Mass Asymmetric Fission of Iridium Nucleus
Mass Asymmetric Fission of Nucleus Produced in 7Li + 186W
Katsuhisa Nishio
Advanced Science Research Center
Japan Atomic Energy Agency
Tokai, JAPAN
ARIS2014 Tokyo
①
④
②
⑤
③
⑥
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. Ohtsuki
⑤ I.Tsekhanovich
⑥ P. Möller
Properties for Low-Energy Fission
Region of our interest I: betadelayed fission of A~180-200
N/Z~1.22-1.3: Tl,Bi, At, Fr
ISOLDE(CERN)
A. Andreyev et al.,
Phys. Rev. Lett.105,
252502 (2010).
Z=82
180Hg
- particle induced
N/Z=1.25
187Ir
196Au
x - e.m. –induced E*~11 MeV
Calculated Fission Fragment Yield
180Hg
Calculated by P. Möller (LANL) and J. Randrup (LBNL)
193Ir
7Li
+ 186W  193Ir*
P. Möller, 10th ASRC International Workshop,
“ Nuclear Fission and Structure of Exotic Nuclei ”, 2013.March, Tokai, Japan
JAEA at Tokai and Tandem Facility
Tokai Campus, JAEA
20 MV Tandem accelerator (20UR)
J-PARC
Tandem facility
Tokyo
Time difference signal of FFs in 7Li + 186W
MWPC1
10000
Ec.m.= 65.5MeV
5000
7Li
Beam
0
100
8000
44o
186W
150
200
250
300
350
400
40.0 MeV
Counts
Fragment 1
4000
0
100
160
150
200
250
300
350
400
30.0 MeV
Fragment 2
80
0
100
MWPC2
150
200
250
300
TOF Channel
350
400
Time difference (ch)
Fragment Mass Distributions in 7Li + 186W
Elab
68.0 MeV
Fusion reaction is assumed
+ 186W  193Ir*
Events (u)
7Li
41.5 MeV
31.1 MeV
83As
N = 50
110Ru
N = 66
Fragment Mass (u)
Folding Angle between Fission Fragments
Elab = 31.1 MeV
Complete Fusion 7Li + 186W
θfold =169o
FF 1
θ1
FF 2
θ2
Counts
Beam
Recoiled Fissioning Nucleus
θfold = θ1 + θ2 (deg)
Analysis assuming fusion-fission
7Li
+ 192Os  199Au*
7Li
θfold, =167.9o
+ 186W  193Ir*
θfold =167.5o
Ebeam = 41.5 MeV
<TKEViola>
=134 MeV
Fragment Mass (u)
Folding Angle (deg.)
TKE (MeV)
TKE (MeV)
Folding Angle (deg.)
Z=118
Fragment Mass (u)
Viola Formula from Phys. Rev. C 31, 1550 (1985)
<TKEViola>
=129 MeV
7Li
7Li
+
186W, 192Os
+ 186W
7Li
180
EBeam = 64.0 MeV
180
σfiss
170
= 67 μb
qfold (deg)
160
41.5 MeV
+ 192Os
170
180
180
170
170
160
14 μb
110 μb
160
160
2.1 μb
-20
0
180
31.1 MeV
170
0.8 μb
160
-20
0
20
dT (ns)
dT (ns)
20
Break-up Fusion
7Li
 3H + 4He (Q= -2.467 MeV)
187Ir
188Ir
189Ir
190Ir
191Ir
192Ir
193Ir
Counts
p + 192Os
186Os 187Os 188Os 189Os 190Os 191Os 192Os
Fragment Mass (u)
185Re 186Re 187Re 188Re 189Re
186W( 7Li,
184W 185W 186W
t)190Os*
186W( 7Li, α)189Re *
Break-up Fusion and Fission
3H
3H
7Li
4He
4He
186W
+ 186W  190Os*
3H + 186W  189Re*
4He
Fragment 2
Fragment 1
CN
VCoul
Ebeam,thres (7Li)
4He
+ 186W
190Os*
