1. Evolution of N=50 towards 78 Ni: recent inputs from experiments Workshop Espace de Structure Nucléaire Théorique Saclay 3-5 May 2010 Position of the problem : why should we worry about N=50 ? 1 N=50 shell gap evolution: salient features from experimental data 2 deeper into nuclear structure close to 78 Ni : valence space, single particle state effective sequence 3 D. Verney, IPN Orsay 0 Introduction: recent progress in experiment north north-east to 78 Ni

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3. N=50 : recent experimental breakthrough (d,3He) -decay « border » of the knowledge on nuclear structure fission (t,p) Zendel et al Inorg Nucl Chem 42, 1387 (1980) Kratz et al Nucl Phys A 250, 13 (1975) Del Marmol et al Nucl Phys A 194, 140 (1972) Hoff -Fogelberg Nucl Phys A 368, 210 (1981) Ge83 Experimental status in year 2003 fragmentation Winger et al Phys Rev C 36, 758 (1987) Beginning of -decay studies at PARRNe OSIRIS /Studsvik TRISTAN /Brookhaven On-line mass separation Chimical separation First structure data (  ’s) came from  -decay (for N=50) 1 Fission + ISOL technique ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 3/52 main nuclear mechanisms used : -fragmentation of stable beams -fission

4. Sr88 Rb87 Kr86 Br85 Se84 As83 Ge82 Ga81 Zn80 Cu79 Ni78Ni77Ni71Ni72Ni73Ni74Ni75Ni76Ni70Ni69Ni68Ni67Ni66Ni65Ni64 Ge76 Ge74Ge72 Y89 Zr90 Z=40 28 50 Cu65 Zn66Zn67Zn68Zn70 Ga69Ga71 Ge70Ge73 As75 Se76Se74Se77Se78Se80Se82 Br79Br81 Kr78Kr80Kr82Kr83Kr84 Rb85 Sr86Sr87Sr84 Zr91 Ge84 Ge83 isomeric decay: LISE-GANIL radioactive beam: REX ISOLDE Cu77 Zn78Zn79 As84 Se85Se86  -decay Orsay direct reaction in inverse kinematics : Oak Ridge DIC at Legnaro ISOLDE laser Experimental status in year 2010  -decay is still in the competition, good complementarities with DIC 2 Fission + ISOL technique + post acceleration BE(2) Spectroscopic factors DIC at LegnaroFusion-fissionSpontaneous fission JYFLTRAP IGISOL  -decay Orsay N=50 : recent experimental breakthrough main nuclear mechanisms used : -fragmentation of stable beams -fission -deep inelastic collisions ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 4/52

5. Position of the problem : why should we worry about N=50 ? 1

6. Why should we worry about N=50 ? Historically from astrophysical considerations (and  -decay experiments) By Kratz et al. PRC 38 (1988) Waiting point nucleus at N=50 80 Zn By Winger et al. PRC 36 (1987) « » « it’s a joke » M. Bernas, private communication (2001) 1 ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 6/52

7. ground state of 42 Si N=28 is observed deformed B. Bastin et al., Phys. Rev. Lett. 99 (2007) 022503 spin-orbit origin Why should we worry about N=50 ? ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 7/52 “A full treatment of Hm shows no magicity at 30Ne and 32Mg, while 34Si (or any other Si isotope) exhibits a clear shell effect. It just so happens that the full Hm reproduces the observed robustness of the SO closures, and the fragility of those of other origins. Whether they survive or not depends mainly on the possibility of developing quadrupole coherence in a given space.” A.P. Zuker PRL 91 (2003)

8. O. Sorlin, M. Porquet Prog. Part. Nucl. Phys. 61 (2008) 602 N=50 gap extrapolation → 78 Ni =3.0(5) MeV 100 Sn 78 Ni from binding energies of the states below and above Z=28 and N=50 78 Ni 56 Ni Z=28 gap extrapolation → 78 Ni =2.5 MeV Why should we worry about N=50 ? 44 46 48 50 ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 8/52 T. Otsuka et al. PRL95, 232502 (2005)

9. Why should we worry about N=50 ? ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 9/52 extracted from J. Van de Walle et al PRC 70 (2009) 014309 Their is a N=50 shell effect with strong influence on nuclear structure close to 78 Ni Now, the real question becomes : how the shell gap associated to the N=50 magic number evolves towards 78 Ni or is there any evolution at all ?

