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Structural Evolution of Neutron-Rich Nuclei Using Thin-Target Deep-Inelastic Reactions

Structural Evolution of Neutron-Rich Nuclei Using Thin-Target Deep-Inelastic Reactions. Paddy Regan Dept. of Physics University of Surrey, UK e-mail: P.REGAN@SURREY.AC.UK. Outline. Physics of high spins in 100 Mo, n -rich SD shell gaps

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Structural Evolution of Neutron-Rich Nuclei Using Thin-Target Deep-Inelastic Reactions

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  1. Structural Evolution of Neutron-Rich Nuclei Using Thin-Target Deep-Inelastic Reactions Paddy Regan Dept. of Physics University of Surrey, UK e-mail: P.REGAN@SURREY.AC.UK

  2. Outline • Physics of high spins in 100Mo, n-rich SD shell gaps • Importance of using all the experimental parameters to get at the important physics • emission angle • recoil velocity • reaction fold • angular distribution of fragments • isomer tagging ? • Our recent thin-target experiences using CHICO+GAMMASPHERE • 100Mo+136Xe + future work aims for • 208Pb/238U + 100Mo

  3. 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)

  4. 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

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

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

  7. 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.N=58 and Mo-Cd seem most dramatic cases. Special type of crossing, Vibrator to Rotor ‘backbend’ PHR, Beausang,Zamfir,et al., PRL 90 (2003) 152502 also using Cranked IBM, see Cejnar and Jolie, PRC69 (2004) 011301

  8. From Dudek et al., Phys. Rev. Lett. 59 (1987) p1405 Single particle spectra (for minimised LDM energy at spin 60 hbar) shows distinct gaps for b2~0.5 at Z=42, N=58 (100Mo). Note these are the homologs of A~80 SD (N=42) and A~130 SD (Z=58)

  9. SD (b2=0.4) minimum • predicted in 100Mo to • become yrast around • spins 25-30 h. • ‘Doubly-Magic’ SD • shell gaps at • (Z=42, N=58) = 100Mo. J. Skalski et al.,Nucl. Phys. A617 (1997) p282

  10. Backed target studies of DICs see eg. Broda et al. Phys. Rev Lett. 74 (1995) p868 Juutinen et al. Phys. Lett. 386B (1996) p80 Wheldon et al. Phys. Lett. 425B (1998) p239 Cocks et al. J. Phys. G26 (2000) p23 Regan et al., Phys. Rev. C55 (1997) 2305 Krolas et al., Nucl. Phys. A724 (2003) 289 Aim? To perform high-spin physics in stable and neutron rich nuclei. Problem: Fusion makes proton-rich nuclei. Solutions? (a)fragmentation (b) binary collisions/multi-nucleon transfer Modified from Introductory Nuclear Physics, Hodgson, Gadioli and Gadioli Erba, Oxford Press (2000) p509

  11. PHR et al., Phys. Rev. C55 (1997) 2305, backed target with DORIS 0.5% array with ~1010pps beam for 4 days (c 1997), g-g trigger single gates, backed target 8p data

  12. BGO Fold from 8p back target 136Xe+100Mo data

  13. Bock et al., Nukleonika 22 (1977) 529

  14. 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)~700 MeV, in lab qblf~30o and qtlf~50o. 100Mo +136Xe (beam) DIC calcs.

  15. z x q1 q2 f1 f2 y

  16. b=0.5 Dq=10o b=0.3 b=0.1 scales linearly with Dq. b=0.5 b=0.3 Db=0.03 b=0.1 scales linearly with Db. b=0.5 b=0.3 b=0.1 From T. Glasmacher, Ann, Rev. Nucl. Part. Sci. 48 (1998) p1

  17. Ge TLF beam qtlf,ftlf qblf,fblf BLF Simon et al., Nucl. Inst. Meth. A452, 205 (2000) Rochester Group TOF ~5-10 ns. ns-ms isomers can de-excite in be stopped byCHICO position detector. Delayed gs can still be viewed by GAMMASPHERE.

  18. 100Mo + 136Xe @ 700 MeV GAMMASPHERE + CHICO PHR, A.D. Yamamoto et al., AIP Conf. Proc. 701 (2004) p329

  19. A.D.Yamamoto, Surrey PhD thesis (2004) Wilczynski (‘Q-value loss) Plot

  20. 100Mo + 136Xe at 700 MeV BLFs TLFs elastics PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313

  21. PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313

  22. Crossing and alignments well reproduced by CSM, although AHVs

  23. 4+ -> 2+relative intensities.

  24. Gating on angle gives a dramatic channel selection in terms of population. Relative Intensities of 6+->4+ yrast transitions in TLFs (relative to 100Mo) for 136Xe beam on 100Mo target at GAMMASPHERE + CHICO.

  25. Q-values show how one expects the compound fragments to split.

  26. BLFs TLFs elastics

  27. Emission angle of TLFs can give information/selection on reaction mechanism (and maybe spins input ?)

  28. PHR, A.D.Yamamoto et al., Phys. Rev. C68 (2003) 044313 +2p -2n +2n

  29. Timing relative to prompt-gamma-triples master gate (Xe+Pt expt.).

  30. Isomer gating very useful in DIC experiments. Test with known case….. PHR, A.D.Yamamoto et al., Phys. Rev. C68. (2003) 044313

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

  32. 100Mo target + 136Xe beam 100Mo beam + 208Pb target 208Pb beam + 100Mo target

  33. In general, larger mass beam provides higher spin input, but beware of.…… Q-value effects. Need to think carefully about Beam/target combinations to maximise spine input for nucleus of Interest…flow could go away from nucleus of choice depending on Q-value.

  34. Summary and Conclusions • Gammasphere + CHICO results for 100Mo+136Xe @700 MeV show importance of using ALL parameters (H,K,Q,q) to get channel selection. • AGATA for use with DIC must have ancillary detector to tag recoil direction and velocity (PRISMA, VAMOS, CHICO?). What about isomer tagging ? • Fold (isolated hit probability) and neutrons may be problematic for the highest spins (100 hbar internally between the two fragments is likely!)

  35. NUSTAR’05International Conference onNUclear STructure, Astrophysics and Reactions The University of Surrey, Guildford, UK5-8 January 2005 http://www.ph.surrey.ac.uk/cnrp/nustar05

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