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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


protons

neutrons

Nuclear LandscapeNuclear Landscape

82

50

28

28

50

82

2082

28

20

126The N/Z Plane


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


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)


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


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 …


• 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)


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


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)


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


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


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*


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.


Gain 1-2 hbarper neutron !

~ 8-10 hbar !!


~ 8-10 hbar !!


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


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


Shapes and Symmetries

From RIABrochure


Shapes and Symmetries

stablep-dripline

n-dripline

NpNnNp+Nn

~ 5

A~110 Zr, Mo

• Critical point• Tetrahedral• SD

Stable Beams• Deep Inelastic

RIBS• Coulex


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


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


“Low-Energy” Coulex~104 pps with milligram targets

112Mo (108Zr)

GRETA + super Chico

Measure B(E2)

Coulex with re-accelerated (RIBS) beams


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


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


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”


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.)


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)


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


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


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)


Proton Rich – effects of isospin symmetry in heavy N=Z nuclei

IsospinPairing (T=0)Mixing (CED)

Deformations (np,nh)- shape coexistence

Isomers (94Ag)


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


Proton Rich – 94Ag high spin isomer

Structure of 21+ Isomer – excited states built on isomer (deformed)


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


• 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


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


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)


Angular Momentum Limit

new spin regime– new physics

95Kr+26Mg ..





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!

workshop on greta physicsfsunuc.physics.fsu.edu/~gretina/static_gretina/~gretina/...e. ideguchi et...

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