Nuclear Mixed-Symmetry States as Probe for pn Effective Valence Shell Interaction

Norbert Pietralla Isolde WS2007

Nuclear Mixed-Symmetry States as Probe for pn Effective Valence Shell Interaction

Institut fInstitut fürür Kernphysik, TU-Darmstadt Kernphysik, TU-Darmstadt

•Mixed Symmetry States•Recent Progress•Research with RIBs•Outlook & Summary

OutlineChristoph FransenGeorgi Rainovski

Jason HoltNico Orce

Oleksiy BurdaPeter von Neumann-Cosel

Volker WernerTan Ahn

ANL

Collaborators

Norbert PietrallaNorbert Pietralla

CRE Nuclear/Radiation physics

SFB634

S-DALINAC, TUD


Heavy Atomic nucleus

• many-body system

• consists of two equivalent entities (protons-neutrons)

• quantum system

• COLLECTIVITY

• ISOSPIN SYMMETRY

• SHELL STRUCTURE

Two-fluid quantum system

Generic Aspects of Nuclear Structure

Coexist, interplay, and compete?

Study collective isovector valence shell excitations(combine all 3 aspects)

Study mixed symmetry (MS) structures !


Model pn-symmetry in valence shell

F-spin = Isospin in Systems of “elementary” Bosons

Approximation:

IBM, analytic solutions

Contain pn-antisymmetric boson pairsSignature: enhanced M1 radiation


Simple Example: Harmonic Oscillator, N=2

E

2+n

2+1

2+ms

2+p

Vpn


Experimental signature for MSSs: M1 transitions

tot(1)

νν(1)

ππνπ L)]d[d]d)([dg(gT(M1) ~~

g 1 N, g 0 N

M1 forbidden between FSSs!

L L


Richter,Kneissl,von Brentanoet al.

Sensitivity to Shell Structure

MSSs at the analytical Limits

N = N =1

•Status of MS structures in vibrational nuclei

M1 phenomena in the valence shell

E2M1Scissors

mode

Measure of quadrupolecollectivity

2+

0+2+

4+

0+2+

SU(3)Rotor 2+

3+

1+

Scissors ModeA. Richter et al.

TU Darmstadt, 1983

K=1

Stuttgart-Darmstadt-Köln

1+

0+

4+ 2+ 0+

2+

2+

1+3+U(5)

Vibrator

Fmax-1

MS multi-Phononstructure

N. Pietralla et al., PRC 58, 184 (1998)


Mixed symmetry phonon structure at N = 52

93NbOrce et. al (2006)


Identification of multi-phonon MSSsM1 strength, 2+ 2+

1

E2 strength from g.s.


First observation of vibrational MS structure in odd-mass nuclei

J.N. Orce et al, PRL 97, 062504 (2006).

93Nb94Mo

B(M1)93Nb = 0.32(11)[0.62(24)]N2

B(M1)94Mo = 0.56(5) N2

0+

2+

2+ms

1196

871

Doppler-shift lifetimesfrom (n,n‘) at Lexington


Systematic SM calculations from NN interaction with Vlow-k

J. D. Holt et al, (submitted)

Yale-Rutgers collaboration(preliminary)

x

Inverse kinematics Coulomb excitation


Program at S-DALINAC

M1/g-factor = integral one value

Cross sections = differential a function(1-dim more structure information)

Electron Spectrometer

130 MeV in-house electron LINAC

ideal for nuclearstructure studies


Electron scattering on vibrational multi-phonon MSSs

94Mo(e,e’)

• Ideal for one-phonon states• Sensitive to 14 lowest 2+ states

94Mo(p,p’)iThembaLabs data

with H.FujitaP.von Neumann-Cosel

et al.

Darmstadt datawith O.Burda,

P.von Neumann-CoselA.Richter et al.


94Mo(e,e’) Form FactorsTest of quantum mechanical wavefunction

IBM-2 and SM Vlow-k in good agreement with experiment.

combination with hadronic probe [forward-angle (p,p’) at iThembaLabs] allows for isospin-sensitivity.

