Coulomb excitation with radioactive ion beams

1
Coulomb excitation with radioactive ion beams

• Motivation and introduction
• Theoretical aspects of Coulomb excitation
• Experimental considerations, set-ups and analysis
  techniques
• Recent highlights and future perspectives

Lecture given at the Euroschool 2009 in
Leuven Wolfram KORTEN CEA Saclay
2
Experiments with Miniball at ISOLDE-Cern
3
Coulomb excitation set up at Rex-Isolde
Particle detector Double-Sided Si Strip Detector
Germanium detector array Miniball 8 triple
cluster Ge detectors, each consisting of three
6-fold segmented HPGe detectors
1st post-accelerated beam and Coulomb excitation
in 2001
4
Extraction of electromagnetic matrix elements

• Coulomb excitation of 30,32Mg at Rex-Isolde/CERN
• limits of the island of inversion (measurement
  of b2)

O. Niedermaier et al., PRL94, 172501 (2005)
M. Scheidlitz, P. Reiter et al. in preparation
Excitation probability normalised to target
excitation (Ni, Ag)
Corrections needed for beam contamination,
possible 2nd order exc.
5
Limits of the 1st order perturbation analysis

• 1st order perturbation theory requires
• ? Only excitation of the first 2 state is
  relevant
• Virtual excitations of higher lying states are
  negligible

W. Schwerdtfeger et al., PRL 103, 012501 (2009)
6
Comparison with high-energy Coulomb excitation
O. Niedermaier et al., PRL94, 172501 (2005)
Good agreement between low-energy (safe)
Coulomb excitation and some of the results
obtained from electromagnetic excitation at high
energies
7
Coulomb Excitation of 20-21Na,21Ne
1st TIGRESS Experiment, Aug 2006
1x10cm collimator
Bambino T 20-50o
Pb shielding
plastic scintillator
8
Properties of mirror nuclei 21Na/21Ne
t(5/2) 1/ltot l(M15/2?3/2) l(E2
5/2?3/2)-1 with I(M1) gtgt I(E2)
with d(E2/M1 5/2 ?3/2) 0.05(2) ? B(E2)
14?12 W.u.
with d(E2/M1 5/2 ?3/2) -0.074(1) ?B(E23/2?5
/2) 24?3 W.u.
9
21Ne, 21Na Heavy-ion gated ?-ray spectra

• Clean ?-ray spectra with negligible influence of
  511 keV due to intense beam ß activity
• For Ti Doppler correction shows both 46Ti and
  48Ti 2 decay transitions

10
GOSIA analysis and results

• ? ray yields of 5/2 ?3/2 transition were
  measured in coincidence with ? and f gates on the
  recoiling ions.
• Matrix elements were fit to the measured yields
  using the GOSIA search code assuming the
  following level scheme.
• Known lifetimes and branching ratios as input
  parameters

1 R.B. Firestone, NDS 103 (2004) 269 with NNDC
10/10/2006 erratum
Wrong M1/E2 mixing ? Stronger E2 component than
previously reported Comprehensive Error analysis
includes uncertainties in beam energy, target
thickness, detector geometry (Clovers), unknown
matrix elements and their signs, etc.
M.A. Schumacher et al., PRC78 (2008) 044321
11
1st TIGRESS experiment at ISAC-II Aug 2007
Electronics shack
Lead shielding wall

• Beam dump on rails
• Faraday cup
• YAPCe Scintillator
• Channeltron detector

Six tigress modules mounted on one half of the
mechanical support structure
BAMBINO CD-S3 ? 20-50 deg.
12
Coulomb Excitation Coulex of 29Na Probing the
Transition to the Island of Inversion

• 29Na beam 400 ions/s, 110Pd target 2.94 mg/cm2
• TIGRESS-Bambino Coincidences 0.001 Hz
• Room background in TIGRESS 1.2 kHz

