Gamow-Teller Transitions studied by (3He,t) reactions and the comparison with analogous transitions

Transcription

1 Gamow-Teller Transitions studied by (3He,t) reactions and the comparison with analogous transitions Yoshitaka FUJITA (Osaka Univ.) Spin-Isospin excitations probed by Strong, Weak and EM interactions ECT*, Trento Sep. 28 Oct. 02, 2009 GT : Important weak response, simple στ operator Good Probe to Study the Vital Part of the Nuclear Structure Astrophysical Interest β decay : absolute B(GT), limited to low-lying state ( 3 He,t) reaction : relative B(GT), Highly Excited States ** both are important for the GT studies!

2 Properties of GT transitions Caused by the στ operator : a simple operator! 1) i> and f> states should have similar spatial shapes. - there is no space-type operator - 2) σ operator: states with j > and j < configurations are connected. 3) τ operatpr: isospin quantum number T plays an important role (isospin selection rule) GT transitions in each nucleus are UNIQUE!

3 Counts β intensity (relative) Simulation of β-decay spectrum g.s.(ias), , , Cr( 3 He,t) 50 Mn E=140 MeV/nucleon θ=0 o Q EC =8.152 MeV E in 50 Mn (MeV) x g.s.(ias), , , E in 50 Mn (MeV) x 3.392,1 + β-decay: 50 Fe --> 50 Mn *expected spectrum assuming isospin symmetry 3.392,1 + Q EC =8.152 MeV f-factor (normalied)

4 Comparison of (p, n) and ( 3 He,t) 0 o spectra Counts 58 Ni(p, n) 58 Cu E p = 160 MeV 58 Ni( 3 He, t) 58 Cu E = 140 MeV/u GTGR J. Rapaport et al. NPA ( 83) Y. Fujita et al., EPJ A 13 ( 02) 411. H. Fujita et al., PRC 75 ( 07) S Excitation Energy (MeV) p

5 High-resolution Experiment -beam matching techniques- (dispersion matching techniques)

6 RCNP (Osaka) Ring Cyclotron Good quality 3 He beam (140 MeV/nucleon)

7 Grand Raiden Spectrometer Large Angl Spectromet ( 3 He, t) reaction 3 He beam 140 MeV/u

8 E=30 kev RCNP, Osaka Univ. Dispersion Matching Techniques were applied! E=150 kev

9 Counts Comparison of (p, n) and ( 3 He,t) 0 o spectra 58 Ni(p, n) 58 Cu E p = 160 MeV High selectivity for GT excitations. Proportionality: 58 Ni( dσ/dω 3 He, t) 58 Cu B(GT) GTGR E = 140 MeV/u J. Rapaport et al. NPA ( 83) Y. Fujita et al., EPJ A 13 ( 02) 411. H. Fujita et al., PRC 75 ( 07) Excitation Energy (MeV)

10 **( 3 He,t): high resolution and sensitivity!

11 9 Be( 3 He,t) 9 B spectrum (II) Isospin selection rule prohibits proton decay of T=3/2 state! C. Scholl, Koeln

12 Relationship: Decay and Width Heisenberg s Uncertainty Priciple x p h t E h Width Γ = E *if: Decay is Fast, then: Width of a State is Wider! *if t =10-20 sec E ~100 kev (particle decay t =10-15 sec E ~ 1 ev (fast γ decay)

13 Isospin Selection Rule : in p-decay of 9 B + p + 8 Be* 1p-1h 9 B* p n p n T z : -1/2 + 0 = -1/2 T : 1/2 + 0 (low lying) = 1/2 T : 1/2 + 1 (higher Ex) = 1/2 & 3/2 *T=1 state in 8 Be is only above E x =16.6 MeV

14 Shell Structure and Cluster Structure T=3/2 Excited state: SM-like 9 Li 9 C T z =3/2 T z =-3/2 g.s.: Cluster-like neutron: p 3/2 closed proton: p 3/2 closed α α α n α p 9 Be 9 B T z =1/2 T z =-1/2 suggestion by Y. Kanada-En yo

15 9 Be( 3 He,t) 9 B spectrum (III) Information on: Excitation Energy Transition Strength Decay Width 14.7 MeV T=3/2 state is very weak! Strength ratio of g.s. & 14.7 MeV 3/2 - states: 140:1

