Silvia M. Lenzi University of Padova and INFN. Silvia Lenzi, 10th Int. Spring Seminar on Nuclear Physics, Vietri sul Mare, May 21-25, 2010

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1 Structure of Neutron-Rich Nuclei near N=40 Silvia M. Lenzi University of Padova and INFN 10th International Spring Seminar on Nuclear Physics Vietri sul Mare, May 21-25, 2010

2 Collaboration Theory: F. Nowacki, A. Poves, K. Sieja Experiments: F. Recchia, S. Lunardi, D. Bazzacco, E. Farnea, J.J. Valiente-Dobon, D.R. Napoli, G. de Angelis, A. Gadea, N. Marginean, M. Ionescu-Bujor, A. Iordachescu, S. J. Freeman, R. Chapman, D. Mengoni, R. Orlandi, A. Bracco, G. Benzoni, S. Leoni, B. Million, O. Wieland, R. Broda, B. Fornal, J. Wrzesinski et al.

3 Outlook Introduction Experimental data on neutron-rich Cr, Fe and Co LNL Theoretical description of deformation and shape coexistence Conclusions and perspectives 3

4 Some open questions How does the nuclear force depend on isospin? What are the limits of existence for bound nuclei? Which are the properties of exotic nuclei at the limits of binding? What s new? collective motion, shapes, decay modes?

5 Shell evolution far from stability The neutron-rich side shell evolution along isotonic and isobaric chains 42 Si Island of inversion B. Bastin et al., PRL 99, (2007) T. Otsuka EPJ S. Top. 156, 169 (2008)

6 Explaining monopole drifts Attempts to explain, reproduce and predict shell structure far from stability proton-neutron spin-flip interaction V στ = τ τσ σ f στ ( r) tensor force = τ τ ([ ] ( ) ( ) σ σ 2 Y ) f ( r) V T 2 three-body forces

7 Neutron excess and shell migration ([ ] ( ) ( ) σ σ 2 Y ) f ( r) V T 2 = τ τ νg 9/2 40 νf 5/2 νp 1/2 νp 3/2 neutrons 32 T. Otsuka et al., PRL 95 (2005) πf 7/2 protons Z = 20 protons 0f 7/ neutrons 0g 9/2 0f 5/2 1p 1/2 1p 3/2 0f 7/2 Z = protons 28 0g 9/2 0f 5/2 1p 1/2 1p 3/2 0f 7/2 0f 7/2 neutrons

8 The Ni isotopic chain N=40 E(2 + ) N=28 B(E2)

9 Removing protons from the f 7/2 shell Cr Fe

10 The deformation region towards N=40 Cr Ε.Χαυριερ ετ αλ., Ευρ. Πηψσ. ϑ. Α 15 (2002) 145 ΛΣΣΜ Χαλχυλατιονσ N= N=36 N= Cr 38

11 Collectivity at N~40, Z<28 56 Cr 58 Cr 60 Cr single particle energies in a deformed WS potential S. Zhu et al., PRC 74, (2006) Ground-state potential energy surfaces (TRS) Cr isotope seem to exhibit γ softness for large N values Skyrme-HFB K. Yoshida and M. Yamagami, PRC 77, (2008) N=38 N=40 H. Oba and M. Matsuo, Prog. Theo. Phys. 120, 143 (2008)

12 The CLARA+PRISMA setup at Legnaro A & Z identification MWPPAC IC in-beam γ-ray 25 Euroball Clover detectors for Eγ= 1.3MeV Efficiency ~ 3 % Peak/Total ~ 45 % FWHM ~ 10 kev (at v/c = 10 %)

13 Deep inelastic collisions 70 Zn 64 Ni 66 Fe 68 Fe 58 Cr 60 Cr Populate mainly yrast states in neutron-rich products after multinucleon transfer and deep-inelastic collisions fission events proton pick-up Beam proton stripping

14 The Chromium isotopic chain: shape evolution 14

15 Spectroscopy of heavy Cr isotopes 64 Ni U at E L = 400 MeV N. Marginean et al., Phys. Lett. B 633 (2006)696 S. Zhu et al., PRC 74, (2006) 15

16 58 Cr and the shape phase transition critical point 4680 τ = Cr: E 4+ /E 2+ = 2.20 E 6+ /E 2+ = 3.65 E 8+ /E 2+ = 5.31 Marginean, Lenzi et al. Phys. Lett. B 633 (2006) Cr A possible bridge between shell model, algebraic and analytical approaches Need to measure transition probabilities 16

17 Heavier Cr isotopes Proton inelastic scattering in inverse kinematics pf-shell calculations 60 Cr pf 40 g 9/2 pf 62 Cr The energy levels at N=40 cannot be described within the pf or fpg space The experimental level schemes are more collective than the calculated ones.

