1. EWON – Prague May 10, 2007 Collaboration NIPNE Bucharest -- LSF LN Legnaro Studies of N≈Z nuclei above mass 80

2. EWON – Prague May 10, 2007 M.Axiotis 1, D.Bazzacco 2, D.Bucurescu 3, G. de Angelis 4, E.Farnea 2, A.Gadea 4, M.Ionescu-Bujor 3, A.Iordǎchescu 3, W.Krolas 5, Th.Kröll 6, S.Lenzi 2, S.Lunardi 2, N.Mǎrginean 3,4, T. Martinez 4, R.Menegazzo 2, D.R.Napoli 4, P.Pavan 2, B.Quintana 7, C.Rossi Alvarez 2, C.Rusu 3,4, P.Spolaore 4, C.A.Ur 2,3, J. Wrzesinski 5 recent youngs: C. Mihai 3, G. Suliman 3 [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. EWON – Prague May 10, 2007 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. EWON – Prague May 10, 2007 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. EWON – Prague May 10, 2007 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’ Ancillary detectors γ-ray Spectroscopy Ge arrays Beta-decay studies 32 S+ 58 Ni, 105 MeV Charged particle balls Neutron arrays Mass spectrometers

6. EWON – Prague May 10, 2007 Experimental Facilities GASP GASP ( config. 1 )  abs (40 HPGe)  3% Peak/Total  60%  abs (80 BGO)  76% ISIS (40 ΔE-E Silicon telescopes)  p  56-60%    35-38% N-Ring  n  2-5% Beam

7. EWON – Prague May 10, 2007 p-drip line: G.A.Lalazissis et al, Nucl. Phys. A719,209c(2003): Relativistic HB calc.

8. EWON – Prague May 10, 2007 N. Mărginean et al. Phys. Rev. C 63 (2001) 032303(R) N. M ăr ginean et al. Phys. Rev. C 65 (2002) 051303(R)

9. EWON – Prague May 10, 2007 New data: 72 Kr : C.Andreoiu et al., Phys. Rev. C75(2007)041301(R) 76 Sr : 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 (isovector np pairing + isospin symmetry conservation) [ Afanasjev & Frauendorf, PRC71(2005)064318 ] (CRHB calculations) Signature of T=0 np pairing ? Delayed Alignment in N=Z Nuclei: J=0 T=1 J=1…2j T=0

10. EWON – Prague May 10, 2007 Projected Shell Model Calculations N. Mărginean et al. Phys. Rev. C 65 (2002) 051303(R)

11. EWON – Prague May 10, 2007 N=Z+1 81 Zr Experiment: 28 Si(90 MeV) + 58 Ni Target: 2 x 0.5 mg/cm 2 58 Ni 81 Zr - αn channel, intensity  2·10 -4 N. Mărginean et al. Phys. Rev. C 69 (2004) 054301

12. EWON – Prague May 10, 2007 N=40 [422]5/2 [301]3/2 [431]1/2 1 neutron hole + 82 Zr N=40 [422]5/2 [301]3/2 [431]1/2 1 neutron particle + 80 Zr Fermi

13. EWON – Prague May 10, 2007

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

15. EWON – Prague May 10, 2007 E3  isomeric decay 95 Ag τ isomer > ≈ 1 μs [predicted by Ogawa, Phys.Rev. C28,958(1983)]

16. EWON – Prague May 10, 2007 Shell Model Effective Interactions SLGT0 - Serduke, Lawson, Gloeckner, NPA256(1976)45; Herndl, Brown, NPA605(1996)195 A>86, N,Z=[38-50] π,υ(2p 1/2,1g 9/2 ) 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)

17. EWON – Prague May 10, 2007 ν,π(p 1/2,g 9/2 ) SLGT0 resid. inter. C. Rusu et al, Phys. Rev. C 69 (2004) 024307 N.Mǎrginean et al, Phys. Rev. C67(2003)061301(R)

