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Isotopic Yields of Fission Fragments from Transfer-Induced Fission

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Isotopic Yields of Fission Fragments from Transfer-Induced Fission. F. Rejmund, M. Caama ñ o, X. Derkx, C. Golabek , J. Frankland, M. Morjean, A. Navin, M. Rejmund GANIL, France M. A ï che , G. Barreau, S. Czajkowski, B. JuradoCENBG, France - PowerPoint PPT Presentation
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Isotopic Yields of Fission Fragments from Transfer-Induced Fission F. Rejmund, M. Caamaño, X. Derkx, C. Golabek, J. Frankland, M. Morjean, A. Navin, M. Rejmund GANIL, France M. Aïche, G. Barreau, S. Czajkowski, B. Jurado CENBG, France K.-H. Schmidt, A. Kelic, GSI, Germany C. Shmitt IPNL, France G. Simpson LPSC,France J. Benlliure, E. Casarejos, USC, Spain L. Audouin, C.-O. Bacri, L. Tassan-Got, IPNO, France T. Enqvist, CUPP, Finland D. Doré, S. Panebianco, D. Ridikas CEA SPhN L. Gaudefroy, J. Taieb CEA DIF Shell effects in fission-fragment yields Presentation of the project Even-odd effects in fission-fragment yields
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Page 1: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Isotopic Yields of Fission Fragments from Transfer-Induced Fission

F. Rejmund, M. Caamaño, X. Derkx, C. Golabek,J. Frankland, M. Morjean, A. Navin, M. Rejmund GANIL, France M. Aïche, G. Barreau, S. Czajkowski, B. Jurado CENBG, FranceK.-H. Schmidt, A. Kelic, GSI, GermanyC. Shmitt IPNL, FranceG. Simpson LPSC,FranceJ. Benlliure, E. Casarejos, USC, SpainL. Audouin, C.-O. Bacri, L. Tassan-Got, IPNO, FranceT. Enqvist, CUPP, FinlandD. Doré, S. Panebianco, D. Ridikas CEA SPhNL. Gaudefroy, J. Taieb CEA DIF

Shell effects in fission-fragment yieldsPresentation of the projectEven-odd effects in fission-fragment yields

Page 2: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Fission fragments from irradiation

• Mass distribution

n

• Isotopic distribution– Spectrometer=>light fragments Spectroscopy=>branching ratio, unknown isomers

• Limitations due to target activity, neutron energy

PF1

PF1E,ToF =>M

Page 3: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

- Stabilisation of heavy fragment when changing mass of the fissioning nucleus

-Two fission modes (spherical and deformed )

N=82 spherical shell

N~ 88 deformed shell

Mass distribution of fission fragments

Closed shell at N=86,88,90 ?? Still under debate!!

Page 4: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Profi, K.-H. SchmidtExp. data

Wide systematcis on element yields for U fragmentation products

GSI data in inverse kinematics

Af=Zf+Nf

Average charge constant=>Influence of moving neutron shell=>Existence of proton closed shell ?

J. Benlliure et al, EPJA 13(2002)

Necessity to get isotopic yields in heavy FF!!

Page 5: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Cheifetz et al,,1981

232Th(12C,8Be) 236U234U(t,pf) 235U(n,f)

Multi-nucleon transfer reaction

236U(12C,8Be) 240Pu238Pu(t,pf)239U(n,f)

•Large range of transfer Channels 238U+12CEje Rec Q(MeV) (mb)13C 237U -1.2 2314C 236U 1.8 811B 239Np -10 2512B 238Np -13 513B 237Np -14 0.810Be 240Pu -15 109Be 241Pu -17 58Be 242Pu -12 511Be 239Pu -21 0.87Li 243Am -26 0.56Li 244Am -19 3 4He 246Cm -17 3 6He 244Cm -24 0.5

•High resolution of the fissioning system

Page 6: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Transfer-induced fission reactions: wide range of fissioning systems

• Neutron-rich actinides : 238U beam, 12C Target• Energy range 0-40 MeV

Page 7: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

-Inverse kinematics (high Z resolution)-Isotopic identification (spectrometer)-Wide range of actinidesPrecise measure of the excitation energy (particle detection)

Multinucleon induced fission in inverse kinematics@GANIL

238U

12C

recoilheavy FF

light FF

FF

Page 8: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

A =2Ev2

Bρ =f (x,y, θ,ϕ )

Bρ =AQ

vX,Y,θ,

ToFEE

Identification of fission fragments in VAMOS

E ∝Z2

v2

M. Rejmund et al. PRC76(2007)

238U+48Ca

Page 9: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Seeking for information..