18 The Iron isotopic chain: beyond N=40 18

19 Neutron-rich Fe isotopes CLARA_PRISMA experiment 64Ni MeV S. Lunardi et al., Phys. Rev. C 76, (2007) 19

20 Even-even Fe isotopes Shell model calculations Core 48 Ca valence space: full fp for protons p 3/2,f 5/2, p 1/2, g 9/2 for neutrons S. Lunardi, SML et al., Phys. Rev. C 76, (2007) pf 40 g 9/2 fp Previous data on 62 Fe: (GASP) T. Pawlat et al., Legnaro Annual Report 1995, p.7 (GAMMASPHERE) A.N. Wilson et al., EPJ. A9, 183 (2000). fpg Interaction described in O. Sorlin et al., PRL 88, (2002). Data on 64 Fe: (GANIL) O. Sorlin et al., NPA 660, 3 (1999). (GAMMASPHERE) N. Hoteling et al., PRC74, (2006)

21 The 70 Zn U reaction Observed the first excited state in 68 Fe (N=42) p 66 Zn Cu Ni 68 C F Ni Co 26-2p +4n 66 Fe 25 Mn Cr Ni MeV with Clara + Prisma 21

22 Beyond N=40 N=40 N=42 νf / 2g9 / 2 νf / 2g9 / 2 SML et al., LNL Ann. Rep. 2008

23 Shell model description: the LNPS interaction 23

24 Building quadrupole collectivity Rotational features are determined by the interplay of the quadrupole force with the central field in the subspace spanned by a sequence of j = 2 orbits that come lowest by the spin-orbit splitting. π ( fp) 4 ν( sdg ) 4

25 Islands of inversion 32 Mg p 3/2 f 7/2 quasi-su3 sd 64 Cr d 5/2 g 9/2 quasi-su3 pf

26 Development of deformation at N=40 LNPS interaction: renormalized realistic interaction + monopole corrections 48 Ca core protons: pf shell neutrons: p 3/2,f 5/2, p 1/2, g 9/2, d 5/2 N=40 E (2 + )(kev) 62 Ti 64 Cr 66 Fe 68 Ni SML, F. Nowacki, A. Poves and K. Sieja, in preparation 26

27 The evolution of Cr isotopes Chromium neutron-rich isotopes 58 Cr 60 Cr 62 Cr 64 Cr E(2 + ) B(E2) ground states g9/2 d5/2 fractional occupation of intruder orbitals

28 The Cobalt isotopic chain: shape coexistence 28

29 Evolution of yrast levels in Co isotopes Ni 60 Ni 62 Ni 64 Ni 66 Ni 68 Ni / / /2-1/2-57 Co 59 Co 61 Co 63 Co 65 Co 67 Co 65Co: D.Pawels et al., 67Co: F. Recchia et al. Phys. Rev. C 79, (2009) 29

30 Proton intruder states in odd Co isotopes π ( ) 2 1 f 7 p / 2 3/ 2 The 1/2 - state lowers due to deformation increase at Z<28 N=40 Courtesy D. Pauwels and P. Van Duppen

31 Shape coexistence in 67 Co ( f ) π 7 / 2 p3 / /2-1/2 - The 1/2 - state gains a total of ~ 8 MeV of correlation energy and ~ 5 MeV relative to the ground state D. Pauwels et al., PRC 78, (2008) and PRC 79, (2009) 67Co: F. Recchia et al., to be published The LNPS interaction reproduces the shape coexistence in 67 Co

32 AGATA Demonstrator at PRISMA Conclusions and perspectives The mass region studied shows a development of collectivity (deformation) towards N=40 with rapid changes of shape along the isotopic chains. The clover array CLARA is now replaced with the AGATA construct the level schemes. demonstrator 5 triple-clusters 36-fold segmented crystals 540 segments Complementary experimental techniques are needed to The LNPS effective interaction in the fpgd space accounts for the monopole migrations and is able to describe collectivity and shape coexistence in this third island of inversion. Measurement of transition probabilities is needed to study the evolution of deformation. The AGATA Demonstrator coupled to PRISMA at LNL opens new possibilities to the spectroscopy and, in particular to the measurement of lifetimes in neutron rich nuclei.