Relativistic Coulomb Excitation: from RISING to PreSPEC Outline Rare ISotope INvestigation at GSI Coulomb excitation experiments at relativistic energies PreSPEC & AGATA Characteristic CE parameters Experimental conditions for relativistic CE Feasibility studies for future experiments Multi-step excitations Investigation of symmetries M1 & E2 excitations Hans-Jürgen Wollersheim GSI Helmholtzzentrum für Schwerionenforschung for the PreSPEC Collaboration
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Relativistic Coulomb Excitation: from RISING to PreSPEC
Relativistic Coulomb Excitation: from RISING to PreSPEC. Outline R are IS otope IN vestigation at G SI Coulomb excitation experiments at relativistic energies PreSPEC & AGATA Characteristic CE parameters Experimental conditions for relativistic CE - PowerPoint PPT Presentation
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Relativistic Coulomb Excitation:from RISING to PreSPEC
Outline
Rare ISotope INvestigation at GSI Coulomb excitation experiments at relativistic energies PreSPEC & AGATA Characteristic CE parameters Experimental conditions for relativistic CE Feasibility studies for future experiments
Multi-step excitations Investigation of symmetries M1 & E2 excitations
Hans-Jürgen Wollersheim
GSI Helmholtzzentrum für Schwerionenforschung
for the PreSPEC Collaboration
Rare ISotope INvestigation at GSI
Nuclear structure of exotic nuclei studied by secondary fragmentation and relativistic Coulomb excitation
g-factor measurements
Isomeric γ- and β-decay studies
The Accelerators:UNILAC (injector) - E<15 AMeV
SIS – E<2 AGeV HI beams ranging up to 238U
Beam Currents: 109 - 1010 pps
FRS → secondary radioactive ion beams:
• Fragmentation or fission of primary beams
• High secondary beam energies (100 -700 AMeV)
• Fully stripped ions
• Reactions on a secondary target
• Implantation inside a stopper
Rare ISotope INvestigation at GSI
Fast beam campaign (2003-2005)
g-factor campaign (2005)
Stopped beam campaign (2006-2009)
EUROBALL Cluster Detectors
beam tracking system
+ Miniball – Hector
• FRS: excellent spectrometer with in-flight A and Z selection energy resolution: ~ 1 GeV • EUROBALL: excellent γ-ray spectrometer intrinsic energy resolution: ~ 2 keV
CATE : ΔE-E telescope event by event beam identification
Coulomb Excitation at Relativistic Energy
New Shell structure at N>>Z Relativistic Coulomb excitation of nuclei near 100Sn Triaxiality in even-even core nuclei of N=75 isotones E1 Collectivity in neutron rich nuclei 68Ni
Pure Coulomb excitation requires amuch larger distance between the nuclei”safe energy” requirement
35.649.4int
TPTP
CCCCR
100 AMeV
100 AMeV
‘Safe‘ bombarding energy requirement
fmCCD TP 5min
Rutherford scattering only if Dmin is large compared to nuclear radii + surfaces:
CP, CT half-density radii
choose adequate beam energy (D > Dmin for all ) low-energy Coulomb excitation limit scattering angle, i.e. select impact parameter b > Dmin
high-energy Coulomb excitation
Dmin < 1% deviation from Coulomb excitation
Electromagnetic interaction acting between two colliding nuclei. Inelastic scattering: kinetic energy is transferred into nuclear excitation energy Monopole-multipole interaction Target and projectile excitation possible
Coulomb excitation of exotic nuclei
Excitation probability
(or inelastic cross section) is a
measure of the collectivity of
the nuclear state of interest
100 AMeV
100 AMeV
High-energy Coulomb excitationstraight line approximation
distance of closest approach:
impact parameter:
2
θsin1
a )(θ D cm1-
cm
2
θcot
a b cm
straight line approximation
DZ
2- D b 22
0
2P2
cm
eZT
straight line for large Ecm: b = D
zero degree detector
LYCCALYCCA
Lund York Cologne CAlorimeter
TOF
ΔEE
s = 3.1 m
High-energy Coulomb excitationgrazing angle and angular coverage of LYCCA
b=5.2 fm D
For nonrelativistic projectiles:
220
2
int
1/4
2sin2
cm
eZZawith
aR
a TP
For relativistic projectiles ( ):
int22
0
2
1/4
12
Rcm
eZZ TP
labcm
distance of closest approach: 2
θsin1
a )(θ D cm1-
cm
at 100 MeV/u
graz
ing
angl
e (m
rad)
projectile mass number A1
Coulomb excitation: 4/11 lab
High-energy Coulomb excitationgrazing angle
136Xe on 208Pb at 700 MeV/u
excitation of giant dipole resonance
A.Grünschloß et al., Phys. Rev. C60 051601 (1999)
Protons Neutrons
π ν
mradfmR 7.50.15 4/1int Coulomb ex.
