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Workshop LEA COLLIGA Catania – 13 - 16 Oct 2008

The N=50 shell closure and beyond. Structure of nuclei “Northeast of 78 Ni”. D. Verney, IPN Orsay. Position of the problem : why should we worry about N=50 ?. 1. Valence space above 78 Ni ?. 2. Collectivity in the vicinity of 78 Ni ?. 3. N=50 status D. Verney Page 1 /33.

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Workshop LEA COLLIGA Catania – 13 - 16 Oct 2008

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  1. The N=50 shell closure and beyond Structure of nuclei “Northeast of 78Ni” D. Verney, IPN Orsay Position of the problem : why should we worry about N=50 ? 1 Valence space above 78Ni ? 2 Collectivity in the vicinity of 78Ni ? 3 N=50 status D. Verney Page 1/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  2. N=50 : a bit of history Experimental status in year 2003 Zr90 Zr91 Z=40 Y89 Sr84 Sr86 Sr87 Sr88 Rb85 Rb87 Kr78 Kr80 Kr82 Kr83 Kr84 Kr85 Kr86 Br79 Br81 Br85 Se74 Se75 Se76 Se77 Se78 Se79 Se80 Se81 Se82 Se83 Se84 As75 As83 Ge70 Ge72 Ge73 Ge74 Ge76 Ge82 Ga69 Ga71 Ga79 Ga80 Ga81 Zn66 Zn67 Zn68 Zn70 Zn75 Zn76 Zn77 Zn78 Zn80 Cu65 Cu74 Cu79 Ni64 Ni65 Ni66 Ni67 Ni68 Ni69 Ni70 Ni71 Ni72 Ni73 Ni74 Ni75 Ni76 Ni77 Ni78 28 50 N=40 b-decay (d,3He) Zendel et al Inorg Nucl Chem 42, 1387 (1980) (t,p) Chimical separation Kratz et al Nucl Phys A 250, 13 (1975) Del Marmol et al Nucl Phys A 194, 140 (1972) fission Hoff -Fogelberg Nucl Phys A 368, 210 (1981) OSIRIS /Studsvik fragmentation Ge83 Winger et al Phys Rev C 36, 758 (1987) On-line mass separation TRISTAN /Brookhaven Beginning of b-decay studies at PARRNe « border » of the knowledge on nuclear structure First structure data (g’s) came from b-decay (for N=50) 1 Fission + ISOL technique N=50 status D. Verney Page 2/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  3. N=50 : present status Experimental status in year 2008 Zr90 Zr91 Z=40 Y89 Sr84 Sr86 Sr87 Sr88 Rb85 Rb87 Kr78 Kr80 Kr82 Kr83 Kr84 Kr86 Br79 Br81 Br85 b -decay Orsay b -decay Orsay Se74 Se76 Se77 Se78 Se80 Se82 Se84 Se85 Se86 As84 As75 As83 direct reaction in inverse kinematics : Oak Ridge Ge70 Ge72 Ge73 Ge74 Ge76 Ge82 Ge83 Ge84 Ga69 Ga71 Ga81 DIC at Legnaro Fusion-fission DIC at Legnaro Spontaneous fission Zn66 Zn67 Zn68 Zn70 Zn80 Zn77 Zn78 Zn79 radioactive beam: REX ISOLDE Cu75 Cu65 Cu79 Ni64 Ni65 Ni66 Ni67 Ni68 Ni69 Ni70 Ni71 Ni72 Ni73 Ni74 Ni75 Ni76 Ni77 Ni78 28 ISOLDE laser JYFLTRAP IGISOL 50 isomeric decay: LISE-GANIL b-decay is still in the competition, good complementarities with DIC 2 Fission + ISOL technique + post acceleration BE(2) N=50 status D. Verney Page 3/33 Spectroscopic factors Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  4. Why should we worry about N=50 ? Historically from astrophysical considerations (and b-decay experiments) 1 By Winger et al. PRC 36 (1987) By Kratz et al. PRC 38 (1988) «  »  « it’s a joke » M. Bernas, private communication (2005) Waiting point nucleus at N=50 80Zn N=50 status D. Verney Page 4/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  5. Why should we worry about N=50 ? Historically from structural considerations 2 N=5 - h11/2 From Dobaczewski et al. PRL72 (1994) 981. 