Katsuhisa Nishio

Advanced Science Research CenterJapan Atomic Energy Agency

Tokai, JAPAN

ARIS2014 Tokyo

Mass Asymmetric Fission of Iridium NucleusMass Asymmetric Fission of Nucleus Produced in 7Li + 186W

①　 K. Nishio, K. Hirose, I. Nishinaka, H. Makii, R. Orlandi, R. Léguillon, J. Smallcombe, S. Mitsuoka, T. Ishii, H. Ikezoe

② A. Andreyev ③ N. Tamura, S. Goto

④ 　 T. Ohtsuki⑤ 　 I.Tsekhanovich⑥ 　 P. Möller

①　

②　

③　

④⑤　

⑥　

- particle induced x - e.m. –induced E*~11 MeV187Ir 196Au

Z=82Z=82Z=82Z=82

180Hg N/Z=1.25

Region of our interest I: beta-delayed fission of A~180-200N/Z~1.22-1.3: Tl,Bi, At, FrISOLDE(CERN)

Properties for Low-Energy Fission

A. Andreyev et al., Phys. Rev. Lett.105, 252502 (2010).

Calculated Fission Fragment Yield

180Hg Calculated by P. Möller (LANL) and J. Randrup (LBNL)

P. Möller, 10th ASRC International Workshop, “ Nuclear Fission and Structure of Exotic Nuclei ”, 2013.March, Tokai, Japan

193Ir

7Li + 186W 193Ir*

JAEA at Tokai and Tandem Facility

20 MV Tandem accelerator (20UR)Tokai Campus, JAEA

Tokyo

Tandem facility

J-PARC

Time difference signal of FFs in 7Li + 186W

186W

MWPC2

MWPC1

Fragment 2

Fragment 1

7Li Beam

100 150 200 250 300 350 4000

5000

10000

100 150 200 250 300 350 4000

4000

8000

TOF Channel

100 150 200 250 300 350 4000

80

160

Time difference (ch)

Coun

ts

Ec.m.= 65.5MeV

40.0 MeV

30.0 MeV

44o

Fragment Mass Distributions in 7Li + 186W 　

31.1 MeV

68.0 MeV

41.5 MeV

Elab

Fragment Mass (u)

110Ru83As

Eve

nts

(u)

Fusion reaction is assumed7Li + 186W 193Ir*

N = 50 N = 66

Folding Angle between Fission Fragments

θfold = θ1 + θ2 (deg)

Complete Fusion 7Li + 186W θfold =169o

Elab = 31.1 MeV

Beam

FF 1 FF 2

θ1

Recoiled Fissioning Nucleus

θ2

Cou

nts

Analysis assuming fusion-fission

Viola Formula from Phys. Rev. C 31, 1550 (1985)

7Li + 192Os 199Au*

Fragment Mass (u)

TKE

(M

eV)

Folding Angle (deg.)

<TKEViola>=134 MeV

θfold, =167.9o

TKE

(M

eV)

7Li + 186W 193Ir* θfold =167.5o

Fragment Mass (u)

<TKEViola> =129 MeV

Folding Angle (deg.)

Ebeam = 41.5 MeV

Z=118

7Li + 186W, 192Os

31.1 MeV

41.5 MeV

EBeam = 64.0 MeV

qfo

ld (d

eg)

dT (ns)-20 0 20

180

170

160

180

170

160

180

170

160

180

170

160

180

170

160

7Li + 186W 7Li + 192Os

σfiss

= 67 μb 110 μb

14 μb 2.1 μb

0.8 μb

-20 0 20

dT (ns)

192Os191Os

Break-up Fusion

187Re 188Re 189Re

188Os 189Os 190Os

185W

186Re

187Os

189Ir 190Ir 191Ir188Ir 192Ir 193Ir

184W

185Re

186Os

187Ir

186W 186W( 7Li, α)189Re *

186W( 7Li, t)190Os* 189Re

193Ir

p + 192Os

Coun

ts

Fragment Mass (u)

190Os

7Li 3H + 4He (Q= -2.467 MeV)

Break-up Fusion and Fission

Fragment 1

Fragment 2

186W7Li4He

3H + 186W 189Re*

4He3H

4He + 186W 190Os*

3H

CN VCoul Ebeam,thres (7Li)

