Isotopic Fission-Fragment Distributions as a

Deep Probe to Fusion-Fission Dynamics

Fanny Farget, Manuel CaamañoUniversidade de Santiago de Compostela (Spain)

O. Delaune, X. Derkx, C. Rodríguez, C. Golabek, A. Navin, M. Rejmund, T. Roger, M.G. Saint-Laurent, H. Savajols, C. Schmitt, C. Stodel, J.C. Thomas, A.C. Villari

GANIL (France)

D. Ramos, J. Benlliure, D. Cortina, B. Fernández USC (Spain)

O. Tarasov, D. Bazin, W. Mittig, D.J. Morrisey, J. Pereira, B.M. Sherrill NSCL (USA)

K.-H. Schmidt, B. Blank, S. Grévy, B. Jurado CENBG (France)

E. Casarejos U. de Vigo (Spain)

L. Audouin, C-O Bacri, L. Perrot IPNO (France)

A. Heinz U. of Chalmers (Sweden)

D. Doré, M. Delphine de Salsac SPhN (France)

S. Lukyanov FNLR (Russia)

L. Gaudefroy CEA DIF (France)

Experimental observables

Mass, Z, and TKE showed that shell effects come

into play

Measurements of fragment distributions and yields hints

on the dynamics of fission

K.F. Flynn et al. PRC 5 (1972) 1725 C. Böckstiegel et al. NPA 802 (2008) 12

B. Jurado et al. PRL 93 (2004) 072501

Y. Ayyad, PhD U. Santiago C (2012)2

Fission probabilities reveal barrier’s features

C. Rodríguez-Tajes et al., to be published

Experimental observablesDifferent reactions grant the access to different observables and conditions

neutron - induced fission: - control of E*- no high L------ limited to stable targets- no access to Z

spallation/EM - induced fission: - inverse kinematics (A, Z of fragments)- access to unstable FS- no high L------ no control of E*- reduced control on FS

fusion - induced fission: - control of E*- access to unstable FS------ high L- quasi-fusion

transfer - induced fission:- control of E*- inverse kinematics (A, Z of fragments)- access to unstable FS- includes fusion for free------ high L- quasi-fusion

3

Dire

ct ki

nem

atics Inverse kinem

atics

Transfer/fusion-induced fission: three flavors

238U (6.1 AMeV) + 12C 238U (24 AMeV) + 12C/9Beat VAMOS at LISE

!"

!"#$%

&'()%&*%+%,$-%

.$%.$%

/0%12345%67"7%

,8!9%:;<"%=">%%

238U (6 AMeV) + 12C/2H/1Hwith MAYA

4

238U (6.1 AMeV) + 12C at VAMOS- Setup based on inverse kinematics

- Transfer reactions produce unstable species, induce fission.

FS’s observables: Z, A, E*. Fragments’ observables: Z, A, q, angles, velocity, gammas.

Fragment 1MW: ToFCD: x, y positionsIC, Si: dE-E Target-like recoil

SPIDER (double stripped Si detector): dE-E, angles

Fragment 2MW: ToFIC, Si: dE-E

Exogam: Gammas

5

238U (6.1 AMeV) + 12C at VAMOSA from 80 to 160 (σ/A~0.3 %) and Z from 30 to 70 (σ/Z~0.9 %)

confirmed by gamma identification.

~10 q states per isotope

D. Ramos, PhD at U. Santiago de Compostela6

238U (6.1 AMeV) + 12C at VAMOSThe target-like recoil tags the different FS

the E* (σ~1 MeV) is deduced from kinematics.

