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

Ch. SCHMITT, IPNLyon Our schedule: How does dissipation influence the evolution of the system ? How does dissipation influence the evolution of the system ? - theoretical aspects - experimental observables Optimal conditions for bringing dissipation to light Optimal conditions for bringing dissipation to light - reaction mechanism -> relativistic heavy-ion collisions - pertinent signatures -> saddle-point clock or thermometer Set-Up 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 Analysis and dynamical ABRABLA calculations Data vs. calculations: what can we learn about dissipation ? Data vs. calculations: what can we learn about dissipation ? - strength  and transient delay  trans Explanation for some previous reported contradictions Explanation for some previous reported contradictions Conclusion and Outlooks Conclusion and Outlooks

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

Ch. SCHMITT, IPNLyon 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 cooling down of the decaying nucleus change of the fission properties: B f, Z 2 /A… change of the fission properties: B f, Z 2 /A… Experimental signatures used to estimate the dissipation strength  : fission and evaporation residue cross sections fission and evaporation residue cross sections n, LCP and  -rays pre-scission multiplicities n, LCP and  -rays pre-scission multiplicities powerful Particle Clock to study dynamics Results: …. rather unclear in fact … Results: …. rather unclear in fact … difficult to discriminate the pre- and post- saddle point stages difficult to discriminate the pre- and post- saddle point stages still unknown deformation, T, Z 2 /A dependence of  and  trans still unknown deformation, T, Z 2 /A dependence of  and  trans complex side effects inherent to fusion-fission (L, initial conditions?) complex side effects inherent to fusion-fission (L, initial conditions?)

Ch. SCHMITT, IPNLyon How to go further ?  Restriction to the pre-saddle region: track down dissipation at small deformation track down dissipation at small deformation via the transient time  trans via the transient time  trans  trans  M pre saddle  E * saddle what allows the translation clock  thermometer  saddle   saddle E * saddle  signature of E * saddle :  Z 2 = = width of the fission fragment Z distribution T saddle ___ C Z  (E * saddle /a) _____ C Z  part  trans  fast clock to ensure  part ~  trans : high excitation energies  well defined initial conditions far from quasi-equilibrium   Request :   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 Set-Up : secondary beam experiment: 60 p-rich actinide beams ( 205 At up to 234 U) at disposal 1 rst stage: production, separation and beam identification (thanks to the FRS) 2 nd 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 How do our data look like ? Pertinence of the (Z 1, Z 2 ) measurement: Z 1 +Z 2  fissioning element Z fiss  prefragment Z prf  initial E * prf low post-scission LCP low pre-scission LCP ‘Raw Data’: fission fragment Z distributions  Extraction of the  Z widths Analogy with fusion-fission: Z prf  Z CN and E * prf  E * CN

Ch. SCHMITT, IPNLyon How do our data look like ? Pertinence of the (Z 1, Z 2 ) measurement: Z 1 +Z 2  fissioning element Z fiss  prefragment Z prf  initial E * prf low post-scission LCP low pre-scission LCP With decreasing (Z 1 +Z 2 ) (further away from the projectile):  E * prf increases   Z increases

Ch. SCHMITT, IPNLyon ABRABLA Reaction Code Prefragment Equilibrated nucleus Fission 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  conserved  Simultaneous break up for T after abrasion > 5MeV (~T freeze 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

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

Ch. SCHMITT, IPNLyon 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 when moving further away from the projectile from the projectile   fingerprint of transient effects ‘observability’ at high enough E* (  150MeV)

Ch. SCHMITT, IPNLyon Data vs. calculations Extraction of the dissipation strength  Filters used to sort the data: -Z 1 +Z 2 allows to select  E* (function of the projectile)  E* (function of the projectile)  fissility Z fiss 2 /A fiss (roughly)  fissility Z fiss 2 /A fiss (roughly) -  Z = Z proj – (Z 1 +Z 2 ) allows to select  E* (independently of the projectile)  E* (independently of the projectile) Examples: Z 1 +Z 2 =84  E*~400MeV for 224 Th (Z proj =90) E*~200MeV for 217 Fr (Z proj =87) E*~200MeV for 217 Fr (Z proj =87)  Z=4  E*~270MeV for all beams

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

Ch. SCHMITT, IPNLyon Data vs. calculations Extraction of the dissipation strength  Overview for all beams (~ 1/10 of the whole data set)  = (4.5  0.5 ) s -1 for beams  = (4.5  0.5 ) s -1 for beams from At up to Th from At up to Th remaining discrepancy for remaining discrepancy for the heaviest U and Pa beams 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 Data vs. calculations Peculiaritiy of the heaviest actinide beams Nuclei with N  134 are sizeably deformed (  2 ~ )  initial (pre-fragment) configuration closer to the saddle point  initial (pre-fragment) configuration closer to the saddle point  smaller transient time  smaller transient time U, Pa At up to Th Langevin calculations:  trans (  2 =0.25)   trans (  2 =0.) / (2-3) Pavel Nadtochy Pavel Nadtochy   = (4.5  0.5 ) s -1 is 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)

