High-resolution Study of Gamow-Teller Transitions

Transcription

1 High-resolution Study of Gamow-Teller Transitions Yoshitaka Fujita, Osaka 04.Aug Nucleus : 3 active interactions out of 4 Strong, Weak, EM Comparison of Analogous Transitions High resolution ( 3 He,t) experiment at 0 o E = kev β-decay experiment, γ-decay, (e, e ) measurements detailed GT responses up to high excitation energies!

2 Direct Reactions with Light Projectiles Coulomb Excitation Elastic Scattering Inelastic Scattering 3 He Target Pick-up Stripping Projectile by Berta Rubio Similarity with β decay! Charge-exchange t

3 Resolutions Now and Then Y. Fujita et al., EPJ A 13 ( 02) 411. H. Fujita et al., Dr. Th. & PRC

4 37 Cl( 3 He,t) 37 Ar spectrum Y.Shimbara et al. 37 Cl( 3 He,t) 37 Ar 140 MeV/u θ=0 o E=30 kev

5 ( 3 He,t) & (p,n) on 37 Cl E=30 kev Original ( 3 He,t) ( 3 He,t) convoluted with (p,n) resolution Original (p,n) IAS E=250 kev Convolution by Y. Shimbara

6 Key Words High Resolution In Charge Exchange Reactions --at Intermediate Incident Energies-- ( 3 He,t) reaction : one order better resolution than in a (p,n) reaction Active Operators Similarity of Active Operators Gamow-Teller operator in β decay (weak interaction) Spin-isospin interaction in reactions (strong interaction) EM-M1 interaction in γ decay (electro-magnetic int.) Isospin Symmetry Analog States, Analogous Transitions

7 Vibration Modes in Nuclei (Schematic) IS-M1 IV-M1 GT

8 Vibration Modes in Nuclei (Operators) An operator is a hammer to exite nuclei!

9 Supernova SN1987A

10 Crucial Weak Processes during the Collapse K.L &G.M-P Rev.Mod.Phys.75( 04)819 (A,Z)=nuclei of Fe Ni region mainly by στ can be studied by ( 3 He,t)

11 B(GT) derivation β decay :fundamental, but Ex range :limited "Q-window limitation" (p, n) reaction at intermediate energies (E = MeV) "proportionality" : B(GT) and σ(0 o ) σ(0 o ) = KNστ Jστ(0 o ) 2 B(GT) Breakthrough against "Q-window limitation" but resolution : rather poor ( E = kev) ( 3 He, t) reaction at intermediate energies (E = MeV/u) "high resolution" ( E < 50 kev) magnetic spectromerter, matching techniques "proportionality" : good (B(GT) > 0.03) Breakthrough against "Energy resolution limitation" Reliable B(GT) values for individual transitions

12 Nucleon-Nucleon Int. : E in dependence at q =0 Strength central-type interactions Simple one-step reaction mechanism at intermediate energies! V 0 V στ V τ V σ Energy/nucleon

13 N.-N. Int. : στ & Tensor-τ q-dependence στ largest at q=0! larger than others! Tτ Love & Franey PRC 24 ( 81) 1073

14 Analogous Structures and Transitions in T=1/2 System Real Energy Space Isospin Symmetry Space (p,n)-type (p,n)-type γ-decay β+-decay g.s. γ-decay γ-decay γ-decay g.s. β+-decay Q EC g.s. Tz=+1/2 (Z,N+1) (stable) Tz=-1/2 (Z+1,N) g.s. Tz=+1/2 (Z,N+1) (stable) 7 15 N 8 Tz=-1/2 (Z+1,N) 8 15 O 7 T z =(N-Z)/ N O 7

15 T=1/2, 3/2 Isospin Symmetry for A=15 Nuclei 6 15 C 9 T Z =3/ F 6 T Z =-3/ N O 7

16 T=1/2 Mirror Nuclei : Structures & Transitions (e,e') M1 (Z,N+1) Tz=+1/2 (p,n)-type Vστ γ-decay M1 τ+στ Vτ+Vστ β + -decay στ γ-d ecay M1 (Z+1,N) Tz=-1/ Mg Al 12 Analogous Transitions in β decay in CE reaction in γ-decay in IE reaction

