Dynamical fragment productionin non-central heavy-ion collisions

E*, J

PLF*

TLF*

Sylvie Hudan, Indiana University

Evaporation Binary breakup fragmentation

See R.T. de Souza on Friday

Binary breakup : dynamical effect

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)

• U+C at 24 MeV/n : aligned/binary 3%• U+U at 24 MeV/n : aligned/binary 20%• Xe+Sn at Ebeam > 40 MeV/n : aligned/binary 70%

Large cross-section

See J. Colin in this session

Large asymmetries

LH

LH

ZZ

ZZasymmetry

1

0.5

Nor

mal

ized

sca

le

Experimental setup

Ring Counter :Annular Si (300 m) – CsI(Tl) (2cm)2.1 lab 4.21 unit Z resolutionMass deduced†

LASSA : Mass resolution up to Z=97 lab 58

Detection of charged particles in 4† : Modified EPAX K. Sümmerer et al., PRC 42, 2546 (1990)

Beam

114Cd + 92Mo at 50 A.MeV

Selected events : 2 fragments (Z4) detected in the Ring Counter

Reconstruction of the PLF* : PLF* Heavy + Light ZPLF*, APLF*, vPLF*

Characteristics of the selected events

Correlation between ZPLF* and the total multiplicity

Selection of peripheral events

Asymmetry of the angular distributionsPLF* frameHeavy

Heavy more forward focused

Distinction of 2 cases : forward and backward

6 Nc 10

PLF*v

Heavy emitted backward to the PLF*

PLF*v

Heavy emitted forward to the PLF*

backward

forward

Deviation from standard statistical fissionB. Davin et al., PRC 65, 064614 (2002)

Different charge correlation

In both cases ZPLF* 41

Peak at Z=6 §§ : Consistent with Montoya et al., PRL73, 3070 (1994)

6 Nc 10

Different asymmetry

LH

LH

ZZ

ZZη

backward

forward

Deviation from standard statistical fission

Different relative velocities

Large effect ( 50%)

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

backward

forward

Viola systematics

Velocity dissipation

Similar vPLF* distribution

When selected on vPLF* :Different charge asymmetries

forward :

Strong asymmetry for all vPLF*

B. Davin et al., PRC 65, 064614 (2002)

6 Nc 10

backward : compatible with standard statistical fissionforward : dynamical features

backward

forwardvPLF*

E*, J

Z=6

backward forward

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

Anti-correlation

expected if vPLF* and (vPLF*) correlated to a common quantity

Same correlation

correlated to E*

Statistical

Dynamical

Dynamical

Statistical

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* increasesvPLF* E*

39Z35 PLF*

Process probability : opening channel39Z35 PLF*

Dynamical process appear at lower velocity damping

Up to 10% of the cross-section in binary breakup

Dynamical

Statistical

1 fragment case (x 0.1)

Charge split and Coulomb cost39Z35 PLF*

LH

LH

ZZ

ZZη

Higher asymmetry for the dynamical case

Different Coulomb cost

Less damping required for the dynamical case

DynamicalStatistical

DynamicalStatistical

Kinetic energy transferred39Z35 PLF*

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

Dynamical

Statistical

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*

AMD : descriptionAntisymmetrized Molecular Dynamics :

Microscopic approach to nuclear collision dynamics

• Slater determinant of Gaussian packets• TDVP Equation of Motion for centroids• Quantum branching processes

NN collisionsWave packet diffusion/shrinking

114Cd+92Mo @ 50 MeV/n : b = 0 - 9.2 fmDynamical calculation At t = 300 fm/c :

Clusterization (dR<5fm) Statistical decay

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)

AMD : global features

For all impact parameters

PLF and TLF branches Fragment production at mid-rapidity

Large production of Z=5-6 at all v// (already before decay)

AMD : alignment

Heavy mostly forward peaked in the PLF* frame

High cross section :forward : /TOT

0.23backward : /TOT

0.10

We select events with 2 fragments (Z4) emitted forward to the CM

INDRA data, Gd+U @ 36 MeV/uF. Bocage et al., NP A676, 391 (2000)

Heavy

PLF* frame

backward

forward

AMD : charge asymmetry

forward: peaked at large asymmetry

backward: flat distribution

Cd+Mo @ 50 MeV/n B. Davin et al., PRC 65, 064614 (2002)

backwardforward

backward

forward

AMD : relative velocity

forward case is characterized by a higher relative velocity as compared to the backward case

10% effect (25% in the data)

Cd+Mo @ 50 MeV/nB. Davin et al., PRC 65, 064614 (2002)

backward

forward

AMD : Influence of the target

114Cd+12C @ 50 MeV/n

Few fragments produced at mid-rapidity

binary/tot < 2%

ConclusionsThe 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.”

Acknowledgments

S. Hudan , B. Davin, R. Alfaro, R. T. de Souza, H. Xu, L. Beaulieu, Y. Larochelle, T. Lefort, R. Yanez and V.

ViolaDepartment 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 the LASSA collaboration :

To A. Ono for the AMD calculations

To J. Colin for providing figures