Spin-isospin correlation in 8 He and 12 Be(p,n)

Transcription

1 Mini-workshop 18 November 2014 Spin-isospin correlation in 8 He and Be(p,n) H. Sakai 1, H. Sagawa 1,2, M. Kobayashi 3, S. Shimoura 3, T. Suzuki 4 and K. Yako 3 For the SHARAQ Collaboration 1 RIKEN Nishina Center 2 University of Aizu 3 CNS, The University of Tokyo 4 Nihon University

2 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? % of 3(N-Z) found Charge-exchange (p,n)/(n,p) reactions on stable target nuclei C. Garrde, NPA396(1982)7c. Wakasa et al., PR C55, 2909 (1997) GT strength quenching problem C. Gaarde NP A396, 7c(1983) Wakasa et al., PR C 55, 2909 (1997)

3 Gamow-Teller responses in isospin extreme This century Unstable beams extend the horizon of spin-isospin responses Today s subject GTGR under isospin extreme condition Large (N-Z)/A asymmetry GTGR in very neutron rich light nuclei Today s concern E GT E IAS E GT - E IAS Peak energy represents the spin-isospin correlations.

4 Spin-isospin correlations in schematic model GTGR (IAS) induced by ph residual interaction: V Dispersion relation for the collective state(gtgr) j> ( N j> Z στ )( 1 0 > < στ 0 + f ) j 2( j N Z) f 1 + = ε i ε ε ε ε i + ε + s ε ε C. Garrde, NPA396(1982)7c. i i ( κ τ ) 2 = κστσ 1σ 2τ 1τ 2 τ 1τ s κ στ στ s f 1-f p n Nakayama et al.,plb114(1982)217 J< J> κ στ =19/A κ στ =23/A E GT E IAS = s + 2( κ GT F ( N Z) κ ) A

5 GTGR in 8 He & Be 8 He & Be Target nuclei: 8 He and Be Large neutron to proton ratio (N-Z)/A = 0.33( Be), 0.5( 8 He) 8 He : neutron skin (+halo) α+4n Be: neutron halo admixture of 2s-orbit into 1p-shell large deformation (2:1) cluster structure α+α+4n Experiment (p,n) reaction in inverse kinematics 8 He(p,n) by Kobayashi et al., Be(p,n) by Yako et al.,

6 Collectivity in (N-Z)/A>0.21:very nuetron rich nuclei K.Nakayama et al, PLB114(1982)217. Be 8 He E GT -E IAS (MeV) Data: (N-Z)/A < (N-Z)/A

7 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 E GT E IAS <0 8 He : E GT E IAS = 4.3 MeV (f=0.44) Stable targets κ στ =20/A

8 8 He/ Be(p,n) measurements at RIBF 18 O SRC 8 He/Be 200 MeV/u 8 He(p,n) Kobayashi exp. Be(p,n) Yako exp. Target Target F-H9 F-H10

9 Measurement on 8 He(p,n) MeV/u 8 He(200 MeV/u) beam 2 Mpps CH 2 and C Neutrons(TOF) by a half of WINDS Residual nucleus( 7 Li/ 8 Li) WINDS 8 He WINDS Under inverse kinematics FH9 target 8 Li * Neutron θθ llllll 10 m STQ TOF TT nn FH10 MWDC Plastic

10 Measurement on Be(p,n) 200 MeV/u Be(200 MeV/u) beam Mpps Liq. Hydrogen target Neutrons(TOF) by WINDS Residual nucleus(sharaq) Neutron detector TOF method Wide-angle Inverse-kinematics Neutron Detectors for SHARAQ 18 O beam + Be Be Achromatic transport Lab Be En n θ lab B* WINDS 59 plastic scintillators (BC408) (H BC408, 60 x 10 x 3 cm 3 ) θ = 60-0, FPL = 180 cm Liquid hydrogen target SHARAQ B, 11 B, 10 B LH 2 Liq H 2, 14 mmt Acceptances δ < 1% θ < 36 mr, Ф < 68 mr SHARAQ