16 β-decay & Nuclear Reaction β-decay GT tra. rate = 1 t 1/ 2 = f 2 λ K B(GT) B(GT) : reduced GT transition strength Study of Weak Response of Nuclei (matrix element) 2 by means of *Nuclear (CE) Strong reaction Interaction rate (cross-section)! = reaction mechanism using β-decay as a reference x operator x structure =(matrix element) 2 A simple reaction mechanism should be achieved! we have to go to high incoming energy

17 **Connection between β-decay and ( 3 He,t) reaction** by means of Isospin Symmetry

18 T=1/2 Isospin Symmetry slight asymmetry due to the Coulomb force GT&Fermi Koelner Dom in Germany (157m high) Al Si 13 T z = +1/2 T z = -1/2

19 T=1/2 Mirror Nuclei : Structures & Transitions (e,e') M1 (p,n)-type Vστ γ-decay M1 GT γ-d ecay M1 ( 3 He,t) τ+στ β + -decay στ (Z,N+1) Tz=+1/2 Vτ+Vστ GT + Fermi (Z+1,N) Tz=-1/ Al Si 13

20 Symmetry in A=27 System d d q 0 KN J 2 B GT 2J π J π ( 3 He,t) β decay g.s. g.s Good proportionality between both B(GT)s! Al Si 13 T z =1/2 T z =-1/2

21 T=1 Isospin Symmetry GT GT Mg Al Si 12 T z = +1 T z = 0 T z = -1

22 T=1 symmetry : Structures & Transitions T z =+1 T z =0 T z =-1 (in isospin symmetry space*) (p,n)-type V στ β + -decay στ 0+ 0+, IAS V τ τ 0+ V στ 1+ στ T z =+1 T z =0 T z =-1 26 Mg Z=12, N=14 26 Al Z=13, N=13 26 Si Z=14, N=12

23 26 Mg(p, n) 26 Al & 26 Mg( 3 He,t) 26 Al spectra R. Madey et al., PRC 35 ( 87) 2001 IAS, 0 + Y. Fujita et al., PRC 67 ( 03) Prominent states are GT states and the IAS!

24 B(GT) values from Symmetry Transitions (A=26) ( 3 He,t) from ( 3 He,t) β-decay from β-decay B(GT) B(GT) 0.106(4) (4) (5) 0.112(4) 0.527(15) (4) 0.537(14) 1.081(29) (22) IAS Mg Al Si T z =+1 T z =0 T z =-1 Y. Fujita et al., PRC 67 ( 03)

25 34 S( 3 He,t) spectrum g.s., , , , , 1 +

26 B(GT) values from Symmetry Transitions (A=34) from ( 3 He,t) B(GT) normalized 1.369(99) 0.304(23) from β-decay B(GT) (99) (29) 1d 5/2 1d 3/2 2s 1/2 2s 1/ (8) 0.023(2) (3) (2) 0+ IAS S 34 Cl 34 Ar T z =+1 T z =0 T z =-1 Y. Fujita et al., PRC 75 ( 07)

27 pd 3/2 d 34 S( 3/2 3 He,t) : low-lying GT states Z=16 N=18

28 (p, n ) spectra for Fe and Ni Isotopes

29 54 Fe(p,n) & 54 Fe( 3 He,t) B(GT) 0.74(5) 54 Fe(p, n) 54 Co Ep = 135 MeV B.D. Anderson et al., PRC 41 ( 90) 1474 B(GT)=0.50(6): (preliminary)

30 54 Fe(p,n) & 54 Fe( 3 He,t)+width Counts g.s. (IAS) at N=28: Good agreement! 0.973, Fe( 3 He,t) 54 Co with 250 kev width E in 54 Co (MeV) x

31 56 Fe(p,n) 56 Co & 56 Fe( 3 He,t) 56 Co analysis: H. Fujita Fe(p,n) 56 Co J. Rapaport et al.

32 56 Fe target: ( 3 He,t ) vs. (p, n) ( 3 He,t) with 600 kev width 1.7 MeV GT state enhanced! 140 MeV/nucleon 12 N g.s. at N=30, exceptional enhancement of lowest GT state! (p, n) Ep=160 MeV

33 56 Fe( 3 He,t) : low-lying GT states 2p 2p 1f 1f Z=26 N=30

34 Interaction Dependence Calculation by Honma

35 **GT transitions in each nucleus are UNIQUE! (I) T=1/2 nuclei in p-shell and sd-shell region

36 (p,n) and ( 3 He,t) Spectra on 11 B 11 B(p, n) 11 C E p =200 MeV T.N. Taddeucci et al., PRC 42 (1990) 935 Y. Fujita et al., PRC 70 (2004) (R)

