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From Vibrations to Rotations as a Function of Spin

From Vibrations to Rotations as a Function of Spin. Paddy Regan Dept. of Physics, University of Surrey, Guildford, GU2 7XH, UK e-mail: p.regan@surrey.ac.uk. Outline. Main physics question, Are nuclei (with Z=40-50) Rotators or Vibrators ?

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From Vibrations to Rotations as a Function of Spin

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  1. From Vibrations to Rotations as a Function of Spin Paddy Regan Dept. of Physics, University of Surrey, Guildford, GU2 7XH, UK e-mail: p.regan@surrey.ac.uk

  2. Outline Main physics question, Are nuclei (with Z=40-50) Rotators or Vibrators ? * Signatures of vibrator-rotor structural evolution. * 102Ru from WNSL-Yale * 99-102Mo alignments/phase changes (using DICs). * 112,114Cd medium spins from WNSL-Yale * Odd-A cases, 101Ru

  3. Nuclear Rotations and Vibrations • What are the signatures (in even-even nuclei) ? • (extreme) theoretical limits

  4. En n=3 n=2 n=1 n=0 b2 V http://npl.kyy.nitech.ac.jp/~arita/vib b2

  5. Signatures of (perfect) vibrators and rotors State lifetimes, i.e., B(E2) values and selection rules (eg. Dn=1).

  6. Nuclei in the Sr-Sn region show dramatic change in structure around N~60. Sudden explosion of b2 deformation in Sr-Ru isotopes at N=60 has been explained by strong spatial overlap of Spin-Orbit Partners (SOPs) g9/2 protons and g7/2 neutrons. (see Federman and Pittel, Phys. Rev. C20 (1979) p820)

  7. Alignments and rotational motion in ‘vibrational’ 106Cd (Z=48, N=58), PHR et al. Nucl. Phys. A586 (1995) p351

  8. Can subtract off a reference (core) aligned angular momentum to see effect of quasi-particle alignments as a function of frequency. Dix=5h CSM ref. Bengtsson Frauendorf and May, At. Data. Nuc. Data. Tab. 35 (1986) p15

  9. h11/2 neutron orbital responsible for 1st crossing in even-even systems. Energy appears to correlate with transition to deformed ground states at N~60

  10. 82 1h11/2 50 [550]1/2- 1g9/2 Alignment (rotational picture at least) driven by Coriolis interaction on high-j, low-W orbitals (ie. ones with large jx on collective rotation axis. Vcor = -jx.w eg. nh11/2 [550]1/2 ‘intruder’ FS for N~57, b2~0.15->0.2 jx [541]3/2-

  11. Ru (Z=44) in the centre of the ‘deformed’ region for N=56-58 Anharmonic vibrator for the ground state ‘band’ is the usual explanation for 100Ru and neighbours....but mid-shell (Z=40-50) nature is consistent with largest collectivity in the region. Q.Are these nuclei deformed or vibrational ? Zr Mo Ru Pd Cd Sn

  12. Experimental Details 96Zr (9Be,3n)102Ru, space~100mb Enriched (85%) 670mg/cm296Zr foil on 5mg/cm2natPb support. Ebeam=44 MeV, lmax~25 h YRASTBALL array at WNSL 6 clover germaniums @ 90o 5 co-axial detectors @ 50o + 126o 3 co-axial detectors @ 160o

  13. See PHR, Beausang, Zamfir, Casten, Zhang, Yamamoto et al., PRL in press.

  14. If we parameterize with (Eg / J) vs. J Can see if rotor or vibrator by inspection

  15. Structural change from vibrator to rotator appears to be a regular feature of this region. Rotation stabilized by core stiffening due to population of ‘rotation-aligned’ h11/2 neutrons. Special type of crossing, Vibrator to Rotor !!!

  16. Q. Are backbends necessarily due to rotational alignment ? A. NO ! Can be vibrational – rotational structure change!!

