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

On-line mass separation N=50 : a bit of history Experimental status in year 2003 Sr88 Rb87 Kr86 Br85 Se84 As83 Ge82 Ga81 Zn80 Cu79 Ni78 Ni77 Ni71 Ni72 Ni73 Ni74 Ni75 Ni76 Ni70 Ni69 Ni68 Ni67 Ni66 Ni65 Ni64 Ge76 Ge74 Ge72 Y89 Zr90 Z=40 28 N=40 50 Cu65 Zn66 Zn67 Zn68 Zn70 Ga69 Ga71 Ge70 Ge73 As75 Se76 Se74 Se77 Se78 Se80 Se82 Br79 Br81 Kr78 Kr80 Kr82 Kr83 Kr84 Rb85 Sr86 Sr87 Sr84 Zr91 Se75 Se79 Se81 Se83 Kr85 Cu74 Zn75 Zn76 Zn77 Zn78 Ga79 Ga80 b-decay (d,3He) Zendel et al Inorg Nucl Chem 42, 1387 (1980) (t,p) Kratz et al Nucl Phys A 250, 13 (1975) Chimical separation 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 Workshop LEA COLLIGA Catania – 13 - 16 Oct 2008 N=50 status D. Verney Page 2/33

direct reaction in inverse kinematics : Oak Ridge N=50 : present status Experimental status in year 2008 Zr90 Zr91 Z=40 Y89 DIC at Legnaro Sr84 Sr86 Sr87 Sr88 Fusion-fission Rb85 Rb87 Kr78 Kr80 Kr82 Kr83 Kr84 Kr86 Spontaneous fission Br79 Br81 Br85 Se74 Se76 Se77 Se78 Se80 Se82 Se84 Se85 Se86 b -decay Orsay direct reaction in inverse kinematics : Oak Ridge As75 As83 As84 Ge70 Ge72 Ge73 Ge74 Ge76 Ge82 Ge83 Ge84 b -decay Orsay Ga69 Ga71 Ga81 DIC at Legnaro Zn66 Zn67 Zn68 Zn70 Zn77 Zn78 Zn79 Zn80 radioactive beam: REX ISOLDE Cu65 Cu75 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 Workshop LEA COLLIGA Catania – 13 - 16 Oct 2008 N=50 status D. Verney Page 3/33 BE(2) Spectroscopic factors

« » 1 « it’s a joke » 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 Workshop LEA COLLIGA Catania – 13 - 16 Oct 2008 N=50 status D. Verney Page 4/33

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

Proton single particles Why should we worry about N=50 ? 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 E (MeV) -14,386 -13,233 -11,831 -7,121 40 f5/2 p3/2 p1/2 g9/2 Proton single particles From Ji et Wildenthal Phys. Rev. C 38, 2849 (1988) Workshop LEA COLLIGA Catania – 13 - 16 Oct 2008 N=50 status D. Verney Page 6/33

Neutron single particles Proton single particles Why should we worry about N=50 ? 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? Zr90 Zr91 Zr92 Zr93 Zr92 Zr93 Zr94 Zr95 Zr96 Y89 d5/2 gZ/2 s1/2 d3/2 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 f5/2 p3/2 p1/2 g9/2 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 Workshop LEA COLLIGA Catania – 13 - 16 Oct 2008 N=50 status D. Verney Page 7/33

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

Private communication Single particle ordering close to 78Ni Protons : odd-N=50 isotones Zr90 Zr91 Zr92 Zr93 Zr92 Zr93 Zr94 Zr95 Zr96 = 2p3/2 qp state Y89 Ga 81 31 50 Sr88 3 protons out of a 78Ni core Rb87 Kr86 Br85 Se84 Se85 Se86 As83 As84 Ge82 Ge83 Ge84 Ga81 Zn80 Cu79 Ni78 2p3/2 1f5/2 81Ga Z=31 N=50 83As Z=33 N=50 50 Exp 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) Workshop LEA COLLIGA Catania – 13 - 16 Oct 2008 N=50 status D. Verney Page 9/33

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

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

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

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

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

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

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

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

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

Neutron single particles Proton single particles Single particle ordering close to 78Ni How fast those collectivity sets in? Zr90 Zr91 Zr92 Zr93 Zr92 Zr93 Zr94 Zr95 Zr96 Y89 s1/2 d5/2 d3/2 gZ/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 f5/2 p3/2 p1/2 g9/2 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 Workshop LEA COLLIGA Catania – 13 - 16 Oct 2008 N=50 status D. Verney Page 19/33

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

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

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

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

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

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

REX-ISOLDE 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 Workshop LEA COLLIGA Catania – 13 - 16 Oct 2008 N=50 status D. Verney Page 26/33

d5/2 50 g9/2 40 p1/2 p3/2 f5/2 28 f7/2 + - Ge : a special case ? 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) - f7/2 p3/2 p1/2 f5/2 g9/2 28 50 40 d5/2 protons neutrons + Workshop LEA COLLIGA Catania – 13 - 16 Oct 2008 N=50 status D. Verney Page 27/33

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

Collectivity close to 78Ni Even-even nuclei Zr90 Zr91 Zr92 Zr93 Zr92 Zr93 Zr94 Zr95 Zr96 Y89 Zn 80 30 50 1492 keV Sr88 Rb87 Kr86 Br85 Se84 Se85 Se86 As83 As84 Ge82 Ge83 Ge84 Ga81 Zn80 REX ISOLDE 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.” Workshop LEA COLLIGA Catania – 13 - 16 Oct 2008 N=50 status D. Verney Page 29/33

Zn 80 30 50 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 Zr90 Zr91 Zr92 Zr93 Zr92 Zr93 Zr94 Zr95 Zr96 Y89 Zn 80 30 50 Sr88 Rb87 Kr86 Br85 Se84 Se85 Se86 As83 As84 Ge82 Ge83 Ge84 Ga81 Zn80 Cu79 Ni78 50 Workshop LEA COLLIGA Catania – 13 - 16 Oct 2008 N=50 status D. Verney Page 30/33

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

Proton single particles Neutron single particles Conclusions f5/2 p3/2 p1/2 g9/2 Proton single particles Neutron single particles A new single particle ordering appears close to 78Ni 1 gZ/2 N=50 offers nothing but a local parenthesis of rigidity 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 3 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 ? Bohr dynamics very efficient…. Workshop LEA COLLIGA Catania – 13 - 16 Oct 2008 N=50 status D. Verney Page 32/33

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