11 Results 8 He(p,n) at 200 MeV/u Be(p,n) at 200 MeV/u θθ cm = MeV B(GT)=0.24 GT ~8.3 MeV E IAS =10.8 MeV GT ~ MeV E IAS =.8 MeV E GT - E IAS = 2.5 ± 0.5 MeV (B(GT)=8±4) E GT - E IAS = 1.2 ± 0.4 MeV (B(GT)=7±2)

12 Comparison to model predictions Significantly deviate from empirical line. κ στ =22/A : good job CK (8-16)POT : poor job New SFO(6-16) : better SHI: poor job κ στ =28/A fixed

13 Comparison of κ στ Present result 8 He and Be SHI (PL B303 (1993) 215) HF+TDA Gaarde (NP A 396 (1983)7c) 208 Pb Nakayama (PL 114B (1982) 217) 90 Zr Pb Aκστ (MeV) Aκτ (MeV) (N-Z)/A > 0.22 < 0.22

14 Comparison to 8 He β-decay β-decay n t-decay α+t+n 4.5 ISOLDE Borge et al., NP A560 (1993) 664 t-channel Ex(GT)= 9 MeV BR=(0.8±0.5)% log ft=2.87 B(GT)=5.18 R matrix fit F.C. Barker, NP A609 (1996) 38 8 He β-decay (cluster model) tetra-neutron decay to t+n Ex(GT)= 9.7 MeV log ft=2.91 B(GT)=4.75 Compilation by Tilley, NPA745(2004)153 By Marek Pfutzner 7 Li channel Ex(GTGR) β-decay 9(9.7) MeV (p,n) 8.3 MeV Two different states?

15 8 He β-decay in OTPC (Warsaw group) OTPC Marek Pfutner, S. Mianowski, Zenon Janas (p,n) Kobayashi β-decay Mianowski Very good agreement!

16 0+ isomer in Be at MeV Shimoura et al., PL B645(2007) T 1/2 =229ns 4hω Shell model by Toshio Suzuki + 0 2nd + 0 1st 4 ( 0s) (0 p 60 % 25 % ) 8 N=8 closed shell structure sd shell contri. 2hω config. Be 0 + 0hω(%) 2hω(%) 4hω(%) 0+ (g.s.) (2 nd ) AMD calc. by Kanada-En yo PRC 85, (20) π+σ π+π

17 1 H( Be,n) at 200 MeV/u in inverse kinematics Be beam produced via fragmentation process consists of Be gnd (0+) + Be iso (0+) 1 H( Be gnd,n) B + 1 H( Be iso,n) B Be iso (0+) is < 5 % (unfortunate?) Toshio Suzuki s 4hω Shell model prediction MeV 5 1 st 0+ states 2 nd 0+ states Be 0+ GTGR 1+ q=(0.95) Q-value=+11 MeV B(GT)=0.63 B(GT)= B Huge difference!

18 Isomer-tagging: 1 H( Be iso,n) B reaction at RIBF SRC Employing high resolution BL and TOF production target TOF start dm m = dp p 2 4 dβ + γ β 100 m! 2 = (10 4 ) 2 + ( ) 2 = Feasible! 4 < Ex m = Diamond det. Diamond det. t<35 ps p : BigRIPS 10 p 4 β : TOF time resolution β Diamond det. t<35 ps TOF start SHARAQ spectr

19 Summary GTGRs measured for 8 He ((N-Z)/A =0.5) and Be (=0.33) by SHARQ Collaboration E=E(GT)-E(IAS) deduced E= 2.5 MeV( 8 He)/ 1.2MeV ( Be) ( E> 0 for stable nuclei) Nakayama empirical line: 7.5 MeV( 8 He)/ 2.5 MeV ( Be) Compared to schematic model and to shell model κ στ 22/A MeV (κ τ 28/A MeV) 20/A MeV by SHI of 1993 (HF+TDA) 23/A MeV for 208 Pb by Gaarde CK(8-16)POT: poor description SFO(6-16) constructed: reasonable description Puzzle of 8 He β-decay Be: isomer Highly interesting to measure GTGR/IAS of 14 Be ((N-Z)/A=0.43), 22 C ((N-Z)/A=0.46), 24 O ((N-Z)/A=0.33) etc.