallon GRETA Physics Workshop FSU 2006
Neutron rich nuclei – A~110, Zr, MoShapes and Symmetries
• Multinucleon Transfer (stable beams)— 98Zr,100Mo + 236U/208Pb — GRETA ~1000 x Gammasphere— GRETA + super Chico (6n transfer)
104Zr, 106Mo
• Coulex (~5 MeV/A) — re-accelerated RIBS ~104 pps
108Zr, 112Mo
22Paul Fallon GRETA Physics Workshop FSU 2006
Neutron Rich – “towards the driplines”
• Are there “clean” rotational bands?• neutron separation energy is small• neutron pairing correlations may rapidly vary (2+, 4+, 6+ ..)
• How does neutron pairing change when Fermi level approaches zero?• is it weaker, stronger ? • rotational spectrum (M.O.I.) will be sensitive to this.
• What is the limit of spin for nuclei far from stability?(is it different from stable system with same A)
• Are there “clean” rotational bands?• neutron separation energy is small• neutron pairing correlations may rapidly vary (2+, 4+, 6+ ..)
• How does neutron pairing change when Fermi level approaches zero?• is it weaker, stronger ? • rotational spectrum (M.O.I.) will be sensitive to this.
• What is the limit of spin for nuclei far from stability?(is it different from stable system with same A)
1. Collectivity in the presence of weak binding2. Interplay of deformation, rotation, and pairing
Qu. Can we study the evolution from physics dominated by n-p coupling (N=20)to dripline (n-p may decouple)?
Response of n-rich nuclei to rotations
23Paul Fallon GRETA Physics Workshop FSU 2006
Changes in shell structure- Deformations
“Island of Inversion”
Binding of dripline nuclei
Neutron rich s-d-f nuclei exhibit a rich variety of physics
Neutron Rich – “towards the driplines”
24Paul Fallon GRETA Physics Workshop FSU 2006
GRETINA n-rich nuclei from fragmentation reactions
Gamma-ray energy (2keV/channel)
30Na from 30Mg Beam340
370410
250
175
770430 (3+--2+)
Simulation SeGA Simulation GRETINA
30Mg (pn) → 30Na (100 MeV/u)v/c=0.43
charge exchange reactionGamma-gamma coincidence
NSCL data SeGA(E. Rodriguez-Vieitez et al.)
25Paul Fallon GRETA Physics Workshop FSU 2006
Mapping collective and single-particle strengths with GRETA (I)
• gamma-rays needed to determine exclusive cross-sectionsefficient (30%) gamma-ray detector (Doppler Corrections, Granularity)(2/3) GRETA
),(),()( 2
jnsp SjInjSCnI σσ ππ =∑
nuclear structureinformation
reaction process
• Direct reactions with fast beams (knockout reactions)
26Paul Fallon GRETA Physics Workshop FSU 2006
Mapping collective and single-particle strengths with GRETA (II)
Coulex/Transfer reaccelerated beams5-10 MeV/A
— 36Mg — 42Si — Mγ ~5-10 v/c ~0.1
4π array GRETA + super Chico 100 times greater RP.
SiSi
42Si42Si
104104
Response of n-rich nuclei to rotationsunique information on basic properties
27Paul Fallon GRETA Physics Workshop FSU 2006
Neutron Rich – Exotic Phenomena
Skins and Skin Modes
N=ZcoreN=Zcore nnn
ppnnn
ppnnn
Soft Diplole Modes (pygmy resonances)208Pb – NRF (γ,γ’), 140Ce (α,α’)Ca, Sn Isotopes
Coulomb/Inelastic Scattering 20 MeV/A
γ-decay of “resonant” states near to threshold provides data on the nature ofhigh-lying sates
• High-Eγ – low Eγcoincidence
GRETA ~30x better than Gammasphere
• GRETA 4π coverage selects 1 and 2 fold events
~8 MeV
28Paul Fallon GRETA Physics Workshop FSU 2006
5.51
2
6.265 6 7 8B(E
1) (1
0-3e2 f
m2 )
4
0
8
Cou
nts
Energy (MeV)
NRFKVIKVI
PDR - Strong (heavy-ion) versus EM (photons) Interaction
170+208PbLBNL
170+208PbLBNL
208Pb(γ, γ’) vs 208Pb(17O,17O’ γ) 208Pb(γ, γ’) vs 208Pb(17O,17O’ γ)
29Paul Fallon GRETA Physics Workshop FSU 2006
Proton Rich – effects of isospin symmetry in heavy N=Z nuclei
IsospinPairing (T=0)Mixing (CED)
Deformations (np,nh)- shape coexistence
Isomers (94Ag)
30Paul Fallon GRETA Physics Workshop FSU 2006
Opportunity for complimentary“high-spin” studies in superfluid region
Fusion reactions with 60Zn40Ca(60Zn,2α)92Pd32S(60Zn,2α)84Mo28Si(60Zn,2α)80Zr
Opportunity for complimentary“high-spin” studies in superfluid region
Fusion reactions with 60Zn40Ca(60Zn,2α)92Pd32S(60Zn,2α)84Mo28Si(60Zn,2α)80Zr
Proton Rich
Fusion reactions Rotational bands in heavy N=Z – terminating states – signatures for T=0 pairing - Coulomb energy differences
Fusion reactions Rotational bands in heavy N=Z – terminating states – signatures for T=0 pairing - Coulomb energy differences
31Paul Fallon GRETA Physics Workshop FSU 2006
Proton Rich – 94Ag high spin isomer
Structure of 21+ Isomer – excited states built on isomer (deformed)
32Paul Fallon GRETA Physics Workshop FSU 2006
High-Z Structure of neutron rich Transfermiums
251Md
132Sn + 130Te149In + 136Xe....
