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

131Sn 132Sn

Rare ISotope INvestigation at GSI

EUROBALL Cluster Detectors Miniball: HPGe segmented detectors

HECTOR Large 14.5 x 17 cm BaF2 Detectors

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

nucleus σ (mb)

56Cr 91

108Sn 314

136Nd 338 / 2180

beam

Relativistic Coulomb Excitationof 54,56,58Cr → 197Au

Identification before the secondary target

after secondary target

γ-efficiency = 2.8% , ΔEγ = 1.6% (1.3MeV, d=70cm)

2

22

0

0

cos1

sin

E

E

mmmmR

mmd

30arctan622.0

mmR 700

mmd 59

with

Doppler Effect Doppler Broadening Δ

%6.10

0

E

E

2

2

2 cos11

cos

2

0

int

E

E r 00pfor

2

2

2

2

0

0

cos11

cos

E

E

Doppler EffectDoppler Broadening Δβ

%6

ring angular range

1 10.50-21.30

2 27.60-38.40

3 30.60-41.40

2

0

int

E

E r

2

2

cos1

sin

00pfor

Velocity distribution at the moment of a prompt γ-ray decay after the production of 36Ca.

(E=130 AMeV and different 9Be target thicknesses)

target thickness

[mg/cm2]

ΔEγ0/Eγ0

[%]

300 3.4

500 3.8

700 5.3

ring angular range

1 10.50-21.30

2 27.60-38.40

3 30.60-41.40

Doppler EffectDoppler Broadening Δβ

%9

DSAM lifetime method

P. Doornenbal et al. Nucl.Instr.Meth. A613 (2010), 218

2

2

2

2

0

0

cos11

cos

E

E

2

0

int

E

E r

2

2

cos1

sin

00pfor

PreSPEC and AGATA

LYCCA

BeamDirection

Detectorat rear

10 ATC+ 5 double Cluster detectors beam pipe diameter = 12cm

chamber diameter = 46 cm

S2´-configuration:10 AGATA Triple Cluster+ 5 double Cluster detectors

γ-efficiency = 17.5% γγ-efficiency = 2.5%

resolution (FWHM)

intrinsic spatial

resolution

8.5 keV 5 mm

4 keV 2 mm

Coulomb excitation of exotic nucleibasic concepts

r

V

r

below Coulomb barrier

Mapping energy to radial separation

21 iii RRC 3/13/1 8.076.028.1 ii AAR

Nuclear half-density radius of a Fermi mass distribution:

with

100 AMeV

Inter-nuclear potentialTwo forces:1. Coulomb force (long range, repulsive)2. Nuclear force (short range, attractive)

Potential barrier due to the compensation between the two

(Coulomb barrier)

Validity of classical Coulomb trajectoriesbasic concepts

wave

particle

η calculated at 100AMeV

1v

eZZaη

2TP

Sommerfeld parameter:

>> 1 requirement for a (semi-) classical treatment of equations of motion (hyperbolic trajectories )

100 AMeV

Classical Coulomb trajectoriesbasic concepts

1cosh war

Hyperbolic trajectory:

ε = sin-1(θcm/2) eccentricity of orbit

wwv

at

sinh

distance of closest approach:

impact parameter:

angular momentum :

2

θsin1

a )(θ D cm1-

cm

2

θcot

a b cm

2cot cmL

100 AMeV

100 AMeV

Nuclear interaction radius

fmCCR TP 3int Nuclear interaction radius:

CP, CT half-density radii

nuclear absorption:

35.649.4int

TPTP

CCCCR

dttrW2

expP-1 abs

Wa

CCtrWtrW 21

0 exp

σtotal = σel + σinel + σreactionσtotal ≈ σinel + σreaction

‘Safe‘ bombarding energy requirement

fmCCR TP 3int Nuclear interaction radius:

CP, CT half-density radii

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

p1/2 ???

1/2-

3/2-

5/2-

15071745

0

15071745

89Y

1/2-

3/2-

5/2-

845

403

0403

845

87Rb

1/2-

3/2-

5/2- 345

1191

0345

1191

85Br

(1/2)-

(5/2,3/2)- -

(3/2,5/2)- -

0

306

669

306

363

83As

1p (ℓ=1)

j < =

ℓ-½

1p1/2

j> = ℓ+½

1p3/2

B(M1;j>j<) 1 N2

Unique signature!!!

N=50

rate = 105 s-1 · 1021 cm-2 · 0.5·10-27 cm2 · 10% = 22 h-1

85Br → 197Au at 100 MeV/u

• Neutron-deficient sd-shell nuclei and mirror symmetry at the proton drip line: 25Si, 29S and 33ArProposal by P. Reiter, M.A. Bentley, D. Rudolph

• Coulomb excitation of 104SnProposal by M. Gorska, J. Cederkall

• Mixed-symmetry states and Coulomb excitation of 88KrProposal by J. Jolie, N. Marginean

First Fast-Beam PreSPEC Proposals

AGATA Physics Workshop 2010 (AGATA@GSI) 4-7 May 2010 Istanbul, TURKEY

30 LOI´s for fast-beam campaign

Relativistic Coulomb excitation B(E2)-values lifetimes (DSAM, RDDS) g-factor (high-velocity transient field technique)

Fragmentation reactions lifetimes (DSAM, RDDS)

Proton scattering (LH2 target) spectroscopic factors

Call for Fast-Beam PreSPEC Proposals

Recoil-Distance Doppler-Shift Method

AGATA increases-sensitivity ≈ 10x

LYCCA-0 provides mass resolution up to A ≈ 100

SIS/FRS intensitiesincrease up to ≈ 10x

Tracking det. and EDAQ upgrade increase max. rate and throughput 10x

PreSPEC Fast Beam Campaignconvener: M. Bentley

Very attractive and competitivespectroscopy themes

Unique combination of beams, set-up and people

PreSPEC Fast-Beam Campaigngreat perspectives …