Studies of Gamow-Teller transitions using Weak and Strong Interactions

Transcription

1 Studies of Gamow-Teller transitions using Weak and Strong Interactions High-resolution Spectroscopy & Tensor Nakanoshima, Osaka Nov. 16 Nov. 19, 2015 Yoshitaka FUJITA RCNP, Osaka Univ.

2 Neptune driving Waves Neptune = weak interaction decay Powerful Waves = strong interaction) Charge-Exchange Reaction

3 Gamow-Teller transitions Mediated by operator: both S &W int. has this Op. S = -1, 0, +1 and T = -1, 0, +1 ( L = 0, no change in radial w.f. ) no change in spatial w.f. Accordingly, transitions among j > and j < configurations j > j >, j < j <, j > j < example f 7/2 f 7/2, f 5/2 f 5/2, f 7/2 f 5/2 Note that Spin and Isospin are unique quantum numbers in atomic nuclei! GT transitions are sensitive to Nuclear Structure! GT transitions in each nucleus are UNIQUE!

4 **Basic common understanding of -decay and Charge-Exchange reaction decays : Absolute B(GT) values, but usually the study is limited to low-lying states (p,n), ( 3 He,t) reaction at 0 o : Relative B(GT) values, but Highly Excited States ** Both are important for the study of GT transitions!

5 -decay & Nuclear Reaction 1 2 f B(GT) t1/ 2 K B(GT) : reduced GT transition strength (matrix element) 2 = <f i> 2 -decay GT tra. rate = *Nuclear (CE) reaction rate (cross-section) = reaction mechanism x operator x structure =(matrix element) 2 *At intermediate energies (100 < E in < 500 MeV) d /d (q=0) : proportional to B(GT)

6 Counts β intensity (relative) Simulation of -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), , , Y.F, B.R, W.G, PPNP, 66 (2011) 549 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)

7 Comparison of (p, n) and ( 3 He,t) 0 o spectra Counts GT IAS 58 Ni(p, n) 58 Cu E p = 160 MeV 58 Ni( 3 He, t) 58 Cu E = 140 MeV/u GTR 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)

8 ( 3 He,t) CE RCNP (Osaka) θlab = 0 (3He,t) CE reaction Stable Target 3He WS course (beam line) Commissioning: 2000 T. Wakasa, K. Hatanaka, Y. Fujita, G.P.A. Berg, H. Fujimura, H. Fujita, M. Itoh, J. Kamiya, T. Kawabata et al., N.I.M. A 482 (2002) He triton

9 Matching Techniques a) b) c) Y. Fujita et al., N.I.M. B 126 (1997) 274. H. Fujita et al., N.I.M. A 484 (2002) 17. Focal plane Magnetic Spectrometer Target -Δp 0 +Δp -Δp 0 +Δp Achromatic beam transportation E ~200 kev for 140MeV/u 3 He beam Lateral dispersion matching E ~ 35 kev Horiz. angle resolution sc > 15mrad Angular dispersion matching sc ~ 5mrad

10 E=30 kev RCNP, Osaka Univ. Dispersion Matching Techniques were applied! Y. Fujita et al, NIM B 126 (1997) 274. H. Fujita et al, NiM A 484 (2002) 17. E=150 kev

11 Connection: Charge Exchange & decay 0 + & 1 + relationship in A=58 Nuclei (in real energy space) (p,n)-type (stable) 58 Ni T z = , IAS 58 Cu -decay Tz=0 Q EC =8.56 ** 0 + & 1 + relationship of g.s log ft 58 Ni 62 Ni 68 Zn 78 Se 104 Ru 118 Sn 120 Sn 136 Ba 140 Ce 178 Hf Cu 62 Ni 68 Ga 78 Br 104 Rh 118 Sb 120 Sb 136 La 140 Pr 178 Ta

12 ***Isospin Symmetry an important idea to see the connection of decays and excitations caused by Strong, EM and Weak interactions! There are many cases that the operators are the same in transitions caused by strong, EM and weak int.

13 T=1/2 Isospin Symmetry Koelner Dom Koeln, Germany (157m high)

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

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

16 Analogous relationship: A=9, 13 system 3/2-9 Li 9 C log ft = B log ft =4.0 3/ g.s. 9 Be 9 B 13 C 13 N log ft = O log ft =4.1 T =1/2 T =3/2 log ft =3.7 All of them are T z =+3/2 T z = +1/2 T z = -1/2 T z = analogous -3/2! *Small isospin asymmetry can be seen for T z =+3/2 +1/2 and T z =-1/2-3/2 GT transitions.

17 T=1 Isospin Symmetry Byodoin-temple, Uji, Kyoto

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

19 Tz= Symmetry -direction (p,n)-type + direction (n,p)-type [e-capture]

20 Super-Byodoin 平等院 T=2 Isospin Symmetry GT CE-reaction GT + -decay 52 Cr 52 Mn 52 Fe 52 Co 52 Ni

21 Isospin Structure of T=2 system Talk by S. Orrigo: 48 Fe, 52 Ni, 56 Zn decay

22 **GT transitions in each nucleus are UNIQUE! - pf-shell nuclei -

23 Z rp -process Path (T=1 system) 54 Ni 58 Zn 50 Fe 58 Ni 42 Ti 46 Cr N=Z line 50 Co 54 Fe 46 Ti 42 Ca N

24 Z rp -process path nuclei (T = 1 symmetry) 58 Ni N=Z line 54 Fe 50 Cr 46 Ti Talk: B. Rubio 42 Ca N

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

26 GSI RISING set up Active Beam Stopper Campaign July-August, 2007

27 ( 3 He,t), RCNP Osaka, T. Adachi et al. Talk: B. Rubio Newly observed! Corresponding Transitions were observed in a wide E x range! decay, GSI, Rising 2007 F. Molina et al., PRC 91, ( 15)

28 42 Ca( 3 He,t) 42 Sc in 2 scales B(F)=2 B(GT) = 2.2 (from mirror decay) 80% of the total B(GT) strength is concentrated in the excitation of the MeV state.

