1 / 44

Studies of N≈Z nuclei above mass 80

Collaboration NIPNE Bucharest -- LSF LN Legnaro. Studies of N≈Z nuclei above mass 80.

lee
Télécharger la présentation

Studies of N≈Z nuclei above mass 80

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Collaboration NIPNE Bucharest -- LSF LN Legnaro Studies of N≈Z nuclei above mass 80

  2. M.Axiotis1, D.Bazzacco2, D.Bucurescu3, G. de Angelis4, E.Farnea2, A.Gadea4, M.Ionescu-Bujor3, A.Iordǎchescu3, W.Krolas5, Th.Kröll6, S.Lenzi2, S.Lunardi2, N.Mǎrginean3,4, T. Martinez4, R.Menegazzo2, D.R.Napoli4, P.Pavan2, B.Quintana7, C.Rossi Alvarez2, C.Rusu3,4, P.Spolaore4, C.A.Ur2,3, J. Wrzesinski5 recent youngs: C. Mihai3, G. Suliman3 [1] - N.R.C. Demokritos Athens [2] - Università Padova [3] - H.H.-NIPNE Bucharest [4] - INFN, L.N. Legnaro [5] - H.N. – INP Krakow [6] - T.U. München [7] - Universidad Salamanca The collaboration

  3. Short history of collaboration: • Since 1990, γ-ray spectroscopy with fusion-evaporation reactions, first with GAMIPE, then with GASP. (NIPNE-INFN collab. agreement; since 2000: LSF-TRM) • High-spin states in different nuclei • Highly-deformed & SD structures (decay out, • lifetimes, A≈130) • Spectroscopic studies of nuclei in the • exotic region N≈Z, A=80-90 • Static moments of isomeric states in exotic nuclei • Spectroscopy of n-rich nuclei with CLARA- PRISMA

  4. Topics • (prompt γ-ray spectroscopy of N≈Z nuclei above mass 80) • T=0 np pairing • Spin-gap isomers • Shell model description • Evolution of collectivity

  5. Experimental Studies of “heavy” N≈Z Nuclei Production • Fusion-evaporation • Fragmentation Identification • Coincidence with evaporated particles • Direct A and Z measurement Low cross sections (with stable beams) High ‘background’ γ-ray Spectroscopy Ge arrays Beta-decay studies 32S+58Ni, 105 MeV Ancillary detectors Charged particle balls Neutron arrays Mass spectrometers

  6. Experimental Facilities GASP GASP (config. 1) abs (40 HPGe)  3% Peak/Total  60% abs (80 BGO)  76% Beam ISIS (40 ΔE-E Silicon telescopes) p  56-60%   35-38% N-Ring n  2-5%

  7. p-drip line: G.A.Lalazissis et al, Nucl. Phys. A719,209c(2003): Relativistic HB calc.

  8. N. Mărginean et al. Phys. Rev. C 63 (2001) 032303(R) N. Mărginean et al. Phys. Rev. C 65 (2002) 051303(R)

  9. Delayed Alignment in N=Z Nuclei: Signature of T=0 np pairing ? J=0 T=1 J=1…2j T=0 • New data: • 72Kr : C.Andreoiu et al., Phys. Rev. C75(2007)041301(R) • 76Sr : P.J.Davies et al., Phys. Rev. C75(2007)011302(R) • No evidence for isoscalar (T=0) np pair field  isovector mean-field theory OK (isovectornppairing + isospin symmetry conservation) [ Afanasjev & Frauendorf, PRC71(2005)064318 ] (CRHB calculations)

  10. Projected Shell Model Calculations N. Mărginean et al. Phys. Rev. C 65 (2002) 051303(R)

  11. Experiment:28Si(90 MeV) + 58Ni Target: 2 x 0.5 mg/cm258Ni 81Zr - αn channel, intensity  2·10-4 N=Z+1 81Zr N. Mărginean et al. Phys. Rev. C 69 (2004) 054301