Cross Section for Fusion of“Symmetric” Systems
(taken from P. ArmbrusterAnn Rev Nucl Part Sci 2000)
Fusion with heavy neutron-rich beamsIn-beam study of rotational properties (σ ~μb)
Potential Problem with large Z1*Z2 > ~1600- fusion hindrance
33Paul Fallon GRETA Physics Workshop FSU 2006
• In-beam studies — Gamma-ray detection + recoil tag (Gas filled separator)— Gammasphere detectors limited to ~2π (with e.g. BGS, RITU)
— GRETA is compact – can approach ~full coverage— GRETA + Gas Filled Separator ~ 5-10x gain in efficiency
— current σ limit ~ 100nb GRETA gives σ ~ 10nbRutherfordium (Z=104) !
+ ~50 gain for γγ in 100nb channels (problem - internal conversion)
• Stable beams of 48Ca, 50Ti …
High-Z Structure of neutron rich Transfermiums
34Paul Fallon GRETA Physics Workshop FSU 2006
Excitations around closed shells
Light N=Z Magic Nuclei eg. 40Ca – high spin
What about other regions ? 208Pb, 132Sn, 78Zn,
76Ge(132Sn,xn)208-xPb70Zn(142Xe,xn2p)212-xPb ?82Se(132Sn,xn2p)212-xPb ?
132Sn : Transfer 136Te beams78Ni : Transfer 81Ga
Closed Shells - Anchors for theory – key to understanding nucleiTopic spans all regions of N-Z Rich physics multiple particle-hole configurations
35Paul Fallon GRETA Physics Workshop FSU 2006
Summary
• There is a strong case for a next generation 4π gamma-ray tracking array - GRETA; it remains a major initiative for our field that will be an essential part of the future RIA facility and establish a world-class capability in the US in the meantime.— physics case spans existing and future facilities
• GRETA essential for physics of excited nuclear states with moderate to high γ-ray multiplicities and reaction-energies of order 1-4 times Coulomb barrier (say < 20MeV/A).
• GRETA will have “niche” capabilities for other physics(need to consider Astrophysics, Weak Interactions)
36Paul Fallon GRETA Physics Workshop FSU 2006
Angular Momentum Limit
new spin regime– new physics
95Kr+26Mg ..
Gain 1-2 hbarper neutron !
A new regime for very high spin Increase spin limit near stability using intense n-rich beams fusion reactions10 ħ more in many systems - a new unexplored regime.
A new regime for very high spin Increase spin limit near stability using intense n-rich beams fusion reactions10 ħ more in many systems - a new unexplored regime.
37Paul Fallon GRETA Physics Workshop FSU 2006
Sample calculations (R.Herzberg)
Thic
knes
sRe
actio
nI_
Beam
X Se
ctRe
ac/h
No d
etM
(g)
Eff
G/h
T_to
t
XS_s
fFi
ss/s
M(s
f)G/
sfGa
mm
a BG
Ge_r
ate
/ det
ecto
rDa
tara
teTr
ansm
issio
n
(ug/
cm^2
)(p
nA)
(nb)
% dete
cted
(day
)
(mb)
(kHz
)
(kHz
)
raw
(MB/
s)%
EXOGAM:500 2n 20 1000 650 64 5 10 194 1 500 90000 10 1.00 315 4.9 2.4 60500 2n 20 100 65 64 5 10 19 11 500 90000 10 1.00 315 4.9 2.4 60500 2n 20 10 7 64 5 10 2 107 500 90000 10 1.00 315 4.9 2.4 60500 2n 200 10 65 64 5 10 19 11 500 900000 10 1.00 3147 49.2 24.0 60
AGATA:500 2n 50 100 163 192 5 50 168 1 500 225000 10 2.50 1969 10.3 15.0 60500 2n 50 10 16.3 192 5 50 16.8 12 500 225000 10 2.50 1969 10.3 15.0 60
Compare Lines 3 and 4: Fission can become the bottleneck!
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