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The Giant Dipole Resonance, new measurements
F. CameraUniversity of Milano and INFN sect. of Milano
HECTOR Collaboration
• Giant Dipole Resonance in very Hot Nuclei
• Temperature dependence of the GDR width
• Dipole Response in neutron rich nuclei
• Pigmy Dipole Resonance in 68Ni
GDR in HOT nuclei
from 16O induced reaction will be discussed in a following paper [ref]
5 10 15 20 25 30
100
101
102
103
104
E*=200MeV
Yie
ld [
a.u
.]
E [MeV]
64Ni+68Zn statistical
Model
5 10 15 20 25 30
100
101
102
103
104
64Ni+68Zn statistical
Model
E*=150MeV
Yie
ld [
a.u
.]
E [MeV]
5 10 15 20 25 30
100
101
102
103
104
64Ni+68Zn statistical
Model
E*=100MeV
Yie
ld [
a.u.
]
E [MeV]
5 10 15 20 25 30
0,04
0,08
Eb=500MeVlinea
risi
zed
Yie
ld [
a.u
.]
E [MeV]
64Ni+68Zn statistical
Model
5 10 15 20 25
0,02
0,04
0,06
0,08
0,10
0,12
Eb=400MeVlinea
risi
zed
Yie
ld [
a.u.
]
E [MeV]
64Ni+68Zn statistical
Model
5 10 15 20
0,05
0,10
0,15
0,20
Eb=300MeVlinea
risi
zed
Yie
ld [
a.u
.]
E [MeV]
64Ni+68Zn statistical
Model
Pygmy Dipole Resonance in neutron rich g.s. nuclei
v/c < 5 %
Fusion-Evaporation reactions
from 16O induced reaction will be discussed in a following paper [ref]
5 10 15 20 25 30
100
101
102
103
104
E*=200MeV
Yie
ld [
a.u
.]
E [MeV]
64Ni+68Zn statistical
Model
5 10 15 20 25 30
100
101
102
103
104
64Ni+68Zn statistical
Model
E*=150MeV
Yie
ld [
a.u
.]
E [MeV]
5 10 15 20 25 30
100
101
102
103
104
64Ni+68Zn statistical
Model
E*=100MeV
Yie
ld [
a.u.
]
E [MeV]
5 10 15 20 25 30
0,04
0,08
Eb=500MeVlinea
risi
zed
Yie
ld [
a.u
.]
E [MeV]
64Ni+68Zn statistical
Model
5 10 15 20 25
0,02
0,04
0,06
0,08
0,10
0,12
Eb=400MeVlinea
risi
zed
Yie
ld [
a.u.
]
E [MeV]
64Ni+68Zn statistical
Model
5 10 15 20
0,05
0,10
0,15
0,20
Eb=300MeVlinea
risi
zed
Yie
ld [
a.u
.]
E [MeV]
64Ni+68Zn statistical
Model
CN -decay spectra +Statistical Model
GDR (EWSR, Eo , lineshape)
Relativistic Coulomb excitation (v/c ~ 0.8%)
Coulex
Ground State -decay spectra
GDR/PDR (EWSR, Eo , lineshape)
D.R. Chakrabarty et al. Phys. Rev. C36(1987)1886A. Bracco et al. Phys. Rev. Lett. 62(1989)2080 R. Vojetech et al. Phys. Rev. C 40(1989)R2441 G. Enders et al. Phys. Rev. Lett. 69(1992)249 H.J. Hoffman et al Nucl. Phys. A571(1994)301
GDR width in hot 132Ce Nuclei
For E*/A < 1.2 (T < 2 MeV) the GDR width increases with excitation energy
• Mostly Spin induced effect
• As the beam energy increases
• Compound nucleus E* increases • Compound nucleus average spin increases • The nucleus becomes more and more deformed • The GDR components splits• The GDR width increases
For E*/A > 1.2 (T > 2 MeV) the GDR width seams to saturate
• Saturation of the angular momentum that compound nucleus may sustain
• Compound decay width• TFM prediction• Alternative models to TFM predict that 0 increases
