Structure of few-nucleon systems near and beyond the dripline Haik Simon Gesellschaft f

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Structure of few-nucleon systems near and beyond
the driplineHaik SimonGesellschaft für
Schwerionenforschung / Darmstadt

• Ab initio calculations available now (e.g. FMD
  PVIX, HK 6.8)
• (Two) particle correlations vs. mean field
• Shell model evolution (residual interactions)
• How to measure that ?

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Shell evolution ( N 7 )
L. Chen, et al. , PLB505(2001)21
I. Talmi, I. Unna, PRL4 (1960) 469 P.G. Hansen,
NUPA682 (2001) 310c
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Gamov-Teller b-decay
ISOLDE/CERN
3/2-
11Li
b-
b 6.3(6)
504 keV
320 keV
1/2-
E1
1/2
T1/2 8.2 ms
Q 20.62 MeV
log ft 5.73
11Be
? 11Lig.s. (1s1/2)2 / (0p1/2)2 ? 1
M.J.G Borge et al. PRC55(1997)R8
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2n transfer reaction
JINR/DUBNA

• 6He is clustered
• i.e. a n n
• Dominantly
• in di-neutron
• configuration

G.M. Ter-Akopian et al., PLB 426 (1998) 251
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Region of Interest near and beyond the dripline
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Example Reaction mechanism for two-neutron halo
break-up

• vbeam ? 0.7 0.9 c
• Neutron multiplicity final state
• Choice of target

Knock-out ( 1n )
Nuclear excitation ( 2n )
Coulomb excitation ( 2n )
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Experimental Setup
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Experimental Method

• Problem reconstruct 3 body system from 2 body
  final state !
• Correlations from the missing particle
• momentum
• angular
• invariant mass of the subsystem(s)
• Remaining structure
• core polarization

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Angular correlation 6He
p5He -pn1
W(?nf) 1 A cos2 ?nf
?nf
a
A 1.50 (3) ? 6Heg.s (0p1/2)2 ? 7.
n2
d?/ dcos (?nf )
5He
n2
n1
A3
a
6Heg.s
cos (?nf)
L.Chulkov, G.Schrieder ZPA359(1997)231
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Valence neutron momentum distribution for the
two-neutron halo nucleus 11Li
Neutron momentum distribution
9Li
10Li
n2
n1
H.S. et al. PRL83 (1999) 496
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Angular correlation 11Li
s-shell isotropic
p-shell S1 ? sin2 ?nf
p-shell S0 ? cos2 ?nf
Interference (s- and p- shell) S0 ?
cos ?nf
W(?nf) 1 1.03(4) cos ?nf 1.41(8) cos2 ?nf ?
H.S. et al. PRL83 (1999) 496
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Conclusion 11Li

• 11Li properties are reflected in the population
  of states in 10Li following the knockout
  reaction.
• Consistent picture in different observables.
• Continuum spectroscopy of an unbound system
  10Li.

M. Meister, H.S., et al., in preparation
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Experimental Method

• Problem characterize a three body final state in
  the continuum !
• Test model assumption
• test deduced observable (e.g. sum rule)
• Measure directly
• ? how to measure a three body correlation ?

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Coulomb break-up 6He
Ex ? 10 MeV 100 cluster sumrule ?
B(E1) 1.37 e2 fm2
B.V. Danilin et al., NUPA632 (1998) 383
ra-nn 3.4(4) fm
dnn 4.0(4) fm
rHalo 3.0(3) fm
T. Aumann et al., PRC59(1999)1252
P. Egelhof et al., EPJA15(2002)27
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Three body continuum

• Reduction of coordinates
• 9 variables ? 6 variables ? 5 variables
  ? 2 variables ( e, q )
• c.m. E
  rot. inv.
• e is the fraction of total energy in a
  subsystem (e.g. e Enn/Ennf)
• q is the angle between the relative momenta
  (e.g. pnn, pf-nn)
• Three body correlation function (expansion in
  hyperspherical harm.)
• Complex coefficients C depend on quantum numbers
  aK,L,S,lx,ly

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Coulomb break-up 6He
B.V. Danilin et al., NUPA632 (1998) 383
2n
5He
L.V. Chulkov, H.S., I.Thompson, et al., in
preparation
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Beyond the dripline 5H
C(6He,tnn)
M. Meister et al., PRL91(2003)162504
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Summary / Outlook
Supported by BMBF and GSI

• Reaction Mechanism
• is understood
• different processes can be separated
  experimentally
• Nuclear Structure
• evolution of shell structure towards the drip
  lines
• residual interaction clusters, pairing
  important
• Perspectives
• excitation modes of exotic nuclei
• extreme states of nuclear matter (4n, 7H, )

Thanks to all my collaborators of the
FRS/ALADIN-LAND experiments !
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Large Area Neutron Detector
Efficiency
1
Resolution sTof 200 ps sp
5 - 10 MeV/c sIVM 0.1 - 1. MeV
Nucl. Instr. Meth. A314 (1992) 136
Neutron Energy (MeV)