B(E2) 0.237(21) eb Consistent with MCSM
prediction of Otsuka large B(E2) requires
narrowing sd-pf (N20) shell gap
374 keV 110Pd
72 keV 29Na
A Hurst et al Phys Lett B674(2009) 168
13
Shape coexistence in N28 isotones
Ca 40 96.94
Ca 42 0.65
Ca 44 2.08
Ca 46 0.003
Ca 48 0.19
Ca 50 13.9 s
Rapid onset of deformation in N28 nuclei below
Ca ?
20
Ar 38 0.07
Ar 40 99.59
Ar 42 32.9 y
Ar 44 11.9 m
Ar 46 8.4 s
Ar 48 0.48 s
18
All N28 isotones predicted to show shape
coexistence
S 36 0.015
S 40 8.8 s
S 42 1.01 s
S 44 123 ms
S 46 50 ms
S 38 170 m
16
Precision measurement of e.m. matrix elements in
44Ar
Si 34 2.77 s
Si 36 0.45 s
Si 38 gt1 ?s
Si 40 33 ms
Si 42 13 ms
Si 44 10 ms
14
Mg 32 86 ms
Mg 34 20 ms
Mg 36 3.9 ms
Mg 38 gt260 ns
Mg 40 1 ms
12
20
22
24
26
28
30
14
Coulomb excitation set-up for RIBs (ex. SPIRAL)
16 large Ge Clover detectors 4 ? 4
segmented photopeak efficiency ? 20
Double-sided Si detector 48 rings ? 16 sectors
15
Coulomb excitation of 44Ar at SPIRAL / GANIL
109Ag
EXOGAM
44Ar 109Ag ?cm35, 72
DSSD
44Ar
SPIRAL beam 44Ar 3105 pps 2.8A MeV
(Ag) 3.8A MeV (Pb)
109Ag
208Pb
16
Determination of quadrupole moments
Sensitivity to Q2 by varying Z, q, ?(a,v?)
17
Determination of quadrupole moments
18
Coulomb excitation of 44Ar at SPIRAL / GANIL
Ag target, 35??cm?70
Ag target, 70??cm?130
Pb target, 30??cm?130

• good agreement for B(E2) and Q
• energy spectrum too spread out

(4) 2.746
2 2.011
2 1.158
4.6(8)
76(10)
0
experiment B(E2?) in e2fm4
19
Shape coexistence around A70
oblate
prolate
Possible 0 shape isomers and configuration
mixing
20
Coulomb excitation of 70Se at CERN / ISOLDE

• 70Se on 104Pd at 2.94 MeV/u
• integral measurement
• excitation probability P(2) via
• normalization to known 104Pd

A.M. Hurst et al., PRL 98, 072501 (2007) (Univ.
Liverpool)
? (2) 1.5(3) ps J. Heese et al., Z. Phys. A
325, 45 (1986)
?
Coulomb excitation probability (1?)
68Se intermediate-energy Coulex GANIL E. Clément
et al., NIM A 587, 292 (2008)
21
Recoil-Distance Doppler Shift Method
target and stopper foil at distance d
gamma rays emitted

• in flight ? Doppler-shifted peak

• at rest ? narrow peak at E0

lifetime extracted from intensities as a function
of distance d
22
Lifetimes in 70Se revisited
Recoil-distance Doppler shift
40Ca(36Ar,?2p)70Se
beam
GASP and Köln Plunger at Legnaro

• literature value ? 1.5(3) ps
• J. Heese et al., Z. Phys. A 325, 45 (1986)
• new lifetime for 2 in 70Se ? 3.2(2) ps
• J. Ljungvall et al., Phys. Rev. Lett. 100,
  102502 (2008)

70Se 2 ? 0
shifted
stopped
23
Coulomb excitation of 74,76Kr at SPIRAL
EXOGAM
SPIRAL beams 76Kr 5?105 pps 74Kr 104 pps
4.5 MeV/u
Pb
Acta Phys. Pol. B 36, 1281 (2005)
24
Shape coexistence in 74Kr

