innovative reaction mechanism relevant experimental signatures

Fission and Dissipation Studies Fission and Dissipation Studies via Peripheral Heavy Ion Collisions via Peripheral Heavy Ion Collisions

at Relativistic Energyat Relativistic Energy

Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon

Innovative Reaction MechanismInnovative Reaction Mechanism

Relevant Experimental SignaturesRelevant Experimental Signatures

Collaboration IPN Lyon – GSI DarmstadtCHARMS group

Origin? Origin?

interaction/collisions nucleon-moving system (1 body)interaction/collisions nucleon-moving system (1 body)individual nucleon-nucleon collisions (2 body)individual nucleon-nucleon collisions (2 body)

Motivations:- fundamental interest- fundamental interest

- applications- applicationsnuclide production for secondary beam facilitiesnuclide production for secondary beam facilitiessuper heavy element synthesissuper heavy element synthesisenhancement of SD and HD bands populationenhancement of SD and HD bands population

Collective degrees of freedom Intrinsic degrees of freedomdissipation dissipation


Our schedule:Our schedule:

How does dissipation influence the evolution of the system ?How does dissipation influence the evolution of the system ?- theoretical aspectstheoretical aspects- experimental observables- experimental observables

Optimal conditions for bringing dissipation to lightOptimal conditions for bringing dissipation to light- reaction mechanism -> relativistic heavy-ion collisions- reaction mechanism -> relativistic heavy-ion collisions- pertinent signatures -> saddle-point clock or thermometer- pertinent signatures -> saddle-point clock or thermometer

Set-Up Set-Up - about 60 RIB’s ranging from At up to U at disposal- about 60 RIB’s ranging from At up to U at disposal- devoted to in-flight fission fragment detection- devoted to in-flight fission fragment detection

Analysis and dynamical ABRABLA calculationsAnalysis and dynamical ABRABLA calculations

Data vs. calculations: what can we learn about dissipation ?Data vs. calculations: what can we learn about dissipation ?- strength - strength and transient delay and transient delay transtrans

Explanation for some previous reported contradictionsExplanation for some previous reported contradictions

Conclusion and OutlooksConclusion and Outlooks


How does dissipation influence the evolution of the How does dissipation influence the evolution of the system ?system ?

1. 1. Theoretical aspectsTheoretical aspects

en

er

gy

CN

Saddle point

deformation

Scission

Langevin equation of motion:Langevin equation of motion: individual trajectory step by stepindividual trajectory step by step

)(qM

p

dt

dq

)()(/)()()(

)(2

12

tTqMqpqq

V

q

qM

qM

p

dt

dpL

(NB: coupling to particle evaporation)(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 : Kramers reduction of the stationary fission decay width : KK = K = K .. BWBW < < BWBW

Transient effects: fission is delayed by a time lapse of ~ Transient effects: fission is delayed by a time lapse of ~ transtrans

-> crucial for experimental data analysis !-> crucial for experimental data analysis !

f (t)


How does dissipation influence the evolution of the How does dissipation influence the evolution of the system ?system ?

2. 2. Experimental point of viewExperimental point of view

Dissipation Dissipation transtrans transient delay transient delay more particles more particles emittedemitted

cooling down of the decaying nucleuscooling down of the decaying nucleus change of the fission properties: change of the fission properties: BBff , , ZZ22/A…/A…

Experimental signatures used to estimate the dissipation strength Experimental signatures used to estimate the dissipation strength : : fission and evaporation residue cross sectionsfission and evaporation residue cross sections n, LCP and n, LCP and -rays pre-scission multiplicities-rays pre-scission multiplicities

powerful Particle Clock to study dynamicspowerful Particle Clock to study dynamics

Results: …. rather unclear in fact … Results: …. rather unclear in fact … difficult to discriminate the pre- and post- saddle point difficult to discriminate the pre- and post- saddle point stagesstages still unknown deformation, T, Zstill unknown deformation, T, Z22/A dependence of /A dependence of and and transtrans complex side effects inherent to fusion-fission complex side effects inherent to fusion-fission (L, initial (L, initial conditions?)conditions?)


How to go further ?How to go further ?

