giant resonances in exotic nuclei experimental status and perspectives
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Giant Resonances in Exotic NucleiExperimental Status and Perspectives
Thomas Aumann
Gesellschaft für Schwerionenforschung
INPC 2007
Tokyo, June 6th 2007
• Introduction
• The dipole response of neutron-rich nuclei
- Coulomb breakup of halo nuclei
- Giant and Pygmy collective excitations
- Asymmetry energy and neutron skin
• Future perspectives
The collective response of the nucleus: Giant Resonances
IsovectorIsoscalar
Monopole (GMR)
Dipole(GDR)
Quadrupole (GQR) B
erm
an a
nd
Fu
lz, R
ev. M
od
. Ph
ys. 4
7 (1
975)
47
208Pb
120Sn
65Cu
Photo-neutron cross sections
Electric giant resonances
The dipole response of neutron-rich nuclei
Neutron-Proton asymmetric nuclei: low-lying dipole strength
threshold strength
spectroscopic tool:
The one-neutron Halo 11Be
!non-resonant transitions
100% of the E1 strength absorbed into the Giant Dipole Resonance (GDR)
Stable nuclei:
120Sn
Two-neutron Halos: Correlations
T. Nakamura et al., Phys. Rev. Lett. 96 (2006) 252502.
n-n distance (fm) core-nn distance (fm)
|(6 H
e)|
2 RIKEN Data on 11Li
Calculation for 6He: Danilin
Non-energy weighted sum rule
→ T. Nakamura, F7-1
The dipole response of neutron-rich nuclei
Neutron-Proton asymmetric nuclei: low-lying dipole strength
new collective soft dipole mode
(Pygmy resonance)
Prediction: RMF (N. Paar et al.)
132Sn
? strong fragmentation
16O
20O
22O
! threshold strength
spectroscopic tool:
The one-neutron Halo 11Be
!non-resonant transitions
100% of the E1 strength absorbed into the Giant Dipole Resonance (GDR)
Stable nuclei:
120Sn
Experimental Tool: Electromagnetic excitation at high energies
High velocities v/c0.6-0.9 High-frequency Fourier components
E,max 25 MeV (@ 1 GeV/u)
b>RP+RT
Pb Absorption of
‘virtual Photons’
elm ~ Z2
Semi-classical theory:
delm / dE = N(E) (E)
Determination of ‘photon energy’ (excitation energy) via a kinematically complete
measurement of the momenta of all outgoing particles (invariant mass)
adiabatic cut-off:
Experimental Approach: Production of (fission-)fragment beams
B
Z
A
cm
e
u
Bρ – from position at middle focal plane of the FRS
β – from TOF
Z – from ΔELAND
Primary: 3*108 238U/spill @550MeV/u Secondary (mixed): 50 ions 132Sn/spill (~10/sec @500 MeV/u)
132Sn
Experimental Scheme: The LAND reaction setup @GSI
Excitation energy E* from kinematically complete measurement of all outgoing particles:
Neutrons
ToF, E
LANDtracking → BA/Q
Charged fragments
PhotonsALADINlarge-acceptance dipole
ToF, x, y, z
Crystal Ball and TargetBeam
projectiletracking
~12 m
Mixed beam
Dipole-strength distributions in neutron-rich Sn isotopes
Electromagnetic-excitation cross section
Photo-neutron cross section
P. Adrich et al., PRL 95 (2005) 132501
stable
radioactiveA
PDR GDR
Ecentr
[MeV]
sum
rule fraction
[%]
Ecentr
[MeV]
Γ
[MeV]
sum
rule fraction
[%]
124Sn - -15.3 4.8 116
130Sn10.1
(0.7)
7.0
(3.0)
15.9
(0.5)
4.8
(1.8)
145
(19)
132Sn9.8
(0.7)
4.0
(3.1)
16.1
(0.8)
4.7
