Deformation in Fe and Cr nuclei

1. Deformation in N=40 nucleiG. Duchêne , R. Lozeva, C. Beck, D. Curien, F. Didierjean, Ch. Finck, F. Nowacki, K. SiejaIPHC StrasbourgC. Domingo-Pardo, J. Gerl and the GSI groupGSI DarmstadtD. Verney, F.Azaiez, S. Franchoo, F. Ibrahim, F. Le Blanc, I. Matea, M. Niikura, I. StefanIPN Orsay

2. Deformation in Fe and Cr nuclei E. Caurier et al., Eur. Phys. J A15 (2002) 145 Fe Cr Cr

3. 68Ni K. Langanke et al., Phys. Rev. C67 (2003) 044314 • Is 68Ni a magic nucleus ? • Increase of the 21+ excitation energy • Reduction of the B(E2) value • No pronounced irregularity in the 2-neutron separation energy • Strong 2p-2h component -> excitation of a neutron pair into g9/2 orbital • Major part of the B(E2) strength around 5 MeV • Deformation in 68Ni • 68Ni gs is spherical (Gaudefroy et al., Phys. Rev. C80 (2009) 064313) • Main 01+ state configuration is 4p-4h • Does not generate much deformation

4. 67Co Collective 1p-2h proton intruder First excited ½- state with large quadrupole deformation β ~ 0.25-0.4 D. Pauwels et al., Phys. Rev. C 78, 041307(R) (2009) 69Cu Measured magnetic moment of 13/2+ state Considerable proton excitations across the Z=28 proton gap Deviate from sphericity G. Georgiev et al., J. Phys. G: Nucl. Part. Phys. 28, 2993 (2002) 70Zn Given as a γ-soft nucleus (Gaudefroy et al., Phys. Rev. C80 (2009) 064313) Hunt for deformation with np-nh configurations (n=6, 8) at higher excitation energy In the vicinity of 68Ni

5. Valence space 4020Ca20 core π: f7/2 + fp shell υ: f7/2 frozen + fp shell (p3/2 frozen)+ g9/2 + d5/2 68Ni: 8p-8h excitations 70Zn: 6p-6h excitations Huge matrices to diagonalise ~(500 106)² to more than (109)² Several days calculation Results 68Ni 8p-8h config: B(E2)down ~ 690 e²fm4 Q2 = -49 e.fm² β2 ~ 0.32 E* ~ 13 MeV 6p-6h config: B(E2)down ~ 190 e²fm4 Less deformation driving E* ~ 10 MeV 70Zn 6p-6h config: B(E2)down ~ 695 e²fm4 Q2 = -48 e.fm² β2 ~ 0.32 E* ~ 10 MeV All configurations are spread over many states when configuration mixing is allowed ! Mean field calculation in the β-γ plan Shell-model calculations

6. Angular momentum and particle rates • High-angular momentum states feeding • Several nucleon knock-out lead to « high-spin » transfers • 8+ fed ~10 time less than 2+ state • Hypothesis: deformed structure feeding of 10% at 8 ħ • Nuclei production rate • Primary beam: 76Ge -> Imax = 3 108 p/s • Primary Be/Nb target of 2.5 g/cm² • Al degrader of 1.5 g/cm² • Intermediate fragments: 73Ga or 72Zn • Rates calculations (slits cuts in S1, S3, S4) 105 Hz/wire 104 Hz Lycca AGATA

7. Gamma-ray statistics • S’2 geometry • Full configuration: 10TC + 5DC -> 17% • Min. configuration: 5TC + 3DC -> 9% • Intermediate fragment 72Zn; 1.5 MeV gamma ray • Experiment duration: 7 days

9. Ni-Zn-Ge J. Van de Walle et al., Phys. Rev. Lett.99 (2007) 142501 Gaudefroy et al., Phys. Rev. C80 (2009) 064313

10. Attractive between spin-flip orbitals Attractive interaction πf5/2-νd5/2 Relaxed when removing protons from πf5/2 orbital Excitation energy of νs1/2 state apparently decreases vs νd5/2 state Tensor force g7/2 s1/2 j+1/2 d5/2 g9/2 p1/2 p3/2 j-1/2 f5/2 f7/2 ν π