heavy-ion double charge exchange study via 12 c( 18 o, 18 ne) 12 be reaction motonobu takaki (cns,...
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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 Tokyo2National Institute of Radiological Science (NIRS)
3RIKEN Nishina Center4Research Center for Nuclear Physics, Osaka University
5Department of Physics, Kyoto University6Department 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 investigateIV Double Giant Resonances
• DIAS, DIVDR…
2
12C(π-,π+)12Be
J.E. Ungar et al., PLB, 144 333 (1984)S. Mordechai et al., PRL 60, 408 (1988).
HIDCX with Missing mass method at Intermediate energy
Heavy-ion
• Double Spin and/or Isospin flip (ΔS=2, ΔTz=2)
Missing mass method
• measure All excitation energy regionon a same footing
Intermediate energy (~ 100MeV/u)
• direct reaction process dominance
- simple reaction mechanism
• ΔL sensitivity of angular distributions
- multipole assignment
3
Co
unt
s
25 20 15 10 5 0 Ex
12C(14C,14O)12BeElab=24A MeV
W. Oertzen et al.,NPA, 588 129c (1995)
24Mg(18O,18Ne)24Ne at 76A MeV
30
20
10
0
1
0d2 σ/dΩ
c.m
.dE
(nb
/sr/
(0.5
MeV
))0 5 10 15 20
24Ne excitation energy (MeV)
J. Blomgren et al.PLB, 362 34 (1995) We performed 12C(18O,18Ne) reaction experiment
in normal kinematics at 80 MeV/nucleon.
Sn
(18O,18Ne) reaction
Ground states of 18O and 18Ne are among the same super-multiplet.
• simple transition process
• large transition probability
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
τ τ
στστB(GT)=3.15 B(GT)=1.05
18O18F
18Ne
B(GT)=0.11
B(GT) ~ 0.07
B(GT) ~ 0
Setup of the experiment
5
12C target (2.2 mg/cm2)
MWDCs and plastic scinti.
18O beambeam: 18OEnergy: 80A MeVΔE: ~ 1 MeVintensity: 25 pnA
Ring Cyclotron Facility, Research Center for Nuclear Physics,
Osaka University
Grand Raiden
Energy resolution = 1.2 MeV(FWHM)
A/Q1.7 1.8 1.9 2.0 2.1 2.2
ΔE
in P
L S
cin
t.
18Ne
18Ne
Good PID resolution
Successful result
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
2+/3-
Coupled-channel calculation with microscopic form factors
Reaction calculation
7
0+ 2+
preli
mina
ry
preli
mina
ry
one body transition density (OBTD)
form factors diff. cross section (dσ/dθ)
Shell model double folding coupled channel
NN effective int.(Love-Franey 100 MeV)
SFO int.USD int.
optical potentialglobal (double folding)
normalization factor=0.7 normalization factor=1.3
ΔL=0 ΔL=2
With appropriate normalizations, the experimental distributions were reproduced.
Probing of the configuration mixing
Mixing degree between p- and sd-shell components in 0+ states of 12Be
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.
sd
1p3/2
1s1/2
1p1/2
}mixing
12Beproton neutron
8
(p)2 dominance
Evaluation of p-shell contribution to 0+ states of 12Be
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)
relative cross section between 0+g.s. and 0+
2
←→ ratio of p-shell contributions
Similar spectroscopic value with earlier works
9
Assumption:1. 12C g.s. has only p-shell configuration. 2. The transition occurs in the 0hω
only statistical error
Double Gamow-Teller transition
B(GT2)
• 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
12Be(0+, g.s.)1st 2nd
B(GT) B(GT) B(GT2)
This work 0.17±0.04
Reference 0.999±0.005 0.184±0.008 0.184±0.009
12Be(0+2)
1st 2nd
B(GT) B(GT) B(GT2)
This work 0.27±0.07
Reference 0.999±0.005 0.214±0.051 0.214±0.05
very
preliminary
very
preliminary
Conclusion
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
2+/3-
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 suggesta 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.
Backup
13
12C(π+,π-)12O
S. Mordechai et al.,PRC, 32 999 (1985)
0 10 20 30 Ex
Co
un
ts
Co
un
ts
25 20 15 10 5 0 Ex
12C(14C,14O)12BeElab=24A MeV
W. Oertzen et al.,NPA, 588 129c (1995)
Reaction calculation scheme
14
single particle wave function one-body transition density
n-n effective interaction
double-folding transition form factor
transition density
coupled channel calculation
Calculate cross sections for various paths.
12C
12B
12Be
0+
1+
1-
0+
2+
g.s.
4.56
g.s.
7.7
Target Projectile18Ne (g.s., 0+)
18O (g.s., 0+)
18F (g.s., 1+)
GT
GT
Mixing degree between p- and sd-shell components in 0+ states of 12Be
Configuration mixing of 0+ states in 12Be
sd
1p3/2
1s1/2
1p1/2
}mixing
12Beproton neutron
(p)2 dominance
(sd)2 dominance
16
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
Test Experiment to prove experimental feasibility
511keV
511keV
12Be
t
BG due to particlemis-identification with γ-tag
×10
w/o γ-tag
18O(12C,12Beγ)18Ne(gnd)2γ time spectrum
Time [ns]
decay time constant: 395+173 ns⇔ 331 ns in literature
-92
Dominance of double Gamow-Teller transition
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 0 ωℏ configuration
Our experimental result
Single charge exchange reaction result