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K. Asahi Tokyo Institute of Technology ( Tokyo Tech )

The 18th International Spin Physics Symposium (SPIN2008) 6 - 11 Oct. 2008, Univ. of Virginia, Charlottesville, Virginia, USA. Nuclear structure studies with polarized radioactive beams. K. Asahi Tokyo Institute of Technology ( Tokyo Tech ). OUTLINE :

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K. Asahi Tokyo Institute of Technology ( Tokyo Tech )

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  1. The 18th International Spin Physics Symposium (SPIN2008) 6 - 11 Oct. 2008, Univ. of Virginia, Charlottesville, Virginia, USA. Nuclear structure studies with polarized radioactive beams K. Asahi Tokyo Institute of Technology (Tokyo Tech) OUTLINE: 1. Spin in Low-energy Nuclear Structure Physics 2. History of the Spin-polarized/Aligned Radioactive Beams (RIB) 3. Nuclear Moment Measurements with Polarized/Aligned RIB 4. Recent Results on n-rich Al isotopes and the Island of Inversion

  2. Chart of Nuclei Proton number Z Neutron number N

  3. Nucleus: Many-body system of fermions of two types ●Bunching of the single-particle levels ⇒ determinesthe Nuclear Structure (Nucleus along the stability line)

  4. Nucleus: Many-body system of fermions of two types ●Bunching of the single-particle levels ⇒ determinesthe Nuclear Structure 16 New magic numbers ?? 6 2 (Neutron-rich nucleus) (Nucleus along the stability line) increase of N/Z

  5. j'< j'> j< j> proton neutron In fact, the shell does evolve, ..... due to the tensor force. [Otsuka et al., PRL95 (05) 232502] [Otsuka et al., PRL97 (06) 162501] ● Monopole energy of the tensor interaction is ・attractive for j> - j<', j< - j>' ・repulsive for j> - j>', j< - j<'

  6. j'< j'> j< j> proton neutron In fact, the shell does evolve, ..... due to the tensor force. [Otsuka et al., PRL95 (05) 232502] [Otsuka et al., PRL97 (06) 162501] ● Monopole energy of the tensor interaction is ・attractive for j> - j<', j< - j>' ・repulsive for j> - j>', j< - j<' j'< j'> Thus, the single-particle orbits may migrate leading to a possible change in shell structure. Note that the s.p. orbits are characterized by the angular momentum j. j< j> proton neutron

  7. + + + Also, decoupling of neutron from the core ebare(n) = 0 core eeff(n)  0 ?? eeff(n)  0.5 (in a n-rich nucleus) (in a normal nucleus) Such an effect can be detected through measurement of electric quadrupole moments Q associated with nuclear spin.

  8. Thus, the spin plays vital roles in structural change of nuclei towards far from stability

  9. Observation of spin-alignment in projectile fragments RIKEN-GANIL collab. (at LISE/GANIL, 1987) 18O (60 MeV/u) 14B fragment 9Be target 2- b 14B 1- 6.094 MeV g 0+

  10. Angular momentum introduced in a projectile fragment in the intermediate-energy PF reaction Fragment Projectile (internal Fermi motion) Pfrag = Mv0-P'part p'i v0 R P'part = Sp'i Target LFrag= -R  P'Part -- Angular momentum introduced in the fragment PLB 251, 499 (1990)

  11. Spin polarization found in RI beams from PF reaction p|| z∥ki kf

  12. Result of the RIKEN-GANIL collab. experiment: Expected spin alignment in the 14B fragment Goldhaber distribution

  13. Result of the RIKEN-GANIL collab. experiment: Expected spin alignment in the 14B fragment Goldhaber distribution Alignment result at GANIL '87

  14. Polarization - at RIKEN, '90 Analyzer qL

  15. Spin Rotation of aligned fragments, - at FRS/GSI, '93 43mSc (19/2-) TD-PAD B0 = -0.265 T B0 = +0.265 T Z. Phys. 350, 215 (1994)