  12. 1 neutron hole + 82Zr N=40 1 neutron particle + 80Zr [431]1/2 [431]1/2 [301]3/2 [301]3/2 N=40 [422]5/2 [422]5/2 Fermi

  13. Projected Shell Model Calculations (empty symbols) N. Mărginean et al. Phys. Rev. C 69 (2004) 054301

  14. E3isomeric decay τisomer > ≈ 1 μs 95Ag [predicted by Ogawa, Phys.Rev. C28,958(1983)]

  15. Shell Model Effective Interactions SLGT0 - Serduke, Lawson, Gloeckner, NPA256(1976)45; Herndl, Brown, NPA605(1996)195 A>86, N,Z=[38-50]π,υ(2p1/2,1g9/2) Gross-Frenkel -Gross, Frenkel, NPA267(1976)85 F-FIT, … -Johnstone, Skouras,EPJA11(2001)125 (fit to increased number of exc. energies in mass 86-100 nuclei) Other SM calculations: Hasegawa et al., P+QQ Hamilt., (2p1/2,1g9/2,1f5/2,2p3/2 ) (88,89,90Ru)

  16. C. Rusu et al , Phys. Rev. C 69 (2004) 024307 ν,π(p1/2,g9/2) SLGT0 resid. inter. N.Mǎrginean et al, Phys. Rev. C67(2003)061301(R)

  17. 1.75 2.30 2.52 1.5 2.86 2.0 2.84 2.75 2.25 2.5 2.5 2.0 2.25

  18. Shape phases, phase transitions and critical points Stable quadrupole deformation Axially symmetric rotor -soft rotor 134Ba 152Sm (F. Iachello Phys. Rev. Letters 85 (2000) 3580) (F. Iachello Phys. Rev. Letters 87 (2001) 052502) Unharmonic vibrator Critical points: parameter-free analytical approximations

  19. Prediction of X(5) nuclei 4.5 < NpNn/(Np+Nn) < 5.5 N=Z = 38,40 (N.V. Zamfir, private comm.)

  20. Quasi- bands identified or extended in 78Sr, 80Sr, 82Zr, 84Zr, 86Zr, 86Mo, 88Mo

  21. 4+ 3+ 4+ 2+ 2+ * 0+ * New parameters: Phase Transition in IBA Triangle • Fine grid on parameter space • 2 merit function including both energy and branching ratios 78Sr 82Zr 80Sr

  22. Conclusions • N≈Z nuclei, mass 80 - 100: theatre of many interesting nuclear • structure phenomena • First spectroscopic measurements of the heaviest known • N=Z (88Ru) and N=Z+1 (81Zr, 85Mo, 89Ru, 91Rh, 93Pd,95Ag) • nuclei. • ”Systematic delay” in alignment frequency in N=Z even-even nuclei. • Is it “abnormal”? (T=0 neutron-proton pairing?) • need for: - measurements at higher spins; • - direct determinations of: s.p. energies, deformations. • Deformed Odd-A (N=Z+1) nuclei: rich information (more bands) • - possible delayed alignment observed. Implications for the • N=Z core? (polarization of the mean-field; the T=1 pair field • induced by additional neutron in 81Zr).

  23. Shell model (Z≥44; N≥45): old residual interactions (SLGT0, GF, JS) • in (p1/2,g9/2) space perform reasonably well. Isomers explained. • But: yrast π = + (g9/2) states are not so sensitive – not critical tests! • Evolution of the Collectivity: maximum of collectivity (deformation) • around N,Z=38,40 but still far from ideal rotor; X(5) “island”? • (new “indicators” needed for 76,78Sr, 80Zr, (78Zr) ) • Extensions of these data are necessary (in spin: e.g.,88Ru to higher states; • in mass: 92Pd; N=Z+1 nuclei). • Exceptional support within LSF LN-Legnaro; full use of the capabilities • of GASP and its ancillaries: ISIS and N-wall.

