Dynamical fragment production in noncentral heavyion collisions

1
Dynamical fragment productionin non-central
heavy-ion collisions
Sylvie Hudan, Indiana University
E, J
See R.T. de Souza on Friday
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Binary breakup dynamical effect

• UC at 24 MeV/n ?aligned/?binary ? 3
• UU at 24 MeV/n ?aligned/?binary ? 20
• XeSn at Ebeam gt 40 MeV/n ?aligned/?binary ?
  70
• Large cross-section

F. Bocage et al., NP A676, 391 (2000) J. Normand,
PhD Thesis, université de Caen (2001) S.
Piantelli et al., PRL 88, 052701 (2002) B. Davin
et al., PRC 65, 064614 (2002)
See J. Colin in this session
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Experimental setup
LASSA Mass resolution up to Z9 7? ? ?lab ?
58?
114Cd 92Mo at 50 A.MeV
Ring Counter Annular Si (300 ?m) CsI(Tl)
(2cm) 2.1? ? ?lab ? 4.2? 1 unit Z
resolution Mass deduced
Beam
Modified EPAX K. Sümmerer et al., PRC 42,
2546 (1990)
? Detection of charged particles in 4p
Selected events 2 fragments (Z?4) detected in
the Ring Counter
Reconstruction of the PLF PLF ? Heavy
Light ? ZPLF, APLF, vPLF
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Characteristics of the selected events

• Correlation between ZPLF and the total
  multiplicity

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Asymmetry of the angular distributions
6 ? Nc ? 10
PLF frame
Heavy

• Heavy more forward focused

Distinction of 2 cases forward and backward
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Deviation from standard statistical fission
B. Davin et al., PRC 65, 064614 (2002)
6 ? Nc ? 10

• Different asymmetry

forward
backward

• Different charge correlation
• In both cases ZPLF ? 41

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Deviation from standard statistical fission
6 ? Nc ? 10
B. Davin et al., PRC 65, 064614 (2002)
Viola systematics

• Different relative velocities
• Large effect (? 50)

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Velocity dissipation
6 ? Nc ? 10
B. Davin et al., PRC 65, 064614 (2002)

• Similar vPLF distribution

forward
backward

• When selected on vPLF
• Different charge asymmetries
• forward
• Strong asymmetry for all vPLF

backward compatible with standard statistical
fission forward dynamical features
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Velocity damping and excitation energy

• Same trend for both cases
• More dissipation and fluctuations as ZPLF
  decreases
• For a given size, less dissipation in the
  dynamical case

Dynamical
Statistical

• Anti-correlation
• ? expected if ?vPLF? and ?(vPLF) correlated to
  a common quantity
• Same correlation
• ? correlated to E

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Damping and excitation fission case

• Deviation from the Viola systematics
  (predominantly Coulomb) as damping increases

• More fluctuations on the kinetic energy released
  in the fragments

As velocity damping increases, E increases vPLF
? E
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Process probability opening channel
1 fragment case (x 0.1)
Dynamical
Statistical

• Dynamical process appear at lower velocity
  damping
• Up to 10 of the cross-section in binary breakup

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Charge split and Coulomb cost
Dynamical
Statistical

• Higher asymmetry for the dynamical case

Statistical
Dynamical

• Different Coulomb cost
• ?Less damping required for the dynamical case

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Kinetic energy transferred

• More kinetic energy in the fragments for the
  dynamical case
• For a given velocity damping, difference of ?
  20-30 MeV
• Constant offset with velocity damping when
  Coulomb subtracted

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Deviation from the Viola systematic
Dynamical

• Deviation of the statistical case from Viola
  (E?0)
• Offset of the dynamical case

Statistical
Offset(vPLF9.3) 0
Statistical

• Offset independent of velocity damping (?E)

Dynamical
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Observation of a dynamical component

• Process with a large cross-section
• As compared to standard fission, the dynamical
  process has
• ? Lower E threshold
• ? Large asymmetry (dependent on E)
• ? Strong alignment
• ? Large kinetic energy in the 2 fragments, for
  all E
• ? Constant ?(TKE-Coulomb) for all E

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AMD description

• Antisymmetrized Molecular Dynamics
• Microscopic approach to nuclear collision
  dynamics
• Slater determinant of Gaussian packets
• TDVP ?Equation of Motion for centroids
• Quantum branching processes
• NN collisions
• Wave packet diffusion/shrinking

114Cd92Mo _at_ 50 MeV/n b 0 - 9.2 fm Dynamical
calculation At t 300 fm/c Clusterization
(dRlt5fm) Statistical decay
AMD
A. Ono et al., Prog. Theor. Phys. 87, 1185
(1992) A. Ono and H. Horiuchi, Phys. Rev. C59,
853 (1999) A. Ono, S. Hudan, A. Chbihi and J.D.
Frankland, Phys. Rev. C66, 014603 (2002)
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AMD global features
AMD decay
For all impact parameters

• PLF and TLF branches
• Fragment production at mid-rapidity
• Large production of Z5-6 at all v// (already
  before decay)

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AMD hot and cold fragments
AMD
Characteristics before decay
Before decay
After decay
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AMD alignment
We select events with 2 fragments (Z?4) emitted
forward to the CM

• Heavy mostly forward peaked in the PLF frame
• High cross section
• forward ?/?TOT ? 0.23
• backward ?/?TOT ? 0.10

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AMD charge asymmetry
CdMo _at_ 50 MeV/n B. Davin et al., PRC 65,
064614 (2002)
DATA
forward
backward

• forward
• peaked at large asymmetry
• backward
• ? flat distribution

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AMD relative velocity
DATA
CdMo _at_ 50 MeV/n B. Davin et al., PRC 65, 064614
(2002)
forward
backward

• forward case is characterized by a higher
  relative velocity as compared to the backward
  case
• 10 effect (25 in the data)

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AMD Influence of the target
114Cd12C _at_ 50 MeV/n

• Few fragments produced at mid-rapidity
• ?binary/?tot lt 2

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Conclusions

• The AMD calculations show the trends observed in
  the experimental data
• alignment
• asymmetry
• relative velocity with a lower magnitude
• influence of the target
• A total of ?8000 events have been calculated,
  representing ?160000 cpuhours (? 18 years).
• Thanks to the UITS and RATS group at IU.
• This work was supported in part by Shared
  University Research grants from IBM, Inc. to
  Indiana University.

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Acknowledgments
To the LASSA collaboration
S. Hudan , B. Davin, R. Alfaro, R. T. de Souza,
H. Xu, L. Beaulieu, Y. Larochelle, T. Lefort, R.
Yanez and V. Viola Department of Chemistry and
Indiana University Cyclotron Facility, Indiana
University, Bloomington, Indiana 47405 R. J.
Charity and L. G. Sobotka Department of
Chemistry, Washington University, St. Louis,
Missouri 63130 T.X. Liu, X.D. Liu, W.G. Lynch,
R. Shomin, W.P. Tan, M.B. Tsang, A. Vander Molen,
A. Wagner, H.F. Xi, and C.K. Gelbke National
Superconducting Cyclotron Laboratory and
Department of Physics and Astronomy, Michigan
State University, East Lansing, Michigan 48824
To A. Ono for the AMD calculations To J. Colin
for providing figures