  16. RIPS/RIKEN, present RIPS RIPS K=540 RIKEN Ring Cyclotron • Isotope separation • magnetic analysis (A/Z) • + • momentum-loss analysis (A2.5/Z1.5) • Production of spin polarization • scattering-angle selection • + • momentum analysis

  17. Fragmentation-induced spin polarization Detector Detector Large-Z target Small-Z target ● The kinematical model reproduce quite well the observed behavior of polarization P as a function of momentum and target Z-number. ● However, ‥‥ the observed magnitudes of P are by ～1/4 smaller than predicted. far-side trajectory near-side trajectory Au Nb Nb Al Au 70AMeV 110AMeV 40AMeV 70AMeV 70AMeV H. Okuno et al., PL B 335, 29 (1994)

  18. ●With spin-polarized fragment beams .... TITech / RIKEN Osaka / RIKEN Nuclear moments measured at RIPS/RIKEN • g-Factors measured at RIKEN • Boron isotopes : 14B, 15B, 17B • Carbon isotopes : 9C, 15C, 17C • Nitrogen isotopes : 17N, 18N, 19N • Oxygen isotopes : 13O • Fluorine isotopes : 21F • Aluminum isotopes : 23Al, 30Al, 32Al • Q-moments measured at RIKEN • Boron isotopes : 14B, 15B, 17B • Nitrogen isotopes : 18N • Oxygen isotopes : 13O • Magnesium isotopes : 23Mg • Aluminum isotopes : 31Al, 32Al Spin-parity assignment <s> from mIS Effect of n-excess Reduction of E2 effective charges Spherical or deformed?

  19. ●Reduction of effective charges

  20. ●Reduction of effective charges Thus, effective charges have been shown to reduce significantly as N/Z increases! aj'j≈ 0.5 (sd orbits) This also explains the anomalously hidered E2 transition in 16C reported recently.

  21. qL ●With spin-polarized fragment beams .... Many important works also at ... (a.f.a.I.k.) GANIL (France) g-factor: 18N, 32Cl, 31Al, 32Al, 33Al, 34Al, 35Si, ... Q-moment: 18N, 31Al, 33Al, ... MSU (U.S.A.) g-factor: 9C, 35K, 57Cu, ... Q-moment: 37K, ... NIRS (Japan) g-factor: 21F, 27Si, 35Ar, ... Q-moment: 21F, 23Mg, 27Si, 39Ca, ... RCNP (Japan) Snow ball exp. with highly polarized 12B (P~ 40 % !) Present status of the “Island of inversion” (Himpe et al.) Polarization in pick-up channel (Groh, Mantica et al.)  A precursor expt. for the recent development, "OROCHI" technique (Optical RI-atom Observation in Condensed Helium as Ion-catcher) (Matsuo, Furukawa, Shimoda et al.)

  22. ● Improvements in prediction of P By including (Groh, Mantica et al., 2007) ・Deorientation effect due to g-ray de-excitation⇒ ×0.5 ・Out-of -plane acceptance ⇒ ×0.4 ・Angular distribution ⇒ ×0.1 Thus, now the magnitude of polarization that should be obtained in the experiment can be predicted in quite a useful accuracies!

  23. ●With spin-aligned fragment beams .... 61mFe(9/2+) LISE/GANIL (France) g-factor: 61mFe(9/2+), 69mCu(13/2+), 67mNi(9/2+), ... Q-moment: 61mFe(9/2+), ... RISING/GSI (Germany) "g-RISING Campaign" g-factor: 127mSn(19/2+), ...

  24. 43Sc isomer (g-RISING Campaign) FRS/GSI, Present (RIKEN-Goettingen-GSI) FRS/GSI, '93 (RIKEN-GANIL Collab.) at LISE/GANIL, '87 • E437b collaboration • RIKEN Nishina Center • Tokyo Tech • Tohoku • KU Leuven • GANIL • Bruyères-le-Châtel • IPN Orsay • Sofia (RIKEN-TIT-GANIL-Leuven) LISE3/GANIL '08 32Al isomer RIPS/RIKEN '90 RIBF/RIKEN Present