We propose to use multi-nucleon transfer induced fission in inverse kinematics in order to

•Identify isotopic fission yields in complete fragment distribution•Define the fissioning system in excitation energy, mass, charge•Over a broad range of neutron-rich actinides•Study the structure effects as a function of excitation energy and fissioning nucleus

These data would complement GSI data

Important results on shell effects and pairing effects are expected !!

Page 10: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Even-odd staggering in fission-fragment yields

Local even-odd staggering

YG (Z) ≈YG (Z)(1±δZ (Z))

δZ (Z + 32) = 1

8−1( )

Z +1lnY (Z + 3) −lnY (Z) −3 lnY (Z + 2) −lnY (Z + 1)

Global even-odd staggering

δz = Yze- Yz

o/(Yze+Yz

o)δz =40%

Page 11: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Qualitative understanding of the even-odd structure

229Th+n

Pairing gap

saddle scission ?

23090Th

0

5

-25

MeV

•The amplitude of the e-o effects reflects the probability that no pair is broken at scission

Without dissipation there would be no odd-Z fragment

Eintr

+Ecoll

•Even-odd structure : a consequence of dissipation in the descent

Page 12: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Even-odd effect depends on fissility of the system

Global even-odd effect δz = Yz

e- Yzo As the Coulomb repulsion inside

the nucleus increases, the saddle shape becomes more and more compact

Saddle CmSaddle Th

The descent from saddle to scission increases, as Ediss, with fissilityEdiss decreases with scission asymmetry

Page 13: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Electromagnetic induced fission of secondary beams

K.-H. Schmidt et al., NPA665(2000)221

Page 14: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Even-odd staggering in odd-Z nuclei

Zero staggering atsymmetry: Unpaired nucleon chooses both fragments with equal probability

Negative staggering forasymmetry: unpaired nucleon chooses theheaviest fragment

S. Steinhaüser, PhD Thesis

Evidence for the influence of the fission-fragment phase space

Page 15: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Statistical analysis of e-o staggering

level density at Fermi level in FF

S. Steinhauser et al., NPA634(1998)89

g(Z) ∝ g(A)ZCN

ACN

∝ Z

p(Z) ∝g(Z)

g(Z) + g(ZCN −Z)

δp

n(Z) =(1−2p(Z))n

δp

n(Z) =(1−2 ZZCN

)n

δp(Z) =0.1δp

0 (Z) + 0.9δp

2 (Z)

δp(Z) =0.1δp

1 (Z) + 0 .9δp

3 (Z)

Data reproduced with

Relative statistical weight of 1 nucleon in fragment (Z):

p(Z) ∝Z

ZCN

E-o staggering produced with n unpaired uncleons

Page 16: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Probability for a completely proton paired configuration at scission

Level density of only broken neutron pairs

Level density of all possible excitations

ρn =gn(E −n)n−1

(n/ 2)!2 (n−1)!Strutinsky 1958

P0Z (U) =

ρnZ =0 ,nN (U )nN

∑ρnZ ,nN (U )

nN ,nZ

ρn(U) =gn(Ueff )

n−1

(n/ 2)!2 (n−1)!

Ueff =U −14

g( 0 −n) −ΠnIgnatyuk 1973

Page 17: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Statistical description of the even-odd staggering

-Estimation of the dissipated energy-For the first time the difference between proton and neutron number yields is reproduced without further assumption

F. Rejmund et al. NPA678 (2000)215

Page 18: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Systematics on even-odd staggering

Constant e-o staggering at symmetry !!Important impact on our understanding Of fission dynamics

U,Th Ra,Rn

fissility

Page 19: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

E-o effect at symmetry: neutron-induced fission

Difficult to measure Z yields at symmetry in direct kinematics

Page 20: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

E-o effect at symmetry in n-induced fission:constant with fissility ?

δp globalδp local asy(Z=54)δp local reachable sym

No conclusion can be drawn due to the lack of data at symmetry

Page 21: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Statistical description of the even-odd effect for asymmetric split

δp(Z) =0.1δp

0 (Z) + 0.9δp

2 (Z)

GSI data reproduced with

δp

n(Z) =(1−2p(Z))n

δp

n(Z) =(1−2 ZZCN

)n

Probability to have nZ proton pairs broken at scission

PnZ

Z (U) =

ρnZ ,nN (U )nN

∑ρnZ ,nN (U )

nN ,nZ

δp(Z) =P0Zδ

p

0 (Z) + P2Zδ

p

2 (Z) + ..