70 82 70 g7/2 h11/2 d3/2 d3/2 N=4 s1/2 s1/2 g7/2 d5/2 d5/2 N~Z g9/2 + 40 50 40 Diffuse surface N>>Z g9/2 - p1/2 p1/2 N=3 f5/2 f5/2 HO N=50 status D. Verney Page 5/33 N>>Z N~Z Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  6. Why should we worry about N=50 ? E (MeV) -7,121 g9/2 40 -11,831 p1/2 -13,233 p3/2 f5/2 -14,386 Because the N=28 shell effect is seen disappear in 42Si (see L. Gaudefroy’s Talk) 3 B. Bastin et al., Phys. Rev. Lett. 99 (2007) 022503 First occurrence of the vanishing of shell effect originating from spin orbit Probably due to tensor force in the residual interaction via an Otsuka-like mechanism T. Otsuka et al. PRL95, 232502 (2005) The same tragic destiny is predicted for Z=28 Proton single particles From Ji et Wildenthal Phys. Rev. C 38, 2849 (1988) N=50 status D. Verney Page 6/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  7. Why should we worry about N=50 ? g9/2 p1/2 p3/2 f5/2 At the beginning of the PARRNe project at IPN (very end of the 90’s) 4 Is 78Ni doubly magic ? Persistence of Z=28 and N=50 What is the nature of valence space which opens up just above ? How fast those collectivity sets in? Zr96 Zr94 Zr95 Zr92 Zr93 Zr92 Zr93 Zr90 Zr91 Y89 d5/2 d3/2 gZ/2 s1/2 Sr84 Sr86 Sr87 Sr88 Known part of the valence space Rb85 Rb87 Neutron single particles Kr78 Kr80 Kr82 Kr83 Kr84 Kr85 Kr86 p-n Residual interaction Br79 Br81 Br85 Se76 Se77 Se78 Se79 Se80 Se81 Se82 Se83 Se84 OK Proton single particles ? As75 As83 From Ji et Wildenthal Phys. Rev. C 38, 2849 (1988) Unknown part of the valence space Ge74 Ge76 Ge82 Ga79 Ga80 Ga81 OK Zn75 Zn76 Zn77 Zn78 Zn80 ? Cu74 Cu79 ? Ni70 Ni71 Ni72 Ni73 Ni74 Ni75 Ni76 Ni77 Ni78 50 N=50 status D. Verney Page 7/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  8. Single particle ordering close to 78Ni Protons : odd-N=50 isotones PARRNe Zr96 Zr94 Zr95 Zr92 Zr93 Zr92 Zr93 Zr90 Zr91 Y89 81 3 protons out of a 78Ni core Ga Sr88 31 50 Rb87 Kr86 Br85 Se84 Se85 Se86 1236 (9/2-) As83 As84 observed in b-decay at Orsay (PARRNe) D. Verney et al PRC 76 (2007) 054312 Ge82 Ge83 Ge84 Ga81 Zn81 Zn80 hot subject ! b-decay experiment redone at ISOLDE and Oak Ridge (same lines as us) Cu79 Ni78 50 observed in DIC experiments at Legnaro G. De Angelis et al. NPA 787 (2007) 74c unchallenged! nor by spontaneous fission nor by fusion-fission data N=50 status D. Verney Page 8/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  9. Single particle ordering close to 78Ni Protons : odd-N=50 isotones = 2p3/2 qp state Zr96 Zr94 Zr95 Zr92 Zr93 Zr92 Zr93 Zr90 Zr91 Y89 81 3 protons out of a 78Ni core Ga Sr88 31 50 Rb87 Kr86 Br85 Se84 Se85 Se86 As83 As84 Ge82 Ge83 Ge84 Ga81 Zn80 Cu79 2p3/2 2p3/2 Ni78 50 1f5/2 1f5/2 Exp 81Ga Z=31 N=50 83As Z=33 N=50 Ji & Wildenthal, PRC 40, 389 (1989) BA Brown (jj4b) Private communication JW modified, PRC 76 