Mid-peripheral collisions : PLF* decay Statistical behavior  isotropy  v H > v L  v L > v H P T TLF * PLF * 1 fragment v L > v H forward v H > v L backward Sylvie Hudan, Indiana University

Experimental setup Miniball/Miniwall Beam LASSA : Mass resolution up to Z=9 7    lab  58  114 Cd + 92 Mo at 50 A.MeV  Detection of charged particles in 4  Projectile 48 Ring Counter : Si (300  m) – CsI(Tl) (2cm) 2.1    lab  4.2  1 unit Z resolution Mass deduced † † : Modified EPAX K. Sümmerer et al., Phys. Rev. C42, 2546 (1990)

Events with two fragments from a PLF * ZHZH ZLZL ZHZH ZLZL PLF * v L > v H, forward v H > v L, backward

Anisotropy of PLF* decay 6  N C  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, (2002)  Different relative velocities  higher v rel for the backward case

Asymmetry of the breakup : Sensitivity to v PLF* 6  N C  10 v projectile = 9.45 cm/ns  More asymmetric Z distribution for the backward case  Higher asymmetry at high v PLF* (low E *,J)  For all v PLF*, asymmetry for the backward case  An other degree of freedom? v L > v H v H > v L v PLF* E *,J x100 x20 x2 x80 x10 x1 B. Davin et al., Phys. Rev. C65, (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 Z L  dynamical has higher v rel  Different Z distribution for a given (E*,J)

Well-defined PLF* : Z PLF* and v PLF*  Same correlation  expected if v PLF* and E* correlated  More dissipation and fluctuations as Z PLF* decreases  For a given size, less dissipation for the dynamical case v L > v H v H > v L dynamical statistical dynamical

Opening channels  Dynamical emission opens at higher v PLF*, i.e. lower E*  Up to 10% of the cross-section in the 2 fragment decay v L > v H v H > v L 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  Z PLF*  39

Energy in the fragments  More kinetic energy in the 2 fragments for the dynamical case  For a given v PLF*, difference of  MeV

A statistical picture : Viola systematics Comparison statistical / Viola  At large v PLF*, statistical  Viola  Deviation for low v PLF*  Temperature ? Comparison dynamical / Viola  For all v PLF*, dynamical >>Viola  More compact shape needed for the dynamical case

Estimation of the temperature MeasuredEstimated (Viola systematic)  Temperatures between 0 and  MeV  These temperatures are consistent with T=7 MeV from the isotopes in LASSA (for 30  Z PLF*  46) Statistical case : v L > v H

To summarize… v PLF* as a good observable :  Same correlation  (v PLF* )-  v PLF*  for statistical and dynamical cases  Dynamical case appears at higher v PLF*  Coulomb barrier effect   v PLF* (TKE) dynamical > (TKE) statistical by  MeV  Statistical  Viola at high v PLF* and deviation with increasing v PLF*  Temperature  Dynamical case always underestimated by Viola

A law : energy conservation For a selected v PLF*  E*  Kinetic energy in the fragments  Higher for the dynamical case  Q value  Evaporated particles + + PLF * E*, BE PLF* ZHZH TKE H, BE H ZLZL TKE L, BE L TKE evap, BE evap

“Missing” energy : Q value?  Same Q value in both cases for all v PLF* (MeV)

“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% v L > v H v H > v L statistical dynamical

Energy conservation : balance v PLF* fixed Fixed  Suggests a longer time scale in the statistical case for Z=2

A picture of the process TKE Time Saddle-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 Statistical TKE  Q + Coulomb Dynamical TKE  Q + Coulomb + E 0

Conclusions : building a coherent picture We observed… We interpreted… Correlation  (v PLF* )-  v PLF*  v PLF* good selector for E* Correlation v PLF* - M evap Different  TKE  for all v PLF* Initial TKE at scission Different  TKE for all v PLF* for the dynamical case is Correlation TKE-(Q+Coulomb) larger than the statistical case Multiplicities of evaporated Z=2  scission,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 R. J. Charity and L. G. Sobotka Department of Chemistry, Washington University, St. Louis, Missouri 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