4He + 186W 190Os* 20.3 MeV ̴ 36 MeV3H + 186W 189Re* 10.3 MeV ̴ 24 MeV

Fission Barrier Height for 189Re and 190Os

P. Möller, 16th ASRC International Workshop, “ Nuclear Fission and Decay of Exotic Nuclei ”, 2014.March, Tokai, Japan

189Re* or 190Os* should have excitation energy larger than 25 MeV

189Re, 190OsFission Barrier is 25 MeV

dT (ns)

Folding Angle at E* = 25 MeV of Fissioning Nucleus

7Li + 186W = 193Ir*

31.1 MeV

41.5 MeV

Elab

E*max = 36 MeV

180

170

160

180

170

160

-20 0 20

qfo

ld (d

eg)

64.0 MeV

186W(7Li, α) 189Re*, θα = 45o

186W(7Li, t) 190Os* , θt = 45o

186W(7Li, α) 189Re*, θα = 55o

186W(7Li, α) 189Re*, θα = 25o

186W(7Li, t) 190Os* , θt = 45o

180

170

160

ΔE E

Target

7Li186WθLAB

ΔE-E

t, α

7Li Beam

Setup for Break-up Fusion Induced Fission

189Re*…

MWPC1

MWPC2

Summary

Mass-asymmetric fission was observed for nucleus produced in 7Li +186W.

The fissionig nucleus could be populated by break-up fusion.

Coincidence experiment between particle and both fission fragments is planned.

Properties for Low-Energy Fission

180Hg A. Andreyev et al., Phys. Rev. Lett.105, 252502 (2010).

dT (ns)

Folding Angle Distribution at E* = 25MeV

186W(7Li, α) 189Re*, θα = 25o, 173

186W(7Li, α) 189Re*, θα = 45o , 172

186W(7Li, α) 189Re*, θα = 55o, 172

186W(7Li, t) 190Os* , θt = 45o, 170.0

186W(7Li, t) 190Os* , θt = 45o,170.0o

186W(7Li, t) 190Os* , θt = 45o, 170.0

7Li + 186W = 193Ir*

31.1 MeV

41.5 MeV

Elab

E*max = 36 MeV

E* max = 26 MeV

180

170

160

180

170

160

-20 0 20

qfo

ld (d

eg)

64.0 MeV

180

170

160

Summary

Ec.m. (MeV)

Cro

ss s

ectio

n (

mb

)

Fission

Fusion

E* (MeV)

10 20 30 40 50 60 70 8010-3

10-2

10-1

100

101

102

103

104 20 30 40 50 60 70 80

Ec.m. (MeV)

Cro

ss s

ectio

n (

mb

)

Fission

Fusion

E* (MeV)

188Ir187Ir

10 20 30 40 50 60 70 8010-2

10-1

100

101

102

103

104 20 30 40 50 60 70 80

Ec.m. (MeV)

Cro

ss s

ectio

n (

MeV

)

7Li + 186W 7Li + 182W

20 30 40 50 60 7010-2

10-1

100

101

102

103

104

21

22

23

Multi-nucleon Transfer Induced Fission

18O + 232Th

Esum (MeV)

Coincidence between particle and fission fragments

O

F

NC

BBe

15N

232Th(18O, 15N) 235Pa* Transfer of 3H

232Th(18O, 15N) 235Pa* → Fission

Fragment Mass Distributions for 3H Transfer

Fragment mass yield (u)

Exci

tatio

n en

ergy

(MeV

)

Coun

ts

232Th(18O, 18O) 232Th*

Fragment Mass Distributions for 232Th*

26

Fragment mass yield (u)

Exci

tatio

n en

ergy

(MeV

)

Multi-nucleoon Transfer Induced Fission

18O + 232Th

Esum (MeV)

Coincidence between particle and fission fragments

O

F

NC

BBe

New Region for Mass Asymmetric Fission

80100

A.Andreyev et al., Phys. Rev. Lett.105, 252502 (2010).

180Hg

28

T. Ichikawa et al.,Phys. Rev.C.86, 024610 (2012).

Theoretical Mass Yield

193Ir189Ir

Fission Ｑ -value

Fragment Mass (u)

258Fm

236U

180Hg

193Ir

160Gd124Sn

20 40 60 80 100 120 140 160 180 200-50

0

50

100

150

200

250

300

2010

Q-v

alue

for

Fis

sion

(M

eV)

Present

258Fm

238U

193Ir

160Gd

Saddle Point Shape

1980

Large Fission Probability

Small Fission Probability