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

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

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

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

12. 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

13. 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

14. 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

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

16. 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)

17. 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

18. 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

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

20. 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

21. af/an

22. Fragmentation background

23. Transient time

24. Excitation energy vs. Z

25. Outlook