• 74Kr 208Pb at 4.7 MeV/u (SPIRAL)
• ? multi-step Coulomb excitation
• ?-ray yields as function of scattering angle
• (differential excitation cross section)
• experimental spectroscopic data
• (lifetimes, branching ratios)
• least squares fit of 30 matrix elements
• (transitional and diagonal)

0
E. Clément et al., Phys. Rev. C 75, 054313 (2007)
25
Life time results in 74,76Kr

• Fusion-evaporation reactions
• 40Ca(40Ca,a2p)74Kr
• 40Ca(40Ca,4p)76Kr

J. Roth et al., J.Phys.G, L25 (1984)
23.5(1.9) ps 13.2 (7) ps B. Wörmann et al.,
NPA 431, 170 (1984) 35.3 (1.0) ps 4.8 (5) ps
26
Sensitivity to quadrupole moments
74Kr
27
Quadrupole moments (Q0) in 74Kr and 76Kr
74Kr
76Kr

• direct confirmation of the prolate oblate
  shape coexistence
• first reorientation measurement with radioactive
  beam

28
Full results of Gosia analysis

• 14 transitional E2 matrix elements

• 18 transitional E2 matrix elements

29
Experimental results and comparison with theory
Qslt0 prolate
Qsgt0 oblate
? vibration
prolate oblate
E. Clément et al., Phys. Rev. C 75, 054313
(2007)
experimental B(E2?) e2fm4
Calculation HFB-Gogny 5-dim GCM

• complete set of e.m. matrix elements, incl.
  static moments
• quantitative understanding of shape coexistence
  and configuration mixing
• triaxiality is the key to reproduce experimental
  data and shape evolution

30
Coulomb excitation of 74-80Zn at Rex-Isolde
80Zn on 108Pd (2.87 MeV/u, 2.0 mg/cm2, 3000
pps)

• Beam contaminants
• increase for more exotic beams
• must be taken into account when
• calculating the target excitation

J. Van de Walle et al., PRL 99, 142501 (2007) and
PRC 79, 014309 (2009)
31
Coulomb excitation of 74-80Zn at Rex-Isolde
Integral measurement ? one observable total
excitation probability
74Zn
20 ps
25 ps
28.5 ps

• two unknowns
• B(E2)
• Qs

Life time measurements would reduce B(E2) errors
and determine Q0 possible by using RDDS technique
after multi-nucleon transfer reactions
32
Lifetime measurement using multi-nucleon transfer
PRISMA / CLARA _at_ Legnaro
Pilot experiment 48Ca 208Pb, 6.5 MeV/u
targets with degraders at fixed distances
First GANIL experiment (VAMOS EXOGAM) 238U
64Ni, 6.5 MeV/u (inverse kinematics) lifetime
measurement in neutron-rich nuclei below 68Ni
(22.-30.09.2008)
J.J. Valiente-Dobón et al. (Legnaro)
33
Coulomb Excitation of 132Sn at HRIBF

• Opportunity to study a new doubly magic nucleus
• Study collectivity of N82, Z50 core
  excitation
• High E(2) 4MeV small B(E2) weak beam
  (104 pps) ? very low event rate

• Employ high efficiency BaF2 g-array
• 40 full-energy at 4 MeV
• Use high-Z target (48Ti)
• Run at higher (unsafe) energies (495 MeV and
  470 MeV)
• Limit distance of closest approach by looking
  only at forward angles in center of mass

34
Setup for 132,134Sn Coulomb Excitation
BaF2 array (150 crystals) for gamma-rays
Beam
courtesy of D. Radford
35
Setup for 132,134Sn Coulomb Excitation
CD-type Si detector for
scattered Sn and Ti
Beam

• 7 cm diameter
• 48 radial strips
• 16 sectors
• qLAB 7 25
• qCM 30 - 160

courtesy of D. Radford
36
First results on 132Sn

• 132Sn beam, doubly stripped
• - 96 pure
• - 1.3 x 105 ions/s
• - 3.75 3.56 MeV/u
• 48Ti target
• High ? efficiency ( 40)
• Two-week experiment
• Fast ?ion coincidences
• to suppress background