37 GT transitions to J π =3/2 - states: J π allowed Why 3/2-3 so weak! Y. Fujita et al., PRC 70 (2004) (R)

38 Comparison: 11 B( 3 He,t) 11 C & Shell Models non-core SMcal: by Navratil & Ormand Phys. Rev. C 68 ( 03) quenching is needed

39 GT transitions to J π =3/2 - states: J π allowed Why 3/2-3 so weak! Y. Fujita et al., PRC 70 (2004) (R)

40 2α+t 7 Li+α Nature of 3/2-3 state? /2-5/2-5/2-3/2-5/2-3/2-3/2-5/2-1/2-3/ /2+3 7/2+2 (1/2+) 3/2+1 5/2+2 7/2+1 3/2+1 5/2+1 1/2+1 shell model-like strong GT-transition 11 B( 11 C) by Kanata-En yo (few-body WS Dec. 04) 3/2-3 Li+α molecule? 2α+ 3 He 3-body? weak GT-transition 7 Li+α 11 B ( 11 C) 2α+ 3 He -2 see also T. Kawabata et al., PL B646 ( 07) 6 Similarity with 12 C p 3/2 shellmodel-like

41 **GT transitions in each nucleus are UNIQUE! (II) T=1 nuclei in pf-shell region

42 Crucial Weak Processes during the Core Collapse στ: important (A,Z)=nuclei in the Cr, Mn, Fe, Co, Ni region pf -shell Nuclei! Langanke & Martinez-Pinedo Rev.Mod.Phys.75( 04)819 Balantekin & Fuller J.Phys.G 29( 03)2513

43 GT states in A=42-58 T z =0 nuclei

44 SM Configurations of GT transitions πp-νp int. (attractive) Although the IV-type στ int. is expected to be repulsive! πp-νh int. (repulsive) Cooperative with the repulsive nature of IV-type στ int.!

45 ***Exotic GT transitions from Unstable Nuclei - Combined ( 3 He,t) and β-decay Study -

46 **Derivation of absolute B(GT) values β-decay: T 1/2 and absolute B(GT) values but only for the low-lying states *( 3 He,t) reaction: highly-excited states can be accessed but only the relative B(GT) values Let s combine these data!

47 T=1 Isospin Symmetry in pf-shell Nuclei Mirror nuclei 54 Ni N=Z 50 Fe 54 Fe Ni Fe 28 T z =-1 46 Cr ß+ T z =0 ( 3 He,t) T z =1 46 Ti 50 Cr Leuven Valencia Surrey Osaka GSI by B. Rubio

48 Nuclei & Coin = Coin back front = Nuclei Cr Fe Mn 25 T z = +1 T z = 0 T z = -1 isospin T=1 triplet

49 Isospin Symmetry Transitions: 50 Cr( 3 He,t) 50 Mn β-decay 50 Fe 0 + ( 3 He,t) Vστ 50 Cr T z = Mn T z = 0 β + decay τ στ Q EC =8.152(61) MeV B(GT)=0.60 g.s. IAS 0 + T 1/2 =0.155(11) s g.s. Vτ Q EC 50 Fe T z = -1 (Z,N)= (24,26) (25,25) (26,24)

50 **Reconstruction of β decay from ( 3 He,t) ---assuming isospin symmetry ---

51 Counts β intensity (relative) Simulation of β-decay spectrum g.s.(ias), , , Cr( 3 He,t) 50 Mn E=140 MeV/nucleon θ=0 o Q EC =8.152 MeV E in 50 Mn (MeV) x g.s.(ias), , , ,1 + β-decay: 50 Fe --> 50 Mn *expected spectrum assuming isospin symmetry Y. Fujita et al. PRL 95 (2005) E in 50 Mn (MeV) x 3.392,1 + Q EC =8.152 MeV relative intensities of β-decay feeding are deduced! f-factor (normalied)

52 Absolute B(GT) values -via reconstruction of β-decay spectrum- Tra.Strengh 1/t i t i =partial half-life T 1 1/ 2 = t i= GT t Fermi i β-decay B(F)=N-Z experiment T 1/2 =0.155(11) s Relative feeding intensity from ( 3 He,t) Absolute intensity: B(GT) Y. Fujita et al. PRL 95 (2005) GT tra. to the 0.65 MeV state New value B(GT)=0.50(13) *20% smaller than deduced in the β-decay: 0.60(16)

53 T=1 Isospin Symmetry in pf-shell Nuclei Mirror nuclei 54 Ni N=Z 50 Fe 54 Fe Ni Fe 28 T z =-1 46 Cr ß+ T z =0 ( 3 He,t) T z =1 46 Ti by B. Rubio 50 Cr Leuven Valencia Surrey Osaka GSI CNS