  25. Recent result: Q-moments for 31,32,33Al ●31,32Al part: at RIPS/RIKEN ●33Al part: at GANIL The experiment has been done in collaboration of H. Ueno, K. A., K. Shimada, T. Nagatomo, A. Yoshimi, Y. Ichikawa, D. Kameda, T. Sugimoto, D. L. Balabanski, J. M. Daugas, K. Flanagan, G. Georgiev, S. Grevy, R. Lozeva, P. Morel, D. Nagae, G. Neyens, F. de Oliveira Santos, L. Perrot, M. De Rydt, C. Stodel, J. C. Thomas, N. Vermeulen, P. Vingerhoets, D. Yordanov, Y. Utsuno (E437b collaboration) RIKEN, Tokyo Tech, Tohoku, Leuven, GANIL, Sofia, Bruyeres-le-Chatel, IPN Orsay, JAEA at LISE3/GANIL '08

  26. Nuclear moment studies in the vicinity of the island of inversion Na isotopes P Si Al Mg Na Z Ne F 20 N Normal sd-shell configuration Island of Inversion E.K. Warburton, J. A. Becker and B. A. Brown, PRC41(1990)1147. 0p0h, spherical 2p2h (intruder), deformed p3/2 p3/2 f7/2 f7/2 20 d3/2 d3/2 s1/2 s1/2 d5/2 d5/2 n n MCSM with an sdpf model space: Y. Utsuno, et al., Phys. Rev. C 70 (2004) 044307.

  27. What would be happening in the IOI f7/2 d3/2 s1/2 d5/2 p n

  28. What would be happening in the IOI f7/2 (j<) d3/2 s1/2 (j>) d5/2 d5/2 p n T=0 monopole interaction due to tensor force [Otsuka et al., PRL 95 (05) 232502]

  29. What would be happening in the IOI f7/2 d3/2 s1/2 d5/2 p n T=0 monopole interaction due to tensor force [Otsuka et al., PRL 95 (05) 232502]

  30. What would be happening in the IOI f7/2 d3/2 s1/2 d5/2 p n T=0 monopole interaction due to tensor force [Otsuka et al., PRL 95 (05) 232502]

  31. What would be happening in the IOI f7/2 d3/2 s1/2 d5/2 p n T=0 monopole interaction due to tensor force [Otsuka et al., PRL 95 (05) 232502]

  32. What would be happening in the IOI f7/2 d3/2 s1/2 d5/2 p n T=0 monopole interaction due to tensor force [Otsuka et al., PRL 95 (05) 232502]

  33. What would be happening in the IOI f7/2 d3/2 s1/2 d5/2 p n T=0 monopole interaction due to tensor force [Otsuka et al., PRL 95 (05) 232502]

  34. -- Gains correlation energies due to near degenerate f7/2 and d3/2 orbits What would be happening in the IOI f7/2 d3/2 s1/2 d5/2 d d 0 0 p n

  35. -- Gains correlation energies due to near degenerate f7/2 and d3/2 orbits What would be happening in the IOI Question: Where and how steeply does this quantum phase transition take place as a function of N/Z ratio ? [330]3/2 [200]1/2 [211]1/2 [202]5/2 [211]3/2 [220]1/2 d d 0 0 p n

  36. μ(AAl) and Q(AAl) Q (AAl) • Qexp stays almost constant at • N=14,15, but it becomes smaller at Qexp[32Al] • → single-particle(hole)-like structure • spherical shape • Consistent with μ(AAl) • - 27～32Al can be described within • the sd- model space • → normal configuration • →31,32Alare not related to island of inversion |Q |-moment (e· mb) RIKEN 5/2+ 5/2+ 5/2+ 5/2+ 3+ 3+ μ(AAl) | m |-moment (mN) RIKEN 1+

  37. Large-scale shell model & aluminum isotopes 31Al 32Al 33Al 34Al 33Al 33 31 32 34 29 30 Y. Utsuno et al., PRC 64(2001)011301(R) E. Caurier et al., PRC58(1998)2033 • decreases from 31Al(30Al)→33Al • E0p0h-E2p2h > 0 for Al isotopes, but similar to Mg, Na, Ne Z=13 is really a "transitional number"