054312(2007) A.F. Lisetskiy et al., PRC 70 (2004) N=50 status D. Verney Page 9/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  10. Single particle ordering close to 78Ni Protons : odd-N=50 isotones keV 1800 1600 E (MeV) 1400 1200 g9/2 1000 800 f5/22 40 p3/2 600 p1/2 f5/23 f5/23 400 J=3/2 p3/2 J=5/2, v=1 200 f5/2 0 Zr96 Zr94 Zr95 Zr92 Zr93 81Ga Z=31 N=50 Zr92 Zr93 Zr90 Zr91 Y89 81 3 protons out of a 78Ni core Ga Sr88 31 50 Rb87 Kr86 Br85 Proton SPE ordering in a 78Ni mean field Se84 Se85 Se86 J=3/2, v=3 As83 As84 802.8 keV Ge82 Ge83 Ge84 Ga81 451.7 keV Zn80 351.1 keV Cu79 351.1 keV Ni78 0 keV 50 Experiment To be definitely validated in (d,p) reaction (Oak Ridge ? REX ISOLDE ? SPIRAL2 ?) N=50 status D. Verney Page 10/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  11. Single particle ordering close to 78Ni Neutrons : odd-N=51 isotones Zr96 Zr94 Zr95 Zr92 Zr93 Zr92 Zr93 Zr90 Zr91 Y89 83 4 protons + 1 neutron out of a 78Ni core Ge Sr88 32 51 Rb87 Kr86 Br85 Se84 Se85 Se86 As83 As84 Ge82 Ge83 Ge84 Ga83 Ga84 Ga81 Zn80 (3/2,5/2+) observed in b-decay at PARRNe O. Perru et al. EPJ A 28 (2006) 307 Cu79 Ni78 7/2+ observed in bn-decay at ALTO M. Lebois article in preparation 50 247.8 1/2+ observed in 2H(82Ge,p)83Ge at Oak Ridge Thomas et al. PRC 71 (2005) p. 021302 n3s1/2 N=50 status D. Verney Page 11/33 n2d5/2 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  12. Single particle ordering close to 78Ni Neutrons : odd-N=51 isotones L. S. Kisslinger & R. A. Sorensen Rev. Mod. Phys., 35, 853, (1963) Core – particle (weak) coupling model Zr90 Zr91 Core excitation energies taken from experiment : E(2+), E(4+), E(0+2) etc Even-even semi-magic core Y89 Thankappan & True Phys. Rev. B, 137, 793 (1965) Sr89 Sr88 Rb87 Kr87 Neutron single particle Kr86 Br85 Vector space : 0+1 2d5/2 2+1 2d5/2 2+1 3s1/2 Etc… Se84 Se85 Parameters : As83 Ge82 Ge83 Ga81 Zn81 Zn80 Cu79 Ni78 Q>0 Q=0 Q<0 50 N=50 status D. Verney Page 12/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  13. Single particle ordering close to 78Ni Neutrons : odd-N=51 isotones Zr90 Zr91 Y89 Sr89 Sr88 Rb87 Kr86 Br85 Se84 As83 Ge82 Ga81 Zn80 M. Lebois, Thesis Univ. Paris-Sud XI (Sept 2008) Cu79 Ni78 50 N=50 status D. Verney Page 13/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  14. Single particle ordering close to 78Ni Neutrons : odd-N=51 isotones Thomas et al. PRC 71 (2005) p. 021302 n3s1/2 n2d5/2 N=50 status D. Verney Page 14/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  15. Single particle ordering close to 78Ni Neutrons : odd-N=51 isotones Zr90 Zr91 Y89 Sr88 Rb87 Kr86 M. Lebois, Thesis Univ. Paris-Sud XI (Sept 2008) Br85 Se84 As83 Ge82 Ge83 Ga81 Zn80 Cu79 Ni78 50 N=50 status D. Verney Page 15/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  16. Single particle ordering close to 78Ni Neutrons : odd-N=51 isotones N=58 ? N=50 status D. Verney Page 16/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  17. Single particle ordering close to 78Ni Neutrons : odd-N=51 isotones Zr90 Zr91 Y89 