10. N=50 shell gap evolution: prominent features from experimental data 2

11. Evolution of the N=50 shell gap ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 11/52 A Prévost et al. EPJ A 22 (2004) 391 Medium/high spin states obtained from fusion/fission at the Vivitron (Euroball IV) conclusion : N=50 shell gap decrease : yes - f 7/2 p 3/2 p 1/2 f 5/2 g 9/2 28 50 40 f 7/2 p 1/2 g 9/2 d 5/2 p 3/2 f 5/2 protonsneutrons - + + + Yrast structure studies (fusion-fission mechanism)

12. Yrast structure studies (spontaneous fission mechanism) 2 levels added : one of the two “must be” 1p-1h across N=50 T. Rza˛ca-Urban et al. PRC 76 (2007) 027302 Medium/high spin states fed in 248Cm spontaneous fission conclusion : N=50 shell gap decrease : yes ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 12/52 Evolution of the N=50 shell gap 32

13. Y.H. Zhang et al. PRC 70 (2004) 024301 Medium/high spin states fed in DIC at Legnaro (GASP) conclusion : N=50 shell gap decrease : no (same conclusion as Kamila) 84Se SM calculation proton valence space SM calculation proton valence space + neutron 1ph f 7/2 p 3/2 p 1/2 f 5/2 g 9/2 28 p 1/2 g 9/2 d 5/2 protons neutrons 50 4 MeV The gap used in the calculation has the good size Yrast structure studies (deep inelastic mechanism) ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 13/52 Evolution of the N=50 shell gap

14. Mass measurements (IGISOL Jyvaskyla) Evolution of the N=50 shell gap ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 14/52

15. Local minimum at Z=32  =S 2n (52)-S 2n (50) (this quantity is the one traditionnally used to extract shell gaps from mass measurements) Mass measurements (IGISOL Jyvaskyla) Evolution of the N=50 shell gap ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 15/52

16. Koopmans theorem : gap in the single particle levels 50  j’  j  j’ = S n (Z,N) but S n (Z,N+1) is not a good prescription for for the evaluation of  j one has to estimate  j’ and  j  in the same nucleus NPA466 (1987) 189  j —  j’ = S n (Z,N) —S n (Z,N extr ) then the good prescription becomes : Mass measurements : what quantity is truly relevant for nuclear structure Evolution of the N=50 shell gap ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 16/52 Z S n (Z,N)-S n (Z,N+1) S n (Z,N)-S n (Z,N extr ) N N+1 N+3 N+5 N+7 neutron number

17. using data taken from mass evaluation 2010 with kind authorization by G. Audi (AME2010 unpublished - G. Audi private communication)  d 5/2 –  g 9/2 (MeV) Ni ZnGe SeKrSr Duflo Zuker gap PRC59 (1999) 90 Zr =4,7 MeV Duflo Zuker gap 78 Ni =5,7 MeV gap « rough » « prescripted » gap pairing gain(MeV) neutron pairing gain = 2S n (Z,N+1) —S 2n (Z,N+2) Ni Zn GeSe KrSr AME2010 extrapolation Mass measurements : what quantity is truly relevant for nuclear structure Evolution of the N=50 shell gap local minimum at Z=32 ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 17/52 conclusion : N=50 becomes somewhat “porous” relative to pair promotions (towards 78 Ni) what will be the result on structure? what is the microscopic mechanism at play which could explain this local minimum ? Zr