  38. Selected momentum region: 31Al and 32Al RIKEN Projectile fragment separator (RIPS): 40Ar Isotope separation: A Z Br = (mv0/e) (r = 3.6 m) dE dx ∝Z2 • Particle identification: • DE @ F2 SSD • TOF (F2 PPAC - RRC)

  39. Target Achromatic focal plane LISE/GANIL 33Al • 36S16+ • 77.3 A MeV • 3.8 emA Emission angle: 2±1 deg. b-NMR apparatus selection Purity Intensity Momentum dispersive plane selection

  40. b-NMR & b-NMR Apparatus Magnet pole Spin-polarized RI Beam b rays Plastic scintillators ~100mm I.d. Stopper ~22.5x28x1 mm3 a-Al2O3 at 130 K Si at room temp. RF Coil ~20 mm I.d. ~0.1 mT, ~6 MHz 0.5 T

  41. Momentum analysis with the edge-shape degrader Primary beam: 36S, 77.30 A MeV Target: Be 1212 mm Beam-deflection angle: (2±1)° Edge-shape degrader: Be, 1068 mm Br1: 3.1000 Tm Br2: 2.9119 Tm Production of the polarized 33Al beam 32Mg 33Al Purity 75% DE 28Ne 31Mg 30Na TOF

  42. Momentum distribution Accepted momentum region Gaussian fitting 11.87±0.11 GeV/c

  43. 33Al 5.8 – 6.6 MHz @ ～500 mT n-5/2,-3/2 n-3/2,-1/2 n-1/2,1/2 n1/2,3/2 n3/2,5/2 m = -5/2 m = -3/2 m = -1/2 m = 1/2 m = 3/2 nL m = 5/2 nL nL nL nL Energy levels with eqQ interaction 33Al (I = 5/2+) Larmor frequency Quadrupole coupling constant

  44. Spin-polarized beam Nuclear spin = I e- e- e- e- 2I+1 mH/I e- B=０ B≠０ w(t) w0+Dw w0 w0-Dw t Adiabatic Fast Passage - Nuclear Magnetic Resonance Motion of a moment in a rotation coordinate system (with resonance freq. w0) static magnetic field Frequency of the oscillating magnetic field B1 w0+Dw w0 w0-Dw t

  45. e- e- e- e- e- e- e- e- e- e- b-NMR/NQR method Adiabatic Fast Passage NMR W (q )=1+APcosq A : Asymmetry parameter P : Polarization q : Emission angle RF:u0=mH/Ih (Up/Down)with RF (1-AP)/(1+AP) NMR effect = ~ 1 - 4AP = (Up/Down)w/o RF (1+AP)/(1-AP)

  46. n-5/2,-3/2 n-3/2,-1/2 n-1/2,1/2 n1/2,3/2 n3/2,5/2 nL nL nL nL nL n = 5.8 – 6.6 MHz 18 ms RF signal for Q(33Al) measurement

  47. Larmor Frequency determination: NMR spectrum 6216.5 ± 6.5 kHz AP = 1.5% Preliminary Stopper: Si B0 = 498.8 mT g = 1.635 Diamagnetic correction Al in Si: 0.00083 498.8 mT -> 499.2 mT

  48. Q moment measurement: NQR spectrum Stopper: a-Al2O3 B0 = 498.8 mT q = 67.701019 V/m2 = 316 ± 55 kHz |Q| = 129±22 emb Preliminary

  49. Comparison of Q moments with shell models preliminary T. Nagatomo et al., to be published Y. Utsuno, private communication

  50. Recent μ-measurements in the sd shell μ Ｑ I = 0 g-factor known N=20 GANIL ISOLDE RIKEN (Osaka G.) Island of inversion From recent experiments 一連のAl研究 (RIKEN, GANIL) E.K. Warburton et al., Phys. Rev. C 41, 1147 (1990) M. Keim et al., Eur. Phys. J. A 8, 31 (2000). G. Neyens et al., Phys. Rev. Lett. 94, 022501 (2005) G. Huber et al., Phys. Rev. C 18, 2342 (1978)

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