(2.2)
125
(32)
PDR• located at 10 MeV• exhausts a few % TRK sum rule• in agreement with theory
GDR• no deviation from systematics
Low-lying strength in 132Sn mass neighborhood
odd nuclei allow extending (,n) measurements to lower excitation energies
→ comparison to (') data for stable isotopes
Stable nuclei, Photoabsorption, from:
A.Zilges et al., Phys.Lett. B 542,43 (2003)
S.Volz et al., Nucl.Phys. A 779, 1 (2006)
N. Ryezayeva et al., Phys.Rev.Lett. 89 (2002)
K. Govaert et al., Phys. Rev. C 57,2229 (1998)
5 MeV < E* < 9 MeV
A. Klimkiewicz et al, submitted to PRL
Symmetry energy S2(ρ) and neutron skin in 208Pb
• strong linear correlation between neutron skin thickness and parameters a4, p0
R.J.Furnstahl NPA 706(2002)85-110
Alex Brown, PRL 85 (2000) 5296
A
ZNΟSEE
,)()()0,(),( 42
2
...)(18
)(
),(
2
1)(
202
0
002
0
04
02
2
2 |
Kpa
ES
Theory: Precise knowledge of neutron-skin thickness could
constrain the density dependence of S()
Work Hypothesis: Pygmy-Strength (since related to skin)
should do the same job,
but, experimentally, is accessed much easier !
Inspired by recent article of Piekarewicz (Phys. Rev. C 73 , 044325 (2006))
Here:
Quantitative attempt by means of RHB + RQRPA,
(density-dependent meson-exchange DD-ME )
Paar, Vretenar, Ring et al. (Phys. Rev. C67, 34312 (2003))
Symmetry energy and neutron skin form dipole strength
RQRPA – DD-ME
N. Paar et al.
Result (averaged 130,132Sn) :
a4 = 32.0 ± 1.8 MeV
po = 2.3 ± 0.8 MeV/fm3
PDR strength versus a4, po
S() : moderate stiffness
Neutron skin thickness
δrRn-Rp
Rn – Rp :
130Sn: 0.23 ± 0.04 fm
132Sn: 0.24 ± 0.04 fm
LAND
Sn isotopes
A.Krasznahorkay et al.
PRL 82(1999)3216
A. Klimkiewicz, N. Paar, et al,
submitted to PRL
Euroball 15 Clusters
Located at 16.5°, 33°, 36° degreesEnergetic threshold ~ 100 keV
Hector BaF2
Located at 142° and 90° degreesEnergetic threshold ~ 1.5 MeV
Miniball segmented detectors
Located at 46°, 60°, 80°, 90° degrees Energetic threshold ~ 100 keV
Beam identification and tracking detectors
Before and after the target
Calorimeter Telescope
for beam identification(CATE)
RISING ARRAY @GSI
4 CsI9 Si
Coulomb excitation of 68Ni (600 MeV A)
A structure appears at 10-11 MeV in all detector types
8 10 12 140
10
20
30
40
50
60
5.0 7.5 10.0 12.50
5
10
15
20
25
Cou
nts
Energy [MeV]
68Ni
HPGe-Cluster
6 8 10 12 140
10
20
30
40
50
60
5.0 7.5 10.0 12.50
5
10
15
20
25
Counts
Energy [MeV]
68Ni
Baf2 Hector
6 8 10 12 140
10
20
30
40
50
60
5.0 7.5 10.0 12.5 15.00
5
10
15
20
25
Cou
nts
Energy [MeV]
68NiHPGe MiniBall
Preliminary
Preliminary
Preliminary
Preliminary
Preliminary
Preliminary
GEANT Simulations
F. Camera et al, see F8-2
(,n) data from LAND under analysis
The collective response of the nucleus: Giant Resonances
IsovectorIsoscalar
Monopole (GMR)
Dipole(GDR)
Quadrupole (GQR) B
erm
an a
nd
Fu
lz, R
ev. M
od
. Ph
ys. 4
7 (1
975)
47
208Pb
120Sn
65Cu
Photo-neutron cross sections
Electric giant resonances
Elastic (p,p) … Inelastic (p,p’), (,’) ... Charge exchange: (p,n), (3He,t) ... Quasifree (p,pn), (p,2p), (p, p) ...
