Rare ISotope INvestigation at GSI

Spectroscopy at relativistic energies

‰ Physics case & overview

‰ Spectrometer
‰ Relativistic Coulomb excitation
example Cr isotopes
‰ Summary
P. Reiter, University of Cologne
Gamma-Ray Spectroscopy in Europe:
Present and Future Challenges
ECT Trento, May 8 – 12, 2006
 Physics program - Nuclei of interest
134Ce, 136Nd 104-112Sn

69Br 132Sn

53Ni

68Ni

36Ca
58Cr

¾ Shell structure of unstable magic nuclei

N=Z ¾ Symmetry along the N=Z line
32,34Mg ¾ Collective modes, E1 strength distribution
¾ Shapes and shape coexistence
 New Shell Structure at N>>Z
Mirror symmetry of (sub)shell closures

Modified shell structure in neutron-rich

Ca-, Ti-, Cr-Isotopes due to weaker
πf7/2 –νf5/2 monopole pairing interactions?

(sub)shell gaps at N=32 and N=34?

Z=14(16) shell stabilisation and Z=12 shell

quenching in N=20 isotones.
(sub)shell gaps at N=14,16 for Ca isotopes?
 New Shell Structure at N>>Z
Relativistic Coulex in N=28-34 Nuclei

• Large scale shell modell calculations

- GXPF1, GXPF1A
M.Honma et al,
Phys. Rev. C65(2002)061301

- KB3G
E.Caurier et al,
Eur.Phys.J. A 15, 145 (2002)

• Transition matrix elements

- B(E2) in 52,54,56Ti (MSU)
- B(E2) in 54,56,58Cr (GSI)
 Relativistic beams at GSI

accelerators:
UNILAC (injector) - E<15 AMeV
SIS - E < 1 AGeV

beams:
All ion species up to 238U
Currents:
238U - 2* 108 pps
medium mass nuclei- 109 pps
High resolution γ-spectroscopy at the FRS
FRS provides secondary radioactive ion beams:
• fragmentation and fission of primary beams
• high secondary beam energies: 100 – 500 MeV/u
• fully stripped ions

FRS

RISING
 γ-spectroscopy at relativistic energies
High cross sections
• Coulomb excitation
• Secondary fragmentation

Thick targets

Lorentz boost of γ-rays

• Doppler shift
• Gain in geometrical efficiency
• Doppler broadening
Doppler broadening

Atomic background, a limiting factor Detector opening

• X-rays from target atoms
ΔEγ0/Eγ0 [%] angle Δθ=3°
• Radiative electron capture
β=0.57
• Primary Bremsstrahlung
β=0.43
• Secondary Bremsstrahlung β=0.11
• σ (atomic) ~ 10000 * σ (nuclear)

High energetic reactions θlab [deg]

 Coulomb excitation at relativistic energies
• Sommerfeld Parameter η>>1

• adiabaticity parameter ξ
ωph ΔE ΔE b γβhc
ξ≡ ≡ τcoll = for ξ = 1 ΔE max =
ωcoll h hc γβ b min
- higher excitation energies at relativistic energies
- access to GDR range 10 - 20 MeV

• excitation strength parameter χ

(ππλ) Vλ(b) ⋅ τ coll Z t e f M(π(πλ i
χ (b) ≈ ≈
h hγvb λ
- only single step excitation at relativistic energies
 EUROBALL-Cluster array

15 EUROBALL Ring Angle Distance Resolution Efficiency

[deg] [mm] [%] [%]
Cluster detectors 1 15.9 700 1.00 1.00
without ACS 2 33.0 700 1.82 0.91
105 Ge crystals 3 36.0 700 1.93 0.89
Total: 1.56 2.81
H.J. Wollersheim et al.; NIM A 537 (2005) 637
 RISING experimental setup

Ge Cluster detectors
Target chamber

CATE
beam

BaF2
HECTOR
detectors
Ge MINIBALL detectors
 RI beam: fragment identification and tracking
Primary beam 86Kr, 480 MeV/u, 109 p/sec
56Cr
Secondary beams, 136 MeV/u:
• 54Cr: 4 x 103 part./s, 22 h, 45% 54Cr

• 56Cr: 1 x 103 part./s, 20 h, 35% 56Cr Z

• 58Cr: 3 x 102 part./s, 55 h, 25% 58Cr

Fragment identification
A/Q

Tracking before target Multiwire extrapolation to target

mm
MW1 MW2 Target CATE
Si1 Si2 CsI

Θp
Θγ
γ
mm
 CAlorimeter TElescope CATE
Particle Identification and Tracking after Target
R. Lozeva et al, NIM B, 204 (2003) 678

E
• CsI detectors
∆E
• Z identification
• 0.3 mm thick Si detectors
• Z identification
• Position sensitive

56Cr + 197Au Tracking after target

∆E Particle identification Y

56Cr
(Coulomb excitation)
X

E
 Tracking: - Doppler correction
- scattering angle
• velocity v/c from TOF (event-by-event) MW1 MW2 Target CATE
• tracking of ions: γ-ray emission angle Si1 Si2 CsI