ExperimentQPMIBM-2SM (Vlow-k)


Inverse kinematics CoulEx to MSSs at ANL

carbon

G.Rainovski, NP et al, PRL 96 122501 (2006)

138Ce138Ce

Coulomb excitation

Detector array

Study pn-symmetry in valence shell

REX-Isolde, HRIBF, CARIBU,…

exotic nuclei

138Ce@480MeV788 (2+1→0+)

1448

(2+

ms→

2+ 1)

2237

(2+

ms→

0+ 1)

M1

E2

gs

2+ms

2+1


CoulEx of Mixed-Symmetry StatesObserve 2+1,2,3,4,5,6 up to 2.7 MeV

G.Rainovski, NP et al., Phys.Rev.Lett. 96 122501 (2006).Gammasphere at ANL

in collaborationM.P.CarpenterR.V.F.JanssensC.J.ListerS.Zhu

2+ms


1E-4 1E-3 0.01 0.1 10.0

0.3

0.6

0.9

1.2

1.5

1.8

2.1

2.4

2.7

0+

2

E2E3E2+E4

Ex(J

) (M

eV

)

(J)/(2+

1)

4+

1

3-

1

2+

1

2+

2

2+

3

2+

4

2+

5

2+

6

= 1.204(33)ps = 180(9)fs

= 82(5)fs

= 156(10)fs

= 91(36)fsThe population cross-sections at 480 MeV

CLX code (H. Ower – J. Gerl – H. Scheit)Based on Multiple step Coulex theory (Winter – de Boer)

B(E2, 21+)↑=

0.450(30) e2b2

B(, Jj+)

BR

CLX

+ Radiation characterfrom angular distribution


0

1

2

1920212223

2.6

42

2.4

712

.237

2.1

43

1.5

11

B(E

2;2

+ i

0 ) (

W.u

.)

0.7

88

0.00

0.05

0.10

B(M

1;2

+

j2

+

1)

( )

138Ce

0.5 1.0 1.5 2.0 2.5

0.1

1

10

E(2+

i) (MeV)

B(E

2;2

+ i

2 ) (

W.u

.)

Transition Strength Distributions

E2

M1

E2


MSS Investigation @ Argonne (“Missia”) program overview

•ANL ATLAS Superconducting LINAC•Gammasphere

PublishedUnder analysisExpt acceptedproposed

Xe

Ce

Ba

Sm

Chart from: http://www.nndc.bnl.gov

Previous literature


Recent Coulex ExperimentsNovember 2005 at ANL: 136Ce, 134XeJune 2006 at ANL: 124,126,128,130,132Xe (under analysis)

134Xe2+

ms

132Xe 2+ms


Direct evidence for p-n interaction Vpn in the valence shell

• Energy splitting increases with growing valence shell (increasing Np)

Task for Radioactive Beam Accelerators (e.g. HRIBF, REXIsolde…)

Proton Number Z

2+1

One phonon 2+ evolution in N=80 isotones

2+2

132Te

2+ms

Vpn ~ (NpNn)1/2

E

2+n

2+1

2+ms

2+p

Vpn


What RIB intensity needed for studying MSSs?105

104

103

102

103

102

10

104

10

103

102

15 h at 6.109 pps!1/25

1/250

1/2500

107pps for 2 weeks

106pps for 2 weeks

105pps for 2 weeks

To identify excited 2+ state (beyond the 2+

1) in vibrational nucleus (B(E2)~1Wu) with Gammasphere for 2 weeks beam time we need 105pps. For complete spectroscopy 106-107 pps will be needed!

2+ms

2+ms


Outlook (e,e’) transition densities for p and n Trace evolution of Vp-n

RIBS exotic nuclei HRIBF, ANL CARIBU, REX-ISOLDE,

SPIRAL II, …

Proton Number Z

2+1

2+ms

2+ evolution in N=80 isotones

132Te

140Xe

4+

140Xe 2+

FWHM ~9 keVR. Kruecken et al. Munich (2006)

MINIBALL @ CERNREX-ISOLDE

5•105 part/sec


Proton-Neutron Mixed-Symmetry States are sensitive probes of the pn-interaction in the valence shell

94Mo – a textbook example

93Nb – first vibrational MSSs in odd-A nucleus

Advances in nuclear theory (Vlow-k for MS)

First g-factors for MSSs (92,94Zr)

New avenue in (e,e’) @ S-DALINAC

“Missia” program @ ANL

Great potential for RIBs (map Vpn in exotic regions)

Summary

Nuclear Mixed-Symmetry States as Probe for pn Effective Valence Shell Interaction

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