  24. END

  25. GASP experiments

  26. PR C56,2497(1997) PR C65,051303R(2002) PR C61,024310(2000) PR C69,054301(2004) PR C63,031303(2001) PR C65,0334315(2002) PR C70,044302(2004) PR C72,014302(2005) PR C69,024307(2004) PR C67,061301R(2003) Simultaneous publications: 93Pd: D.Sohler et al., EPJ A19,169(2004) 95Ag: J.Döring et al., PR C68,034306(2003)

  27. ~Grodzins estimate β2 ~ A-7/6E(2+)-1/2

  28. Shell model, P+QQ Hamiltonian, (1g9/2,2p1/2,1f5/2,2p3/2)-N max. dimens. for 88Ru (N=12): 165 x 106 Strengthened isoscalar QQ pn interaction M.Hasegawa et al., Phys. Rev. C69,034324(2004)

  29. Experiment:32S(105 MeV) + 58Ni • Target: 1.1 mg/cm258Ni on 10 mg/cm2 Au • 88Ru populated as 2n channel, intensity  4·10-5 • Four gamma-ray cascade identified by coincidence with neutrons and anticoincidence with charged particles Sum of gates 616 + 800 +964 keV: Identification of N=Z: 88Ru GASP + ISIS + 6 n-detectors Matrix projection N. Mărginean et al. Phys. Rev. C 63 (2001) 031303(R)

  30. N=Z+1, 9547Ag48 approaching N,Z=50 : spin gap isomer 1p2n channel predicted Ogawa PR C28,958(1983) τisomer > ≈ 1 μs N. Mărginean et al. Phys. Rev. C 67 (2003) 061301(R)

  31. Estimate for the alignment frequency of 80Zr Missing alignment

  32. 91Rh – comparison with 3 Shell Model calculations EXP. Ecalc. - Eexp. (keV)

  33. 91Rh πυ(2p1/21g9/2) N. Mărginean et al. Phys. Rev. C 72 (2005) 014302 Johnstone-Skouras (2001) – F-FIT eff. inter.

  34. (preliminary)

  35. General structureof acollective nucleus: Basic information on: • g.s.b. • 02+ - band (quasi-beta band) • 2γ+ - band(quasi-gamma band) Energy ratios: E(41+)/ E(21+); E(02+)/E(21+); E(2γ+)/E(21+); etc. Elmag. trans. Probab.: B(E2; 2γ --> 01)/ B(E2; 21 --> 01); B(E2; 2γ --> 01)/ B(E2; 21 --> 21); etc. Ex.: U(5)R(4/2) = 2.0 R(02+/21+) = a(~2)R(22+/21+) = a(~2) O(6) 2.5 a(>~2.0)a(>~2.0) SU(3) 3.33 a(>~12)a(>~12) X(5) 2.91 5.67 4.23 E(5) 2.19 3.03 2.20 a= depends on additional Hamiltonian parameters

  36. N=Z 88Ru with RIB: 56Ni + 40Ca ---> 88Ru + 2α 88Ru cross-sections : with 56Ni beam : ~ 30 mb with 32S beam: 5-10 μb --------------------------------------- R ~ 3 x 103 (56Ni/32S) Beam 56Ni : [~ 3 x 107 ions/sec (2003, ANL)] ------→ ~ 1011 (FAIR) Beam 32S (GASP): ~ 6 pnA ≈ 4 x 1010 ions/sec ---------------------------------------- R ~ 1(56Ni/32S) Overall gain with 56Ni : ~3000 (assuming GASP (3%) γ-efficiency and same target !) with Ge-array of increased efficiency :  gain >> ~ 3000 !

  37. S.Takami et al., Phys. Lett. B431,242(1998) M.Yamagami et al., Nucl Phys. A693,579(2001) J.Dudek et al., Phys. Rev. Lett. 88,252502(2002) Exotic deformation: ~ 80Zr : tetrahedral deformation (spin-gap isomers?)

  38. N=Z+1; odd-Z 23/2+

  39. N=Z+1; even-Z

More Related