Sr88 Rb87 Kr86 Br85 M. Lebois, Thesis Univ. Paris-Sud XI (Sept 2008) Se84 As83 Ge82 Ga81 Zn80 Zn81 Cu79 Ni78 50 N=50 status D. Verney Page 17/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  18. Single particle ordering close to 78Ni Neutrons : odd-N=51 isotones keV 1800 1600 1400 1200 1000 800 600 400 200 0 Zr96 Zr94 Zr95 Zr92 Zr93 Zr92 Zr93 Zr90 Zr91 Y89 81 Ga Sr88 As83 31 50 +5p Rb87 Ge83 Ge82 n 2d5/2 Kr86 1621.6 keV Br85 Ga81 +3p Proton SPE ordering in a 78Ni mean field Se84 Se85 Se86 81Zn Zn80 n 3s1/2? (9/2-) 1236 keV As83 As84 Cu79 +1p Ge82 Ge83 Ge84 Ga81 Ni78 (3/2-) 802.8 keV Zn80 Zn80 gZ/2 451.7 keV Cu79 d3/2 (3/2-) 351.1 keV Ni78 Fed in b-decay Low spins only 351.1 keV 50 (5/2-) 0 keV d5/2 s1/2 N=50 status D. Verney Page 18/33 Neutron single particles Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  19. Single particle ordering close to 78Ni g9/2 p1/2 p3/2 f5/2 How fast those collectivity sets in? Zr96 Zr94 Zr95 Zr92 Zr93 Zr92 Zr93 Zr90 Zr91 Y89 d5/2 d3/2 gZ/2 s1/2 Sr84 Sr86 Sr87 Sr88 Known valence space Rb85 Rb87 Neutron single particles Kr78 Kr80 Kr82 Kr83 Kr84 Kr85 Kr86 p-n Residual interaction Br79 Br81 Br85 Se76 Se77 Se78 Se79 Se80 Se81 Se82 Se83 Se84 OK Proton single particles As75 As83 Unknown valence space Ge74 Ge76 Ge82 Ga81 OK Zn80 ? Cu79 Ni70 Ni71 Ni72 Ni73 Ni74 Ni75 Ni76 Ni77 Ni78 50 N=50 status D. Verney Page 19/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  20. Collectivity close to 78Ni Even-even nuclei Zr96 Zr94 Zr95 Zr92 Zr93 Zr92 Zr93 Zr90 Zr91 Y89 (4¯) 83 84 84 Ga Ge Ga Sr88 31 32 32 53 51 52 Rb87 (0¯) Kr86 n 4 protons + 2 neutrons out of a 78Ni core Br85 Se84 Se85 Se86 As83 As84 Ge82 Ge83 Ge84 Ga84 Ga85 Ga81 247.8 1/2+ Zn80 • -decay ALTO+ ISOLDE and Oak Ridge Cu79 5/2+ Ni78 50 See contribution by F. Ibrahim Wednesday 52 N=50 status D. Verney Page 20/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  21. Collectivity close to 78Ni Z=32 even-even nuclei N=50 status D. Verney Page 21/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  22. Collectivity close to 78Ni N=52 even-even nuclei 0 0 0 0 0 0 0 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.4 0.4 0.4 0.4 0.4 0.4 0.4 N=44 N=42 HFB calculations O Perru thesis Paris-Sud XI (2004) & J. Libert private communication HFB calculation using the Gogny interaction GCM  Bohr dynamics N=48 N=46 N=50 N=50 N=52 41+ hfb 41+ exp N=54 21+ th triaxial static shape predicted ! 21+ exp N=50 status D. Verney Page 22/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  23. Collectivity close to 78Ni N=52 even-even nuclei Strong increase of collectivity Z+40 subshell effect Expected Z=28 shell closure N=50 status D. Verney Page 23/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  24. Ge : a special case ? N=50 status D. Verney Page 24/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  25. Ge : a special case ? Local minimum at Z=32 N=50 status D. Verney Page 25/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  26. Ge : a special case ? Local minimum, not at mid distance Z=28-40 ! 