17 Real Energy Space 1+ T=1 system Coulomb Energy: important (p,n)-type Si A=26 system 1+ T z = , IAS β + -decay 26 Al T z = Mg T z =+1 (stable)

18 T=1 symmetry : Structures & Transitions T z =+1 T z =0 T z =-1 (in isospin symmetry space*) (p,n)-type Vστ β + -decay στ 0+ 0+, IAS Vτ τ 0+ Vστ 1+ στ T z =+1 T z =0 T z =-1 26 Mg 26 Al 26 Si

19 26 Mg(p, n) 26 Al & 26 Mg( 3 He,t) 26 Al spectra R. Madey et al., PRC 35 ( 87) 2001 Y. Fujita et al., PRC 67 ( 03)

20 B(GT) values from Symmetry Transitions (A=26) from ( 3 He,t) from β-decay B(GT) 0.106(4) B(GT) 0.117(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

21 Rome is not made in one day!

22 Grand Raiden Spectrometer Large Angle Spectrometer

23 RCNP Ring Cyclotron

24 Beam line WS-course T. Wakasa et al., NIM A482 ( 02) 79. Grand-Raiden Spectrometer High-dispersive WS-course RCNP Ring Cyclotron

25 Matching Techniques a) b) c) Focal plane Magnetic Spectrometer Target - p 0 + p - p 0 + p Achromatic beam transportation E 200 kev for 140MeV/u 3 He beam Lateral dispersion matching E 35 kev Horiz. angle resolution θ sc > 15mrad Angular dispersion matching θ sc 5mrad

26 Contour Map within the Acceptance Concentric L=0 angular distribution around 0 o

27 Higher-E x region in 26 Al : T=1 & T=2 states T =0 T =1 T =2 With of a state: observed! E t ~ h

28 Importance of Isospin : in p-decay of 26 Al 25 Mg + proton 26 Al decay +Proton p n p Tz : 1/2 + (-1/2) = 0 n T : 1/2 + 1/2 = 0 or 1 3/2 + 1/2 = 1 or 2 #Sp (p-sep. energy) in 26Al : 6.31 MeV #T=3/2 state in 25Mg : Ex > 7.79 MeV effective Sp in 26Al for T = 0, 1 states : Ex = 6.31 MeV for T = 2 states : Ex = 14.1 MeV

29 9 Be( 3 He,t) 9 B spectrum (I)

30 9 Be( 3 He,t) 9 B spectrum (II) x50 Isospin selection rule allows no particle decay of T > state

31 T=3/2 system: structures & transitions T=3/2 (p,n)-type g.s. (stable) IAS IAS g.s. β+-decay T=3/2 β+-decay Tz=+3/2 (Z,N+3) g.s. g.s. T=1/2 Tz=+1/2 Tz=-1/2 Tz=-3/2 (Z+1,N+2) (Z+2,N+1) (Z+3,N) K Ca Sc Ti 19

