Transcript Sub-barrier fusion of weakly bound nuclei: Strong

Reactions with exotic nuclei
( at FLNR )
• Recent experiments on fusion of 6He
• Deep sub-barrier fusion of neutron rich nuclei
• A few words about astrophysics
6He
400-cm cyclotron RIB
radioactive ion beams
Dubna
Radioactive
Ion
Beams
low energy
beam line
0
ISOL
10
m
Electron
accelerator
Acculinna
400-cm cyclotron
7Li
DIRECT
DIRECT
Fusion, transfer and breakup reaction mechanisms induced by halo nucleus 6He
JINR
(Dubna), CSNSM (Orsay), IRS (Strasbourg), ULB (Bruxelles), Vanderbilt Univ. (USA)
166Er(6He,6n)166Yb
3
& 165Ho(6Li,5n)166Yb <==> 166Er(4He,4n)166Yb //PRC48(1993)319//
2
1
6He
+ 166Er
172Yb*
6He
+ 166Er
170Yb*
+ 2n
6He
+ 166Er
168Er*
+ 4He
DRIBs
Dec.- January ’07
U400
166Yb
+ 6n
Complete & incomplete fusion reactions with 6He (E=62 MeV)
6He
+ 166Er → 172Yb* → 166Yb + 6n
→ 167Yb + 5n
→ 170Yb*+2n → 168Yb + 4n
→ 168Er* + α → 168Er
Data analysis using EMPIRE-II code
http://www.nndc.bnl.gov/nndcscr/model-codes/empire-ii/
The statistical model used in the EMPIRE-II is an advanced implementation of
the Hauser-Feshbach theory. The exact angular momentum and parity
coupling is observed. The emission of neutrons, protons alpha-particles and
light ion is taken into account along with the competing fission channel. The
full gamma-cascade in the residual nuclei is considered.
EMPIER-II calculation of sxn and sfus
4n
5n
6n
5n
4n
B(6He+Er) = 16 MeV, B(6Li+Ho) = 26 MeV
6n
At well-above barrier energies
there is no difference between 6He and 6Li
from the point of view of the fusion probability.
Other reaction channels are still under analysis.
Sub-barrier fusion of 6He
M.S. Hussein, M.P. Pato, L.F. Canto and R. Donangelo, Phys.Rev. C 46, 377 (1992).
L. F. Canto, R. Donangelo, P. Lotti and M.S. Hussein, Phys.Rev. C 52, R2848 (1995).
N. Takigawa and H. Sagawa, Phys.Lett. B 265, 23 (1991).
C.H. Dasso and A. Vitturi, Phys.Rev. C 50, R12 (1994).
K. Hagino, A. Vitturi, C.H. Dasso and S.M. Lenzi, Phys.Rev. C 61, 037602 (2000).
A.S. Fomichev et al., Z.Phys. A 351, 129 (1995).
J.J. Kolata et al., Phys.Rev.Lett. 81, 4580 (1998).
M. Trotta, J.L. Sida, N. Alamanos et al., Phys.Rev.Lett. 84, 2342 (2000).
R. Raabe, J.L. Sida, J.L. Charvet et al., Nature 431, 823 (2004).
A. Di Pietro et al., Phys. Rev. C 69, 044613 (2004).
A. Navin et al., Phys. Rev. C 70, 044601 (2004).
C. Beck, N. Keeley, and A. Diaz-Torres, Phys. Rev. C 75, 054605 (2007).
…
Neutron excess itself does not play an important role
Neutron transfer with positive Q-value is important !
Sub-barrier fusion enhancement due to neutron transfer
( sequential fusion, “energy lift” )
Time dependent
Schrödinger equation
( Zagrebaev, Samarin & Greiner, PRC 2006)
Wave functions of valence
neutrons spread over both
nuclei before they reach and
overcome the Coulomb barrier
Proposed experiments
First experiment
SETUP FOR ACTIVATION MEASUREMENTS with MSP-144
MSP-144
dE/dx~40keV/mm
Focal plane
Monitors
Si-detectors
Monitor
Au-targets
Strip-detector
Reaction
chamber
target~20mm
Ionization E ~ 0.4MeV
chamber
Huge enhancement
in deep sub-barrier fusion of weakly bound nuclei
Fusion of light neutron rich and stable nuclei
Light neutron rich nuclei in astrophysical nucleosynthesis ?
in particular,
instead of the bottle-neck three-body reaction
4He
+ 4He (→8Be, 10-16s ) + 4He → 12C,
4He
+ 6He(1s) → 9Be + n
probably may occur.
