 Innovative Reaction Mechanism  Relevant Experimental Signatures

1. Fission and Dissipation Studies via Peripheral Heavy Ion Collisions at Relativistic Energy Collaboration IPN Lyon – GSI Darmstadt CHARMS group  Innovative Reaction MechanismRelevant Experimental Signatures Motivations: - fundamental interest interaction/collisions nucleon-moving system (1 body) individual nucleon-nucleon collisions (2 body) Origin? Collective degrees of freedom Intrinsic degrees of freedom dissipation nuclide production for secondary beam facilities super heavy element synthesis enhancement of SD and HD bands population - applications Ch. SCHMITT, IPNLyon

2. Our schedule:  How does dissipation influence the evolution of the system ? - theoretical aspects - experimental observables  Optimal conditions for bringing dissipation to light - reaction mechanism -> relativistic heavy-ion collisions - pertinent signatures -> saddle-point clock or thermometer  Set-Up - about 60 RIB’s ranging from At up to U at disposal - devoted to in-flight fission fragment detection  Analysis and dynamical ABRABLA calculations  Data vs. calculations: what can we learn about dissipation ? - strength  and transient delay trans  Explanation for some previous reported contradictions  Conclusion and Outlooks Ch. SCHMITT, IPNLyon

3. energy Saddle point CN Scission deformation f (t)    How does dissipation influence the evolution of the system ? 1. Theoretical aspects  Langevin equation of motion: individual trajectory step by step (NB: coupling to particle evaporation) Dissipation slows the nucleus down: 2 effects:  Kramers reduction of the stationary fission decay width : K = K .BW < BW  Transient effects: fission is delayed by a time lapse of ~ trans -> crucial for experimental data analysis ! Ch. SCHMITT, IPNLyon

4. How does dissipation influence the evolution of the system ? 2. Experimental point of view Dissipation trans transient delay  more particles emitted cooling down of the decaying nucleus change of the fission properties: Bf , Z2/A… Experimental signatures used to estimate the dissipation strength :  fission and evaporation residue cross sections  n, LCP and -rays pre-scission multiplicities powerful Particle Clock to study dynamics Results: …. rather unclear in fact …  difficult to discriminate the pre- and post- saddle point stages  still unknown deformation, T, Z2/A dependence of  and trans  complex side effects inherent to fusion-fission (L, initial conditions?) Ch. SCHMITT, IPNLyon

5.  signature of E*saddle: Z2 = =  Request : Tsaddle ___ CZ _____ CZ (E*saddle/a) width of the fission fragment Z distribution fast clock to ensure part ~ trans : high excitation energies well defined initial conditions far from quasi-equilibrium How to go further ?  Restriction to the pre-saddle region: track down dissipation at small deformation via the transient time trans trans  Mpresaddle E*saddle what allows the translation clock thermometer saddle  saddle  Solution : peripheral heavy-ion collisions at relativistic energy  small distortion relative to the projectile deformation  high initial excitation energy  small angular momenta (less complex side effects) Ch. SCHMITT, IPNLyon

6. Set-Up: secondary beam experiment: 60 p-rich actinide beams (205At up to 234U) at disposal 1rst stage: production, separation and beam identification (thanks to the FRS) 2nd stage: detection and Z identification of both FF (thanks to the kinematics and DIC) Z ~ 0.4 See K.-H.Schmidt et al., NPA(2000) for detail Ch. SCHMITT, IPNLyon

7. Analogy with fusion-fission: Zprf  ZCN and E*prf  E*CN How do our data look like ? Pertinence of the (Z1, Z2) measurement: low post-scission LCP low pre-scission LCP Z1+Z2 fissioning elementZfiss  prefragmentZprf  initialE*prf ‘Raw Data’: fission fragment Z distributions  Extraction of the Zwidths Ch. SCHMITT, IPNLyon

8. With decreasing (Z1+Z2) • (further away from the projectile): • E*prfincreases  Zincreases How do our data look like ? Pertinence of the (Z1, Z2) measurement: low post-scission LCP low pre-scission LCP Z1+Z2 fissioning elementZfiss  prefragmentZprf  initialE*prf Ch. SCHMITT, IPNLyon

9. Fission Prefragment Equilibrated nucleus ABRABLA Reaction Code Peripheral Heavy-Ion Collision at Relativistic Energy as a 3 step-process  Abrasion: participation of the projectile/target overlaping zone only  ~ 27MeV of E* induced by nucleon abraded  <N/Z> conserved  Simultaneous break upfor Tafter abrasion > 5MeV (~Tfreeze out)  emission of LCP’s and clusters down to 5MeV  Competition evaporation-fission : equivalent to a dynamical treatment!  Weiskopf theory for particle decay widths n,p,,d,t,…  time-dependent fission decay width f(t) to account for transient effects Ch. SCHMITT, IPNLyon