18. EWON – Prague May 10, 2007 2.86 2.0 2.25 2.75 2.5 2.0 2.25 1.75 1.5 2.30 2.52 2.84 2.5

19. EWON – Prague May 10, 2007 (F. Iachello Phys. Rev. Letters 85 (2000) 3580) 134 Ba (F. Iachello Phys. Rev. Letters 87 (2001) 052502) 152 Sm Unharmonic vibrator Stable quadrupole deformation  -soft rotor Axially symmetric rotor Shape phases, phase transitions and critical points Critical points: parameter-free analytical approximations

20. EWON – Prague May 10, 2007 Prediction of X(5) nuclei 4.5 < N p N n /(N p +N n ) < 5.5 N=Z = 38,40 (N.V. Zamfir, private comm.)

21. EWON – Prague May 10, 2007

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

23. EWON – Prague May 10, 2007 Phase Transition in IBA Triangle 0+0+ 2+2+ 4+4+ 2+2+ 3+3+ 4+4+  Fine grid on parameter space   2 merit function including both energy and branching ratios New parameters: * * 82 Zr 80 Sr 78 Sr

24. EWON – Prague May 10, 2007 Conclusions N≈Z nuclei, mass 80 - 100: theatre of many interesting nuclear structure phenomena First spectroscopic measurements of the heaviest known N=Z ( 88 Ru) and N=Z+1 ( 81 Zr, 85 Mo, 89 Ru, 91 Rh, 93Pd, 95 Ag) 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 81 Zr).

25. EWON – Prague May 10, 2007 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 76,78 Sr, 80 Zr, ( 78 Zr) ) Extensions of these data are necessary (in spin: e.g., 88 Ru to higher states; in mass: 92 Pd; N=Z+1 nuclei). Shell model (Z≥44; N≥45): old residual interactions (SLGT0, GF, JS) in (p 1/2,g 9/2 ) space perform reasonably well. Isomers explained. But: yrast π = + (g 9/2 ) states are not so sensitive – not critical tests! Exceptional support within LSF LN-Legnaro; full use of the capabilities of GASP and its ancillaries: ISIS and N-wall.

26. EWON – Prague May 10, 2007 END

27. EWON – Prague May 10, 2007

28. Reaction Target Beam intens. (8 + ), [pnA] Trigger condition 28 Si ( 90 MeV ) + 58 Ni 2 x 0.5 mg/cm 2 14 2Ge,2BGO 32 S ( 105 MeV ) + 58 Ni 1.1 mg/cm 2 6 2Ge,3BGO 40 Ca( 130 MeV )+ 54 Fe 6.5 mg/cm 2 4 - 6 2Ge,1BGO 40 Ca( 135 MeV )+ 58 Ni 6.0 mg/cm 2 8 2Ge,1BGO GASP experiments

29. EWON – Prague May 10, 2007 ReactionChannelStudied Nucleus σσ (% σ F ) Status 28 Si+ 58 Ni 90 MeV 2n 84 Mo ~ 7 μb ~ 4 10 -5 1 γ known before αn 81 Zr ~ 0.3 mb ~ 2 10 -4 unknown 32 S+ 58 Ni 105 MeV 2n 88 Ru 5-10 μb ~ 4 10 -5 unknown αn 85 Mo 0.13 mb 7 10 -4 unknown 40 Ca+ 54 Fe 130 MeV αn 89 Ru ~ 40 μb ~ 1-2 10 -4 unknown p2n 91 Rh ~ 65 μb ~ 2-3 10 -4 unknown 40 Ca+ 58 Ni 135 MeV αn 93 Pd unknown p2n 95 Ag unknown 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: 93 Pd: D.Sohler et al., EPJ A19,169(2004) 95 Ag: J.Döring et al., PR C68,034306(2003)