P. Chomaz et al. Nucl. Phys. A569(1994)203E. Ormand et al. Phys. Rev. lett. 69(1992)2905A. Smerzi et al. Phys. Lett. B320 (1994)16T. Suomijarvi et al. Phys. Rev. C53(1996)2258J.H. Le Faou et al. Phys. Rev. Lett. 72(1996)2258A. Bracco et al. 62(1989)2080
A ~ 110
M.P. Kelly et al. Phys. Rev. C 56(1997)3201
High energy -rays + Light Charged particles
18O + 100Mo = 118Sn
A stronger than expected, non evaporative, emission forward
focused was measured
M.P. Kelly et al. Phys. Rev. Lett. 82(1999)3404
Pre-equilibrium particles and multiplicity indicate a reduction
in the compound nucleus E*
The data from other groups has been reanalyzed to account
for pre-equilibrium
0 1 2 3 4
4
6
8
10
12
14
0 1 2 3 4
MSU Data Th. Fluc. +
CN
Th. Fluc Seattle GSI Grenoble
FWHM
(MeV
)
T (MeV)
All the ‘high temperature’ points has been corrected and shifted to lower energy
The GDR width does not saturate anymore
M.P. Kelly et al. Phys. Rev. Lett. 82(1999)3404
NEW Exclusive experiment
2 < T < 4 MeV
High energy gamma raysLight charged particles
Fusion residues
No pre-equilibrium emission
HECTOR + GARFIELD HECTOR + GARFIELD ( INFN Legnaro Laboratories)( INFN Legnaro Laboratories)
BaF2 High energy -raysGarfield Charged ParticlesPPAC Mass selection
Two reactions – Same compound
16O (130,250 MeV ) + 116Sn 132Ce*64Ni (300,400,500 MeV) + 68Zn 132Ce*
Alpha particle spectra
Blue = experimental data
Red = moving source fit (CN source)
ALPHA PARTICLE SPECTRA
Same excitation energy from Kinematics but very different alpha particle spectra
Nickel induced reactions have only a thermal emission while Oxygen induced reactions have a strong component of pre-equilibrium emission
GDR data in Nickel induced reactions does not need any ‘correction’ for the compound nucleus temperature
from 16O induced reaction will be discussed in a following paper [ref]
5 10 15 20 25 30
100
101
102
103
104
E*=200MeV
Yie
ld [
a.u
.]
E [MeV]
64Ni+68Zn statistical
Model
5 10 15 20 25 30
100
101
102
103
104
64Ni+68Zn statistical
Model
E*=150MeV
Yie
ld [
a.u
.]E [MeV]
5 10 15 20 25 30
100
101
102
103
104
64Ni+68Zn statistical
Model
E*=100MeV
Yie
ld [
a.u.
]
E [MeV]
5 10 15 20 25 30
0,04
0,08
Eb=500MeVlinea
risi
zed
Yie
ld [
a.u
.]
E [MeV]
64Ni+68Zn statistical
Model
5 10 15 20 25
0,02
0,04
0,06
0,08
0,10
0,12
Eb=400MeVlinea
risi
zed
Yie
ld [
a.u.
]
E [MeV]
64Ni+68Zn statistical
Model
5 10 15 20
0,05
0,10
0,15
0,20
Eb=300MeVlinea
risi
zed
Yie
ld [
a.u
.]
E [MeV]
64Ni+68Zn statistical
Model
64Ni (300, 400, 500 MeV) + 68Zn 132Ce*
Nuclear Temperature
1E-10
1E-09
1E-08
1E-07
1E-06
1E-05
0.0001
0.001
0.01
0.1
1
10
100
1000
2 12 22
Ebeam = 400 MeVTCN = 3.2 MeV
T=3.2 MeV
T=1.6
T=0.7 MeV
High energy -rays (GDR) are emitted inall the decay steps and does reflects GDR emission from hot CN only.
The emission from the hot compound nucleus is the strongest but not the only present in the decay.