Restriction to the pre-saddle region:Restriction to the pre-saddle region: track down dissipation at small deformation track down dissipation at small deformation via the transient time via the transient time transtrans

trans trans M Mprepresaddlesaddle E E**

saddlesaddle

what allows the translation what allows the translation clock clock thermometer thermometer saddle saddle saddlesaddle

signature of EE**saddlesaddle: Z

2 = = width of the fission fragment Z distribution

Tsaddle___ CZ

(E*saddle/a) _____

CZ

fast clock to ensure partpart ~ transtrans : 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)


Set-UpSet-Up: secondary beam experiment:: secondary beam experiment:60 p-rich actinide beams (60 p-rich actinide beams (205205At up to At up to 234234U) at disposalU) at disposal

11rstrst stage stage: production, separation and beam identification : production, separation and beam identification (thanks to the (thanks to the FRS)FRS)

22ndnd stage stage: detection and Z identification of both FF : detection and Z identification of both FF (thanks to the kinematics and DIC)(thanks to the kinematics and DIC)

Z ~ 0.4Z ~ 0.4

See K.-H.Schmidt et al., NPA(2000) for detail


How do our data look like ?How do our data look like ?

Pertinence of the (ZPertinence of the (Z11, Z, Z22) measurement:) measurement:

ZZ11+Z+Z22 fissioning elementfissioning element ZZfissfiss prefragmentprefragment ZZprfprf initial initial

EE**prfprf

low post-scission LCPlow post-scission LCP low pre-scission LCPlow pre-scission LCP

‘Raw Data’: fission fragment Z distributions

Extraction of the Z widths

Analogy with fusion-fission:

Zprf ZCN and E*prf E*

CN


How do our data look like ?How do our data look like ?

Pertinence of the (ZPertinence of the (Z11, Z, Z22) measurement:) measurement:

ZZ11+Z+Z22 fissioning elementfissioning element ZZfissfiss prefragmentprefragment ZZprfprf initial initial

EE**prfprf

low post-scission LCPlow post-scission LCP low pre-scission LCPlow pre-scission LCP

With decreasing (Z1+Z2) (further away from the projectile):

E*

prf increases

Z increases


ABRABLA Reaction CodeABRABLA 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 <N/Z> conserved

Simultaneous break up for 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

Analytical approximation of the time-dependent Analytical approximation of the time-dependent fission decay width fission decay width f f (t)(t)

Fastly calculable realisticFastly calculable realistic expression which can be expression which can be easily plugged in an easily plugged in an evaporation codeevaporation code

B.Jurado, K.-H.Schmidt, Ch.Schmitt, NPA 747(2004) 14

Basis of the derivationBasis of the derivation::exact numericalexact numericalLangevin or Fokker-PlanckLangevin or Fokker-Plancksolutionsolution


Are actually (tiny) transient effects observable ?Are actually (tiny) transient effects observable ?

Relevant probe: comparison betweenRelevant probe: comparison between

KK-type calculations (no -type calculations (no transtrans))

ff(t)-type calculations (with (t)-type calculations (with transtrans))

Kramers-type calculations fail Kramers-type calculations fail when moving further away when moving further away from the projectilefrom the projectile

fingerprint of transient effects ‘observability’ at high enough E* ( 150MeV)


Data vs. calculationsData vs. calculationsExtraction of the dissipation strength Extraction of the dissipation strength

Filters used to sort the dataFilters used to sort the data::

-ZZ11+Z+Z22 allows to select allows to select E* E* (function of the projectile)(function of the projectile) fissility Zfissility Zfissfiss

22/A/Afissfiss (roughly)(roughly)

Z = ZZ = Zprojproj – (Z – (Z11+Z+Z22)) allows to select allows to select E* E* (independently of the projectile)(independently of the projectile)

ExamplesExamples::

ZZ11+Z+Z22=84 =84 E*~400MeV for E*~400MeV for 224224Th (ZTh (Zprojproj=90)=90) E*~200MeV for E*~200MeV for 217217Fr (ZFr (Zprojproj=87)=87)Z=4 Z=4 E*~270MeV for all beams E*~270MeV for all beams



Data best described with Data best described with ff(t) and (t) and = = (4.5(4.50.5)0.5)..10102121ss-1-1



Overview for all beamsOverview for all beams(~ 1/10 of the whole data (~ 1/10 of the whole data set)set)

= (4.5= (4.50.50.5)). . 10102121ss-1-1 for beams for beams from At up to Thfrom At up to Th

remaining discrepancy forremaining discrepancy for the heaviest U and Pa beamsthe 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)


Data vs. calculationsData vs. calculationsPeculiaritiy of the heaviest actinide beamsPeculiaritiy of the heaviest actinide beams

Nuclei with N Nuclei with N 134 are sizeably deformed 134 are sizeably deformed ((22~0.2-0.3)~0.2-0.3)

initial (pre-fragment) configuration closer to the saddle pointinitial (pre-fragment) configuration closer to the saddle point smaller transient timesmaller transient time

U, Pa

At upto Th

Langevin calculations:Langevin calculations:transtrans ((22=0.25)=0.25) transtrans ((22=0.)=0.) / (2-3) / (2-3)