In-Ring Experiments: Light-Hadron Scattering
Selective to SPIN-ISOSPIN (S,T) excitations :
- Giant resonances: Monopole.., GT... isoscalar / isovector
- Low-lying collective modes
- single-particle spectr. factors
- nucleon-nucleon correlations, clusters
Selective to SPIN-ISOSPIN (S,T) excitations :
- Giant resonances: Monopole.., GT... isoscalar / isovector
- Low-lying collective modes
- single-particle spectr. factors
- nucleon-nucleon correlations, clusters
Experimental challenge:
Formfactor (L) at low momentum transfer
in inverse kinematics Storage Ring
Target-Recoil and Gamma Detector
around internal target
Target-Recoil and Gamma Detector
around internal target
NESR
EXLExotic Nuclei Studied in Light-Ion Induced Reactions at NESR
Internal target
ELISeThe Electron-Ion (eA) Collider
Electronspectrometerp/p=10-4
gap 25 cmweight 90 t
Electronspectrometerp/p=10-4
gap 25 cmweight 90 t
RIKEN: Isoscalar excitations in 14O
RIKEN: 60 MeV/u 14O on liquid He target
Preliminary analysis: COMEX 2006, Nucl. Phys. A 788 (2007) 188c
26 cm
20 cm
28 cm
56Ni50 A.MeV104 pps
GANIL: GMR & GQR in the unstable 56Ni
56Ni(d,d’) @ GANILActive Target MAYA
C. Monrozeau et al., Nucl. Phys. A 788, 182c (2007)
Conclusion
• Low-lying dipole strength observed in light and medium-mass neutron-rich nuclei (→ D. Beaumel, F5-5)
• Threshold strength (halo nuclei) established as spectroscopic tool (→ T. Nakamura, F7-1)
• Peak-like structure below the GDR in 130,132Sn at about 10 MeV excitation energy exhausting about 5% of the energy-weighted sum rule
• Parameters of GDR in agreement with systematic trends derived from stable nuclei
• Symmetry energy and neutron-skin thickness from dipole strength: a first attempt
Outlook:
• Systematic measurements of dipole strength in neutron-proton asymmetric nuclei
• Theory+experiment: Relation of low-lying dipole strength to symmetry energy and neutron skin
• Decay characteristics (e.g., decay branch) (,') in 68Ni (RISING → F. Camera, F8-2), (,n) with LAND setup
• Monopole and quadrupole strength: active target (GANIL), liquid He (RIKEN, → H. Baba QW-022), internal gas target in a storage ring (GSI, FAIR)
The LAND/FRS collaboration S221
Uni Frankfurt
Th.W. Elze
R. Palit
Uni Krakow
P. Adrich
A. Klimkiewicz
R. Kulessa
G. Surówka
W. Walus
Uni Mainz
J.V. Kratz
C. Nociforo
GSI
T. Aumann
K. Boretzky
H. Emling
M. Fallot
H. Geissel
U. D. Pramanik
M. Hellström
K.L. Jones
Y. Leifels
H. Simon
K. Sümmerer
Santiago de Compostela
D. Cortina-Gil
208Pb analysis
Rn – Rp = 0.18 ± 0.035 fm
∑Bpdr(E1)=1.98 e2 fm2
from N.Ryezayeva et al., PRL 89(2002)272501
∑Bgdr(E1)=60.8 e2 fm2 from A.Veyssiere et al.,NPA 159(1970)561
RQRPA-
N.Paa
r
RQRPA-
N.Paar
RQRPA-
N.Paa
r
LAND
C.Satlos et al. NPA 719(2003)304
A.Krasznahorkay et al.NPA 567(1994)521
C.J.Batty et al.Adv.Nucl.Phys. (1989)1
B.C. Clark et al. PRC 67(2003)044306
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