20.3 MeV
̴ 36 MeV
3H
+ 186W
189Re*
10.3 MeV
̴ 24 MeV
Fission Barrier Height for 189Re and 190Os
189Re, 190Os
Fission Barrier is 25 MeV
189Re*
or 190Os* should have excitation energy
larger than 25 MeV
P. Möller, 16th ASRC International Workshop,
“ Nuclear Fission and Decay of Exotic Nuclei ”, 2014.March, Tokai, Japan
Folding Angle at E* = 25 MeV of Fissioning Nucleus
7Li
180
Elab
α) 189Re*, θα = 25o
186W(7Li, t) 190Os* , θt = 45o
186W(7Li,
170
64.0 MeV
+ 186W = 193Ir*
41.5 MeV
qfold (deg)
160
180
α) 189Re*, θα = 45o
186W(7Li, t) 190Os* , θ = 45o
t
186W(7Li,
170
160
180
31.1 MeV
186W(7Li,
170
α) 189Re*, θα = 55o
E*max = 36 MeV
160
-20
0
20
dT (ns)
Setup for Break-up Fusion Induced Fission
MWPC1
Target
7Li
Beam
189Re*…
186W
θLAB
t, α
MWPC2
ΔE-E
7Li
ΔE
E
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).
Folding Angle Distribution at E* = 25MeV
180
Elab
7Li
170
64.0 MeV
186W(7Li,
186W(7Li,
41.5 MeV
qfold (deg)
160
180
t) 190Os* , θt = 45o, 170.0
α) 189Re*, θα = 25o, 173
t) 190Os* , θt = 45o,170.0o
186W(7Li, α) 189Re*, θ = 45o , 172
α
186W(7Li,
170
160
E* max = 26 MeV
180
31.1 MeV
+ 186W = 193Ir*
t) 190Os* , θt = 45o, 170.0
186W(7Li, α) 189Re*, θ = 55o, 172
α
186W(7Li,
170
160
-20
0
20
dT (ns)
E*max = 36 MeV
Summary
E* (MeV)
Cross section (mb)
104
103
20 30 40 50 60 70 80
Fusion
102
101
Fission
100
10-1
10-2
10-3
10 20 30 40 50 60 70 80
Ec.m. (MeV)
7
Cross section (MeV)
4
Li +
7
Li +
186
W
182
W
10
3
10
2
10
1
10
0
10
-1
10
-2
10
20 30 40 50 60 70
Ec.m. (MeV)
21
22
23
Multi-nucleon Transfer Induced Fission
18O
+ 232Th
F
O
15N
Be
B
Esum (MeV)
N
C
Coincidence
between particle and
fission fragments
232Th(18O, 15N) 235Pa*
 Transfer of 3H
Fragment Mass Distributions for 3H Transfer
→ Fission
Counts
Excitation energy (MeV)
232Th(18O, 15N) 235Pa*
Fragment mass yield (u)
Fragment Mass Distributions for 232Th*
Excitation energy (MeV)
232Th(18O, 18O) 232Th*
Fragment mass yield (u)
26
Multi-nucleoon Transfer Induced Fission
18O
+ 232Th
Coincidence
between particle and
fission fragments
F
O
N
Be
B
Esum (MeV)
C
New Region for Mass Asymmetric Fission
180Hg
100
80
A.Andreyev et al.,
Phys. Rev. Lett.105, 252502 (2010).
T. Ichikawa et al.,
Phys. Rev.C.86, 024610 (2012).
28
Theoretical Mass Yield
189Ir 193Ir
Fission Ｑ-value
Q-value for Fission (MeV)
300
Large Fission Saddle Point Shape
Probability
258
1980
Fm
250
258
Fm
200
236
150
2010
180
100
193
Present
50
160
124
238U
U
Hg
193Ir
Ir
Gd
Sn
0
Small Fission
Probability
-50
20 40 60 80 100 120 140 160 180 200
Fragment Mass (u)
160Gd