the gamma decay of the gdr at finite temperature and of the pygmy resonance far from stability
DESCRIPTION
The gamma decay of the GDR at finite temperature and of the pygmy resonance far from stability . G. Benzoni INFN sezione di Milano (Italy). Outline 1- Pygmy Dipole Resonance in 68 Ni background experiment results perspectives Preequilibrium Dipole Resonance Background Experiment - PowerPoint PPT PresentationTRANSCRIPT
The gamma decay of the GDR at finite temperature and of the pygmy resonance far
from stability
G. BenzoniINFN sezione di Milano (Italy)
Outline1- Pygmy Dipole Resonance in 68Ni
• background• experiment• results• perspectives
2. Preequilibrium Dipole Resonance• Background• Experiment• Results• perspectives
G.AR.F.I.E.L.D.
Pygmy Dipole Resonance
0
5
10
15
20
25
30
0 20Gamma Energy [MeV]
Phot
oabs
orpt
ion
cros
s se
ctio
n (a
.u.)
P
N
Aver
age
Tran
sitio
n ch
arge
de
nsiti
es
02468
10121416
0 20Gamma Energy [MeV]
Phot
oabs
orpt
ion
cros
s se
ctio
n (a
.u.)
N
Aver
age
Tran
sitio
n ch
arge
de
nsiti
es
Pygmy Dipole 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?
Physics Case:How dipole response changes moving towards neutron rich
nuclei ??? T. Hartmann PRL85(2000)274
40Ca 0.025% EWSR
48Ca 0.29% EWSR
Adrich et al. PRL 95(2005)132501
132Sn 4% EWSR124Sn Exotic nuclei
Virtual photon breakup
LAND experiment
Virtual photon scattering
RISING experiment
How to excite this mode??Stable nuclei photoabsorption
Two experiments performed:
• 400 MeV/u 68Ni (2004) + 197Au
• 600 MeV/u 68Ni (2005) + 197Au
)2()( GDRT.Aumann et al EPJ 26(2005)441
Higher statistics dataset
68Ni beam produced by fragmentation of 86Kr @ 900 MeV/u on thick Be target (4g/cm2):
• 1010 ppspill 86Kr •Spill length 6s, period 10 s
Beam energy selected in order to populate DIPOLE modes more effectively
than other ones
High resolution -spectroscopy at the FRS
RISING
FRS
FRS provides secondary radioactive ion beams:• fragmentation and fission of primary beams • high secondary beam energies: 100 – 700 MeV/u• fully stripped ions
2g/cm2 Au
Euroball 15 ClustersLocated at 16.5°, 33°, 36° degreesEnergetic threshold ~ 100 keV
Hector 8 BaF2
Located at 142° and 90° degreesEnergetic threshold ~ 1.5 MeV
Miniball 7 HPGe segmented detectorsLocated at 46°, 60°, 80°, 90°
degrees Energetic threshold ~ 100 keV
Beam identification and tracking detectors
Before and after the targetCalorimeter Telescopefor beam
identificationCATE
RISING ARRAY
4 CsI9 Si
Coulomb excitation of 68Ni @ 600 AMeV
68Ni
Z
AoQ
Incoming 68Ni beam Outgoing 68Ni
DE (Si)
E (C
sI)
1.2 %
4.4 %
~ 6 Days of effective beam time~ 400 GB of data recorded
~ 3.107 ‘ good 68Ni events ‘
Incoming+Outgoing 68Ni0.00%
5.00%
10.00%
15.00%
20.00%
25.00%
30.00%
35.00%
40.00%
66Co 67Ni 68Ni 69Ni 70Cu
~ 35%
Coulomb excitation of 68Ni (600 MeV A)Pygmy Dipole Resonance
8 10 12 140
10
20
30
40
50
60
5.0 7.5 10.0 12.50
5
10
15
20
25
Coun
ts
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
Coun
ts
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
Coun
ts
Energy [MeV]
68NiHPGe MiniBall
Prelim
inary
Prelim
inary
Prelim
inary
Prelim
inary
Prelim
inary
Prelim
inary
GEANT Simulations
A structure appears at 10-11 MeV in all detectors
4 6 8 10 120
10
20
30
40
5.0 7.5 10.0 12.50
5
10
15
20
25
Coun
ts
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 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 40Energy (MeV)
mb
RPA
G. Colo’ private communication
68Ni 68Ni
Eb (68Ni) 7.8 MeV Eb (67Ni) 5.8 MeV
Predictions are available only for 68Ni
In the case of 67Ni as it is a vibration of the neutron skin the value of the neutron binding energy is important. 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 MeVPre
liminary
Prelim
inary
Conclusions
Measurement of high energy -rays from Coulex of 68Ni at 600 MeV/u.
