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.