2 June 2014

Spin-isospin Correlationin Light Neutron Rich Nuclei

H. Sakai1, H. Sagawa1,2, M. Kobayashi3, S. Shimoura3 , T. Suzuki4 and K. Yako3
For the SHARAQ Collaboration
1 RIKEN Nishina Center2 University of Aizu
3 CNS, The University of Tokyo
4Nihon University

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 C55, 2909 (1997)
GT strength quenching problem

C. Gaarde
NP A396, 127c(1983)

 Wakasa et al., PR C 55, 2909 (1997)

Gamow-Teller responses in isospin extreme
This century
 Unstable beams  extend the horizon of spin-isospin responses
Today’s subject
 Gamow-Teller Giant Resonance(GTGR) under isospin extreme condition Large (N-Z)/A asymmetry GTGR in ery neutron rich light nuclei
Today’s concern

EGTEIAS

EGT - EIASPeak energy represents thespin-isospin correlations.

Spin-isospin correlations in schematic model GTGR (IAS) induced by ph residual interaction:  

V12 = κ στ σ 1σ 2τ 1τ 2

∆ s(κ ττ 1τ 2 ) Dispersion relation for the collective state(GTGR)
−1p−1

< στ
2j>( Nj>− στ− Z− )0f = − 11Z )(−10− +f ) j> 2(jN+=−ε i ε−i ε− εε iε+i +∆ ∆ε
κ στε−s −στsfJ<1-fJ>n Nakayama et al.,PLB114(1982)217

 C. Garrde, NPA396(1982)127c.

κστ=19/A
κστ=23/A
EGT − EIAS = ∆ s + 2(κ GT − κ F )(N − Z)ACollectivity in (N-Z)/A>0.21:very nuetron rich nuclei
K.Nakayama et al, PLB114(1982)217.
8He

EGT-EIAS (MeV)

12Be(N-Z)/A
0.3-1-2-3-4-5-6-7-8

Data: (N-Z)/A < 0.21

0.4

0.5

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

Collectivity in (N-Z)/A>0.21:very nuetron rich nuclei
K.Nakayama et al, PLB114(1982)217.
8He

EGT-EIAS (MeV)

12Be(N-Z)/A-1-2-3-4-5-6-7-80.3

0.5

0.4

SHI

GTGR in 8He & 12Be

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-shelllarge deformation (2:1)
cluster structure α+α+4nExperiment• (p,n) reaction in inverse kinematics• 8He(p,n) by Kobayashi et al.,
• 12Be(p,n) by Yako et al.,

8He/12Be(p,n) measurements at RIBF

18O

SRC

8He/12Be

200 MeV/u

8He(p,n)TargetF-H912Be(p,n)

Target

F-H10

Kobayashi exp.

Yako exp.

Measurement on 8He(p,n)8Li @ 200 MeV/uWINDS

8He(200 MeV/u) beam 2 Mpps
CH2 and CNeutrons(TOF) by a half of WINDS
Residual nucleus(7Li/8Li)

8He

FH9 target
8Li*“WINDS”

Neutron𝜽𝜽𝐥𝐥𝐥𝐥𝐥𝐥

10 m
STQ

FH10MWDC
Plastic

TOF→ 𝑻𝑻𝒏𝒏

 Under inverse kinematics

Measurement on 12Be(p,n)12B @ 200 MeV/u
Wide-angle
Inverse-kinematics
Neutron
Detectors forSHARAQ

12Be(200 MeV/u) beam 0.5-1 Mpps
Liq. Hydrogen target
Neutrons(TOF) by WINDS
Residual nucleus(SHARAQ)

Neutron detector
TOF method

EnLab
Achromatic transport
12Be• 59 plastic scintillators (BC408)(H7195 + BC408, 60 x 10 x 3 cm3)
• θ = 60-120°, FPL = 180 cm

12B*Liquid hydrogen target• Liq H2, 14 mmt

WINDSθlab

18O beam + Be12BeLH２nSHARAQ
12B, 11B,10B• Acceptances|δ| < 1%|θ| < 36 mr, |Ф| < 68 mr

SHARAQ

Results
 8He(p,n) at 200 MeV/u𝜃𝜃cm = 5° − 8°
0.98 MeV
B(GT)=0.24

GT~8.3 MeV

 12Be(p,n) at 200 MeV/u

GT~𝟏𝟏𝟏𝟏. 𝟔𝟔 MeV

EIAS=10.8 MeV

EIAS=12.8 MeV

EGT - EIAS = −2.5 ± 0.5 MeV

EGT - EIAS = −1.2 ± 0.4 MeV

Comparison to model predictions

 Significantly deviate fromempirical line.
 κστ=22/A : good job
 CK (8-16)POT : poor job New SFO(6-16) : betterκστ=28/A fixedComparison of κστ
Present result
8He and 12BeSHI
(PL B303 (1993)
215)

GaardeNakayama(NP A 396(1983)127c)(PL 114B (1982)
217)

HF+TDA208Pb

90Zr - 208Pb

Aκστ (MeV)

22202319Aκτ (MeV)

2828

28

28

(N-Z)/A > 0.22

< 0.22

Summary GTGRs measured for 8He ((N-Z)/A =0.5) and 12Be (=0.33) bySHARQ 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
 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.