IS451-Looking at the shape transition at N=60 by safe Coulex of Sr isotopes

1. IS451-Looking at the shape transition at N=60 by safe Coulex of Sr isotopes E.Clément-GANIL ISOLDE Workshop 2012

2. The n-rich nuclei between Z=37 and Z=40 present at N=60 one of the most impressive deformation change in the nuclear chart • Systematic of the 2+ energy (Raman’s formula : b2~0.17  0.4) ( ) M. Alberset al., Phys. Rev. Lett. 108, 062701 (2012) + 2n  S. Naimi et al., Phys. Rev. Lett. 105, 032502 (2010).

3. 0+2 • Low lying 0+ states were observed in Sr and Zr isotopes • Shape isomer in the odd-mass Sr, Zr • Shape coexistence scenario E(0+) [keV] + 2n

4. 40 • 0+2state created by 2p-2h excitation across Z=40 1h11/2 • Beyond N=60, the p-n interaction participates to the lowering 0+2 state and to the high collectivity of 2+1 state. 1g7/2 K. Sieja et al PRC 79, 064310 (2009) ll 3s1/2 ll 1g7/2 2d5/2 ll ll ll 2d5/2 50 50 1g9/2 2p1/2 40 1f5/2 ll ll ll ll ll 2p3/2 28

5. T. Rzaca-UrbanPhys. RevC 79, 024319 (2009) – SM calculations … H. Goutte et al, CEA-Bruyère-Le-Chatel Private communication • 0+2state created by 2p-2h excitation across Z=40 • Beyond N=60, the p-n interaction participates to the lowering 0+2 state and to the high collectivity of 2+1 state. • In the current valence space, need higher effective charge to reproduce collective properties • pand n orbital from the core or higher shells. • Mean-field calculations reproduce the near spherical and highly deformed configuration away from N=60 • The nuclei here are one of the best examples of the interplay between single-particle and collective modes of excitation in the nuclear matter ²

6. IS451 objectives: electromagnetic properties of the excited states in the Sr isotopes with re-accelerated beam 2007- Coulomb excitation of 96Sr N=58 2011- Coulomb excitation of 98Sr N=60 • The Electric spectroscopic Q0 is null as its B(E2) is rather large •  Quasi vibrator character •  No quadrupole deformation • The GSB seems to be more connected to the 0+2 than 0+3 Q0s = -6 (9) efm² B(E2↓) = 462 (11) e²fm4

7. 98Sr (T1/2 = 653 ms) has a relatively weak extraction/production rate We choose theatomic extraction as 98A+ and relied on the in-trap b-decay of the short –lived 98Rb (T1/2 = 96 ms ) for the purification UCx Target HRS A= 98 98Rb (>95 % ) + 98Sr (< 5%) Trap After several 98Rb periods : 161 + 158 ms Atomic extraction EBIS MINIBALL PSB 98Rb (~2 % ) + 98Sr (~80%) +98Y (~ 9 %) 98Zr (~ 6%) Isr~ 6.104pps Proton beam

8. Trapping time: 100 ms/300ms/500ms • Non-decayed 98Rb • b-decay product •  The peak disappear after a sufficiently long trapping time Several ways of sharpening the time-of-flight distribution for mass 98 were tested, without success Preliminary conclusions It is difficult to clearly state where the in-trap decay is the most efficient (either in the trap or in the EBIS). The daughter nuclides delivered from the trap are not efficiently cooled. This possibly explains why the in EBIS decay was found more efficient during the experiment of J. Van de Walle 61-62Fe from the decay of 61-62Mn (IS468). P. Delahaye et al.

9. Beam composition after post-acceleration 98mRb : 96 ms DE measurement at MINIBALL 98Sr : 653 ms 98Rb :102 ms 98Sr (4,5) :2 sec. (0- ) : 548 ms 98Rb 0+ 98Y 37Cl10+ 61X (short-lived) 15N 83Kr 98Zr 98Y 98Zr : 30 sec. 98Nb 64Zn 38Ar 60Ni EBIS-contamination p off BeamGate close ? ? p off BeamGate open Long livedfromtarget p on BeamGate open Short livedfromtarget Energyloss (MeV)

10. 98Sr : Coulomb excitation results • We used 2 Target : 208Pb & 60Ni • Clean kinematic matrix • Doppler corrected, particle-g prompt gated 60Ni target Target excitation 208Pb target

11. g-g matrix Many transitions are in coincidence 4+ 115 keV Gated on the 2+decay 6+

12. Gate on 115 keV Gate on 319 keV (319) (115) Otherunknown transitions mightbelong to 98Rb

13. Conclusion • We successfully performed the Coulomb excitation of 96-98Sr beams and many transitions have been observed in 98Sr • We used the in-trap and in-ebisb-decay • The effect of different configurations of the trapping and breeding time are not understood • We observed new transitions in 98Sr analyzed using g-g coincidences after coulomb excitation of a RIB. • We might have identified excited states in 98Rb • E2-M1 electromagnetic matrix elements analysis on-going • Next step : Zr beams and transfer reaction on Sr

14. AGATA@GANIL The GANIL facility will host the European AGATA germanium array during 2014 and 2015 • Gamma-ray spectroscopy of very neutron-rich nuclei populated in Deep Inelastic collisions or induced fission • Spectroscopy of heavy elements towards SHE and N=Z nuclei • Spectroscopy using existing and new SPIRAL1 beams Submission of the LoI by February 8th, 2013 AGATA@GANIL Workshop GANIL, 18-20 February, 2013 http://pro.ganil-spiral2.eu/events/cw/agataws.

15. 98Sr : Coulomb excitation results g-ganalysis No coincidence with known transition in 98Sr No excited states are known in 98Rb Level scheme very similar to 96Rb 98Rb ?? (N=61) 165 99 380 94 96Rb (N=59) 51 259

16. 98Sr : Coulomb excitation results Plunger type analysis Pb t = 4 ns ~ t.o.f After DC t.o.fis longer and longer

17. 98Sr : Coulomb excitation results Plunger type analysis Decay curve • Not yet fully understood the difference • Geometrical effect ( cluster) ? • Influence of higher lying states ? Path = t.o.f t = 2.9 (3) ns (4.0(1) ns)

18. 98Sr : Coulomb excitation results Plunger type analysis 144 EDc Cos y Cos y (2+,5-) 319 (0+,3-)m 115 Isomeric state ! t = 1.2 (3) ns

19. 2007 – Coulomb excitation of 96Sr First Sr beam at REX-ISOLDE We choose the molecular extraction as 96Sr19F+ to not suffer from the Rb contamination HRS A= 115 UCx Target 96Rb ( Trap HS ) …. off‏ 7 to 1.3 105 96Sr19F+/C Separator A/Q = 4.17 Molecular extraction EBIS Pure 96Sr23+ REX-beam 2.87 MeV/u 1 to 0.5 ~104pps PSB Proton beam 115In