First experiment of this type ever performed 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
A.Bracco, G. Benzoni, N. Blasi, S.Brambilla, F. Camera, F.Crespi, S. Leoni, B. Million, M. Pignanelli, O. Wieland, P.F.Bortignon, G.Colo’
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 collaboration
GSI
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
Preequilibrium Dipole Resonance
The Preequilibrium Dipole Response
GDR
t=0 fm/c
fusion CN
Dynamic Dipole
Charge NOT equilibrated All degree of freedom
EQUILIBRATED
Charge equilibration in N/Z asymmetric heavy-ion collisions
A rapid re-arrangement of charge accompanied by emission of dipole radiation
The intensity of dipole emission depends on the absolute value of the charge that must be shifted to restore the mass balance (Dipole moment)
o information on the charge equilibration in relation to the reaction mechanism;
o information on the damping of the dipole mode;
o information on the symmetry energy of the nuclear matter at lower densities than the saturation one
132Ce
N/Z=1 N/Z=1.38
+
N/Z=1.25 N/Z=1.29
Z
N Z
N/Z=1.28
N/Z=1.28
N
+
132Ce
96Mo
100Mo32S
36S
D(t=0)=18.2 fm
D(t=0)=1.7 fmtp
tptp
NZ ZN
ZNZZ
ARR
tRtRANZtD
))0()0(()0(
O+Mo @ 4-8-14-20 MeV/u
V. Baran et al . PRL87(2001)182501
THEORY: Preequilibrium dipole radiation present in all N/Z asymmetric
reactions; Dependence on charge asymmetrycharge asymmetry
mass asymmetrymass asymmetry and incident energyincident energy.
Compare the high energy gamma-ray emission from a N/Z SYMMETRIC and a N/Z ASYMMETRIC reaction.
Evidence of a prompt dipole emission: EXCESS of the high energy gamma-ray yield in the asymmetric reaction
reaction CN Proj N/Z Target N/Z CN N/Z40Ca + 100Mo 140Sm* 1 1.38 1.258
36S + 104Pd 140Sm* 1.25 1.26 1.258
Flibotte et al. PRL77(1996)1448
How to distinguish preequilibrium from thermalized emission?
40Ca + 100Mo36S + 104Pd
•The intensity is never higher than 25% of the total yield with stable beams • The measurements need to be extremely clean and exclusive
Linearized spectra40Ca + 100Mo
36S + 104Pd
Garfield + Hector @ Laboratori Nazionali di Legnaro
BaFBaF22
GarfieldGarfield PPACPPAC
• + LCP + residues• comparison btw. N/Z Asymmetric and Symmetric reactions leading to same CN at same E* and I • two different bombarding energies
8.1 AMeV and 15.6 AMEV
reaction Ebeam (MeV/u)
E* (MeV) D (fm)
16O+116Sn 8.1 100 8.664Ni+68Zn 4.7 100 1.216O+116Sn 15.6 200 8.664Ni+68Zn 7.8 200 1.2
Reaction studied to populate 132Ce* CN
O.Wieland et al. PRL 97 (2006) 012501
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
risiz
ed Y
ield
[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
risiz
ed Y
ield
[a.u
.]
