In-beam and isomer spectroscopy in the third island of inversion at EXOGAM+VAMOS E.Clément (GANIL)

Weakness of the N=40 shell gap M. Bernas et al., PLB 113 (1982) R.Broda et al., PRL 74 (1995) O.Sorlin et al.,PRL 88 (2002) C. Guénaut et al., PRC 75 (2007) 68Ni 69Cu 68Cu 67Co 67Ni 70Zn 70Cu 69Ni 66Co 68Co 66Fe 65Mn 65Fe 67Fe 65Co 64Fe 64Mn 63Mn Presence of single particle, collective and core-coupled states. I.Stefanescu et al., PRL 100 (2008) 70Ni Core polarization O. Perru et al., PRL 96 (2006) Presence of core coupled states : Fe-like and Ni-like D.Pauwels et al., PRC 79 (2009) A.Dijon et al, PRC 83 (2011) The mass region around 68Ni remains a real puzzle… It is now established that 68Ni presents some characteristics of a doubly magic nuclei but in the other hand, the N=40 subshell closure appears as a rather open shell. Therefore, interaction between valence proton and this open neutron shell leads to an abrupt evolution of the collectivity. For example, above 68Ni, in copper isotopes, single particle, collectifs and core-coupled states are present. Below 68Ni, in iron isotopes, an onset of deformation from N=36 toward N=40 has been confirmed involving neutron intruder orbitals. In n-rich odd mass Co which are very closed to this border of deformation, a presence of core coupled state has been also made in evidence. In this experiment, we have investigated the core coupled states in this region. Finally at Z=28, as I will show, only few information are known on the proton states. Onset of deformation in Fe isotopes J.Ljungvall et al., PRC 81 (2010) W.Rother et al., PRL 106 (2011)

Single particle state by B(E2) measurement 68Ni 69Cu 68Cu 67Co 67Ni 70Zn 70Cu 69Ni 66Co 68Co 66Fe 65Mn 70Ni 65Fe 69Co 67Fe 69Cu : p(2p-1h) Single particle state by B(E2) measurement (I.Stefanescu et al., PRL 100 (2008) ) 68Ni must present a p(2p-2h) intruder state with E(p(2p-2h) )=E(p(2p-1h) )+E(p(1p-2h)) 0+ state (D.Pauwels et al . PRC 82 (2010)) 67Co : p(1p-2h) Shape isomer at N=40 : proton intruder state p (p1/2)+1 (D.Pauwels et al . PRC 78 (2008)) Indeed , around 68Ni, proton intruder states have been identified. In 69Cu, for example, a single particle state with 2p 1 hole configuration has been mesured and in 67Co,the presence of of shape isomer bellow 500 keV which have 1p-2h configuration has been measured. And more recently, it has been made in evidence a possibility that the ground state in 66Co could be also based on a proton intruder config. So, it must be possible to have a proton intruder state at low excitation energy that could be isomeric or not and it is why we decide to measure the delay and prompt gamma rays. p(2p-2h) intruder states at low energy  π-ν residual energy.

∆M/M=1.2% ∆Z/Z =1.1% 2 Ge Eurogam phase 1 + No Dipole 2 Ge EXOGAM Sed2 6.33 A MeV 70Zn target Sed1 Sed2 11 EXOGAM Ge detectors No Dipole 45° Ionisation chamber (3 pads) + 4 Si detectors 2 Ge Eurogam phase 1 + 2 Ge EXOGAM detectors VAMOS Spectrometer MWPC Q2 Q1 In this experiment, I will present the preliminary results of a second experiment which aimed to perform prompt and delayed gamma rays spectroscopy using a specific configuration of the VAMOS spectrometer so-called the solenoid mode. In this experiment, an Uranium beam at 6.33 MeV/A impinge a 70Zn target. The gamma rays emitted at the target point were measured in the Exogam Ge detector and the target like reaction product are refocalized and identified in the VAMOS spectrometer. No Brho analysis is performed in this configuration. At the focal plane of the VAMOS spectrometer, four germanium detector are used to measure delayed gamma rays. We have achieved very good Z and M resolution allowing an unique identification for mass up to 80. Z identification ∆Z/Z =1.1% ∆M/M=1.2% counts M identification

PRELIMINARY 168(1) keV 68Ni 69Cu 67Ni 69Ni Prompt Isomer Isomer A. Dijon et al, to be submitted very soon … Prompt 168(1) keV T1/2=216 +65/-50 ns Isomer 69Cu 67Ni 69Ni 68Ni Isomer As a main result, we observed for the first time the presence of new isomer transition at 168 keV. We measured a lifetime of 157 ns. Weiskpoff estimate favours an E2 decay leading to a low B(E2) underlining a single particle transition. PRELIMINARY

