Mid-peripheral collisions : PLF* decay

P

T TLF*

PLF*

1 fragment

Sylvie Hudan, Indiana University

vL > vH

forward

vH > vL

backward

More than 2 fragments

Step by step

1) Correlation Size - Velocity

2) Experimental setup

3) The simplest case : 1 heavy fragment

4) Binary breakups : statistical vs. dynamical

5) Summary & Outlook

Fragments from the PLF*

ZMAX Z MAX-1

Z MAX-2 Z MAX-3

« Hierarchy of the velocity and of the angular distribution of the fragments as a fonction of their

charge »

Ta+Au 33 MeV/AINDRA dataINDRA dataJ. Normand, J. Colin and D. CussolJ. Normand, J. Colin and D. Cussol

Comparison with a model :Classical N-Body Dynamics

D. Cussol, PRC65, 054614 (2002)

« As in the data, the heaviest fragment is the fastest and is aligned along the QP velocity »

Experimental setup

Miniball/Miniwall

Beam

LASSA : Mass resolution up to Z=97 lab 58

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

114Cd + 92Mo at 50 A.MeV

Detection of charged particles in 4

Projectile48

† : Modified EPAX K. Sümmerer et al., Phys. Rev. C42, 2546 (1990)

Events with one heavy fragment from a PLF*

PLF frame

Well-defined emission from the PLF

30 ZPLF* 46

One fragment : Isotropic component

PLF frame

Isotropic component

Other component(mid-rapidity, …)

One fragment : reconstruction of the PLF*

Fit of the isotropic component

At = 90, alpha particles 20% of non-statistical emission

Mevap = 6.97

Zevap = 10.6

ZPLF + Zevap 35 +10.6 46

(Zprojectile = 48)

One fragment : temperatures

Data : slope temperature

Simon : emission temperature

Simon* : A = 109 E* 500 MeV J = 0 hbar

* : D. Durand, Nucl. Phys. A541, 266 (1992)

Lower slope temperature for protons and alpha particles

Velocity damping and excitation energy

Strong correlation between the multiplicity of evaporated particlesand the velocity damping

Velocity damping correlated to E*

Strong correlation between the slope temperature and the velocity damping

Events with two fragments from a PLF*

PLF*

ZH

ZL vL > vH, forward

ZHZL vH > vL , backward

LH*PLF ZZZ )f(ZAA *PLFL*PLF HA

*PLF

LLHH*PLF

A

vAvAv

Statistical behavior isotropy vH > vL vL > vH

Two fragments : anisotropy of PLF* decay

6 NC 10

Different charge splits more asymmetric split for the backward case

Different alignments more alignment for the backward case

B. Davin et al., Phys. Rev. C65, 064614 (2002)

Two fragments : relative velocities

6 NC 10

Different relative velocities higher vrel for the backward case

Dependence with the size for the backward case

B. Davin et al., Phys. Rev. C65, 064614 (2002)

Asymmetry of the breakup :

Sensitivity to vPLF*

6 NC 10

vprojectile = 9.45 cm/ns

More asymmetric Z distribution for the backward case

Higher asymmetry at high vPLF* (low E*,J)

For all vPLF* , asymmetry for the backward case An other degree of freedom?

vL > vH vH > vL

vPLF*

9.2

8.9

8.3

8.6

E*,J

x100

x20

x2

x80

x10

x1

B. Davin et al., Phys. Rev. C65, 064614 (2002)

To summarize…

The forward and backward cases are different :

Forward emission is consistent with standard statistical emission

Backward emission is consistent with dynamical decay

Different charge split dynamical has higher asymmetry

Different alignment dynamical is more aligned

Different relative velocity for the same ZL

dynamical has higher vrel

Different Z distribution for a given (E*,J)

Well-defined PLF* : ZPLF* and vPLF*

vL > vH

vH > vL

Same correlation

expected if vPLF* and E* correlated

PLF*PLF* vvσ

More dissipation and fluctuations as ZPLF*

decreases

For a given size, less dissipation for the dynamical case

dynamical

statistical

dynamical

Opening channels

Dynamical emission opens at higher vPLF* , i.e. lower E*

Up to 10% of the cross-section in the 2 fragment decay

vL > vH

vH > vL

1 fragment (x 0.1)

Asymmetry and Coulomb barrier

Higher asymmetry for the dynamical case

Coulomb barrier lower

Dynamical case appears at lower E*

35 ZPLF* 39

LH

LH

ZZ

ZZη

Energy in the fragments

More kinetic energy in the 2 fragments for the dynamical case

For a given vPLF*, difference of 20-30 MeV

A statistical picture : Viola systematics

Comparison statistical / Viola

At large vPLF*, statistical Viola

Deviation for low vPLF*

Temperature ?