At low temperature spectrum reflects more the level density energy dependence then GDR line-shape
E [MeV]
Beam
(MeV)
T CN
(MeV)
T*
(MeV)
<T>
(MeV)
300 2.2 1.9 1.8
400 3.2 2.8 2.2
500 4.1 3.7 2.9
E.F.Garman et al. Phys.Rev. C 28(1983)2554R.K.Voijtech et al. Phys.Rev C 40(1989)2441O.Wieland et al Phys. Rev. Lett. 97, 012501 (2006)
GDR width in 132Ce hot Nuclei
In mass region A ~ 130 the GDR width increases with temperature
The thermal fluctuation model reproduce the experimental data if and only if the compound evaporation width is included in the calculations
Within this scenario there is no space for a significant increase of the intrinsic width o, namely of the collisional damping
0
5
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30
0 20Gamma Energy [MeV]
Photo
abso
rption
cross
sect
ion (
a.u
.)
P
N
Ave
rag
e T
ran
sitio
n c
har
ge
de
nsi
ties
0
2
4
6
8
10
12
14
16
0 20Gamma Energy [MeV]
Photo
abso
rption
cross
sect
ion (
a.u
.)
N
Ave
rag
e T
ran
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har
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d
ens
itie
s
Richter NPA 731(2004)59
Pygmy ResonanceCollective oscillation of neutron skin against the core
Giant Dipole ResonanceCollective oscillation of neutrons against protons
Dipole strength shifts at low energy
Collective or non-collective nature of the transitions?
Stable nuclei photoabsorption
Exotic nuclei
Virtual photon breakup
LAND experiment
Virtual photon scattering
RISING experiment
Physics Case: Relativistic Coulex of 68Ni
How collective properties changes moving to neutron rich nuclei
T. Hartmann PRL85(2000)274
40Ca48Ca
Adrich et al. PRL 95(2005)132501
• 400 MeV/u 68Ni (2004) + 197Au
• 600 MeV/u 68Ni (2005) + 197Au
)2()( GDR
PbO 20816
T.Aumann et al EPJ 26(2005)441
GDR - PYGMY Decay
GDR - PYGMY Excitation
Virtual photon scattering techniquefirst experiment with a relativistic beam
Coulex
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
4 CsI9 Si
Coulomb excitation of 68Ni (600 MeV A)
68Ni
Z
Ao
Q
Incoming 68Ni beam Outgoing 68Ni
E (Si)
E (
CsI
)
1.2 %
4.4 %
0.00%
5.00%
10.00%
15.00%
20.00%
25.00%
30.00%
35.00%
40.00%
66Co 67Ni 68Ni 69Ni 70Cu
~ 6 Days of effective beam time~ 400 GB of data recorded
~ 3 107 ‘ good 68Ni events ‘ recorded
Coulomb excitation of 68Ni (600 MeV A)
Pygmy Dipole Resonance
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
Coulomb excitation of 68Ni (600 MeV A)
Pygmy Dipole Resonance
The structure does not appears at 142° because of the much higher background
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
E [MeV]
6 8 10 12 140
100
200
300
400
500
Energy (MeV)6 8 10 12 14
0
100
200
300
400
500
Energy (MeV)
BaF2 at 142°BaF2 at 90°
Preliminary
Preliminary
Preliminary
Preliminary
4 6 8 10 120
10
20
30
40
5.0 7.5 10.0 12.50
5
10
15
20
25
Counts
Energy [MeV]
67Ni
HPGe Cluster
Coulomb excitation of 67Ni (600 MeV A)Pr
elim
inar
yThe peak structure is roughly 2
MeV lower than in 68NI
There is indication from a more fragmented structure
In all cases the measured width is consistent with that
extracted from GEANT simulations with a
monochromatic source
Resonance width < 1 MeV
Both RPA and RMF approaches predict for 68Ni Pygmy strength at approximately 10 MeV for 68Ni. The degree of collectivity is still debated
D. Vretnar et al. NPA 692(2001)496
RMF
0
2
4
6
8
10
12
14
16
0 5 10 15 20 25 30 35 40
Energy (MeV)
mb
RPA
G. Colo private communications
68Ni 68Ni
Eb (68Ni) 7.8 MeV Eb (67Ni) 5.8 MeV
Prediction are available only for 68Ni
In the case of 67Ni as it is a vibration of the neutron skin it is important the value of the neutron binding energy. As a simple rule the localization in energy
of the strength should be linearly correlated to the neutron binding energy
5.0 7.5 10.0 12.50
5
10
15
20
25
Energy [MeV]
~10 MeV~10 MeVPr
eliminary
Preliminary
Coulomb excitation of 68Ni (600 MeV A)
The extraction of the B(E1) strength requires the estimation of the direct and compound -decay of the dipole state to the ground state
CN
CN
decay CEP00)1(
J.Beene et al PRC 41(1990)920
12 0
0
CN
J.Beene et al PLB 164(1985)19S.I.Al-Quiraishi PRC 63(2001)065803
The compound term depends on theratio between the gamma and total decay width
The gamma decay width depends on The value of the level density at the resonance energy
Conclusions
The GDR width has been measured in 132Ce up to T=4 MeV, a linear increase with temperature has been observed.