10. Basis of the derivation: exact numerical Langevin or Fokker-Planck solution Analytical approximation of the time-dependent fission decay width f (t) Fastly calculable realistic expression which can be easily plugged in an evaporation code B.Jurado, K.-H.Schmidt, Ch.Schmitt, NPA 747(2004) 14

11. Are actually (tiny) transient effects observable ? • Relevant probe: comparison between • K-type calculations (no trans) • f(t)-type calculations (with trans) Kramers-type calculations fail when moving further away from the projectile fingerprint of transient effects ‘observability’ at high enough E* ( 150MeV) Ch. SCHMITT, IPNLyon

12. Data vs. calculations Extraction of the dissipation strength  • Filters used to sort the data: • Z1+Z2allows to select •  E* (function of the projectile) •  fissility Zfiss2/Afiss(roughly) • Z = Zproj – (Z1+Z2) allows to select • E* (independently of the projectile) Examples: Z1+Z2=84  E*~400MeV for 224Th (Zproj=90) E*~200MeV for 217Fr (Zproj=87) Z=4  E*~270MeV for all beams Ch. SCHMITT, IPNLyon

13. Data vs. calculations Extraction of the dissipation strength  Data best described with f(t) and  = (4.50.5).1021s-1 Ch. SCHMITT, IPNLyon

14. Data vs. calculations Extraction of the dissipation strength  Overview for all beams (~ 1/10 of the whole data set)  = (4.50.5). 1021s-1 for beams from At up to Th  remaining discrepancy for the heaviest U and Pa beams Impressive description over an uncommonly broad range ! Reliability of the physical arguments in ABRABLA (from the early collision down to the fragments de-excitation)  Ch. SCHMITT, IPNLyon

15. Data vs. calculations Peculiaritiy of the heaviest actinide beams Langevin calculations: trans(2=0.25) trans(2=0.) / (2-3) U, Pa At up to Th  Pavel Nadtochy • = (4.50.5). 1021s-1is required for U and Pa as well, but trans is reduced due to the onset of large g.s. deformation above N  134 Inclusion of initial deformation in f(t) in progress (A. Kelic, K.-H. Schmidt) Nuclei with N  134 are sizeably deformed(2~0.2-0.3)  initial (pre-fragment) configuration closer to the saddle point smaller transient time Ch. SCHMITT, IPNLyon

16. Extraction of the transient time trans Nearly spherical beams: trans = (3.40.7). 10-21s No clear evidence on nor a fissility, neither an excitation energy influence Deformed U and Pa beams: trans ~ ((1.1-1.7)0.4). 10-21s roughly According to the fragmentation process used to induce fission and to the set-up: still crude E* and Z2/A selections  To track down weak effects might need dedicated experiment for which E* and Z2/A are well defined Ch. SCHMITT, IPNLyon

17. Comparison with previous work At day, we know for sure that :   [0.5 - 10] . 1021 s-1  trans [~ 0 - 30] . 10-21 s Present conclusions in agreement !  … the contrary would have been surprising … A few comments about fair comparison and data (mis)interpretation :  fusion-fission(  [2-10] . 1021 s-1 and  trans [5-30] . 10-21 s1) : usually E* 150-200 MeV : do we have an effect of E* ? what about the influence of L ? well defined initial CN conditions / influence of fusion dynamics ? contribution from incomplete fusion and/or quasi-fission ? energetic p and p induced fission : at variance since Pf (E*) gives trans ~ 0 s ! crucial importance of realistic input parameters: e.g. - af/an=1 combined to trans ~ 0 s can mock up af/an|Ignatyuk combined to trans 0 s - reliable f(t) in-growth function mandatory ! danger of comparing experiments done under various conditions – Ch. SCHMITT, IPNLyon

18. Input parameter uncertainty – af/an New fission fragment Z signature : BW coupled to af/an = 1 definitely ruled out only f(t) coupled to af/an|Ignatyukworks !  Spallation at GSI : J. Benlliure et al. (USC Spain), T.Enqvist, J.Taieb, M.Bernas et al. (IPN Orsay), S.Leray, A.Boudard et al. (DAPNIA-SPhN/Saclay), K.-H.Schmidt, A.Kelic, M.V.Ricciardi, P.Armbruster. Residue cross sections : BW coupled to af/an = 1 can mock upf(t) coupled to af/an|Ignatyuk Ch. SCHMITT, IPNLyon