Comparison dynamical / Viola

For all vPLF*, dynamical >>Viola

More compact shape needed for the dynamical case

7.3AA

ZZ*0.755Viola

1/32

1/31

21

Estimation of the temperature

T2CoulombTKE Measured Estimated

(Viola systematic)Statistical case : vL > vH

Temperatures between 0 and 10-12 MeV

These temperatures are consistent with T=7 MeV from the isotopes in LASSA

(for 30 ZPLF* 46)

To summarize…

vPLF* as a good observable :

Same correlation (vPLF*)-vPLF* for statistical and dynamical cases

Dynamical case appears at higher vPLF* Coulomb barrier effect

vPLF* (TKE)dynamical > (TKE)statistical by 20-30 MeV

Statistical Viola at high vPLF* and deviation with increasing vPLF*

Temperature

Dynamical case always underestimated by Viola

A law : energy conservation

ZH ZLPLF* + +

E* , BEPLF* TKEH , BEH TKEL , BEL TKEevap , BEevap

For a selected vPLF* E*

Kinetic energy in the fragments Higher for the dynamical case

Q value

Evaporated particles

nevaporatioQTKEE* fragments

“Missing” energy : Q value?

Same Q value in both cases for all vPLF*

vL > vH

vH > vL

statistical

dynamical

44Z35 *PLF

“Missing” energy : evaporation?Multiplicity of Z=2 emitted forward to the PLF* (in LASSA)

Dependence of the multiplicity with VPLF* (E*)

Higher average multiplicities for the statistical by 10-20%

Energy conservation : balance

vPLF* fixed

lstatisticadynamical

lstatisticadynamical

lstatisticadynamical nevaporatio

Q

TKEE* fragments

Fixed

Longer time scale in the statistical case ?

for Z=2

Neutrons

Evaporation before/after breakup

A picture of the process

TKE

TimeSaddle-point Scission-point

Q

Coulomb

Collective

“Extra” energy

Initial kinetic energy?

Fluctuations of TKE(Q+Coulomb)-TKE correlation

TKE : width of the distribution

More fluctuations in the dynamical case

consistent with an additional kinetic energy at the scission-point

Conversion : Q + Coulomb to TKE

StatisticalTKE Q + Coulomb

DynamicalTKE Q + Coulomb + E0

Conclusions : building a coherent picture

vPLF* good selector for E*

scission,dynamical < scission,statistical

Initial TKE at scission for the dynamical case is larger than the statistical case

We observed…

Correlation (vPLF*)-vPLF*

Correlation vPLF* - Mevap

Multiplicities of evaporated Z=2

Different TKE for all vPLF*

Different TKE for all vPLF*

Correlation TKE-(Q+Coulomb)

We interpreted…

Influence of the target

LH

LH

ZZ

ZZ

rela ti ve v eloci ty

INDRA dataINDRA dataJ. Normand, J. Colin and D. CussolJ. Normand, J. Colin and D. Cussol

Ratio of the standard fission

« For heavy systems the importance of the isotropic component depends on:the size of the PLF(fissility)the size of the targetthe incident energy »

REVERSE Data preliminary results

Nautilus Data

F.Bocage et al., NPA676 (2000) 391

Process with a big cross-section

Same process for the most central collisions?

Description by a model : need of a dynamical description

Summary & Outlooks

C.P. Montoya et al., Phys. Rev. Lett. 73, 3070 (1994)

B. Davin et al., Phys. Rev. C65, 064614 (2002)

S. Piantelli et al., Phys. Rev. Lett. 88, 052701 (2002)F. Bocage et al., Nucl. Phys. A65, 391 (2000)J. Colin et al., in preparation

Collaboration

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

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

Specials Thanks To …

Thesis in 2001, LPC Caen, FRANCE

Jean Colin

Daniel Cussol

Jacques Normand