δp(Z) = PnZ

Z δp

nZ (Z)nZ

nZ=0nZ=2nZ=4nZ=6

E-o staggering:

Page 22: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Statistical description Estimated dissipated energy for asymmetric split

δp(Z) = PnZ

Z δp

nZ (Z)nZ

symmetric fission : Common asymptotic energy δ~5% <-> Edis~ 9 MeVAsymmetric fission232Th 236U 240PuX= 34.9 35.7 36.8

δ 0.32 0.25 0.1 5.7 6.2 7.1 MeV

Page 23: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Neutron evaporation and energetic balance

Cf

Cm U

Q=TKE+TXE

TXE=Edef(F1)+Edef(F2)+Eintr

Eintr(Z) = Q(Z) - TKE(Z) - Edef(Z) - Edef(ZCN-Z))

Edef(Z) ~ (n+Bn(Z))1,2

Page 24: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Dissipated energy deduced from neutron evaporation…

236U

248Cm252Cf244Cm

And compared to statistical analysis of e-o staggering

Qmax=max(MCN-MF1-MF2))TKE from experiment

Page 25: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

E-O staggering : summary

•Different sets of data (fission yields in e-m fission and neutron yields) give a coherent picture of a dissipation at symmetry independent on fissility.

•This should have important impact on our understanding of the descent dynamics

•Statistical analysis of even-odd effect :•description of the even-odd effect at symmetry and asymmetry •dissipated energy at asymmetry taking into account the phase space effect in the final fragments•Improvement can be achieved by using a rigorous description of the level density in the Fission fragments

•Importance of systematic measures to point out new properties/ideas•Importance of reverse kinematics to have an access to the complete fission fragment characterization =>Transfer-induced fission @GANIL

Page 26: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Additional diapositives

Page 27: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Electromagnetic induced fission of secondary beams

E* distribution<E*> ~12 MeV for all pre-actinides

Page 28: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Quantitative description of the even-odd structure

A combinatory analysis, H. Nifenecker et al., 1982

N the maximum possible number of broken pairs N = Ediss/ the broken pair is a proton pair Zf/Af0.4q break a pair when the required energy is available 0.5p the 2 protons of a given pair to end up into 2 different fragments 0.5

Bag of broken pairs

FF2FF1

Ediss =-4ln(δZ )δZ=(1-2pq)N

Page 29: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Limitations of the combinatory analysis

•Model is based on the number of broken pairs and NOT on the available phase space

As a consequence the model cannot reproduce

•the variation of δz with Z of the fission fragment (p=0.5)

•the amplitude of δn (Edissn=2*Ediss

p)•the even-odd structures in odd-Z fissionning systems (q=1)

S. Steinhauser et al., 1998M. Davi et al., 1998

Page 30: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Lohengrin (ILL)

-Only the LIGHT fragments are identified=>No experimental evidence ofshell effects in heavy fragments

Radiochemical methods

Small part of the distribution :distortions in the neutron yields

Exfor data base

Rochman PhD, Lohengrin 2001

Isotopic distribution in direct kinematics

Page 31: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

• High radioactivity : the production of samples for irradiation is difficult (=>systematics in direct kinematics is limited)

• Combined with a spectrometer isotopic resolution of the full isotopic distribution

(light and heavy fragments)in-flight measure of the isotopic distribution

(before beta decay)• Using transfer reaction to induce fission precise knowledge of the excitation energy

Advantage of inverse kinematics

Page 32: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Liquid drop model : symmetric fission in equally deformed fragments

Shell effects:Minima of the potential landscape are modified

Spherical shell

Deformed shell

Closed shell at N=86,88,90 ?? Still under debate!!

Description of fission fragment distribution

Page 33: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Counting rates

Reasonable statistics: 104 fission events detectedAcceptance of VAMOS&TIARA: 105 fission eventsThin secondary target : 6 1019at/cm2 dSecondary target limited by energy resolution && XS Cd2 <0.5mg/cm2fis ~5mbarn Total number of actinide: Ninc=Nfis/(fis Ntar)= 3 1011

Primary target limited by the 2nd beam kin. Energy &alpha acceptance==>1mg/cm2 Ninc= fus *Ntar *Iinc *time*q =5 10-27*7 1019*5 1010*1.3 106*0.2 =3 109

Primary beam intensity: >x20Fusion evaporation <x2 Gas secondary target >x30 Impinging energy x2

Page 34: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Advantages

reaction with cross section >mb => sufficient statistics

Disadvantage

Imprecision on the excitation energy (excitation energy distributed to ejectile)Threshold ??

Page 35: Isotopic Yields of Fission Fragments from Transfer-Induced Fission

Predictions for SPIRAL2

PROFI code (K.H. Schmidt) reproduces the mass distributionsAnd the isotopic distributionfrom ISOLDE and GSI

(fissioning system and excitationenergy are model dependent)


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