30. EWON – Prague May 10, 2007 ~ Grodzins estimate β 2 ~ A -7/6 E(2 + ) -1/2

31. EWON – Prague May 10, 2007 M.Hasegawa et al., Phys. Rev. C69,034324(2004) Shell model, P+QQ Hamiltonian, (1g 9/2,2p 1/2,1f 5/2,2p 3/2 ) -N max. dimens. for 88 Ru (N=12): 165 x 10 6 Strengthened isoscalar QQ pn interaction

32. EWON – Prague May 10, 2007 Identification of N=Z: 88 Ru Experiment: 32 S(105 MeV) + 58 Ni –Target: 1.1 mg/cm 2 58 Ni on 10 mg/cm 2 Au – 88 Ru 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: GASP + ISIS + 6 n-detectors N. Mărginean et al. Phys. Rev. C 63 (2001) 031303(R) Matrix projection

33. EWON – Prague May 10, 2007 τ isomer > ≈ 1 μs N=Z+1, 95 47 Ag 48 approaching N,Z=50 : spin gap isomer N. Mărginean et al. Phys. Rev. C 67 (2003) 061301(R) 1p2n channel predicted Ogawa PR C28,958(1983)

34. EWON – Prague May 10, 2007

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

36. EWON – Prague May 10, 2007

37. J Π Ex (keV) SLGT0 GF F-FIT (9/2+) 0 0 0 0 (13/2+) 840 112 22 56 (17/2+) 1787 48 -116 -42 (21/2+) 2655 -81 -308 -226 (25/2+) 3103 -75 -316 -241 (29/2+) 4136 -365 -245 (1/2-) 173 112 186 (5/2-) 792 195 330 187 (9/2-) 1292 258 368 208 (13/2-) 1905 82 168 2 (17/2-) 2278 97 190 46 EXP.E calc. - E exp. (keV) 91 Rh – comparison with 3 Shell Model calculations

38. EWON – Prague May 10, 2007 91 Rh Johnstone-Skouras (2001) – F-FIT eff. inter. πυ(2p 1/2 1g 9/2 ) N. Mărginean et al. Phys. Rev. C 72 (2005) 014302

39. EWON – Prague May 10, 2007 (preliminary)

40. EWON – Prague May 10, 2007 General structure of a collective nucleus: Basic information on :  g.s.b.  0 2 + - band (quasi-beta band)  2 γ + - band (quasi-gamma band) Energy ratios: E(4 1 + )/ E(2 1 + ); E(0 2 + )/E(2 1 + ); E(2 γ + )/E(2 1 + ); etc. Elmag. trans. Probab.: B(E2; 2 γ --> 0 1 )/ B(E2; 2 1 --> 0 1 ); B(E2; 2 γ --> 0 1 )/ B(E2; 2 1 --> 2 1 ); etc. Ex.: U(5) R(4/2) = 2.0 R(0 2 + /2 1 + ) = a (~2) R(2 2 + /2 1 + ) = 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

41. EWON – Prague May 10, 2007 56 Ni + 40 Ca ---> 88 Ru + 2α 88 Ru cross-sections : with 56 Ni beam : ~ 30 mb with 32 S beam: 5-10 μb --------------------------------------- R ~ 3 x 10 3 ( 56 Ni/ 32 S) Beam 56 Ni : [~ 3 x 10 7 ions/sec (2003, ANL)] ------→ ~ 10 11 (FAIR) Beam 32 S (GASP): ~ 6 pnA ≈ 4 x 10 10 ions/sec ---------------------------------------- R ~ 1 ( 56 Ni/ 32 S) Overall gain with 56 Ni : ~3000 (assuming GASP (3%) γ-efficiency and same target !) with Ge-array of increased efficiency :  gain >> ~ 3000 ! N=Z 88 Ru with RIB:

42. EWON – Prague May 10, 2007 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: ~ 80 Zr : tetrahedral deformation (spin-gap isomers?)

43. EWON – Prague May 10, 2007 23/2 + N=Z+1; odd-Z

44. EWON – Prague May 10, 2007 N=Z+1; even-Z