18. 32 Evolution of the N=50 shell gap ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 18/52 in particular : could provide a simple explanation to the Yrast structure behavior

19. Local minimum, not at mid distance Z=28-40 REX-ISOLDE J. Van de Walle et al. PRL 99, 142501 (2007) 80Zn 82Ge 84Se 86Kr 88Sr 90Zr Evolution of the N=50 shell gap and also the peculiar evolution of the E(2+) of the even- even N=50 isotones ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 19/52

20. from  -decay at ALTO Evolution of the N=50 shell gap ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 20/52 52

21. N=42 0.10.20.30.40 N=44 0.10.20.30.40 N=46 0.10.20.30.40 N=48 0.10.20.30.40 Ge isotopic chain Evolution of the N=50 shell gap and connection with collectivity N=50 0.10.20.30.40 N=52 0.10.20.30.40 N=54 0.10.20.30.40 O Perru thesis Paris-Sud XI (2004) & J. Libert and M. Girod private communication D1S Gogny HFB calculation GCM  Bohr dynamics ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 21/52

22. Ge HFB + GCM (GOA) Evolution of the N=50 shell gap and connection with collectivity ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 22/52

23. Collectivity close to 78Ni N=52 even-even nuclei Z=28 shell closure Z=40 subshell effect N=52 Evolution of the N=50 shell gap and connection with collectivity ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 23/52

24. deeper into nuclear structure close to 78 Ni : valence space, single particle state effective sequence 3

25. Proton structure above 78 Ni K. Flanagan et al. N=40N=42 N=44 N=46N=48 N=50 but already hinted at in the 80’s !! (from shell model, empirical interaction) E (MeV) -14,386 -13,233 -11,831 -7,121 40 f 5/2 p 3/2 p 1/2 g 9/2 Proton single particles From Ji et Wildenthal Phys. Rev. C 38, 2849 (1988) 28 50 ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 25/52 Proton structure above 78 Ni

26. shell model calculation : Ji et Wildenthal Phys. Rev. C 38, 2849 (1988) TBME and SP energies fitted to the data Proton structure above 78 Ni E (MeV) -14,386 -13,233 -11,831 -7,121 40 f 5/2 p 3/2 p 1/2 g 9/2 Proton single particles 28 50 Zn Ge Se Kr ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 26/52

27. A. Pfeiffer et al. NPA 455 (1986) 381 Proton structure above 78 Ni ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 27/52 E (MeV) -14,386 -13,233 -11,831 -7,121 40 f 5/2 p 3/2 p 1/2 g 9/2 Proton single particles From Ji et Wildenthal Phys. Rev. C 38, 2849 (1988) 28 50

28. 1236 (9/2-) hot subject -  -decay experiment redone at ISOLDE and Oak Ridge (same lines as us) observed in  -decay at Orsay (PARRNe) D. Verney et al PRC 76 (2007) 054312 observed in DIC experiments at Legnaro G. De Angelis et al. NPA 787 (2007) 74c Zn81 Sr88 Rb87 Kr86 Br85 Se84 As83 Ge82 Ga81 Zn80 Cu79 Ni78 Y89 Zr90 50 Zr91 Zr93Zr92 Zr93 Zr94Zr95 Zr96 Se85Se86 As84 Ge83Ge84 Ga 81 31 50 3 protons out of a 78 Ni core PARRNe Proton structure above 78 Ni ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 28/52