  17. Detailed spectroscopy allowed by investigating gamma-decay sequences from high-spin states. YRASTBALL allows triple coincidences to be routinely observed. Band-like structures are clearly observed in 101Ru. (a) gamma-gamma (b) triple coincidences

  18. Decay scheme for 101Ru Band-like sequences observed on ‘intrinsic’ 11/2-, 5/2+ and 7/2+ states. Backbending observed in positive parity bands (1 and 2), but not in negative parity band (band 3). Pauli blocking arguments suggest aligning particles are therefore of h11/2 neutron nature. see A.D.Yamamoto et al. Phys. Rev. C66 (2002) 024302

  19. Quasi-particle alignments and kinematic moments of inertia nh11/2 band Dix=10 nh11/2 band

  20. TRS calculations for 101Ru by Furong Xu (Bejing) for different parity (and signature) configs. g b2 w=0.2MeV w=0.3MeV w=0.4MeV w=0.6MeV

  21. See PHR, Yamamoto, Beausang, Zamfir, Casten, Zhang et al., AIP Conf. Proc. 656 (2002) p422

  22. For Odd-A (Carl Wheldon’s idea)

  23. (iii) (ii) (i) Ebeam ~15-20% above Coulomb barrier beam target Z N Can not use fusion-evaporation reactions to study high-spin states (and thus vibrational-rotational transitions, alignments etc.) in beta-stable and neutron-rich systems. Use deep-inelastic reactions.

  24. Kinematics and angular mom. input calcs (assumes ‘rolling mode’) for 136Xe beam on 100Mo target. Estimate ~ 25hbar in TLF for ~25% above Coul. barrier. For Eb(136Xe)~750 MeV, qblf~30o and qtlf~50o. 100Mo +136Xe (beam) DIC calcs.

  25. 100Mo + 136Xe @ 750 MeV GAMMASPHERE + CHICO BLFs TLFs elastics

  26. z x q1 q2 f1 f2 y

  27. Isomer gating very useful in DIC experiments. Test with known case…..

  28. Use known delayed lines in 101Mo (182 and 57 keV) to identify previously unknown nh11/2 band (+ 34 keV E1 decay).

  29. 112Cd

  30. Vib. rotor

  31. (ph11/2)2 alignment in A~130 region appears to have analogous behaviour to (nh11/2)2 alignment in A~100 region. Conclusion? In many cases, ‘rotational alignment’ is actually a crossing between a quasi-vibrational ground state configuration and a deformed rotational sequence caused by stiffening of potential by population of high-j, equatorial (h11/2) orbitals

  32. Summary and Future Look • 101,102Ru (and neighbours) look like g-soft, anharmonic vib. nuclei at low-spins (eg. E(4+)/E(2+)~2.3)..... BUT also have apparent rotational-like behaviour eg. band-crossing, alignments etc. • Paradoxically, Coriolis (rotational) effects are largest in nuclei which have SMALL deformations (ie. require large energies/frequencies to rotate). ‘Vibrational’ A=100 may be the best tests of nuclear Coriolis effects. • Vibrational – Rotational ‘phase’ change around spin 10? Smooth evolution with crossing of anharmonic vibrational states and rotation-aligned configurations. • Plot of Eg /J verses J gives model independent crossing.

  33. many thanks to...... • Arata Yamamoto (Surrey/Yale student). • 101-102Ru Expt. Con Beausang (+ Yalies) • 100Mo+136Xe CHICO, Rochester (Chin-Yen Wu et al.,), Manc. (John Smith et al,) + LBNL • 7Li+110Pd, Scott Langdown (+Yalies + Paisley) • Vibrator-Rotator (E-GOS) plots, Con B., Rick Casten, Victor Zamfir, Jing-Ye Zhang et al., • Odd-A, Carl Wheldon (now at GSI)

  34. NUSTAR’05International Conference onNUclear STructure, Astrophysics and Reactions The University of Surrey, Guildford, UK9-12 January 2005

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