Fission probability shows barrier’s features

C. Rodríguez-Tajes et al., to be published

7

FSbeam

recoil

FF

FF

238U (6.1 AMeV) + 12C at VAMOS

-210

-1101 Se34

-210

-1101 Br35

-210

-1101 Kr36

50 60 70-210

-1101 Rb37

Sr38

Y39

Zr40

50 60 70

Nb41

Mo42

Tc43

Ru44

60 70 80

Rh45

Pd46

Ag47

Cd48

60 70 80

In49

Sn50

Sb51

Te52

70 80 90

I53

Xe54

Cs55

Ba56

70 80 90

La57

Ce58

Pr59

70 80 90

Nd60

Neutron number

Nor

mal

ized

yiel

ds

12C ( 238U , 240Pu (E*~9 MeV) ) 10Be

Z30 40 50 60

Nor

mal

ized

yiel

d

0

5

10

15

(a)<N

>/Z

1.4

1.45

1.5

1.55

1.6

1.65

A80 100 120 140 160

Nor

mal

ized

yiel

d

2

4

6

8 (b)

M. Caamaño et al. PRC 88 (2013) 024605

A. Bail et al. PRC 84 (2011)

034605

C. Schmitt et al. NPA 430 (1984) 21

8

238U (6.1 AMeV) + 12C at VAMOS

- evolution of A, Z, <N>/Z distributions with E*

- gradual disappearance of shell effects

D. Ramos, PhD at U. Santiago de Compostela

– – GEF (K.-H. Schmidt & B. Jurado)

9

240Pu (E*~9 MeV)

238U (6.1 AMeV) + 12C at VAMOS<N

>/Z

1.45

1.5

1.55

1.6 (a)

Z35 40 45 50 55 60

(Z)

!

-20246 (b)

LD scission-point model

the obtained results can be linked to deformed shell effects

(b)

LD scission-point modelEtot = ELD(Z1,A1) + ELD(Z2,A2)

M. Caamaño et al. PRC 88 (2013) 024605

B.D. Wilkins et al. PRC 14 (1976) 1832

D. Ramos, PhD at U. Santiago de Compostela10

240Pu (E*~9 MeV)

238U (6.1 AMeV) + 12C at VAMOS

Z30 40 50 60

> (c

m/n

s)fis

s<v

0.8

1

1.2

1.4

1.6

1.41.61.8 Zn30

Y39

Cd48

La57

Ga31

Zr40

In49

40 60 80 1000.81

1.2 Ce58

Ge32

Nb41

Sn50

40 60 80 100

Pr59

As33

Mo42

0.81

1.2

Sb51

40 60 80 100

Nd60

Se34

Tc43

Te52

40 60 80 100

Pm61

Br35

11.21.4

Ru44

I53

40 60 80 100

Sm62

Kr36

Rh45

Xe54

40 60 80 100

Eu63

1.21.41.6 Rb37

Pd46

Cs55

40 60 80 100

Gd64

Sr38

Ag47

Ba56

Neutron number

(cm

/ns)

fiss

v) (cm/ns)fisscos(fissv-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8

) (cm

/ns)

fiss

sin(

fiss

v

0

0.2

0.4

0.6

0.8

1

1.2

1.4

The fragments’ velocities are also available.240Pu follows the systematics of Wilkins.250Cf deviates at light fragments.

250Cf240Pu

M. Caamaño et al. PRC 88 (2013) 024605

11

240Pu (E*~9 MeV)

A80 100 120 140 160

Nor

mal

ized

yiel

d

0

1

2

3

4

(b)

Z30 35 40 45 50 55 60 65

Nor

mal

ized

yiel

d

0

2

4

6

8

10

12 (a)<N

>/Z

1.35

1.4

1.45

1.5

1.55

238U (6.1 AMeV) + 12C at VAMOS12C ( 238U , 250Cf (E*~45 MeV) )