29. 0 200 400 600 800 1000 1200 1400 1600 1800 keV 3/2- 5/2- 64 keV 0 keV 679 keV 3/2- 1279 keV 1/2- 5/2- 1368 keV 3/2- 1897 keV 81 Ga Z=31 N=50 351.1 keV 0 keV 802.8 keV 1236 keV Experiment empirical effective interaction : fit on a series of carefully selected states Valence space N=50 closed & Z=28 closed (the doubly magical nature of 78Ni is assumed) The valence space is reduced to proton orbitals Theory Ji & Wildenthal, PRC 40, 389 (1989) 306.51 keV 83 As Z=33 N=50 0 keV 711.66 keV 1193.7 keV 1196.53 keV 1256.76 keV 1329.87 keV 1415.11 keV 1434.92 keV 1525.52 keV 1804.76 keV 1977.9 keV Experiment (3/2-) (5/2-) Winger et al, PRC 38, 285 (1988) 1/2- 0 keV 189 keV 353 keV 589 keV 990 keV 1115 keV 1253 keV 1382 keV 1455 keV 1643 keV 1845 keV 1857 keV 1879 keV 1985 keV 5/2- 3/2- 1/2- 3/2- 7/2- 5/2- 3/2- 1/2- 5/2- 9/2- 3/2- 7/2- 9/2- Theory 351.1 keV 451.7 keV (5/2-) (3/2-) (9/2-) Proton structure above 78 Ni ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 29/52

30. Proton structure above 78 Ni ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 30/52 what to do ? remember the textbooks and assume  1f 5/2 is indeed the first proton orbit filled above 78 Ni Talmi : = single particle (binding) energy number of particles in the configuration seniority number for identical particles in j<=7/2 there exists a closed formula expressing the configuration energy (by Talmi) 82Ge81Ga 80Zn n=4, =0 0+ 5/2+ 3/2+ 0+ 2+ n=3, =1 n=3, =3 1492 keV 803 keV n=2, =2 n=2, =0 BE(f 5/2 )= -13.576 MeV………JW give -14.386 MeV E(9/2-) in 81 Ga=1250 keV ……experiment :1236 keV E(4+) in 80 Zn=1809 keV ………experiment :?  1f 5/2 ) 4  1f 5/2 ) 3  1f 5/2 ) 2 but also extract : J=0 J=2 J=4

31. Proton structure above 78 Ni f 5/2 pairing looks small ! back to the Ji Wildenthal proton-proton residual interaction : Is it possible to find a simple cure to the interaction ? ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 31/52

32. A.F. Lisetskiy et al., PRC 70 (2004) Ji & Wildenthal, PRC 40, 389 (1989) Z=31 N=50 JW+rustine Proton structure above 78 Ni ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 32/52 1qp  f5/2 1qp  p3/2 v=3(  f5/2) 3

33. A.F. Lisetskiy et al., PRC 70 (2004) Ji & Wildenthal, PRC 40, 389 (1989) Z=33 N=50 711 keV JW+rustine Proton structure above 78 Ni ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 33/52 1qp  f5/2 1qp  p3/2 1qp  p1/2

34. Z=35 N=50 JW+rustine ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 34/52 1qp  f5/2 1qp  p3/2 1qp  p1/2 Proton structure above 78 Ni

35. 2p 3/2 1f 5/2 81 Ga Z=31 N=50 2p 3/2 1f 5/2 83 As Z=33 N=50 2p 3/2 1f 5/2 85 Br Z=35 N=50 2p 1/2 the conclusion is : this proton sequence is confirmed E (MeV) -14,386 -13,233 -11,831 -7,121 40 f 5/2 p 3/2 p 1/2 g 9/2 Proton single particles From Ji et Wildenthal Phys. Rev. C 38, 2849 (1988) 28 50 and the observed structure of the odd-proton N=50 isotones simply (and naturally) reflects the change of the Fermi level Proton structure above 78 Ni ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 35/52

36. Neutron structure above 78 Ni ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 36/52 O. Sorlin, M. Porquet Prog. Part. Nucl. Phys. 61 (2008) 602 centroides from (d,p) g 7/2 goes up 91 Zr 89 Sr g 7/2 nearly constant K. Sieja et al. PRC 79, 064310 (2009) EXPERIMENT THEORY (SM) g 7/2 goes down SM calculations in valence space above 78 Ni From Duflo Zuker PRC 59, R2347 (1999)

