Fission and Dissipation Studies via Peripheral Heavy Ion Collisions at Relativistic Energy Ch....
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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
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
Our schedule:Our schedule:
How does dissipation influence the evolution of the system ?How does dissipation influence the evolution of the system ?- theoretical aspects- theoretical 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
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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)
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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?)
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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)
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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)
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
Data vs. calculationsData vs. calculationsExtraction of the dissipation strength Extraction of the dissipation strength
Data best described with Data best described with ff(t) and (t) and = = (4.5(4.50.5)0.5)..10102121ss-1-1
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
Data vs. calculationsData vs. calculationsExtraction of the dissipation strength Extraction of the dissipation strength
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)
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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)
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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
–
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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 !
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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 !
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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 …
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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*
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
Dynamical versus Statistical limitsDynamical versus Statistical limitsLangevin calculationsLangevin calculations
(Pavel Nadtochy, GSI-Omsk)(Pavel Nadtochy, GSI-Omsk)
Zstat at saddle
Zstat at scission
Zdyn
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
Dissipation strength : variety of the theoretical predictionsDissipation strength : variety of the theoretical predictions
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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 !
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
ExperimentExperiment
First stage: separation and event-by-event (A,Z) beam identification
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
Nuclear vs. Electromagnetic induced processes Nuclear vs. Electromagnetic induced processes
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
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!
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
The future : R3B
Charge and Mass of (both?) fission fragments
Neutrons
Gammas
Ch. SCHMITT, IPNLyonCh. SCHMITT, IPNLyon
Excitation energy and/or fissility influence ?