19. Conclusions • Saddle clock concept to study dissipation at small deformation • Transient effects delay the fission process •  Establish a thermometer-clock at the barrier to track down trans • 2. Optimal conditions •  Peripheral heavy-ion collisions at relativistic energy •  high excitation energy, low angular momentum, small shape distortion •  no quasi-fission, incomplete fusion-fission, transfer induced fission contribution •  Charge distribution of the fission fragments as a pertinent signature •  Elaborate ABRABLA reaction code • realistic dissipation modelling is crucial • 3. Confrontation data-calculations •  Over the whole range  = (4.50.5). 1021s-1 at small deformation •  While transdepends on initial deformation: • trans = (3.40.7). 10-21s for nearly spherical systems • trans reduced by about a factor of 2-3 for 2~0.2-0.3 deformed systems Effects revealed thanks to the uncommon size of the data set ! Ch. SCHMITT, IPNLyon

20. Outlooks Meticulous investigation of the E* and Z2/A dependence of dissipation First option: at GSI via fragmentation:  Many species with various E* and Z2/A are produced simultaneously ! Experimental observables that allow an univocal selection of either E* or Z2/A  Measure of the FF charge and mass to reconstruct E*  Large acceptance spectrometer at the FRS exit - ALADIN? combined to the Neutron Wall? - FAIR project Second option: at Ganil/SPIRAL2 via fusion: Long isotopic chains and great energy range available ! The beam itself allows to vary independently either E* or Z2/A  Measure of the FF charge to determine Z  Large acceptance spectrometer Ch. SCHMITT, IPNLyon

21. Thanks to: Karl-Heinz Schmidt, GSI Darmstadt Aleksandra Kelic , GSI Darmstadt Andreas Heinz, Yale University Beatriz Jurado, CENBG Pavel Nadotchy , GSI – Omsk José Benlliure, Santiago del Compostella and many others … Ch. SCHMITT, IPNLyon

22. Sorting of the data – Experimental filters • Pertinence of the Z1+Z2 selection (or equivalently, Z) Correlation Z1+Z2 -Zfiss - Zprf – E*prf: Correlation Z - E*prf ABRABLA calculations Ch. SCHMITT, IPNLyon

23. Progressive showing up of transient effects  K progressively fails as Z increases i.e. E*prf increases Ch. SCHMITT, IPNLyon

24. Dissipation strength  versus Transient time trans trans = 1/. ln(10Bf/T) for  < 2g (under-damped) trans = /2g2. ln(10Bf/T) for  > 2g (over-damped)  = (4.50.5). 1021s-1 < trans > ~ (3.40.7). 10-21s Ch. SCHMITT, IPNLyon

25. Dissipation as revealed in spallation • nuclei between U and Pb do not survive due to high fissility • the U curve joins the Pb curve for larger mass losses •   • clear proof that fission is hindered at high E* Ch. SCHMITT, IPNLyon

26.  Zstat at saddle  Zstat at scission  Zdyn Dynamical versus Statistical limits Langevin calculations (Pavel Nadtochy, GSI-Omsk) Ch. SCHMITT, IPNLyon

27. Dissipation strength : variety of the theoretical predictions Ch. SCHMITT, IPNLyon

28. Neutron evaporation Fission Z,N-1 Z,N Energy Energy Deformation Deformation Transition State Model The probability related to a given (exit) channel is governed by the available phase space single-particle degrees and collective degrees of freedom are treated in the same way Ch. SCHMITT, IPNLyon

29. Influence of dissipation on the evolution of the system: delay ! D. Hilscher, Ann. Phys. Fr. 17 (1992) 471 Ch. SCHMITT, IPNLyon

30. Neutron Clock Tool Pre-scission time: • final angular momentum • initial angular momentum • final excitation energy • particle spin • particle kinetic energy • transmission coefficient • level density • particle binding energy • particle orbital angular momentum The non-linearity of neutron emission times with E* calls for high enough E* to observe an effect Ch. SCHMITT, IPNLyon

31. Experiment First stage: separation and event-by-event (A,Z) beam identification Ch. SCHMITT, IPNLyon

32. Nuclear vs. Electromagnetic induced processes In the plastic: only nuclear-induced fission In the Pb target : nuclear and electromagnetic-induced fission Ch. SCHMITT, IPNLyon

33. Nuclear vs. Electromagnetic induced processes Ch. SCHMITT, IPNLyon

34. Partial Fission Cross Sections Similar amount of data ----> a talk on its own! Ch. SCHMITT, IPNLyon

35. The future : R3B • Charge and Mass of (both?) fission fragments • Neutrons • Gammas Ch. SCHMITT, IPNLyon

36. Excitation energy and/or fissility influence ? Ch. SCHMITT, IPNLyon