Fusion of light neutron rich nuclei produced in the r-process
may significantly change the nucleosynthesis scenario ?
Experiments which could be performed
•
1H(6He,nγ)6Li
•
1H(9Li,nγ)9Be
•
3He(6He,2nγ)7Be
•
3He(9Li,2nγ)10B
•
6Li(6He,nγ)11B
•
6Li(9Li,2nγ)13C
•
9Be(6He,2nγ)13C
•
9Be(9Li,2nγ)16N
•
10B(6He,2nγ)14N
•
10B(9Li,3nγ)16O
•
12C(6He,2nγ)16O
•
12C(9Li,2nγ)19F
•
14N(6He,2nγ)18F
•
14N(9Li,2nγ)21Ne
•
…
•
…
Reactions with 6He
Reaction
Barrier
Energy (c.m.)
lab.
Q (MeV)
6He
+ p → 7Li
0.4
(0.2 – 0.5)
1.4 – 3.5
+10
6He
+ 3He → 9Be
0.8
(0.4 – 1.2)
1.2 – 3.6
+21
Reaction channels
1H ( 6He, 7Li
γ)
1H ( 6He, 6Li n γ)
3He ( 6He, 8Be
3He ( 6He, 7Be
+ 6Li → 12B
1.0
(0.5 – 1.5)
1.0 – 3.0
+18
n γ)
6Li ( 6He, 10B 2n γ)
6He
+ 9Be → 15C
1.3
(0.6 – 1.6)
1.0 – 2.7
+19
9Be ( 6He, 14C
6He
+ 10B → 16N
1.6
(0.8 – 2.4)
1.3 – 3.8
+24
1.9
(1.0 – 3.0)
1.5 – 4.5
+18.4
6He
+ 14N → 20F
2.2
(1.1 – 3.1)
1.6 – 4.5
+20.5
(1.2 – 3.3)
1.7 – 4.5
+20.9
6He
+ 16O → 22Ne
2.5
6Li ( 6He, 11B
3.6, 0+
2.2, 3+
g.s., 1+
10B:
2.2, 1+
1.7, 0+
0.7, 1+
g.s., 3+
16O:
6.9, 2+
6.1, 36.0, 0+
g.s., 0+
n γ)
9Be ( 6He, 13C 2n γ)
10B ( 6He, 15N
n γ)
2n γ)
10B ( 6He, 14N
+ 12C → 18O
6Li:
n γ)
2n γ)
6He
6He
Gamma-lines
12C ( 6He, 17O
n γ)
12C ( 6He, 16O 2n γ)
14N ( 6He, 19F
14N ( 6He, 18F
n γ)
2n γ)
16O ( 6He, 21Ne
16O ( 6He, 20Ne
n γ)
2n γ)
Reactions with с 9Li
Reaction
Barrier
Energy (c.m.)
lab.
Q (MeV)
Reaction channels
9Li
+ 3He → 12B
1.2
(0.5 – 1.2)
2.0 – 4.8
+26.5
3He ( 9Li, 10B
9Li
+ 6Li → 15C
1.5
(0.7 – 1.5)
1.7 – 3.7
+29.1
6Li ( 9Li, 13C
9Li
+ 10B → 19O
2.4
(1.1 – 2.4)
2.1 – 4.7
+33.7
10B ( 9Li, 17O
9Li
+ 14N → 23Ne
3.3
(1.5 – 3.3)
2.5 – 5.5
+33.0
14N ( 9Li, 21Ne
2n γ)
2n γ)
6Li ( 9Li, 11Be + 4He)
2n γ)
10B ( 9Li, 15C + 4He)
14N ( 9Li, 19O
2n γ)
+ 4He)
Gamma-lines
10B:
13C:
2.2, 1+
1.7, 0+
0.7, 1+
g.s., 3+
3.9, 5/2+
3.7, 3/23.1, 1/2+
g.s., 1/2-
Standard scenario
for nucleosynthesis
Уровни
7Li
и
9Be