12
220
2
cm
eZZD TP
For relativistic projectiles ( ):labcm
High-energy Coulomb excitationangular momentum transfer
Excitation occurs only if nuclear (rotational) period is long compared to the collision time:
„sudden approximation“ if >> ~ 10-22 s
2sin
/
/ 1 cmexc
av
E
20
2
4 av
QeZq P
ξ measures suddenness of interaction
qJL cm 20max 2
3
q measures strength
maximum angular momentum transfer
2sin 1 cm
cmcoll v
a exc
nucl E
aD
c
Eexc
VC
High-energy Coulomb excitationangular momentum transfer
Excitation occurs only if nuclear (rotational) period is long compared to the collision time:
„sudden approximation“ if >> ~ 10-22 s
2sin
/
/ 1 cmexc
av
E
20
2
4 av
QeZq P
ξ measures suddenness of interaction
q measures strength
maximum angular momentum transfer
2sin 1 cm
cmcoll v
a exc
nucl E
aD
c
Eexc
qJL cm 20max 2
3
High-energy Coulomb excitationenergy transfer
1 ξ measures suddenness of interaction
aD
c
Eexccm
„adiabatic limit“ for (single-step) excitation ξ=1
aDcEexc
maximum energy transfer:VC
High-energy Coulomb excitationexcitation energy and angular momentum transfer
1
aDcEexc
energy transfer (for single-step excitation):
VC VC
cmP
av
QeZL
14 2
02
max
angular momentum transfer:
High-energy Coulomb excitationtriaxiality in even-even nuclei (N=76)
T.R. Saito et al. Phys.Lett. B669 (2008), 19
21+→0+
22+→0+
22+→21
+
22+→21
+
22+→0+
First observation of a second excited 2+ state populated in a Coulomb experiment at 100 AMeV using EUROBALL and MINIBALL Ge-detectors.
shape symmetry collective strength
Symmetries of the Intrinsic Hamiltonian:axial symmetry, reflection-symmetric
P: parity (reflection)R: rotation by 1800
T: time reversal
P: parity (reflection)RT: rotation by 1800
AND time reversal(which reverses K)
K = angular momentum projection on symmetry axis
high-K orbitals near the Fermi surface
178Hf
31y
K=0
J
Kmax
J
2/72/112/132/7 :: ghif E. Lubkiewicz et al. Z. Phys. A355 (1996), 191
abrasion ablation
Production of isomeric beams:
Symmetries of the Intrinsic Hamiltonian:axial symmetry, reflection-asymmetric
RP: rotation & reflectionT: time reversal
RPT: need all three operations
K = angular momentum projection on symmetry axis
In a nucleus with octupole deformation, the center of mass and center of charge tend to separate, creating a non-zero electric dipole moment.
226Ra 226Ra
H.J. Wollersheim et al. Nucl. Phys. A556 (1993), 261
High-energy Coulomb excitationcross sections for E1, E2 and E3 excitations
beEB
MeVE255.0)10;1(
3.13
WuEB
MeVE
9)20;2(
086.4
WuEB
MeVE
34)30;3(
615.2
Conclusion:
1) The lower multipolarities are dominant
136Xe → 208Pb
1/ln2
210;
1
222
22
forbb
forB
bec
eZ
a
P
*10
)(),(
)(),(
022
2
1
022
2
1
MfM
EfE
fIIMBac
eZ
fIIEBav
eZ
K. Alder et al., RMP 28 (56) 432
Coulomb excitationM1 and E2 excitations, full analytical description
200~%7~;~2
M
E
M
E cvv
c
Conclusion:1) The lower multipolarities are dominant
2) For a given multipole order, electric transitions
are more likely than magnetic transitions
High-energy Coulomb excitationM1 and E2 excitations