37. E (MeV) 0.00 1.00 2.45 3.04 82 Neutron single particles From T.A. Hughes Phys. Rev. 181, 1586 (1969) d 5/2 d 3/2 s 1/2 g 7/2 50 in 89 Sr ? h 11/2 but in fact the problem of the position of h11/2 remains unsolved → need for the observation of negative parity Yrast states in N=51 Neutron structure above 78 Ni ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 37/52 experiment and theory agree close to stability

38. Ga84 247.8 1/2+ observé en 2 H( 82 Ge,p) 83 Ge à Oak Ridge Thomas et al. PRC 71 (2005) 021302 observé en décroissance  - decay à PARRNe O. Perru et al. EPJ A 28 (2006) 307 et thèse Paris 11 Ga83 Sr88 Rb87 Kr86 Br85 Se84 As83 Ge82 Ga81 Zn80 Cu79 Ni78 Y89 Zr90 50 Zr91 Zr93Zr92 Zr93 Zr94Zr95 Zr96 Se85Se86 As84 Ge83Ge84 Ge 83 32 51 4 protons + 1 neutron au dessus de 78 Ni observé en décroissance  n avec ALTO M. Lebois et al. PRC 80 (2009) 044308 et thèse Paris 11 2d 5/2 3s 1/2 (3/2,5/2 + ) 7/2 + Neutron structure above 78 Ni experiment and theory agree close to stability ? ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 38/52

39. (1/2+)? E(2+) of the even-even core(semi-magic N=50) Neutron structure above 78 Ni systematics for the odd-neutron N=51 isotones ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 39/52

40. Even-even semi-magic core single particle Q>0 Q=0 Q<0 2+ 1 2d5/2 J=1/2 J=3/2 J=9/2 J=5/2 J=7/2 Neutron structure above 78 Ni ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 40/52

41. (1/2+)? N=51 E(2+) of the even-even core(semi-magic N=50) Neutron structure above 78 Ni ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 41/52

42. (1/2+)? S=0.84 non-stripped S=0.49 S=0.016 d 3/2 g 7/2 S=0.06±0.02 S=0.77±0.27 from J. S. Thomas et al. PRC 76, 044302 (2007) not observed in (d,p) Neutron structure above 78 Ni ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 42/52 first 7/2 state is 2+*d 5/2 coupled state, g 7/2 is higher in energy

43. (1/2+)? s 1/2 d’après J. S. Thomas et al. PRC 76, 044302 (2007) S=0.90 5 S=0.46 S=0.31 S=0.18 non-stripped not observed (dp) S=0.52 s 1/2 down sloping of the s 1/2 is firmly established Neutron structure above 78 Ni ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 43/52

44. Core – particle coupling model Even-even semi-magic core L. S. Kisslinger & R. A. Sorensen Rev. Mod. Phys., 35, 853, (1963) Thankappan & True Phys. Rev. B, 137, 793 (1965) Neutron single particle Core excitation energies taken from experiment : E(2+) Parameters : Vector space : 0+ 1 2d5/2 2+ 1 2d5/2 2+ 1 3s1/2 Etc…  =  = Quadrupole moment of the 2+ state  Phenomenological model with a clear underlying physical image. All parameters with straightforward interpretation: Example : harmonic vibrator : Q 2+ =0   2 =0 how to extract (at least approximately) effective single particle energies when no direct reaction data is available ? use a simple empirical model Neutron structure above 78 Ni ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 44/52