37
First results on 132Sn

• 132Sn beam, doubly stripped
• - 96 pure
• - 1.3 x 105 ions/s
• - 3.75 3.56 MeV/u
• 48Ti target
• High ? efficiency ( 40)
• Two-week experiment
• Fast ?ion coincidences
• to suppress background

38
First results on 132Sn

• 132Sn beam, doubly stripped
• - 96 pure
• - 1.3 x 105 ions/s
• - 3.75 3.56 MeV/u
• 48Ti target
• High ? efficiency ( 40)
• Two-week experiment
• Fast ?ion coincidences
• to suppress background

B(E2 0?2) 0.11(3) e2b2
R. Varner et al., EPJ. A 25, s01, 391 (2005)
39
Coulomb Excitation Results for Sn isotopes

• 132Sn B(E2) 0.11(3) e2b2
• 14 Isoscalar E2 EWSR
• 134Sn B(E2) 0.029(5) e2b2

New facilities needed in order to fully explore
this mass region
40
Coulomb excitation studies with low-energy RIBs

• Drip lines and shell Structure in light nuclei
• Drip-line nuclei 10Be
• Mirror nuclei 20,21Na, 21Ne
• The island of inversion 29Na, 30,31,32Mg

N82
Z82
N40
N50
Z50
Z28
20,21Na,21Ne
29Na,30,31,32Mg
10Be
20
41
Coulomb excitation studies with low-energy RIBs

• Evolution of Shell Structure far from stability
• 44Ar (N28)
• 68-78Ni (Z28, N40-50) 68Ni, 67,69,71,73Ci,
  68,70(m)Cu, 74,76,78,80Zn, 61Mn, 61Fe
• 100Sn 106,108,110Sn, 100,102,104Cd
• 132Sn (Z50, N82) 122-126Cd, 126-134Sn,
  132-136Te, 140Ba

N82
Z82
N40
N50
106,108,110Sn
Z50
122,124Cd, 126-134Sn 132-136Te,
138,140Xe 140,148,150Ba
Z28
74,76,78,80Zn, 82Ge
67,69,71,73Cu, 68Cu, 70(m)Cu 68Ni
20
42
Coulomb excitation studies with low-energy RIBs

• Evolution of nuclear shapes and shape coexistence
• NZ ? 34 70Se, 74,76Kr,
• N ? 60 88-94Kr, 96Sr
• N ? 104 182,184,186,188Hg, 202,204Rn

182,184,186,188Hg 202,204Rn
N82
Z82
N40
N50
Z50
74,76Kr 70Se
96Sr, 88-94Kr
Z28
20
43
Perspectives
Ho 67
165
Dy 66
Quadrupole deformation zone
164
Tb 65
159
Gd 64
146
160
Eu 63
153
Sm 62
154
Pm 61
Nd 60
150
Pr 59
141
102
Ce 58
142
La 57
Octupole deformation gaps 
100
139
145
Ba 56
138
145
Cs 55
133
Xe 54
98
136
I 53
94
96
127
Te 52
130
Sb 51
123
Sn 50
92
124
132
In 49
115
Cd 48
88
90
116
Ag 47
109
Pd 46
110
62
64
66
68
70
72
74
76
78
80
82
84
86
Rh 45
103
Spherical robust gaps
Ru 44
104
Tc 43
99
Mo42
100
Nb 41
93
Zr 40
96
90
Spherical fragile gaps
89
Y 39
Sr 38
88
98
100
Rb 37
87
Kr 36
86
Br 35
Fission region
81
Se 34
82
As 33
75
Ge 32
76
Ga 31
Deformed gaps
71
Zn 30
70
Cu 29
65
Ni 28
64
78
courtesy D. Verney (IPNO)
44
Shapes in neutron-rich A100 nuclei
45
Coulomb excitation measurement towards 100Sn
106-108Sn Ni _at_ 2.8 MeV/u
A. Ekstrom et al., PRL101 (012502) 2008