29 GT states in A=42-54 T z =0 nuclei Y. Fujita et al. PRL 2014 PRC 2015 B(F)=N-Z Peak heights are proportional to B(GT) values T. Adachi et al. PRC 2006 Y. Fujita et al. PRL 2005 T. Adachi et al. PRC 2012

30 SM Configurations of GT transitions particle-hole configuration + IV-type int. = REPULSIVE

31 Role of Residual Int. (repulsive) Single particle-hole strength distribution Graphical solution of the RPA dispersive eigen-equation positive = repulsive strength p-h configuration + IV excitation = repulsive Collective excitation formed by the repulsive residual interaction strength 1p-1h strength collective strength (GR) Ex Ex Ex

32 Role of Residual Int. (repulsive) Collective excitation formed by the repulsive residual interaction strength 1p-1h strength Ex Ex strength collective strength (GR) Ex

33 42 Ca( 3 He,t) 42 Sc in 2 scales B(GT) = 2.2 (from mirror decay)

34 SM Configurations of GT transitions p - -p configurations sensitive to IS pairing int. attractive (spin-triplet, IS int. is stronger than spin-singlet, IV int.) particle-hole configurations + IV-type excitation ( ) repulsive by Engel, Bertsch, Macchiavelli

35 SM Configurations of GT transitions particle-particle int. (attractive) (IS p-n int. is attractive) Overwhelming Isoscalarthe interaction repulsive can nature play of Important int.! roles! particle-hole int. (repulsive)

36 QRPA-cal. GT-strength (with IS-int.) Bai, Sagawa, Colo et al., PRC 90 (2014) Ca 42 Ca 42 Sc (Q-value)

37 QRPA cal. including IS int. Bai, Sagawa, Colo et al., PRC 90 (2014) Configurations are in phase! Low-energy collective GT excitation! (collectivity is from IS p-n int.!)

38 Role of Residual Int. (attractive) Collective excitation formed by the attractive IS residual interaction strength Ex 42 Ca( 3 He,t) 42 Sc Ex strength collective strength (GR) Ex

39 42Ca 42Sc: Shell Model Cal.: Transition Matrix Elements SM cal: M. Honma Matrix Elements are in-phase!

40 42 Ca( 3 He,t) 42 Sc in 2 scales GT IAS Low-energy collective GT excitation! (collectivity is from IS p-n int.!) B(GT) = 2.2 Low Energy Super GT state Suggestion in p-prpa calculation (K. Yoshida) Precursory soft mode of the IS pairing condensation! Phys. Rev. C 90, (R) (2014). Y. Fujita, et al., PRL 112, (2014). PRC 91, (2015).

41 Super-allowed GT transitions in decay GT (smaller log ft larger B(GT)) Fermi log ft 6 He, Li, 1 + log ft = Ne, F, 1 + log ft = Ti, Sc, 1 + log ft = 3.2 Super-allowed GT transitions

42 Super-Multiplet State *proposed by Wigner (1937) In the limit of null L S force, SU(4) symmetry exists. We expect: a) GT excitation strength is concentrated in a low-energy GT state. b) excitation energies of both the IAS and the GT state are identical. Super-Multiplet State In 54 Co, we see a broken SU(4) symmetry. In 42 Sc, we see a good SU(4) symmetry. attractive IS residual int. restores the symmetry! MeV state in 42 Sc has a character close to Super-Multiplet State! We call this state the Low-energy Super GT state!

43 18 O( 3 He,t) 18 F at 0 o Talk: H. Fujita Low-energy collective GT excitation: B(GT)=3.1 Low Energy Super GT state

44 J = O n 2 H (d) GT transitions forming Low-Energy Super GT state g.s. (Sum rule) = 3 x N-Z = 6 B(GT) = 6.0? Large! 6 He 6 Li g.s. B(GT) = O 18 F g.s. B(GT) = Ca 42 Sc B(GT) = 2.17 Smaller! 1 st E x state (IAS is the g.s.)

45 ***from p-p to p-h configuration LESGT stae GTR structure in A= 42 to 48 Ca isotopes

46 GT Configurations in Sc isotopes particle-particle int. (attractive) particle-hole int. (repulsive)

47 42 Ca( 3 He,t) 42 Sc

48 44 Ca( 3 He,t) 44 Sc Y. Fujita et al., PRC 88, (2013)

49 48 Ca( 3 He,t) 48 Sc H.F analysis

50 GT Configurations in Sc isotopes particle-particle int. (attractive) Low-Energy Super GT state Is formed! particle-hole int. (repulsive) Gamow-Teller Resonance Is formed!

51 Summary GT ( ) operator : a simple operator! * GT transitions: sensitive to the structure of i> and f> High resolution of the ( 3 He,t) reaction * Fine structures of GT transitions Mirror decays and Isospin Symmetry * Giving the Absolute GT strength GT transitions in each nucleus are UNIQUE! Low-energy Super GT state (LESGT state) Assuming T-symmetry GT in unstable nuclei! We can learn a lot by the comparison of analogous GT transitions!

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

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