Θp
Ö γ-ray energy resolution Θγ
Ö scattering angle γ
Limit in scattering
angles 0.6o to 2.8o
200 corresponds to
30 keV
impact parameters:
40 to 10 fm

Counts
Counts

16 keV

835 scattering angle (deg)

γ-ray energy (keV)
 New Shell Structure at N>>Z
Relativistic Coulex in N=28-34 Nuclei

A. Bürger et al., Phys. Lett B 622, 29 (2005)

 Comparison with 52,54,56Ti

D.-C. Dinca et al., Phys Rev. C 041302(R) (2005)

 Stable beam lifetime measurement in 56Cr
Doppler shift:
Recoil Distance Doppler Shift
ΔE=E0· v/c ·cos(θ)
Plunger Method
detector E0
48Ca
E‘
target
stopper
ΔE
11B beam
v1
θ
v2=0
Set up: Cologne plunger
x ; t=x/v1 Foreward: EUROBALL Cluster
48Ca(11B,p2n)56Cr Backward: 5 Ge-detector
@ 30 MeV
Cologne tandem accelerator

Potential difficulties:
Feeding: observed; unobserved γγ coincidences with plunger
Deorientation, …. Differential Decay Curve method

D. E. Appelbe et al. Phys. Rev. C 67, 034309 (2003)

 stable beam, lifetime measurement in 56Cr
Differential Decay Curve method

Eγ RISING Plunger B(E2)

[keV] B(E2) [Wu] B(E2) [Wu] [Wu]

54Cr 835 Normali- 14.6(6)

sation

56Cr 1006 8.7 (3.0) ---

11.1 (3)
58Cr 880 14.3 (4.2) ---
- RISING result confirmed ~ 3 % error
- 58,60,62...Cr radioactive beams or
M. Seidlitz et al. deep inelastic reactions
Triaxiality in even-even core nuclei of N=75 odd-odd isotones

2+1 → 0+ 134Ce
B(E2)
2+2
(2+2 → 2+1) [W.U.]
557
2+1 53±5
(2+2 → 0+) 966
409 < 12 *
0+
< 206 *

2+1 → 0+ 136Nd
B(E2)
2+2
2+2 → 2+1 [W.U.]
489
2+1 862 90±11
2+2 → 0+
374 12±3 *
0+
251±95 *

T. Saito et al. next contribution

 AGATA performance in
FAIR experiments
RISING AGATA-15
(2004/5) ~2010

Efficiency : 1-3% 10.5%

FWHM: 25 keV ~7 keV
at v/c~0.5, multiplicity: 1-5, target-detector distance: 15 cm

Much increased sensitivity

Angular distribution and polarisation measurements,

γγ-coincidence measurements, g-factors
background suppression through determination of source
 AGATA vs. RISING Coulomb excitation of 54Cr
RISING AGATA-15
exp. data simulation

Counts/4 keV
Counts/4 keV

390 cts 830 cts

σ: 6.7 keV σ: 3.1 keV

RISING AGATA-180
simulation simulation
Counts/4keV
Counts/4 keV

400 cts 4950 cts

σ: 8.4 keV σ: 4.9 keV

Calculation by A. Bürger, W. Korten

 Summary
Coulomb excitation results from fast beam RISING
¾ Coulex at 130-150 MeV established
¾ Coulomb excitation of 2+1 in 108,112Sn
A. Banu et al., Phys. Rev. C 72, 061305(R) (2005)
¾ Coulomb excitation of 2+1 in 54,56,58Cr
A. Bürger et al., Phys. Lett B 622, 29 (2005)
¾ RDDS results confirms B(E2) of 56Cr
¾ Collective modes and E1 strength distribution: 68Ni
talk by F. Camera
¾ Coulomb excitation of 2+1 and 2+2 in 134Ce, 136Nd
talk by T. Saito

Future challenges
9 fast beam RISING
9 AGATA demonstrator
 RISING collaboration

Local FRS & RISING group:

A. Banu, T. Beck, F. Becker, P. Bednarczyk, K.-H. Behr, P. Doornenbal,
H. Geissel, J. Gerl, M. Gorska, J. Grebosz, M. Hellström, M. Kavatsyuk,
O. Kavatsyuk, I. Kojouharov, N. Kurz, R. Lozeva, S. Mandal, N. Saito, T. Saito,
H. Schaffner, H. Weick, M. Winkler, H.J. Wollersheim
GSI Darmstadt, Germany
 Coulomb excitation cross section

GSI

GANIL, NSCL, RIKEN

H. Scheit, thesis (1998)

 Coulomb excitation parameters

Coulomb excitation: 56Cr → 197Au

E/A 5 60 130 500

AMeV AMeV AMeV AMeV
Adiabaticity 0.6 0.17 0.11 0.05
parameter
Emax 1.6 5.7 8.6 18.6
MeV MeV MeV MeV
Strenght 0.15 0.11 0.07
parameter*

* For 2+ excitation B(E2) =300 e2fm4