45. unperturbed theory experiment 0 + d5/2 0 + s1/2 2 + d5/2 0 + d3/2 0 + g7/2 0 2 + d5/2 2 2 + d5/2 2 + s1/2 5 2 1 2 3 2 7 2 5 2 1 2 3 2 5 2 7 2 9 2 5 2 5 2 7 2 1 2 7 2 7 2 5 2 5 2 3 2 9 2 3 2 9 2 3 2 3 2 1 2 7 2 1 2 3 2 5 2 7 2 9 2 1 2 0.26ps 0.19ps 0.10ps 0.21ps 0.11ps 0.16ps 0.02ps 0.09ps 1.85ps S=0.79 S=0.905 S=0.091 S=0.46 S=0.34 S=0.74 S=0.88 S=0.78 S=0.016 S=0.053 S=0.64 S=0.15 S=0.84 89 Sr 3 2 5 2 >1 ps  1/2 calculated assuming only M1 and E2 transitions e( )=1 and g s =0.6 g sfree  2 =0.56 (M1+E2)  2 =0.87 (M1+E2) Q exp = -0.28(3) eb / -0.32(2) eb  exp = -1.1481 n.m. Q calc = -0.27 eb  calc = -1.020 n.m. experimentcore-particle coupling not included in the model space

46. unperturbed theory experiment 0 + d5/2 5 2 5 2 5 2 S=0.90 S=0.56 0 + s1/2 1 2 2 + d5/2 1 2 3 2 5 2 7 2 9 2 0 + d3/2 3 2 0 + g7/2 7 2 4 + d5/2 3 2 5 2 7 2 9 2 2 11 2 13 2 2 + d5/2 1 2 3 2 5 2 7 2 9 2 2 + s1/2 3 2 5 2 1 2 3 2 9 2 7 2 5 2 3 2 1 2 7 2 5 2 S=0.68 S=0.20 S=0.02 S=0.06 S=0.43 S=0.27 S=0.84 S=0.03 7 2 3 2 5 2 9 2 S=0.46 1 2 S=0.23 9 2 3 2 5 2 S=0.02 3 2 5 2 S=0.09 1 2 S=0.18 11 2 3 2 5 2 S=0.3 S=0.49 7 2 87 Kr

47. 85 Se 0 + d5/2 0 + s1/2 2 + d5/2 1 2 3 2 5 2 7 2 9 2 0 2 + d5/2 1 2 5 2 5 2 4 + d5/2 3 2 5 2 7 2 9 2 2 11 2 13 2 + s1/2 3 2 5 2 0 + d3/2 0 + g7/2 3 2 7 2 1 2 5 2 unperturbed theory experiment 7 2 9 2 5 2 3 2 3 2 7 2 1 2 5 2 1 2 7 2 9 2 3 2 5 2 1 2 ? 1 2 9 2 7 2 ? - 11 2 3 2 5 2 3 2 1 2 9 2 3 2 5 2 7 2 2 13 2 3 2 5 2 7 2 ? ? ? S=0.38 S=0.31 S=0.77 or 0.06 S=0.90 S=0.86 S=0.09

48. g7/2 d3/2 d5/2 s1/2 Neutron structure above 78 Ni on the overall neutron single particle sequence appears to be : ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 48/52

49. d5/2 s1/2 d3/2 g7/2 MeV N=58 ? if we extract the effective single particle energies using the core-particle coupling model : Neutron structure above 78 Ni ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 49/52 conclusion : appearance of a new neutron subshell gap close to 78 Ni ?

50. d5/2 s1/2 d3/2 g7/2 MeV ? N=58 ? is there a simple explanation to the s1/2 down sloping ? Neutron structure above 78 Ni ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 50/52

51. 80 10 0 60 is there a simple explanation to the s1/2 down sloping ? Neutron structure above 78 Ni ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 51/52

52. s1/2 g7/2 d3/2 Neutron structure above 78 Ni K. Sieja private communication (yesterday) ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 52/52

53. Proton single particles d 5/2 d 3/2 s 1/2 g 7/2 Neutron single particles f 5/2 p 3/2 p 1/2 g 9/2 Single particle sequence in 78Ni mean- field Conclusion What we think we have understood : 1 2 the N=50 shell gap is effective towards 78 Ni though it varies a little in amplitude impact on collectivity ESNT Workshop – Saclay – 3-5 May 2010 D. Verney Page 53/52