90Zr 88Sr 86Kr 84Se 80Zn 82Ge J. Van de Walle et al. PRL 99, 142501 (2007) REX-ISOLDE N=50 status D. Verney Page 26/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  27. Ge : a special case ? d5/2 + 50 g9/2 g9/2 + + 40 p1/2 p1/2 p3/2 - p3/2 - f5/2 f5/2 28 f7/2 f7/2 protons neutrons A first explanation for the observed downsloping of the p-h states A Prévost et al. EPJ A 22 (2004) 391 Medium/high spin states obtained from fusion/fission at the Vivitron (Euroball IV) N=50 status D. Verney Page 27/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  28. Ge : a special case ? Y.H. Zhang et al. PRC 70 (2004) 024301 Medium/high spin states fed in DIC at Legnaro (GASP) The gap used in the calculation has the good size d5/2 50 4 MeV g9/2 g9/2 84Se p1/2 p1/2 p3/2 SM calculation proton valence space + neutron 1ph SM calculation proton valence space f5/2 28 f7/2 N=50 status D. Verney Page 28/33 protons neutrons Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  29. Collectivity close to 78Ni Even-even nuclei Zr96 Zr94 Zr95 Zr92 Zr93 Zr92 Zr93 Zr90 Zr91 Y89 80 1492 keV Zn Sr88 30 50 Rb87 Kr86 Br85 Se84 Se85 Se86 As83 As84 Ge82 Ge83 Ge84 Ga81 REX ISOLDE Zn80 J. Van de Walle et al. PRL 99, 142501 (2007) Cu79 Ni78 50 “The results for N=50 isotones indicate a good N=50 shell closure and a strong Z=28 proton core polarization.” N=50 status D. Verney Page 29/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  30. Collectivity close to 78Ni Even-even nuclei O Perru thesis Paris-Sud XI (2004) & J. Libert private communication HFB calculation using the Gogny interaction GCM  Bohr dynamics Zr96 Zr94 Zr95 Zr92 Zr93 Zr92 Zr93 Zr90 Zr91 Y89 80 Zn Sr88 30 50 Rb87 Kr86 Br85 Se84 Se85 Se86 As83 As84 Ge82 Ge83 Ge84 Ga81 Zn80 Cu79 Ni78 50 N=50 status D. Verney Page 30/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  31. Collectivity close to 78Ni Even-even nuclei Zr96 Zr94 Zr95 Zr92 Zr93 Zr92 Zr93 Zr90 Zr91 66Zn 68Zn 70Zn Y89 80 Zn Sr88 30 50 Rb87 Kr86 Br85 Se84 Se85 Se86 As83 As84 76Zn 74Zn 72Zn Ge82 Ge83 Ge84 Ga81 Zn80 Cu79 Ni78 50 80Zn 78Zn Potentials Zn N=50 status D. Verney Page 31/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  32. Conclusions g9/2 p1/2 p3/2 f5/2 Proton single particles Neutron single particles A new single particle ordering appears close to 78Ni 1 gZ/2 d3/2 Local minimum of the N=50 shell gap for Z=32 seems to have considerable influence on structure d5/2 Collectivity sets in very rapidly just below and just above N=50 s1/2 The underlying microscopic mechanism remains to be understood N=50 offers nothing but a local parenthesis of rigidity 2 From the shell model point of view : description is alright up to N=50, beyond N=50 much work to do. Is 78Ni a good core ? 3 Bohr dynamics very efficient…. N=50 status D. Verney Page 32/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

  33. Thank you ! N=50 status D. Verney Page 33/33 Workshop LEA COLLIGACatania – 13 - 16 Oct 2008

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