Pavel NadtochyPavel Nadtochy

= (4.5= (4.50.50.5)). . 10102121ss-1-1 is required for U and Pa as well, but is required for U and Pa as well, but transtrans is is reduced due to the onset of large g.s. deformation above N reduced due to the onset of large g.s. deformation above N 134 134

Inclusion of initial deformation in Inclusion of initial deformation in ff(t) in progress (A. Kelic, K.-H. Schmidt)(t) in progress (A. Kelic, K.-H. Schmidt)


Extraction of the transient time Extraction of the transient time transtrans

Nearly spherical beamsNearly spherical beams::

Deformed U and Pa beamsDeformed U and Pa beams: : transtrans ~ ((1.1-1.7) ~ ((1.1-1.7)0.40.4)). . 1010-21-21s s roughlyroughly

transtrans = (3.4 = (3.40.70.7)). . 1010-21-21s s

No clear evidence onNo clear evidence on

nor a fissility, neither nor a fissility, neither

an excitation energy an excitation energy

influenceinfluence

According to the fragmentation process used to induce fission According to the fragmentation process used to induce fission and to the set-up: and to the set-up: still crude Estill crude E** and Z and Z22/A selections /A selections To track down weak effects might need dedicated To track down weak effects might need dedicated experiment for which Eexperiment for which E** and Z and Z22/A are well defined/A are well defined


Comparison with previous workComparison with previous work

At day, we know for sure that : At day, we know for sure that : [0.5 - 10] [0.5 - 10] .. 10 102121 s s-1-1

transtrans [~ 0 - 30] [~ 0 - 30] .. 10 10-21-21 s s

Present conclusions in agreement !Present conclusions in agreement !

… … the contrary would have been surprising …the contrary would have been surprising …

A few comments about fair comparison and data (mis)interpretation : A few comments about fair comparison and data (mis)interpretation :

fusion-fissionfusion-fission (( [2-10] [2-10] .. 10 102121 s s-1-1 and and transtrans [5-30] [5-30] .. 10 10-21-21 s s11)) : : usually Eusually E** 150-200 MeV : do we have an effect of E 150-200 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 fissionenergetic p and p induced fission : at variance since : at variance since PPf f (E*)(E*) gives gives transtrans ~ 0 s ! ~ 0 s ! crucial importance of crucial importance of realistic input parametersrealistic input parameters:: e.g. - ae.g. - aff/a/ann=1 combined to =1 combined to transtrans ~ 0 s can mock up a ~ 0 s can mock up aff/a/ann |Ignatyuk|Ignatyuk combined to combined to transtrans 0 s 0 s - reliable - reliable ff(t) in-growth function mandatory !(t) in-growth function mandatory ! danger of comparing experiments done under various conditionsdanger of comparing experiments done under various conditions

–


Input parameter uncertainty – aInput parameter uncertainty – aff/a/ann

Spallation at GSI : Spallation at GSI : J. Benlliure et al. (USC Spain), T.Enqvist, J.Taieb, M.Bernas et al. (IPN Orsay),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.S.Leray, A.Boudard et al. (DAPNIA-SPhN/Saclay), K.-H.Schmidt, A.Kelic, M.V.Ricciardi, P.Armbruster.

Residue cross sectionsResidue cross sections : : BWBW coupled to a coupled to aff/a/ann = 1 = 1 can mock upcan mock up ff(t) coupled to a(t) coupled to aff/a/ann ||

IgnatyukIgnatyuk

New fission fragment New fission fragment ZZ signature : signature : BWBW coupled to a coupled to aff/a/ann = 1 = 1 definitely ruled out definitely ruled out

only only ff(t) coupled to a(t) coupled to aff/a/ann|Ignatyuk|Ignatyuk works ! works !


ConclusionsConclusions

1.1. Saddle clock concept to study dissipation at small deformationSaddle clock concept to study dissipation at small deformation

Transient effects delay the fission processTransient effects delay the fission process Establish a thermometer-clock at the barrier to track down Establish a thermometer-clock at the barrier to track down transtrans

2. Optimal conditions 2. Optimal conditions

Peripheral heavy-ion collisions at relativistic energyPeripheral heavy-ion collisions at relativistic energy high excitation energy, low angular momentum, small shape distortionhigh excitation energy, low angular momentum, small shape distortion

no quasi-fission, incomplete fusion-fission, transfer induced fission contributionno quasi-fission, incomplete fusion-fission, transfer induced fission contribution

Charge distribution of the fission fragments as a pertinent signatureCharge distribution of the fission fragments as a pertinent signature Elaborate ABRABLA reaction code Elaborate ABRABLA reaction code

realistic dissipation modelling is crucialrealistic dissipation modelling is crucial

3. Confrontation data-calculations3. Confrontation data-calculations

Over the whole range Over the whole range = (4.5 = (4.50.50.5)). . 10102121ss-1 -1 at small deformation at small deformation While While transtrans depends on initial deformation:depends on initial deformation: transtrans = (3.4 = (3.40.70.7)). . 1010-21-21s for nearly spherical systemss for nearly spherical systems transtrans reduced by about a factor of 2-3 for reduced by about a factor of 2-3 for 22~0.2-0.3 deformed systems~0.2-0.3 deformed systems

Effects revealed th

anks to th

e

Effects revealed th

anks to th

e

uncommon size of the data set !

uncommon size of the data set !


