1. Probing core polarization around 78Ni:
intermediate energy Coulomb excitation of 74Ni.
T. Marchi

2. T. Marchi INPC 2013 Florence June 6, 2013
Outline
Introduction: shell evolution along Ni isotopic chain, towards 78Ni.
74Ni: what has been measured so far.
74Ni: intermediate energy Coulomb excitation (NSCL – De Angelis Feb 2011)
Exotic Beam production;
Experimental setup;
Data analysis and B(E2)↑ extraction;
Discussion and outlook.
T. Marchi INPC Florence June 6, 2013

3. T. Marchi INPC 2013 Florence June 6, 2013
Introduction
Motivation:
1-Study the evolution of nuclear Shells far from stability, towards 78Ni.
2-Test model space and interactions far from stability.
[B. Pritychenko et al, arXiv: v2 ]
T. Marchi INPC Florence June 6, 2013

4. T. Marchi INPC 2013 Florence June 6, 2013
74Ni
What has been measures so far – 74Co decay
T. Marchi INPC Florence June 6, 2013

5. 74Ni What has been measures so far - proton scattering
Proton inelastic scattering
[N. Aoi et al, Phys. Lett. B 602, 302 (2010)]
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74Ni
radioactive beam production
74Ni ≈ 0.7 pps
dp/p = 3%
74Ni/77Zn ≈ 0.3
74Ni purity ≈ 1.5%
140 AMeV
9Be 399 mg/cm2
T. Marchi INPC Florence June 6, 2013

7. 74Ni Experimental setup Object scintillator S800 Analysis line
Focal Plane detectors
Object scintillator
S800 Analysis line
S800 Spectrometer
Secondary target position 197Au 640 mg/cm2
CAESAR array
T. Marchi INPC Florence June 6, 2013

8. 74Ni CAESAR scintillator array
[D. Weisshaar et al., NIM A 624, 615 (2010)]
Experimental gamma-rays multiplicity
CAESAR Resolution
CAESAR Efficiency
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74Ni
S800 Focal Plane Detectors
P10
500 Torr
80% CF4
20% C4H10
[D. Bazin et al., NIM B 204, 629 (2003)]
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10. T. Marchi INPC 2013 Florence June 6, 2013
74Ni
The S800 spectrometer and the CAESAR array
CAESAR array
CAESAR array + S800 spectrometer
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11. T. Marchi INPC 2013 Florence June 6, 2013
74Ni
Beam Tagging and Particle Identification
Beam Tagging
Focal plane PID
Runs without target
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74Ni
Data analysis: particles information and gamma rays time gate
Beam energy:
Energy-time gamma-rays gate:
Impact parameter selection:
T. Marchi INPC Florence June 6, 2013

13. P RELIMINARY 74Ni Event by event analysis and gamma-ray spectra
Fit: GEANT4 + exponential bkg
P RELIMINARY
[A. Winther and K. Alder, Nucl. Phys. A319, 518 (1979)]
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Results
V low k
Monte Carlo Shell model
LNPS
The B(E2; 0+ →2+) value obtained in the intermediate energy Coulomb excitation provides new important information for the understanding of the Ni isotopic chain towards the 78Ni doubly magic nucleus.
1-The collectivity enhancement suggested by the (p,p’) experiment seems quenched when using purely electromagnetic probes;
2-The obtained values can be used to benchmark the Model Space and interaction used for several Shell Model Calculations far from stability.
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Discussion and outlook
1.In principle the inelastic scattering data compared to Coulex results allow to disentangle the proton/neutron excitation matrix elements. For the 74Ni isotope, their difference could be an indication of the relative proton/neutron cores polarization leading to different deformation. A higher degree of accuracy is needed to constrain the B(E2) error bar and provide quantitative Mn/Mp ratio information.
For this reason two different experiments have been very recently performed:
72Ni (p,p’) inelastic scattering at NSCL (GRETINA)
74Ni Coulex at RIKEN with higher beam intensity (~ 150 counts in the 2+ peak).
2.Measured values can be used to benchmark the Model Space and interaction definition far from stability. The extension of the model space to the neutron d5/2 orbital reveals necessary for a better data description using the Vlow k effective interaction.
3.The good agreement of the experimental data to the results of the Shell Model Calculation with the LNPS interaction may suggest the underlying presence of the “physics Island of inversion” as treated by Lenzi et al in [S. M. Lenzi et al, Phys Rev C 82, (2010)] .
4-Surprisingly all the models predict an increase of the B(E2) values for the 78Ni nucleus
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Collaboration
T. Marchi,1, 2 G. De Angelis,1 T. Baugher,3 D. Bazin,3 J. Berryman,3 R. Clark,4 E. Crawford,4 M. Doncel,5 E. Farnea,6 A. Gade,3 A. Gadea,7 T. Glasmacher,3 A. Gottardo,1, 2 F. Gramegna,1 S. McDaniel,3 C. Michelagnoli,2, 6 D.R. Napoli,1 B. Quintana,7 A. Ratkiewicz,3 F. Recchia, 2, 6 E. Sahin,1 A. Shore,3 R. Stroberg,3 J.J. Valiente-Dobón,1 D. Weisshaar,3 K. Wimmer,3 and R. Winkler3
1INFN Legnaro National Laboratories, Legnaro (Pd), Italy
2Department of Physics, Padua University, Padua, Italy
3NSCL, Michigan State University, East Lansing, Michigan , USA
4Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
5Ionizing Radiations Laboratory, University of Salamanca, Spain
6INFN Padua, Padua, Italy
7CSIC-IFIC, Valencia, Spain
Thank you!
T. Marchi INPC Florence June 6, 2013