Download 0 + 2 +

Heavy-Ion Double Charge Exchange study
via 12C(18O,18Ne)12Be reaction
Motonobu Takaki
(CNS, The University of Tokyo)
H. Matsubara2, T. Uesaka3, N. Aoi4, M. Dozono1, T. Hashimoto4, T. Kawabata5,
S. Kawase1, K. Kisamori1, Y. Kubota1, C.S. Lee1, J. Lee3, Y. Maeda6, S. Michimasa1,
K. Miki4, S. Ota1, M. Sasano3, T. Suzuki4, K. Takahisa4, T.L. Tang1, A. Tamii4,
H. Tokieda1, K. Yako1, R. Yokoyama1, J. Zenihiro3, and S. Shimoura1
1CNS,
The University of Tokyo
2National Institute of Radiological Science (NIRS)
3RIKEN Nishina Center
4Research Center for Nuclear Physics, Osaka University
5Department of Physics, Kyoto University
6Department of Applied Physics, University of Miyazaki
2nd conference on ARIS 2014, June 2nd 2014
Double Charge eXchange (DCX) reaction
Probe for unstable nuclei
• Using stable target with ΔTz = 2
Powerful tool to investigate
IV Double Giant Resonances
• DIAS, DIVDR…
12C(π-,π+)12Be
J.E. Ungar et al., PLB, 144 333 (1984)
S. Mordechai et al., PRL 60, 408 (1988).
2
HIDCX with Missing mass method
at Intermediate energy
Heavy-ion
12C(14C,14O)12Be
• Double Spin and/or Isospin flip (ΔS=2, ΔTz=2)
Counts
Missing mass method
Sn
Elab=24A MeV
• measure All excitation energy region
on a same footing
Intermediate energy (~ 100MeV/u)
25
20
• ΔL sensitivity of angular distributions
10
5
0 Ex
W. Oertzen et al.,
NPA, 588 129c (1995)
• direct reaction process dominance
- simple reaction mechanism
15
30
24Mg(18O,18Ne)24Ne
at 76A MeV
20
10
0
- multipole assignment
1
We performed 12C(18O,18Ne) reaction experiment
in normal kinematics at 80 MeV/nucleon.
J. Blomgren et al.
PLB, 362 34 (1995)
0
0
24Ne
5 10 15 20
excitation energy (MeV)
3
(18O,18Ne) reaction
Ground states of 18O and 18Ne are among
the same super-multiplet.
• simple transition process
• large transition probability
B(GT) ~ 0.07
B(GT)=0.11
τ
τ
18O
στ
B(GT)=3.15
18F
στ
B(GT)=1.05
B(GT) ~ 0
18Ne
A primary 18O beam is employed
• high intensity (> 10 pnA)
Experiment can be performed at RCNP with GR spectrometer
• high quality data with high energy resolution
4
Setup of the experiment
Good PID resolution
Energy resolution = 1.2 MeV(FWHM)
18Ne
Grand Raiden
12C
target (2.2 mg/cm2)
1.7 1.8 1.9 2.0 2.1 2.2 A/Q
18O
MWDCs and plastic scinti.
beam
beam: 18O
Energy: 80A MeV
ΔE: ~ 1 MeV
intensity: 25 pnA
18Ne
Ring Cyclotron Facility,
Research Center for Nuclear Physics,
Osaka University
5
Successful result
2+/3-
Bound and unbound states were observed
in one-shot measurement.
The 2.2 MeV peak has a larger cross section than the g.s.
Different angular distribution of the 4.5 MeV peak.
6
Reaction calculation
Coupled-channel calculation with microscopic form factors
Shell model
one body transition
density (OBTD)
SFO int.
USD int.
double folding
coupled channel
form factors
diff. cross section (dσ/dθ)
NN effective int.
(Love-Franey 100 MeV)
optical potential
global (double folding)
With appropriate normalizations, the experimental distributions were reproduced.
normalization factor=0.7
normalization factor=1.3
0+
ΔL=0
2+
ΔL=2
7
Probing of the configuration mixing
Mixing degree between p- and sd-shell components
in 0+ states of 12Be
sd
} mixing
1p1/2
1p3/2
(p)2 dominance
1s1/2
proton
12Be
neutron
The cross section for the two 0+ states at forward angle
➡dominated by double Gamow-Teller transition(ΔL=0, ΔS=2, ΔT=2).
➡mainly reflect the p-shell contribution.
