H. Sakai1, H. Sagawa1,2, M. Kobayashi3, S. Shimoura3 , T. Suzuki4 and K. Yako3
For the SHARAQ Collaboration
1 RIKEN Nishina Center 2 University of Aizu 3 CNS, The University of Tokyo 4 Nihon University
Spin-isospin correlation in 8He and 12Be(p,n)
Mini-workshop 18 November 2014
Spin-isospin physics: Gamow-Teller responses Last century
στ± induces GT transition 1963 GT giant resonance predicted, Ikeda sum rule 3(N-Z) collectivity? ∼1980 GT giant resonances established Strength quenched/missing: 50-60% of 3(N-Z) due to ∆h or 2p2h ? 1997 ∼90% of 3(N-Z) found Charge-exchange (p,n)/(n,p) reactions on stable target nuclei
C. Garrde, NPA396(1982)127c.
Wakasa et al., PR C 55, 2909 (1997)
GT strength quenching problem
C. Gaarde NP A396, 127c(1983)
Wakasa et al., PR C55, 2909 (1997)
Gamow-Teller responses in isospin extreme
Unstable beams extend the horizon of spin-isospin responses
GTGR under isospin extreme condition Large (N-Z)/A asymmetry GTGR in very neutron rich light nuclei
Today’s subject
Today’s concern
EGT - EIAS Peak energy represents the spin-isospin correlations.
This century
EGT EIAS
Spin-isospin correlations in schematic model
GTGR (IAS) induced by ph residual interaction:
Dispersion relation for the collective state(GTGR)
στκεε
στ
εε
στ 100 11
−=−∆+
+−
−<−
>−>−
>
sii
jjjj
στκεεεε1212
−=−∆+
−+
−−−
sii
fZNfZN
)())((
Nakayama et al.,PLB114(1982)217
AZN2 FGTsIASGT
)()( −−+∆=− κκEE
C. Garrde, NPA396(1982)127c.
)( 21212112 ττκττσσκ τστ
=V
p n
J<
J> s∆ f
1-f
κστ=23/A
κστ=19/A
GTGR in 8He & 12Be
• Target nuclei: 8He and 12Be • Large neutron to proton ratio
(N-Z)/A = 0.33(12Be), 0.5(8He)
8He : neutron skin (+halo) α+4n 12Be: neutron halo
admixture of 2s-orbit into 1p-shell large deformation (2:1) cluster structure α+α+4n
8He & 12Be
• (p,n) reaction in inverse kinematics • 8He(p,n) by Kobayashi et al., • 12Be(p,n) by Yako et al.,
Experiment
Collectivity in (N-Z)/A>0.21:very nuetron rich nuclei
K.Nakayama et al, PLB114(1982)217.
EG
T-E
IAS (
MeV
)
0.3 0.4
(N-Z)/A
0.5
12Be 8He
-1 -2 -3 -4 -5 -6 -7 -8
Data: (N-Z)/A < 0.21
Schematic model for (N-Z)/A> Predicted in 1993 by Sagawa-Hamamoto-Ishihara(SHI), PL B303 (1993) 215.
Hartree-Fock + RPA (TDA) calculation
For large (N-Z)/A EGT – EIAS <0
8He : EGT – EIAS = − 4.3 MeV (f=0.44)
κστ=20/A Stable targets
8He/12Be(p,n) measurements at RIBF
SRC 18O
8He/12Be 200 MeV/u
Target F-H9
F-H10
8He(p,n) Kobayashi exp.
12Be(p,n) Yako exp.