54 Fe( 3 He,t) 54 Co E = 140 MeV/u, θ = 0 ο E (MeV) x Counts IAS 54 Ni β-decay measurement at Louvain la Neuve (ISOL facility) g.s. IAS Ni β + decay Sp =4.35 Q =8.800 T 1/2 =0.115(4) s

55 Absolute B(GT) values in 54 Ni β-decay -via reconstruction of β-decay spectrum- Tra.Strengh 1/t i t i =partial half-life T 1 1/ 2 = t i= GT t Fermi i β-decay exp. at LLN (Belgium) T 1/2 =0.115(4) s *old β-decay value : 0.68(16) (assuming no higher Ex states) * 54 Fe(p,n) 54 Co value : 0.74(5) B(F)=N-Z B(GT) : 1 st 1 + state at MeV Relative feeding intensity from ( 3 He,t) Absolute intensity: B(GT) New value B(GT)=0.46(8)

56 Fe( 3 He,t) 54 Co E = 140 MeV/u, θ = 0 ο E (MeV) x Counts IAS 54 Ni β-decay measurement at GSI (FRS facility) RISING (stopped beam campaign) 0.937, 1 + g.s. IAS Ni β + decay Sp =4.35 Q =8.800 Energy Resolution : 21 kev

57 GSI: RISING set up - active stopper campaign - FRS Active Beam Stopper Campaign July-August, layors of DSSD active stopper

58 Ph.D. F. Molina (Valencia) ( 3 He,t), RCNP Osaka, T. Adachi et al. Newly observed! Corresponding Transitions were observed in a wide E x range! β decay, GSI, Rising 2007

59 Comparison B(GT) ( 3 He,t) B(GT) β-decay RCNP, Osaka *B(GT) values using T 1/2 =115 ms (Louvain) RISING, GSI

60 T = 2 Isospin Symmetry in pf-shell Nuclei Mirror nuclei 56 Zn 56 Cu N=Z 52 Ni 56 Ni Ni Cr Fe β+ T z =-2 48 Mn T z =-1 T z =0 52 Co 52 Fe 52 Mn 48 Cr 52 Cr 48 V T z =1 ( 3 He,t) T z =2 48 Ti 56 Co 56 Fe by Y. Fujita, B. Rubio

61 Comparison: (p, n) and ( 3 He,t) g.s. IAS 52 Cr(p, n) 52 Mn Ep =120 MeV D. Wang et al., NP A480 ( 88) 285

62 β-decay simulation f-factor f-factor x R 2 /λ 2 for IAS (correction of coupling constant)

63 p-decay of 52 Co p-decay spectrum C. Dossat et al., NPA 792 ( 07) 18 (GANIL data) x R 2 /λ 2 ~4.7 for IAS (correction of coupling constant)

64 p-decay of 52 Co p-decay spectrum C. Dossat et al., NPA 792 ( 07) 18 (GANIL data) (MeV 2 =IAS+GT state S p =

65 Summary GT (στ) operator : a simple operator! * GT transitions: sensitive to the structure of i> and f> * Isospin quantum number T plays an important role High resolution of the ( 3 He,t) reaction * Width & fine structures of GT transitions * Precise comparison with mirror β-decay results GT transitions in each nucleus are UNIQUE! Vital part of the Nuclear Structure is revealed! We got a key to open a jewel box of Nuclear Physics!

66 GT-study Collaborations Bordeaux (France) : β decay GANIL (France) : β decay Gent (Belgium) : ( 3 He, t), (d, 2 He), (γ, γ ), theory GSI, Darmstadt (Germany) : β decay, theory ISOLDE, CERN (Switzerland) : β decay ithemba LABS. (South Africa) : (p, p ), ( 3 He, t) Jyvaskyla (Finland) : β decay Koeln (Germany) : γ decay, ( 3 He, t), theory KVI, Groningen (The Netherlands) : (d, 2 He) Leuven (Belgium) : β decay LTH, Lund (Sweden) : theory Osaka University (Japan) : (p, p ), ( 3 He, t), theory Surrey (GB) : β decay TU Darmstadt (Germany) : (e, e ), ( 3 He, t) Valencia (Spain) : β decay Michigan State University (USA) : theory, (t, 3 He) Muenster (Germany) : (d, 2 He), ( 3 He,t) Univ. Tokyo and CNS (Japan) : theory, β decay