Pre-equilibrium emission strongly depends from the reaction channel. With symmetric reactions and simultaneous measurements of particles and gamma-rays it was possible to establish the excitation energy of the CN.
Data are well reproduced by the thermal fluctuations model if and only if the compound nucleus width is taken into account in the
calculations.
We have measured high energy -rays from Coulex of 68Ni at 600 MeV/u.
Strength at 10.5 MeV has been observed in all three kind of detectors
Peaks line-shape is consistent with GEANT simulations (PDR < 1 MeV)
Low Energy Dipole strength has also been observed in 67Ni and 69Ni
Spectra and Numbers are preliminary
F.C. , A. Bracco, S. Brambilla, G.Benzoni, M.Casanova, F.Crespi, S. Leoni, A.Giussani, P.Mason, B.Million, D.Montanari, A.Moroni, O.Wieland, N.Blasi
Dipartimento di Fisica, Universitá di Milano and I.N.F.N. Section of Milano, Milano Italy
A.Maj, M.Kmiecik, M.Brekiesz, W.Meczynski, J.Styczen, M.Zieblinski, K.ZuberNiewodniczanski Institute of Nuclear Physics Krackow Poland
F.Gramegna, S. Barlini, A. Lanchais, P.F. Mastinu L. Vannucci, V.L.KravchukINFN, Laboratori Nazionali di Legnaro, Legnaro, Italy
M. Bruno, M. D'Agostino, E. Geraci, G. VanniniINFN and Dipartimento di Fisica dell’Universita' di Bologna,, Bologna, Italy
G. Casini, M. Chiari, A. NanniniINFN, Sezione di Firenze, Firenze, Italy
U. Abbondanno, G.V. Margagliotti, P.M. MilazzoINFN and Dipartimento di Fisica Universita' di Trieste, Trieste, Italy
A.OrdineINFN sez di Napoli, Napoli
HECTOR – GARFIELD Collaboration
A.Bracco, G. Benzoni, N. Blasi, S.Brambilla, F. Camera, F.Crespi, S. Leoni, B. Million, M. Pignanelli, O. Wieland,
University of Milano, and INFN section of Milano, Italy
A.Maj, P.Bednarczyk, J.Greboz, M. Kmiecik, W. Meczynski, J. StyczenNiewodnicaznski institute of Nuclear Physics, Kracow, Poland
T. Aumann, A.Banu, T.Beck, F.Becker, A.Burger, L.Cacieras, P.Doornenbal, H. Emling, J. Gerl, M.Gorska, J.Grebozs, O.Kavatsyuk, M.Kavatsyuk, I. Kojouharov, N. Kurtz, R.Lozeva, N.Saito, T.Saito, H.Shaffner, H. Wollersheim
and FRS collaborationGSI
J.Jolie, P. Reiter, N.WardUniversity of Koeln, Germany
G. de Angelis, A. Gadea, D. Napoli, National Laboratory of Legnaro, INFN, Italy
S. Lenzi, F. Della Vedova, E. Farnea, S. Lunardi, University of Padova and INFN section of Padova, Italy
D.Balabanski, G. Lo Bianco, C. Petrache, A.Saltarelli, University of Camerino, Italy
M. Castoldi and A. Zucchiatti, University of Genova, Italy
G. La Rana, University of Napoli, Italy
J.Walker,University of Surrey
RISING Collaboration