8
Evaluation of p-shell contribution to 0+ states of
12Be
Assumption:
1. 12C g.s. has only p-shell configuration.
2. The transition occurs in the 0hω
relative cross section between 0+g.s. and 0+2
←→ ratio of p-shell contributions
only statistical error
Similar spectroscopic value with earlier works
p-shell contribution in 0+g.s. and 0+2
0+g.s.(%)
0+2(%)
0+2/0+g.s.
methods
Meharchant
25
60
2.4±0.5
12B(7Li,7Be)
Fortune
32
68
2.1
SM
Barker
31
42
1.4
SM
R. Meharchant et al., PRL 122501, 108 (2012)
H. T. Fortune et al., PRC, 024301, 74 (2006)
F. C. Barker, Journal of Physics G, 2(4), L45 (1976)
9
Double Gamow-Teller transition
B(GT2)
12Be(0+,
g.s.)
1st
2nd
B(GT)
B(GT)
This work
Reference
12Be(0+ )
2
0.17±0.04
0.999±0.005
0.184±0.008
1st
2nd
B(GT)
B(GT)
This work
Reference
B(GT2)
0.184±0.009
B(GT2)
0.27±0.07
0.999±0.005
0.214±0.051
0.214±0.05
• This work:
- B(GT2 ) values are derived from the OBTD with
the normalization factor of the cross section.
• Reference
-
12C(0+)
-> 12B(1+, g.s.) (I. Daito et al., PLB 418, 27 (1998).)
-
12B(1+,
g.s.) -> 12Be(0+) (R. Meharchand et al., PRL 108, 122501 (2012))
10
Conclusion
2+/3-
The 2.2 MeV peak has a larger cross section than the g.s.
• The p1/2 component dominantly contributes to the 0+2 state.
The different angular distribution of the 4.5 MeV peak
• The HIDCX reaction can assign multipolarities.
11
Summary
HIDCX reactions are unique probe for light unstable nuclei and
IV double giant resonances, especially spin-flip excitations.
The HIDCX 12C(18O,18Ne) reaction experiment was performed.
• Three clear peaks were observed at Ex=0.0, 2.2 and 4.5 MeV.
• Larger cross section for the 12Be(0+2) state reflects
the degree of the p-shell contribution for the two 0+ states in 12Be.
• The different angular distributions of the cross sections suggest
a sensitivity to multipolarities.
The microscopic calculation for the HIDCX was performed.
• The cross section can be reproduced with
the appropriate normalization factors.
• B(GT)2 value is derived.
This study shows that spectroscopic studies
with the HIDCX reaction are a valid and feasible!
Thank you for your attention.
Counts
Backup
12C(14C,14O)12Be
12C(π+,π-)12O
Counts
Elab=24A MeV
0
10
Ex
S. Mordechai et al.,
PRC, 32 999 (1985)
20
30
25
20
15
10
5
0 Ex
W. Oertzen et al.,
NPA, 588 129c (1995)
13
Reaction calculation scheme
single particle wave function one-body transition density
n-n effective interaction
transition density
double-folding transition form factor
coupled channel calculation
14
Calculate cross sections for various paths.
4.56
2+
g.s.
0+
12Be
Target
Projectile
18Ne
1-
7.7
g.s.
(g.s., 0+)
GT
18F
1+
12B
0+
12C
(g.s., 1+)
GT
18O
(g.s., 0+)
Configuration mixing of 0+ states in 12Be
Mixing degree between p- and sd-shell components
in 0+ states of 12Be
sd
} mixing
1p1/2
1p3/2
(p)2 dominance
1s1/2
proton
(sd)2 dominance
12Be
neutron
p-shell contribution in 0+g.s. and 0+2
0+g.s.(%)
0+2(%)
0+2/0+g.s.
methods
Meharchant
25
60
2.4±0.5
12B(7Li,7Be)
Fortune
32
68
2.1
SM
Barker
31
42
1.4
SM
16
Test Experiment to prove experimental feasibility
2γ time spectrum
18O(12C,12Beγ)18Ne(gnd)
decay time constant:
395+173
-92 ns
⇔ 331 ns in literature
w/o γ-tag
Time [ns]
BG due to particle
mis-identification
511keV
with γ-tag
×10
t
12Be
511keV
Dominance of double Gamow-Teller transition
Our experimental result
The cross section for the 0+2 state is larger than 0+1 (g.s.).
Double GT transitions dominate in two 0+ states.
→ Sensitive to the 0ℏω configuration
Single charge exchange reaction result