1. EVIDENCE FOR TRANSIENT EFFECTS IN FISSION AND IMPORTANCE FOR NUCLIDE PRODUCTION B. Jurado 1,2, K.-H. Schmidt 1, A. Kelić 1, C. Schmitt 1, J. Benlliure 3, A. Junghans 4 1 GSI, Darmstadt, Germany 2 GANIL, Caen, France 3 University Santiago de Compostela, Spain 4 RFZ, Rossendorf, Germany

2. Contents Introduction What are transient effects in fission? What are transient effects in fission? How to observe experimentally transient effects? How to observe experimentally transient effects? Quantitative results for transient effects Quantitative results for transient effects Importance of transient effects for nuclide production Importance of transient effects for nuclide production Conclusions Conclusions

3. Dynamical description of the deexcitation process of a heavy nucleus: Collective deg. freedomIntrinsic deg. freedom Dissipation:  (T,q) Langevin/Fokker-Planck eq. Transport theories Single Langevin trajectories in phase space +Evaporation Evaporation code + Γ f (t), Fokker-Planck eq. Γ f (t), Fokker-Planck eq. Two equivalent views of the process:

4. Transient effects in fission Evolution of the probability distribution t = 0 st = 1·10 -21 st = 3·10 -21 s Transient time τ f (β, A, Z, T) To observe transient effects… Small deformation and high E* Small deformation and high E* Appropriate observables Appropriate observables

5. Peripheral heavy-ion collisions at relativistic energies Small shape distortion Small shape distortion Low angular momentum < 20 ħ Low angular momentum < 20 ħ High intrinsic excitation energies E* ~ ∆A High intrinsic excitation energies E* ~ ∆A Inverse Kinematics Inverse Kinematics ?? Fusion-fission reactions

7. Experimental set-up for fission studies in inverse kinematics 238 U (1 A GeV)

8. Z 1 +Z 2 = 92 238 U (1 A GeV) + (CH 2 ) n E * initial Y fiss (Z 1 + Z 2 ) New observables: Partial fission cross sections

9. T fiss Z 1 + Z 2 = 89 E* initial  z 2 = T fiss /C z New observables: Partial fission cross sections Z 1 +Z 2 = 92

10. Realistic description of the time- dependent fission-decay width  = 5  10 21 s -1 T= 3 MeV A = 248 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 (B. Jurado, et al., Phys. Lett. B 553 (2003) 186) f (t) =  f (t)/ħ

11. The model Updated version of GSI code ABRABLA: ABRASION If T< 5 MeV If T > 5 MeV SIMULTANEOUS BREAK-UP Freeze out T = 5 MeV (W. A. Friedman, PRL, 60 (1988) 2125 W. Nörenberg et al. Eur. Phys. J A 9 (2000) 327 K.-H. Schmidt et al., Nucl. Phys. A 710 (2002) 157) EVAPORATION / FISSION a f /a n (Ignatyuk) B f (Sierk)

12. Total fission cross sections  f nucl 238 U(1 A GeV) + Pb Experiment 2.16  0.14 b No transient effects 3.33 b  f (t) step  = 2  10 21 s -1 2.00 b  f (t) ~1-exp(-t/  )  = 4  10 21 s -1 2.04 b  f (t) FPE  = 2  10 21 s -1 2.09 b The value of β depends on the description for  f (t) Total fission cross sections are not sensitive to the shape of  f (t)

13. Sensitivity to the shape of Sensitivity to the shape of  f (t) 238 U (1 A GeV) + (CH 2 ) n Experimental data  f (t) step,  = 2  10 21 s -1  f (t) ~1-exp(-t/  ),  = 4  10 21 s -1  f (t) FPE,  = 2  10 21 s -1

14. Sensitivity to the dissipation coefficient β 238 U (1 A GeV) + (CH 2 ) n Experimental data Transition-state model Kramers  = 4·10 21 s -1  = 2·10 21 s -1  = 0.5·10 21 s -1  = 5·10 21 s -1  = 2·10 21 s -1  f  (1.7±0.4)  10 -21 s

15. (Data from J. Taieb et al., Nucl. Phys A 724 (2003) 413-430) Influence on nuclide production… Experimental Data No transient effects Transient effects β =1·10 21 s -1 238 U (1 A· GeV) + p Calculation INCL-ABLA Calculation INCL-ABLA

16. (PhD. J. Pereira, Univ. Santiago de Compostela) 208 P (1 A GeV) + p Experimental data Transition state model  = 2  10 21 s -1

17. Conclusions Conclusions Experimental observation of transient effects Experimental observation of transient effects All observables described by a constant value of  = 2  10 21 s -1   f ≈ (1.7±0.4)  10 -21 s Transient effects in fission strongly influence nuclide production Transient effects in fission strongly influence nuclide production Very realistic analytical approximation for  f (t) Very realistic analytical approximation for  f (t)