E [MeV]
64Ni+68Zn statistical
Model
5 10 15 20
0,05
0,10
0,15
0,20
Eb=300MeVlinea
risiz
ed Y
ield
[a.u
.]
E [MeV]
64Ni+68Zn statistical
Model
The analysis of the N/Z symmetric reaction lead to important results on
Temperature Temperature dependence of dependence of
different different contributions to GDR contributions to GDR
widthwidth
1
tZN
32.1
pZN
16O+116Sn @ 250 MeV
64Ni+68Zn @ 500 MeV
Large pre-equilibrium component
Cou
nts
[a.u
.]
E [MeV]
Only statistical decay
reaction Ebeam (MeV/u)
E* (MeV)
ECN (MeV)
16O+116Sn 8.1 100 95
16O+116Sn 15.6 200 165
Determination of the preequilibrium
component thanks to the measurement of
the particles
S. Barlini et al., to be published in PRC
Comparison with statistical model using the GDR parameters:EGDR= 14 MeVGDR= 7.3 (8 MeV/u) 12.9 (15 MeV/u)
16O+116Sn@8 AMeV 16O+116Sn@15 AMeV
0,0E+00
5,0E-05
1,0E-04
1,5E-04
2,0E-04
5 10 15 20 25 30E (MeV)
m
16O+116Sn @ 8 AMeV
16O+116Sn @ 15 AMeV
Comparison with statistical model calculations to extract extra yield
•Preequilibrium emission is enhanced at high beam
energy•Same centroid as the GDR
Extra gamma multiplicity
Simulation of reaction dynamics allows the evaluation of the DIPOLE MOMENT during the preequilibrium phase
(dinuclear system before CN equilibration)
2
3
2
)(3
2
DEc
edEdP
Bremsstrahlung formula gives directly the
emission of the dynamical dipole
M. Di Toro, V. Baran, C. Rizzo V.Baran et al., PRL87 (2001) 182501-1
16O+116Sn 8 MeV/ub=0 fm
Excitation of collective dipole mode ~85 fm/c
CN formation (equilibration)
D. Pierroutsakou . et al., PRC 71 (2005) 054605
E (MeV)
6 MeV/nucleon(E*=117 MeV)
9 MeV/nucleon
(E*=173.5 MeV)
16 MeV/nucleon(E*=304 MeV)
Ar + Zr[1] [3]
E (MeV)
S + Mo
[2]S + Mo
F GD
R(E
) (a
rb.
unit
s)
E (MeV)
Centroid energy different from exp.
Yield increasing with energy even if absolute
value is not well reproduced
15 MeV/u8 MeV/u
simulati
on
0,0E+00
5,0E-05
1,0E-04
1,5E-04
2,0E-04
5 10 15 20 25 30E (MeV)
m
8 AMeV
15 AMeVexperim
ent16O+116Sn
PerspectivesStable beams:
measure angular distributions Measure an asymmetric reaction WITHOUT dipole moment in entrance channel
Exotic beams Increase further the N/Z asymmetry
Proj. Energy MeV/u
Ta CN E* fusion mb
Spin D(T=0) fm
(mass)
P.D. Yield*
132Sn 4.9 40Ca 172Yb 98.22
855 77 38 0.18 14
77Ni 3.9 95Mo 172Yb 100 728 88 35 0.03 12140Xe 5.4 32S 172Yb 100 1016 74.8 29 0.22 994Kr 4.2 78Se 172Yb 100 672 88 23 0.03 522Ne 6.4 150Nd 172Yb 100 1443 71.51 10 0.29 248Ca 5 124Sn 172Yb 99.8 857.8 88 5 0.14 1* C. Simenel et al PRL 86 (2001) 2971
The isotopes has been selected from the list of page II-8 of spiral documentation
A.Corsi, O.Wieland, A.Bracco, F.Camera, S.Brambilla, G.Benzoni, M.Casanova, F.Crespi, S.Leoni,
A.Giussani, P.Mason, B.Million, D.Montanari, A.Moroni, 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.Zuber
Niewodniczanski Institute of Nuclear Physics Krackow Poland
F.Gramegna, V.L.Kravchuk S.Barlini, A.Lanchais, P.F.Mastinu and L.Vannucci
INFN, Laboratori Nazionali di Legnaro, Legnaro, Italy
G.Casini, M.Chiari, and A.NanniniINFN, Sezione di Firenze, Firenze, Italy
A.OrdineINFN sez di Napoli, Napoli
Garfield + Hector collaboration
M. Di Toro, V. Baran, C. Rizzo
Conclusions Measurement of high energy -rays from Coulex of 68Ni at 600 MeV/u.