Target
Measurement on 8He(p,n)8Li @ 200 MeV/u
“WINDS” 8He
8Li*
target
MWDC
TOF → 𝑻𝑻𝒏𝒏
𝜽𝜽𝐥𝐥𝐥𝐥𝐥𝐥
Neutron FH9
FH10
10 m
STQ
Plastic
Under inverse kinematics
8He(200 MeV/u) beam 2 Mpps CH2 and C Neutrons(TOF) by a half of WINDS Residual nucleus(7Li/8Li)
WINDS
Measurement on 12Be(p,n)12B @ 200 MeV/u
12Be 12B*
n
θlab
Lab En
12Be(200 MeV/u) beam 0.5-1 Mpps Liq. Hydrogen target Neutrons(TOF) by WINDS Residual nucleus(SHARAQ)
18O beam + Be12Be Achromatic transport
Liquid hydrogen target SHARAQ 12B, 11B,10B
WINDS
• Acceptances |δ| < 1% |θ| < 36 mr, |Ф| < 68 mr
LH2 • Liq H2, 14 mmt
• 59 plastic scintillators (BC408) (H7195 + BC408, 60 x 10 x 3 cm3) • θ = 60-120°, FPL = 180 cm
Wide-angle Inverse-kinematics Neutron Detectors for SHARAQ
Neutron detector TOF method
SHARAQ
Results
8He(p,n) at 200 MeV/u
𝜃𝜃cm = 5° − 8°
0.98 MeV B(GT)=0.24
GT ~8.3 MeV
EIAS=10.8 MeV
EGT - EIAS = −2.5 ± 0.5 MeV EGT - EIAS = −1.2 ± 0.4 MeV
12Be(p,n) at 200 MeV/u
GT ~𝟏𝟏𝟏𝟏.𝟔𝟔 MeV
EIAS=12.8 MeV
(B(GT)=8±4) (B(GT)=7±2)
Comparison to model predictions
Significantly deviate from empirical line. κστ=22/A : good job
CK (8-16)POT : poor job
New SFO(6-16) : better
SHI: poor job
κστ=28/A fixed
Comparison of κστ
Present result 8He and 12Be
SHI (PL B303 (1993)
215) HF+TDA
Gaarde (NP A 396 (1983)127c)
208Pb
Nakayama (PL 114B (1982)
217) 90Zr - 208Pb
Aκστ (MeV) 22 20 23 19 Aκτ (MeV) 28 28 28 28
(N-Z)/A > 0.22 < 0.22
Comparison to 8He β-decay
α+t+n 4.5
β-decay 1+
∼9 t-decay
8He β-decay (cluster model) ≈ tetra-neutron decay to t+n
By Marek Pfutzner
ISOLDE
Ex(GT)=∼9 MeV BR=(0.8±0.5)% log ft=2.87 B(GT)=5.18
Borge et al., NP A560 (1993) 664 ∼8
n
Ex(GTGR) β-decay ∼9(9.7) MeV (p,n) ∼8.3 MeV
Two different states?
Ex(GT)=∼9.7 MeV log ft=2.91 B(GT)=4.75
R matrix fit F.C. Barker, NP A609 (1996) 38
Compilation by Tilley, NPA745(2004)153
7Li channel
t-channel
8He β-decay in OTPC (Warsaw group)
OTPC Marek Pfutner, S. Mianowski, Zenon Janas
(p,n) Kobayashi
β-decay Mianowski
Very good agreement !
0+ isomer in 12Be at 2.251 MeV
12Be 0+
0+
1-
2- 2.107
2.251
2.71
T1/2=229ns
Shimoura et al., PL B645(2007)87
84 )0()0( ps
+st10
+nd20
25 %
60 %
N=8 closed shell structure
sd shell contri. 2hω config.
4hω Shell model by Toshio Suzuki
0hω(%) 2hω(%) 4hω(%)
0+ (g.s.) 30.7 68.6 0.7
0+ (2nd) 58.8 40.7 0.5
AMD calc. by Kanada-En’yo PRC 85, 044320 (2012)
π+σ
π+π
1H(12Be,n) at 200 MeV/u in inverse kinematics
12B
12Be 0+ 0.0
2.24 0+
0.0 1+ Q-value=+11 MeV
0
5 MeV
10-13
B(GT)=0.63 B(GT)=0.54
−5
−10
GTGR 1+
2nd 0+ states
q=(0.95)2
1st 0+ states
Toshio Suzuki’s 4hω Shell model prediction
Huge difference !
12Beiso(0+) is < 5 % (unfortunate ?)
12Be beam produced via fragmentation process consists of 12Begnd (0+) + 12Beiso(0+) 1H(12Begnd,n)12B + 1H(12Beiso,n)12B
Isomer-tagging: 1H(12Beiso,n)12B reaction at RIBF
SHARAQ spectr
SRC
production target
100 m !
Diamond det. △t<35 ps
△t<35 ps Diamond det.
4424242
42
100.2107.1)104.1()10( −−−− ×=<×=×+=
+
=
mExd
pdp
mdm
ββγ
Feasible !
Diamond det.
Employing high resolution BL and TOF
TOF start
TOF start resolution time TOF :
10 BigRIPS: 4
ββ∆
≈∆ −
pp
Summary
GTGRs measured for 8He ((N-Z)/A =0.5) and 12Be (=0.33) by SHARQ Collaboration
∆E=E(GT)-E(IAS) deduced ∆E=−2.5 MeV(8He)/−1.2MeV (12Be) (∆E> 0 for stable nuclei) Nakayama empirical line: −7.5 MeV(8He)/−2.5 MeV (12Be)
Compared to schematic model and to shell model
κστ∼22/A MeV (κτ∼28/A MeV) • 20/A MeV by SHI of 1993 (HF+TDA) • 23/A MeV for 208Pb by Gaarde
CK(8-16)POT: poor description SFO(6-16) constructed: reasonable description
Puzzle of 8He β-decay 12Be: isomer
Highly interesting to measure GTGR/IAS of
14Be ((N-Z)/A=0.43), 22C ((N-Z)/A=0.46), 24O ((N-Z)/A=0.33) etc.
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