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NEW SIGNATURES ON DISSIPATION FROM THE STUDY OF RELATIVISTIC HEAVY-ION COLLISIONS

This study explores the dissipation process in relativistic heavy-ion collisions using a new experimental approach. The experimental setup, observables sensitive to dissipation, and results are discussed. The findings provide insights into fission induced by peripheral collisions and shed light on the deformation dependence of dissipation.

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NEW SIGNATURES ON DISSIPATION FROM THE STUDY OF RELATIVISTIC HEAVY-ION COLLISIONS

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  1. NEW SIGNATURES ON DISSIPATION FROM THE STUDY OF RELATIVISTIC HEAVY-ION COLLISIONS Beatriz Jurado Apruzzese August 2002

  2. Contents • Introduction and motivation • New experimental approach to investigate dissipation • Experimental set-up • Experimental observables sensitive to dissipation • Results • Conclusions

  3. Introduction • Deexcitation process of the nucleus: • Statistical model • Dynamical model Transport theories Two types of degrees of freedom Collectiveintrinsic Dissipation: = dEcoll/dt [1/(Eeqcoll – Ecoll)]  rules the relaxation of the coll. degrees of freedom  (T, q) Fission is an appropriate tool for investigating dissipation

  4. Current knowledge on dissipation Theory: Hilscher et al. Phys. Atom. Nucl. 57 (1994) 1187

  5. Experiment: Standard reaction mechanisms to induce fission Heavy-ion collisions at Eprojectile≈ 5-10 A MeV (Fusion-Fission, Fast fission, Quasifission) ?? Dynamical models needed to describe these reactions Antiproton annihilation and spallation reactions ... Simplified theoretical description Difficulty to reach very high E* with large cross sections

  6. U Deformation (q) Standard experimental observables fiss , evap l-distrib. of evap. residues Even-odd effect TKE Pre-scission part. and -multiplicities Ang., mass and charge distrib.

  7. [NaA02, Pfiss, fiss] Deformation dependence [SaF02,Pfiss] [ChP02, Pre-sadel, Mn] Small deformation [BeA02, fiss, 2z] [LoG01,Pfss] [JiP01, fiss] Large &small deformation [HuS00, Dio01, l-distrib] [DiS01, evap, M] [ShD00, M] [VeM99, A-, - distrib.] [FrG93, fiss, evap, Mp] Latest experimental results Temperature dependence ?? Fissility dependence ??

  8. 238U (1 AGeV) + Pb (Calculation Abrasion Model) P (1.2 GeV) + U (Experimental Data) (Goldenbaum et al., Phys. Rev. Lett. 77 (1996 ) 1230) Peripheral heavy-ion collisions at relativistic energies • Small shape distortion • Low angular momentum • High intrinsic excitation energies E* ~ ∆A • Inverse kinematics

  9. Experimental set-up for fission studies in inverse kinematics

  10. Y Z Energy loss in IC Fission events Fragmentation background Observables Total fission cross sections Beam Target IC Double IC

  11. 238U (1 A GeV) + (CH2)n Yfiss (Z1 +Z2) Z1 + Z2 = 89 Bf z2 = Tfiss/Cz Tfiss E*initial Z1+Z2 = 92 E*initial New observables: Partial fission cross sections & Widths of the charge distributions

  12. SIMULTANEOUS BREAK-UP EVAPORATION / FISSION af/an(Ignatyuk) Bf (Sierk) If T > 5.5MeV Freeze out T = 5.5 MeV M.V. Ricciardi PhD. Thesis The model Updated version of GSI code ABRABLA: If T< 5.5 MeV ABRASION

  13. Model of Grangé & Weidenmüller (1980) Kramers (1940) Numerical solution of the FPE under specific initial conditions f(t) = f(t)/ħ  = 51021s-1 T= 3 MeV A = 248 Transient time f f(t) =Num. Sol. FPE (K.-H. Bhatt, et al., Phys. Rev. C 33 (1986) 954) f(t) = Step Function f(t) ∝(1-exp(-2.3t/f)) f(t) = Analytical approximation

  14. Dependence of on fiss(t) fnucl 238U(1 A GeV) + Pb The value of  depends on the description for f(t)

  15. 238U (1 A GeV) + (CH2)n Experimental data Transition-state model  = 2·1021s-1  = 0.5·1021s-1  = 5·1021s-1  = 2·1021s-1 f  (1.7±0.4)10-21 s Influence of  on f (Z1+Z2) and Z-Width(Z1+Z2)

  16. Target dependence of ftot 238U (1 A GeV) Experimental data Transition-state model  = 2·1021s-1 The minimum at Ztarget = 6 can only be reproduced if dissipation is included

  17. Calculations: For fission events produced 238U(1A GeV)+Pb NO BREAK-UP BREAK-UP Fission is mainly suppressed by dissipation at high E* Fission completely suppressed at E*  350 MeV

  18. Our result! [NaA02] [ChP02] [BeA02] [LoG01] [JiP01] [HuS00, Dio01] [DiS01] [ShD00] [VeM99] [FrG93] Deformation dependence Small deformation Large & small deformation

  19. Conclusions • Fission induced by peripheral heavy-ion collisions at relativistic energies, ideal conditions for the investigation of dissipation at small deformations • Determination of new observables • Total nuclear fission cross sections for different targets • Partial fission cross sections • Partial widths of the charge distributions of fission • fragments • Realistic description for f (t) • All observables described by a constant value of •  = 21021s-1 f≈ (1.7±0.4)10-21 s • (critical damping) • No indications for dependence on T or Z2/A • Evidence for strong increase of  with deformation

  20. af/an

  21. Fragmentation background

  22. Transient time

  23. Excitation energy vs. Z

  24. Outlook

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