First experiment of this type ever performed 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
Dynamical dipole mode measured in N/Z asymmetric reaction 16O+116Sn Complete treatment of preequilibrium particle emission Extra yield increasing with energy (8 MeV/u 15 MeV/u)Accordance with simulation based on bremsstrahlung emission
G.AR.F.I.E.L.D.
Thank you
t=0 fm/ct 10-22s
CN formationt 10-21 s
GDR oscillation
NCMZCM RRANZD ,,
If (N/Z)proj≠(N/Z)targ
the system displays dipole oscillation due to charge equilibration
Simulation code developed by Baran et al. based on BNV model applyed to 16O(@8MeV/u)+116Sn
This oscillation: -displays collective features like GDR-produces emission
Simulation code developed by Baran et al. based on BNV model applyed to 16O(@8MeV/u)+116Sn
This emission can be calculated with the bremsstrahlung formula once known D:
2''3
2
)(3
2
DEc
edEdP
From Centroid energy E0 one can estimate the value of
• bsym vs nuclear density• bsym vs neutron number
From the FWHM extract information on the damping mechanism• Time needed to damp the dipole oscillation• Understand how nucleons move in the fusion process
symbE 0
The Dynamical Dipole Mode – Prompt dipole
Ganil October 2005
Density plots, projected on the reaction plane, for central collisions
Simenel et al. PRL86(2001)2971
REARRANGMENT of p and n to establish the charge to mass equilibrium
A rapid re-arrangement of charge accompanied by emission of dipole radiation (timescale of the order of 10-21 s)
The intensity of dipole emission depends on the absolute value of the charge that must be shifted to restore the mass balance
Time evolution of the dipole moment parallel to the deformation axis for
b=0.
Pre-equilibriumThermal Equilibrium
3.10-21 s
• 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 Excitation
Virtual photon scattering technique first experiment with a relativistic beam
Why Pygmy Resonance is important ?
Pygmy Resonance has an important
impact on the r-process nucleosynthesis
Different mean field approaches give different predictions in terms of collectivity, strength and line-shape of the pygmy resonance
Isovector properties of nuclear force
Goriely et al PLB436(1998)10Nupecc long range plan 2004
NCMZCM RRANZD ,,
If (N/Z)proj≠(N/Z)targthe system displays dipole oscillation due to charge equilibrationdisplays collective features like GDR-produces emission
Simulation code developed by Baran et al. based on BNV model applyed to 16O(@8MeV/u)+116Sn
2''3
2
)(3
2
DEc
edEdP
• Centroid is at lower energies not yet seen exp.
• Still to study angular distribution check if pure dipole• The dinamical contribution will show a clear anisotropic emission• The higher N/Z asymmetry the stronger the effect
Experimental problems:
• the CN has to be produced at the same E* and I• The intensity is never higher than 25% of the total yield with stable beams • The measurements need to be extremely clean and exclusive
• few combination proj-target can produce the same CN• fusion reaction selection • spin selection • No contaminations from target impurities
Open questions:O+Mo @ 4-8-14-20 MeV/u
Baran et al . PRL87(2001)182501
Conclusions
We have measured high energy -rays from Coulex of 68Ni at 600 MeV/u.
First experiment of this type ever performed 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