Nuclear Structure studies using fast radioactive beams

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• Nuclear Structure studies using fast radioactive
  beams

• The RISING experiment
• Relativistic Coulomb excitation
• Spin degree of freedom in fragmentation reactions
• Open questions and future experimental
  possibilities

J. Gerl SNP2008 July 8-11 2008 Ohio University,
Athens Ohio USA
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Physics with RISING at GSI

• Nuclear Shell structure
• N Z 36Ca to 100Sn
• NgtgtZ 56Cr to 132Sn
• Nuclear shapes
• Quadrupole, Octupole, Triaxiality
• High K-isomers
• Collective Modes
• NgtgtZ GDR soft mode
• Nuclear Symmetries
• mirror-isospin, pn-pair correlation
• Nuclear Moments

Coulomb excitation, Fragmentation and Decay
studies using Rare Isotope Beams and
high-resolution ? Spectroscopy
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RISING Fast beam - physics focus
Coulex in triaxial nuclei 136Nd
Coulex in nuclei towards 100Sn
Spectroscopy of mirror nuclei (A50) via two-step
fragmentation
Pigmy resonance in n-rich nuclei
Spectroscopy of 36Ca via two-step fragmentation
Coulex in n-rich Cr isotopes
Convener P. Reiter, University of Cologne
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Layout of the GSI facility
SIS
FRS
RISING
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Fragment Identification Tracking and Spectroscopy
production
selection
spectroscopy
identification
reaction
identification
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Relativistic Coulomb excitation
112Sn ?Au
excited nucleus
Coulomb interaction
E 100 MeV/u ?L 3 Imax 2 ?Emax 10 MeV
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Nuclear Fragmentation
Abrasion-ablation model ABRABLA
Fragmentation vp gtgt vFermi Impact parameter
controls pre-fragment mass Abrasion statistical
process - single particle levels vacated - E
given by sum of hole energy above Fermi
surface - Ipre given by holes Ablation
statistical models - particle evaporation or
fission - Eentry / Ientry (similar to fusion)
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Types of experiments

• Secondary fragmentation
• Be target
• Suppression of the inelastic excitation of the
  projectile
• Broad angular momentum distribution to high spins

• Coulomb excitation
• Au target
• One step excitation
• Low spin

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RISING In-flight set-up
105 Ge crystals Energy resolution (FWHM)
1.24 Total efficiency 2.9 for E? 1.3 MeV at
100 MeV/u
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Hector Array
84Kr
142
90
time
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Atomic Background Radiation
X-rays from target atoms Radiative electron
capture (REC) Primary Bremsstrahlung
(PB) Secondary Bremsstrahlung (SB)
Atomic g background cross section
To measure g- ray above 300 keV
Beam energy 100 MeV/u
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Doppler Effect
Doppler shift
Doppler broadening
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Scattering angle

• reaction selection
• g-ray Doppler shift correction
• atomic background suppression

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Coulomb Excitation of 108Sn

• Shell model comparison
• Core polarization
• multiple proton core particle-hole excitations

A. Banu et al.
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Coulomb Excitation of n-rich Cr Isotopes
A. Bürger et al.
Does a new sub-shell closure exist at N32?
Evidence for reduced B(E2) value at N32
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Coulomb excitation of 136Nd
? 0.277 ? 24.2
GCM
140 MeV/u 136Nd?Pb
21 0
22 21
182
109
(93)
22 0
22.9
11(3)
65.7
80(11)
First observation of second excited state at
relativistic energies Evidence for ?-soft
triaxial behaviour
Energy keV
T. Saito et al.
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Coulomb excitation of pygmy resonance in 68Ni
PDR E 11 MeV 5 EWSR
Contrib. O. Wieland
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Secondary fragmentation of 55Ni on 9Be at 140
MeV/u
Mirror symmetry at N ? Z
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50Cr
extract lifetimes from lineshapes
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Mike Bentley et al.
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(8)
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46Ti
4
6
(8)
First observation of higher spin states at
relativistic energies
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Isomeric ratios
Fragmentation of 208Pb
Fragmentation of 238U
148Tb I 27 R 3.2 (3)
Isomeric ratios I R 211Fr
29/2 5.7 (2) 212Fr 15- 7.5 (2) 213Fr
29/2 12.0 (8) 214Ra 17- 6.8 (2) 215Ra 43/2- 3.1
(6)
Fragmentation populates high spin states
Zs. Podolyak et al.
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High Spin enhancement in massive fragmentation
Comparison with ABRABLA predictions
- Sharp cut off limit - Yrast isomers
Collective spin contribution
148Tb I 27 Rexp/?the 23
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High Spin enhancement in massive fragmentation
massive fragm.
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20
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I (hbar)
Number of fragmented nucleons can not explain
spin distribution! Collective effects add angular
momentum to single particle spin Other
effects??? Better description???
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Experimental opportunites
LYCCA position sensitive ?E/E/ToF detector array
PARIS ?? ?-calorimeter
AGATA high-resolution ?-tracking array
Pph 3 ? 8 (16) ?E 1.2 ? 0.4 (5)
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Spectroscopy program at GSI / FAIR
RISING 2007 2008 Decay with active
stopper PRESPEC 2009 2010 In-beam employing
LYCCA including ToF 2010 2011 Decay and
g-factors 2011 2012 In-beam AGATA demonstrator
together with Euroball detectors HISPEC/DESPEC 20
13 In-beam and decay spectroscopy with
Super-FRS at FAIR/NUSTAR
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Conclusions
Coulomb and nuclear interactions at relativistic
beam energies provide a universal method to
populate excited states in nuclei Coulomb
excitation populates low spin states from the
first excited state up to giant resonances with a
population pattern governed by B(E?)
values Fragmentation reactions seem to populate
low spin states unspecifically up to particle
thresholds High spin states are populated in
massive fragmentation reactions The underlying
reaction mechanism is only qualitatively
understood and more detailed investigations are
required for a quantitative understanding Improve
d instrumentation is coming up soon
PRESPEC In-Beam Physics workshop, Daresbury 8.-9.
October 2008
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Some RISING collaborators
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thank you
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68Ni ?Au