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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. - PowerPoint PPT Presentation
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EVIDENCE FOR TRANSIENT EFFECTS IN FISSION AND
IMPORTANCE FOR NUCLIDE PRODUCTION
B. Jurado1,2, K.-H. Schmidt1, A. Kelić1, C. Schmitt1, J. Benlliure3, A. Junghans4
1GSI, Darmstadt, Germany2GANIL, Caen, France
3University Santiago de Compostela, Spain4RFZ, Rossendorf, Germany
ContentsContents IntroductionIntroduction
What are transient effects in fission?What are transient effects in fission?
How to observe experimentally transient How to observe experimentally transient effects?effects?
Quantitative results for transient effectsQuantitative results for transient effects
Importance of transient effects for nuclide Importance of transient effects for nuclide productionproduction
ConclusionsConclusions
Dynamical description of the deexcitation process of a heavy nucleus:
Collective deg. freedom
Intrinsic deg. freedom
Dissipation: (T,q)
Langevin/Fokker-Planck eq.
Transport theories
Single Langevin Single Langevin trajectories in phase trajectories in phase
space space
+ +
EvaporationEvaporation
Evaporation code Evaporation code
+ +
ΓΓff(t), (t), Fokker-Planck Fokker-Planck eq.eq.
Two equivalent views of the process:
Transient effects in fissionTransient effects in fission
Evolution of the probability distributiont = 0 s t = 1·10-21 s t = 3·10-21 s
Transient time τf(β, A, Z, T)
To observe transient To observe transient effects…effects…
Small deformation and high E*Small deformation and high E*
Appropriate observablesAppropriate observables
Peripheral heavy-ion collisions at relativistic Peripheral heavy-ion collisions at relativistic energiesenergies
Small shape distortionSmall shape distortionLow angular momentum < 20 ħLow angular momentum < 20 ħHigh intrinsic excitation energies E* High intrinsic excitation energies E* ~ ∆A~ ∆AInverse KinematicsInverse Kinematics
??
Fusion-fission reactionsFusion-fission reactions
Experimental set-up Experimental set-up for fission studies in inverse for fission studies in inverse kinematicskinematics
238U (1 A GeV)
Z1+Z2 = 92
238U (1 A GeV) + (CH2)n
E*initial
Y fiss (Z1 + Z2)
New observables: Partial fission cross sectionsNew observables: Partial fission cross sections
Tfiss
Z1 + Z2 = 89
E*initial
z2 = Tfiss/Cz
New observables: Partial fission cross sectionsNew observables: Partial fission cross sections
Z1+Z2 = 92
Realistic description of the time-dependent fission-decay width
= 51021s-1
T= 3 MeVA = 248
f(t) =Num. Sol. FPE(K.-H. Bhatt, et al., Phys. Rev. C 33 (1986) 954)
f(t) = Step functionf(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
The modelUpdated version of GSI code ABRABLA:
ABRASION
If T< 5 MeV
If T > 5 MeV
SIMULTANEOUSBREAK-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
af/an
(Ignatyuk)
Bf
(Sierk)
Total fission cross sections Total fission cross sections
fnucl 238U(1 A GeV) + Pb
Experiment2.160.14
b
No transient effects
3.33 b
f(t) step
= 21021 s-1 2.00 b
f(t) ~1-exp(-t/) = 41021 s-1
2.04 b
f(t) FPE
= 21021 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)
Sensitivity to the shape of Sensitivity to the shape of f(t)238U (1 A GeV) + (CH2)n
Experimental data
f(t) step, = 21021 s-1
f(t) ~1-exp(-t/), = 41021 s-1
f(t) FPE, = 21021 s-1
Sensitivity to the dissipation Sensitivity to the dissipation coefficient βcoefficient β238U (1 A GeV) + (CH2)n
Experimental data
Transition-state model
Kramers = 4·1021s-1
= 2·1021s-1
= 0.5·1021s-1
= 5·1021s-1
= 2·10= 2·102121ss-1-1
f f (1.7±0.4)(1.7±0.4)1010-21 -21 ss
(Data from J. Taieb et al., Nucl. Phys A 724 (2003) 413-430)
Influence on nuclide production…Influence on nuclide production…
Experimental Data
No transient effects
Transient effects β =1·1021s-1
238U (1 A· GeV) + p
Calculation
INCL-ABLA
Calculation
INCL-ABLA
(PhD. J. Pereira, Univ. Santiago de Compostela)
208P (1 A GeV) + p
Experimental data
Transition state model
= 21021 s-1
ConclusionsConclusions Experimental observation of transient effectsExperimental observation of transient effects
All observables described by a constant value of
= 21021s-1 f ≈ (1.7±0.4)10-21 s
Transient effects in fission strongly influence nuclide Transient effects in fission strongly influence nuclide productionproduction
Very realistic analytical approximation for Very realistic analytical approximation for f f (t)(t)