Mid-peripheral collisions : PLF* decay

Statistical behavior isotropy vH > vL vL > vH

P

T TLF*

PLF*

1 fragment vL > vH

forwardvH > vL

backward

Sylvie Hudan, Indiana University

Experimental setup

Miniball/Miniwall

Beam

LASSA : Mass resolution up to Z=97 lab 58

114Cd + 92Mo at 50 A.MeV

Detection of charged particles in 4

Projectile48

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

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

Events with two fragments from a PLF*

ZH

ZL

ZHZL

PLF*

vL > vH, forward

vH > vL , backward

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

*PLF

LLHH*PLF

A

vAvAv

Anisotropy of PLF* decay6 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)

Different relative velocities higher vrel for the backward case

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 > vLvPLF*

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*

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

vL > vH

vH > vL

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 ?

7.3AA

ZZ*0.755Viola

1/32

1/31

21

Comparison dynamical / Viola

For all vPLF*, dynamical >>Viola

More compact shape needed for the dynamical case

Estimation of the temperature

T2CoulombTKE Measured Estimated

(Viola systematic)

Temperatures between 0 and 10-12 MeV

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

(for 30 ZPLF* 46)

Statistical case : vL > vH

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

For a selected vPLF* E*

Kinetic energy in the fragments Higher for the dynamical case

Q value

Evaporated particles

+ +PLF*

E* , BEPLF*

ZH

TKEH , BEH

ZL

TKEL , BEL TKEevap , BEevap

nevaporatioQTKEE* fragments

“Missing” energy : Q value?

Same Q value in both cases for all vPLF*

(MeV

)

44Z35 *PLF

“Missing” energy : evaporation?

Multiplicity of Z=2 emitted forward to the PLF* (in LASSA)

Higher average multiplicities for the statistical case

Deviation of 10-20%

vL > vH

vH > vL

statistical

dynamical

Energy conservation : balance

vPLF* fixed

lstatisticadynamical

lstatisticadynamical

lstatisticadynamicalnevaporatio

Q

TKEE* fragments

Fixed

Suggests a longer time scale in the statistical case

for Z=2

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

We observed… We interpreted…

Correlation (vPLF*)-vPLF* vPLF* good selector for

E*Correlation vPLF* - Mevap

Different TKE for all vPLF* Initial TKE at scission

Different TKE for all vPLF* for the dynamical case is

Correlation TKE-(Q+Coulomb) larger than the statistical case

Multiplicities of evaporated Z=2scission,dynamical < scission,statistical

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