Projectile Fragmentation at the Fragment Separator

1
Projectile Fragmentation at the Fragment Separator

• Andreas Heinz
• Wright Nuclear Structure Laboratory,
• Yale University
• for the CHARMS Collaboration

Symposium on 30 Years of Projectile
Fragmentation, ACS meeting, San Francisco,
September 10-11, 2006
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CHARMSCollaboration for High-Accuracy
Experiments on Nuclear Reaction Mechanisms with
Magnetic Spectrometers

• P. Armbruster1, A. Bacquias1, L. Giot1, V.
  Henzl1,12, D. Henzlova1,12, A. Kelic1, S. Lukic1,
  R. Pleskac1, M.V. Ricciardi1, K.-H. Schmidt1, O.
  Yordanov1, J. Benlliure2, J. Pereira2,12, E.
  Casarejos2, M. Fernandez2, T. Kurtukian2, C.-O.
  Bacri3, M. Bernas3, L. Tassan-Got3, L. Audouin3,
  C. Stéphan3, A. Boudard4, S. Leray4, C. Volant4,
  C. Villagrasa4, B. Fernandez4, J.-E. Ducret4, J.
  Taïeb5, C. Schmitt6, B. Jurado7, F. Reymund8, P.
  Napolitani8, D. Boilley8, A. Junghans9, A.
  Wagner9, A. Kugler10, V. Wagner10, A. Krasa10, A.
  Heinz11, P. Danielewicz12, L. Shi12, T.
  Enqvist13, K. Helariutta14, A. Ignatyuk15, A.
  Botvina16
• 1GSI, Darmstadt, Germany
• 2Univ. Santiago de Compostela, Sant. de
  Compostela, Spain
• 3IPN Orsay, Orsay, France
• 4DAPNIA/SPhN, CEA Saclay, Gif sur Yvette, France
• 5DEN/DMS2S/SERMA/LENR, CEA Saclay, Gif sur
  Yvette , France
• 6IPNL, Universite Lyon, Groupe Materie Nucleaire
  4, Villeurbanne, France
• 7CENBG, Bordeau-Gradignan, France
• 8GANIL, Caen France
• 9Forschungszentrum Rossendorf, Dresden, Germany
• 10Nuclear Physics Institute, Rez, Czech Republic
• 11Wright Nuclear Structure Laboratory, Yale
  University, New Haven, USA
• 12NSCL and Physics and Astronomy Department,
  Michigan State University, East Lansing, USA
• 13CUPP Project, Pyhasalmi, Finland
• 14Univeristy of Helsinki, Helsinki, Finland
• 15IPPE Obninsk, Russia
• 16Institute for Nuclear Research, Russian Academy
  of Sciences, Moscow, Russia

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Topics

• Basic research
• Momentum dependence of the nuclear mean field
  (Talk of V. Henzl)
• Thermal instabilities of nuclear matter (Talk of
  D. Henzlova)
• Dissipation in Nuclear Matter
• Very asymmetric fission
• Structure effects in fission and fragmentation
• Nuclide production in fragmentation and fission
  (Talk of J. Benlliure)
• Applications
• Nuclear astrophysics
• Spin, alignment and polarisation in fragmentation
• Transmutation of nuclear waste
• Nuclear safety
• Production of secondary beams (RIA, FAIR)

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The Heavy-Ion Synchrotron at GSI
Beams from p to 238U Energies of 1-2 A GeV
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The FRagment Separator FRS

• Two natural observables
• Momentum distributions
• Cross sections

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Projectile Fragmentation
Two different time scales for abrasion and
ablation ? (at least) a two-step process!
Ablation
Abrasion
Break-up

• Abrasion of nucleons in a peripheral collision
  produces excited CN (prefragment).
• high ltEgt ? 27 MeV per abraded nucleon
• De-excitation through particle evaporation
  (n,p,?) or fission
• (relatively) low angular momenta (listen tomorrow
  to Z. Podolyak)

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Momentum Distributions
Nucleon excitation in projectile fragmentation
1H(208Pb,208Bi)x at 1 A GeV 2H(208Pb,208Bi)x at 1
A GeV Velocity of 208Bi in the frame of the 208Pb
projectile.