Ch. SCHMITT, IPNLyon Extraction of the transient time  trans Nearly spherical beams: Nearly spherical beams: Deformed U and Pa beams:  trans ~ (( )  0.4 ) s roughly Deformed U and Pa beams:  trans ~ (( )  0.4 ) s roughly  trans = (3.4  0.7 ) s No clear evidence on nor a fissility, neither an excitation energy influence According to the fragmentation process used to induce fission According to the fragmentation process used to induce fission and to the set-up: still crude E * and Z 2 /A selections and to the set-up: still crude E * and Z 2 /A selections  To track down weak effects might need dedicated  To track down weak effects might need dedicated experiment for which E * and Z 2 /A are well defined experiment for which E * and Z 2 /A are well defined

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

Ch. SCHMITT, IPNLyon Input parameter uncertainty – a f /a n  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 a f /a n = 1 can mock up  f (t) coupled to a f /a n |Ignatyuk  BW coupled to a f /a n = 1 can mock up  f (t) coupled to a f /a n |Ignatyuk  New fission fragment  Z signature :  BW coupled to a f /a n = 1 definitely ruled out  BW coupled to a f /a n = 1 definitely ruled out only  f (t) coupled to a f /a n |Ignatyuk works ! only  f (t) coupled to a f /a n |Ignatyuk works !

Ch. SCHMITT, IPNLyon Conclusions 1.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  high excitation energy, low angular momentum, small shape distortion  no quasi-fission, incomplete fusion-fission, transfer induced fission contribution  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  realistic dissipation modelling is crucial 3. Confrontation data-calculations  Over the whole range  = (4.5  0.5 ) s -1 at small deformation  While  trans depends on initial deformation:   trans = (3.4  0.7 ) s for nearly spherical systems   trans = (3.4  0.7 ) s for nearly spherical systems   trans reduced by about a factor of 2-3 for  2 ~ deformed systems   trans reduced by about a factor of 2-3 for  2 ~ deformed systems Effects revealed thanks to the uncommon size of the data set !

Ch. SCHMITT, IPNLyon Outlooks Meticulous investigation of the E * and Z 2 /A dependence of dissipation First option: at GSI via fragmentation:  Many species with various E* and Z 2 /A are produced simultaneously !  Many species with various E* and Z 2 /A are produced simultaneously !  Experimental observables that allow an univocal selection of either E* or Z 2 /A  Experimental observables that allow an univocal selection of either E* or Z 2 /A  Measure of the FF charge and mass to reconstruct E*  Measure of the FF charge and mass to reconstruct E*  Large acceptance spectrometer at the FRS exit  Large acceptance spectrometer at the FRS exit - ALADIN? combined to the Neutron Wall? - ALADIN? combined to the Neutron Wall? - FAIR project - FAIR project Second option: at Ganil/SPIRAL2 via fusion:  Long isotopic chains and great energy range available !  Long isotopic chains and great energy range available !  The beam itself allows to vary independently either E* or Z 2 /A  The beam itself allows to vary independently either E* or Z 2 /A  Measure of the FF charge to determine  Z  Measure of the FF charge to determine  Z  Large acceptance spectrometer  Large acceptance spectrometer

Ch. SCHMITT, IPNLyon 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 Sorting of the data – Experimental filters  Pertinence of the Z 1 +Z 2 selection (or equivalently,  Z) Correlation Z 1 +Z 2 - Z fiss - Z prf – E * prf : Correlation  Z - E * prf ABRABLA calculations

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

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

Ch. SCHMITT, IPNLyon 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 Dynamical versus Statistical limits Langevin calculations (Pavel Nadtochy, GSI-Omsk)   Z stat at saddle   Z stat at scission  Z dyn

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

Ch. SCHMITT, IPNLyon 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 Energy Deformation Z,N-1Z,N Neutron evaporation Fission

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

Ch. SCHMITT, IPNLyon Neutron Clock Tool - 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 Pre-scission time:  The non-linearity of neutron emission times with E* calls for high enough E* times with E* calls for high enough E* to observe an effect to observe an effect

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

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

Ch. SCHMITT, IPNLyon Nuclear vs. Electromagnetic induced processes

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

Ch. SCHMITT, IPNLyon The future : R 3 B  Charge and Mass of (both?) fission fragments  Neutrons  Gammas

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