-210

-1101 Zn30

-210

-1101 Ga31

-210

-1101 Ge32

-210

-1101 As33

40 50 60 70-210

-110

1 Se34

Br35

Kr36

Rb37

Sr38

40 50 60 70

Y39

Zr40

Nb41

Mo42

Tc43

50 60 70 80

Ru44

Rh45

Pd46

Ag47

Cd48

50 60 70 80

In49

Sn50

Sb51

Te52

I53

60 70 80 90

Xe54

Cs55

Ba56

La57

Ce58

70 80 90 100

Pr59

Nd60

Pm61

Sm62

Eu63

70 80 90 100

Gd64

Neutron number

Norm

alize

d yiel

ds

M. Caamaño et al. PRC 88 (2013) 024605

C. Yadav et al. PRC 86 (2012) 034606

12

238U (6.1 AMeV) + 12C at VAMOS

Fusion-fission reaction: angular momentum distribution

High excitation energy: multi-chance fission

Lcrit~23ħ

GEF output for E*=45 L=16

13

250Cf (E*~45 MeV)

238U (6.1 AMeV) + 12C at VAMOS

Widths and shapes behave as expectedwith small differences.

<L> marks the transition to symmetric fission

solid lines: Code GEF (K.-H. Schmidt & B. Jurado)

14

250Cf (E*~45 MeV)

<N>/Z

1.45

1.5

1.55

1.6 (a)

Z35 40 45 50 55 60

(Z)

!

-20246 (b)

238U (6.1 AMeV) + 12C at VAMOS

LD scission-point model

- no polarization at high E*- cannot be reproduced with multi-chance fission and/or <L> influence.

LD scission-point modelEtot = ELD(Z1,A1) + ELD(Z2,A2)

D.J. Hinde et al. PRC 45 (1992) 1229

• Experiment• Experiment

15

250Cf (E*~45 MeV)

238U (24 AMeV) + 12C/9Be at LISE

!"

!"#$%

&'()%&*%+%,$-%

.$%.$%

/0%12345%67"7%

,8!9%:;<"%=">%%

- Setup based on inverse kinematics- Fusion-fission at different E*

Fragment 1MWCP: ToF, x, y positionsSi: dE-E

Fragment’s observables: Z, A, q, angles, velocity, gammas.

Spokesperson:O. Tarasov (NSCL)

16

238U (24 AMeV) + 12C/9Be at LISE

238U + 12C238U + 9Be

132Sn ~10 pps O. Delaune et al., to be published

17

238U + 12C/9Be

250Cf 238U (6.1 AMeV) + 12CE* = 45 MeV<L>~152*<Z>=98 2*<A>=243 (ν~7)

E* = 250 - 200 MeV <L>~952*<Z>=92 2*<A>=219 (ν~?)

E* = 200 - 150 MeV <L>~752*<Z>=96 2*<A>=232 (ν~15)

247Cm 238U (24 AMeV) + 9Be

250Cf ? 238U (24 AMeV) + 12C

no fusion occursO. Delaune et al., to be published

18

Fusion-fission summary

238U + 12C/9Be

U+C 6 AMeVU+Be 24 AMeVU+C 24 AMeVU+d 1 AGeV

U+C 6 AMeVU+Be 24 AMeVU+C 24 AMeVU+d 1 AGeV

polarisation width of isotopic distribution

- As E* diminishes, <N>/Z becomes flat in U+C @ 6 AMeV (!!)- U+Be recovers some shell influence (maybe due to evaporation)

- U+C @ 24 AMeV is remarkably similar to spallation reactions

J. Pereira et al. PRC 75 (2007) 014602

O. Delaune et al., to be published

19

Fusion-fission summary

Summary and conclusions

• The study of transfer- and fusion-induced fission in inverse kinematics allows the access to observables not available so far.• We have shown A, Z, <N>/Z, and velocity distributions for 250Cf, 247Cm, and 240Pu, and their evolution with E* and the reaction mechanism.

• The 240Pu measured distributions are in agreement with their expected behaviour.• 250Cf with E*=45 MeV shows unexpected features in <N>/Z, velocity, and isotopic distributions.

• The results on 250Cf reveal the need for a better understanding of the fission process, post-saddle.• The study of the isotopic distributions of fission fragments proves to be a valid tool to extract new information on the fission dynamics.