• Kelic et al., PRC 70, 064608 (2004)
• Two components can be distinguished
• Quasi-elastic scattering (p replaces n in 208Pb)
• ?(1232) excitation (e.g. n ? ?0 ? p ?-)
• Probability for ? excitation and energy in the
  nuclear medium can be deduced.

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Measured Nuclide Production in Fragmentation and
In-flight Fission
For heavy projectile fission opens up as a decay
channel ? knowledge of the fission properties of
unstable heavy nuclei is necessary
Excellent basis for model development
Data available at http//www-w2k.gsi.de/charms/da
ta.htm
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Experiment
Total Kinetic Energy (TKE) distribution
Charge distribution
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Two Reaction Mechanisms
Plastic only nuclear-induced fission Pb nuclear
and electromagnetic-induced fission Nuclear ZCN
Z1 Z2 Electromagnetic ZCN Z1 Z2 ?
trigger for low excitation energies!
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Experimental Information on Fission at low E
E-Bf lt 10 MeV
A lot of new data!
E. Konecny et al., Proc. Third IAEA Symp. Phys.
Chem. Fission Vol 2, 1974, p. 3
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Transition from Symmetric to Asymmetric Fission

• Data resulted in
• improved models for yield calculations
• better understanding of low-energy fission
  evolution of fission channels, influence of
  pairing,

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GSI code ABLA - Examples low-energy reactions
Excitation function and A- and Z- distributions
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Dissipation and Nuclide Production
J. Taïeb et al.
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Dissipation and Nuclear Fission
Compound Nucleus
Saddle point
Collective motion
Junior researcher
Energy
Potential difference
Fission barrier
Ground state
Collective motion converts into heat due to
friction
Scission
Deformation
What does this have to do with nuclear fission?
tCN-Saddle
tSaddle-Scission
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Dissipation and the Saddle Point Temperature
Compound Nucleus
Saddle point
?E
Energy
If there is any dissipation tneutron lt tfission ?
mneutron and ?E get larger ? Tsaddle is smaller
Reminder the connection between temperature and
excitation energy
Ground state
Deformation
Level density parameter
tCN-Saddle
tSaddle-Scission
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Charge Width as a Thermometer
Asymmetric mass split
Symmetric mass split
Asymmetric mass split
Population
Potential
Mass asymmetry ?
From Bjornholm, Lynn Rev. Mod. Phys. 52, 725
(1980)
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First Results
238U _at_ 1 A GeV on 9Be
Deformed
Spherical
Model description fails for deformed
projectiles ? influence of initial deformation
on dissipation in nuclear fission
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Fine structure in residue yields after violent
nuclear collisions
Caution when interpreting nuclide yields with
thermodynamic approaches without nuclear
structure!
M.V. Ricciardi et al., NPA 733, 299 (2004)
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GSI code ABLA Examples for high-energy reactions
Experiment
Calculation
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The Future R3B

• Measure
• Charge AND Mass of projectile and fission
  fragments
• Neutrons
• Gammas
• Cross sections

Exclusive experiments AND high resolution
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Future (Part II) Electron-Ion scattering in a
Storage Ring (eA Collider) ELISe

• 125-500 MeV electrons
• 200-740 MeV/u RIBs
• achievable luminosity
• 1025-1029 cm-2s-1 depending on ion species
• spectrometer setup at the
• interaction zone
• detection system for RI in
• the arcs of the NESR (see EXL)

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Conclusions

• A lot of progress in the understanding of
  projectile fragmentation.
• Heavy beams and high resolution spectrometers are
  excellent tools.
• Dont forget the influence of nuclear structure
  and nucleonic exciations.
• A wealth of new data from projectile
  fragmentation, spallation, in-flight fission and
  fission of secondary beams allowed for the
  development of realistic models with predictive
  power.
• Applications in accelerator driven systems,
  nuclear astrophysics, ...
• The future looks bright!