Gated on transitions in 67Ni Gated on the 168 keV transition  Observed just for Z=28 Gated on transitions in 69Cu Gated on transitions in 69Ni

168(1) keV 68Ni 69Cu 67Ni 69Ni Prompt Isomer A. Dijon et al, to be submitted very soon … Prompt 168(1) keV T1/2=216 +65/-50 ns Isomer 69Cu 67Ni 69Ni 68Ni As a main result, we observed for the first time the presence of new isomer transition at 168 keV. We measured a lifetime of 157 ns. Weiskpoff estimate favours an E2 decay leading to a low B(E2) underlining a single particle transition.

Transitions Half-life E1 0.1 ps E2 300 ns M1 6 ps M2 20 μs Prompt Prompt 168(1) keV T1/2=216 +65/-50 ns Isomer 69Cu 67Ni 69Ni 68Ni Compatible with small B(E2) value As a main result, we observed for the first time the presence of new isomer transition at 168 keV. We measured a lifetime of 157 ns. Weiskpoff estimate favours an E2 decay leading to a low B(E2) underlining a single particle transition.

Shape Coexistence scenario 4+1 5-2 5-1 2+2 0+3 π(f7/2)-2 0+m2 * 70Zn(14C,16O)68Ni M. Girod et al PRC 37 (1988), at the Orsay Tandem 2+1 0+1 π(f7/2)-2 (p3/2)+1 0+g.s 66Fe 2+ B(E2) =21 W.u 575 π(f7/2)-2 Deformed W.Rother et al., PRL 106 (2011) (1/2-m) (7/2-)g.s 67Co 491 Shape isomer D.Pauwels et al., PRC 78 (2008) 0+ 68Ni Remarkable agreement with the predited position from the p(1p-2h) in 67Co and p(2p-1h) in 69Cu  p(2p-2h) state  Suggest the microscopical configuration D. Pauwels et al, PRC 82, 027304 (2010) Shape Coexistence scenario

Correlation energy : -30.9 MeV Q² = 4520 e²fm4  b ~ 0.4 … 8+1 Correlation energy : -30.9 MeV Q² = 4520 e²fm4  b ~ 0.4 … 0+m2 LSSM – LPNS : F. Nowacki, K. Sieja for A. Dijon et al, to be submitted very soon … B(E2)cal= 0.9 W.u Exp : < 1.4 W.u (E0?) 2+1 0+1 g9/2 d5/2 p1/2 f5/2 p3/2 f7/2 Calculated GS 0+1 0+2 neutron proton Q² = 1579 e²fm4  b ~ 0.24 0+ Occupation number Correlation energy : -7.6 MeV Q² = 899 e²fm4  b ~ 0.18 π(f7/2)-2

n p p × Not present in the ph-RPA calculations × Not present in the 68Ni HFB-D1S p fully consistent QRPA calculations with D1S interaction M. Martini, S. Péru for A. Dijon et al, to be submitted very soon …

The solenoid mode in this experiment shows interesting results: Prompt and delayed gamma rays in coincidence Lifetime of isomer A new isomer has been identified in 68Ni Interpreted as a 2p-2h proton intruder superdeformed state across the Z=28 major shell closure In agreement with SM calculations using the recent LPNS interaction In agreement with QRPA calculations Similar microscopic configuration with 67mCo and 66Fe  Shape coexistence in 68Ni So, to conclude, the preliminary results of this experiment seems to be hopeful and show a possibility of a new 0+ excited state in 68Ni with a pure proton configuration. New gamma prompt are also observed in iron isotopes but also in others nuclei populated in this experiment.

Collaboration

S.M. Lenzi, F.Nowacki, A.Poves and K.Sieja, PRC 82 (2010) K.Heyde and J.L. Woods, Rev.Mod.Phys (in press) F.Nowacki and K.Sieja for A. Dijon et al (2011) Correlation energy : -7.6 MeV Q² = 899 e²fm4  b ~ 0.18 Correlation energy : -30.9 MeV Q² = 4520 e²fm4  b ~ 0.4 D.Pauwels et al., PRC 82 (2010) -3.8 MeV

A 0+ state ? : Looking at the past … M. Girod et al PRC 37 (1988) M. Bernas et al PLB B113,(1982) Remember, at this time the 2+ at 2033 keV was not known : the 2.20(3) MeV state interpreted as a the 2+1 state

A 0+ state ? : Looking at the past … M. Girod et al PRC 37 (1988)