32 N Z Nuclear Chart N=Z line

33 Comparison of two β-decay results Nucl. Phys. A621 (1997) 689 Phys. Rev. C 58 (1998) 2677

34 Comparison with 41 K( 3 He,t) 41 Ca (I)

35 Comparison with 41 K( 3 He,t) 41 Ca (II)

36 Comparison: 41 K( 3 He,t) 41 Ca & Shell Model B.A. Brown

37 Reversed Strength in T z =+-1/2 Off diagonal- Matrix element~7 kev

38 (p, n) spectra for A>90 Nuclei

39 Discrete States and GT GR in 90Nb (II)

40 Fragmented low-lying states in 90Nb Sp=5.08 MeV

41 Strengths: Exp. & Perturbation Th.

42 High resolution ( 3 He,t) spectrum H. Fujita PhD thesis

43 Isospin symmetry structure & στ operator A=58 1 1/2 1/2 1/6 3/6 2/6 58 Co 58 Ni 58 Cu

44 Comparison: 58 Ni( 3 He,t) 58 Cu & 58 Ni(p,p ) H. Fujita PhD thesis

45 High resolution 58 Ni( 3 He,t) 58 Cu spectrum T=2

46 A=58, T=1 symmetry : Structures & Transitions T z =+1 T z =0 T z =-1 (in isospin symmetry space*) (p,n)-type Vστ β + -decay στ known from β decay! 0+ 0+, IAS Vτ τ 0+ Vστ 1+ στ T z =+1 T z =0 T z =-1 58 Ni 58 Cu 58 Zn

47 Supernova Cycle

48 (p, n) spectra for Fe and Ni Isotopes Rapaport & Sugarbaker Rev. Mod. Phys. ( 94)

49 High resolution 54 Fe( 3 He,t) spectrum T. Adachi et al. Target nuclei under study : T 0 =1 46 Ti, 50 Cr, 54 Fe, 58 Ni T 0 =2 48 Ti, 52 Cr, 56 Fe, 60 Ni T 0 =3 50 Ti, 62 Ni

50 GT & Fermi : unit cross sections in (p,n) Taddeucci et al., N.P. A469 (1987) 125 survey at E p =160 MeV R 2 =unit σ GT /unit σ F smooth function of A

51 define Unit σ and R 2 σ GT (0 o ) = KN στ J στ (0 o ) 2 B(GT) σ F (0 o ) = KN τ J τ (0 o ) 2 B(F) R 2 = unit σ GT (0 o )/ unit σ F (0 o ), where unit σ GT (0 o ) = σ GT (0 o )/B(GT) trick unit σ F (0 o ) = σ F (0 o )/B(F) = N-Z Fermi strength concentrates in the IAS B(F) = N - Z Systematics of R 2 value?

52 Connection between Charge Exchange & β decay & 1 + relationship in A=58 Nuclei (in real energy space) (p,n)-type (stable) 58 Ni Tz= , IAS 58 Cu β + -decay T z =0 Q EC = * 0 + & 1 + relationship of g.s. 30 Si 42 Ca 68 Zn 78 Se 118 Sn 136 Ba 178 Hf 30 P 42 Sc 68 Ga 78 Br 118 Sb 136 La 178 Ta * T z =1/2 nucleus : 7 Li 7 Li 7 Be 1 + g.s.

53 R 2 (= unit σ GT /unit σ F ) Preliminary

54 Perspective Accelerator : underway for improvement smaller beam emitance, better beam energy resolution As a Result: smaller beam size samller backbround good chance for (p, p ) at 0 o M1 and E1 response better energy resolution even better spectrum resolution smaller beam spot size angular distribution measurement

55 High-Resolution Collaborations TU Darmstadt (Germany) : (e, e ), ( 3 He, t), (p, p ) Gent (Belgium) : ( 3 He, t), (d, 2 He), (γ, γ ) GSI, Darmstadt (Germany) : inverse kinematics 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) KVI, Groningen (The Netherlands) : (d, 2 He) LTH, Lund (Sweden) Valencia (Spain) : β decay Michigan State University (USA) : (t, 3 He) Muenster (Germany) : (d, 2 He) Rossendorf (Germany) : (γ, γ )

56 Summary Words High Resolution In Charge Exchange and Inelastic Reactions --at Intermediate Incident Energies-- ( 3 He,t) reaction : one order better resolution than in a (p,n) reaction (p, p ) reaction : spectrum as low as E x =5 MeV Active Operators, Isospin Symmetry Similarity of Active Operators for Analog Transitions Gamow-Teller operator in β decay (weak interaction) Spin-isospin interaction in reactions (strong interaction) Spin-Isospin Responses In Various Nuclei with High Resolution