OutlooksOutlooks

Meticulous investigation of the EMeticulous investigation of the E** and Z and Z22/A dependence of dissipation/A dependence of dissipation

First option: at GSI via fragmentationFirst option: at GSI via fragmentation:: Many species with various E* and ZMany species with various E* and Z22/A are produced simultaneously !/A are produced simultaneously !

Experimental observables that allow an univocal selection of either E* or ZExperimental observables that allow an univocal selection of either E* or Z22/A/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 exitLarge 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 fusionSecond 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 ZThe beam itself allows to vary independently either E* or Z22/A/A Measure of the FF charge to determine Measure of the FF charge to determine ZZ

Large acceptance spectrometerLarge acceptance spectrometer


Thanks toThanks 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 …


Sorting of the data – Experimental filtersSorting 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


Progressive showing up of transient effectsProgressive showing up of transient effects

KK progressively fails as progressively fails as Z increases i.e. EZ increases i.e. E**prfprf increases increases


Dissipation strength Dissipation strength versus Transient time versus Transient time transtrans

transtrans = 1/ = 1/ .. ln(10B ln(10Bff/T) for /T) for < 2 < 2gg (under-damped) (under-damped)

transtrans = = /2/2gg22 .. ln(10B ln(10Bff/T) for /T) for > 2 > 2gg (over-damped) (over-damped)

= (4.5= (4.50.50.5)). . 10102121ss-1 -1

< < transtrans > > ~ (3.4 ~ (3.40.70.7)). . 1010-21-21ss


Dissipation as revealed in spallationDissipation 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*


Dynamical versus Statistical limitsDynamical versus Statistical limitsLangevin calculationsLangevin calculations

(Pavel Nadtochy, GSI-Omsk)(Pavel Nadtochy, GSI-Omsk)

Zstat at saddle

Zstat at scission

Zdyn


Dissipation strength : variety of the theoretical predictionsDissipation strength : variety of the theoretical predictions


Transition State ModelTransition State Model

The probability related to a given (exit) channel is governed by the The probability related to a given (exit) channel is governed by the available phase spaceavailable phase space single-particle degrees and collective degrees of freedom are treated in the same way

Energy Energy

Deformation Deformation

Z,N-1 Z,N

Neutron evaporation Fission


D. Hilscher, Ann. Phys. Fr. 17 (1992) 471

Influence of dissipation on the evolution ofInfluence of dissipation on the evolution ofthe system: delay !the system: delay !


Neutron Clock ToolNeutron Clock Tool

prenM

i inpre

1 ,

0 0

**

*

*

)(),(,2

)12(,

l

lIJ

lIJ

BE

iiliii

i

i

dTJBEIE

sIE

- final angular momentum

- initial angular momentum

- final excitation energy

- particle spin

- particle kinetic energy

- transmission coefficient

- level density

- particle binding energy

- particle orbital angular momentuml

B

T

s

E

I

J

i

l

i

i

*

Pre-scission time:Pre-scission time:

The non-linearity of neutron emissionThe non-linearity of neutron emission times with E* calls for high enough E*times with E* calls for high enough E* to observe an effectto observe an effect


ExperimentExperiment

First stage: separation and event-by-event (A,Z) beam identification


Nuclear vs. Electromagnetic induced processes Nuclear vs. Electromagnetic induced processes

In the plastic: In the plastic:

only nuclear-induced fissiononly nuclear-induced fission

In the Pb target :In the Pb target :

nuclear and electromagnetic-induced nuclear and electromagnetic-induced fissionfission


Nuclear vs. Electromagnetic induced processes Nuclear vs. Electromagnetic induced processes


Partial Fission Cross SectionsPartial Fission Cross Sections

Similar amount of data ----> a talk on its own!Similar amount of data ----> a talk on its own!


The future : R3B

Charge and Mass of (both?) fission fragments

Neutrons

Gammas


Excitation energy and/or fissility influence ?

innovative reaction mechanism relevant experimental signatures

Documents

dissipation strength

dissipation studies

fission properties

presaddle region

small deformation

trans complex

experimental data analysis

post saddle point stages