EUR ISOL User Group Workshop Jan 14-18, 2008. Florence, Italy

1. EURISOL User Group Workshop Jan 14-18, 2008. Florence, Italy STRUCTURE NEAR THE NEUTRON DRIP LINE AT N=24 Zdeněk Dlouhý Nuclear Physics Institute ASCR, CZ-25068 Řež, Czech Republic for the GANIL-Orsay-Dubna- Řež -Bucharest collaboration

2. Properties of Neutron-rich nuclei at the drip line Shells at N = 40, 50 Island of inversion- Disappearence of magicity Halo nuclei Magic numbers:2,8,20,28,40,50,82…. Halo nuclei

3. The most well known one- and two-neutron halo nuclei are 11Be and 11Li nuclei 11 Be Z=4, N=7 11 Li Z=3, N=8 10 Be 1n 2n 9 Li

4. Disappearance of standard doubly-magic nucleus near the neutron drip line 10 He Z=2, N=8 A.N. Ostrowski et al., Phys. Lett. B338, 13 (1994). A. Korsheninnikov et al., Phys. Lett. B326, 31 (1994).

5. Island of inversion Island of Inversion Z=8 N

6. Search for existence of neutron-rich isotopes 26,28O

7. GANIL Experimental Areas In-Flight- Fragmentation Method for Radioactive ions beams • Fragment separator LISE3 • Spectrometer SPEG

8. Search for the bound 26,28O nuclei at LISE3 Fragmentation of the36S16+(78.1AMeV) beam with a mean intensity 800 enA has been used for the search for the existence of bound 26,28O nuclei. A dashed and solid lines show N=20 and N=16 isotones. The heaviest known 29F isotope is clearly visible (519 events). No events corresponding to 26O, 28O and to heavier isotopes than N=16 for C and N have been observed. N=16

9. H.Sakurai et al., Phys.Lett. 448B, 180 (1999)

10. Disappearance of standard doubly-magic nuclei near the neutron drip line 10 He Z=2, N=8 A.N. Ostrowski et al., Phys. Lett. B338, 13 (1994). A. Korsheninnikov et al., Phys. Lett. B326, 31 (1994). 28 O Z=8, N=20 O. Tarasov et al., Phys. Lett. B409 64 (1997). H. Sakurai et al., Phys. Lett. B448 180 (1999).

11. Intruder states ѵ 24 28O Z=8 18 18 20 22 16 neutrons

12. dE Z TOF A/Z

14. The evolution of the shell closures at large N/Z ratios is one of the most fascinating quest in nuclear structure. The confirmation of shell closure and magic numbers is evidenced usually using one of following experimental approaches: 1) Study of masses and separation energies 2) Determination of energies of the first excited state (E2) of even-even nuclei, 3) The reduced transition probability B(E2; 0+ → 2+) value along an isotopic chain of proton-magic nuclei, provides a sensitive signature of shell evolution.

15. Study of masses and separation energies

16. The shell structure which is plainly visible when inspecting a graph of the two-neutron separation energy, defined by S2n(N,Z) = M(N-2,Z) -- M(N,Z) + 2 Mn versus the number of neutrons, N. For one-neutron separation energy we get Sn(N,Z) = M(N-1,Z) -- M(N,Z) + 1 Mn but the pairing effect must be avoided. For a given Z, the general tendency for S2n is to fall steadily as an N increases.

17. Nuclear mass measurement at SPEG The masses of 31 neutron-rich nuclei in the range A = 29 - 47 have been measured. The precision of 19 masses has been significantly improved and 12 masses were measured for the first time. The neutron-rich Cl, S, and P isotopes are seen to exhibit a change in shell structure around N = 28. Comparison with shell model and relativistic mean field calculations demonstrate that the observed effects arise from deformed prolate ground state configurations associated with shape coexistence. Evidence for shape coexistence is provided by the observation of an isomer in 43S. F.Sarazin et al., Phys.Rev.Lett. 84, 5062 (2000)

18. S2n versus N

19. S2n versus N

20. S2nversus Z

24. In–beam gamma ray spectroscopy

25. In-beam gamma ray spectroscopy Experimental Setup BaF2 array Exc. De-exc. g.s.

26. In beam gamma ray spectroscopy SPEG BaF2 – upper array HPGe clovers HPGe clovers Beam

28. 24O N=14 and 16 shell gaps in neutron-rich oxygen isotopes The nonobservation of any γ-decay branch in 23O and 24O suggests that their excited states lie above the neutron decay thresholds. From this, as well as from the level schemes proposed for 21O and 22O, the size of the N=14 and 16 shell gaps in oxygen isotopes was discussed in the light of shell-model calculations. M.Stanoiu et al., Physical Review C 69, 034312 (2004)

29. Energies of the first 2+ states vs neutron number O ? ? O Ne Mg Si S ArCa Isotopes near N=20 32S, 34S, 36S, 36Ar, 38Ar, 36Ca, 38Ca, 40Ca Isotopes near N=16 measured at GANIL 20O, 22O, 24O 26Ne, 28Ne, 24Mg, 28Mg, 30Mg, 32Mg 30Si, 32Si, 34Si

30. Changes in neutron magic numbers for neutron-rich nuclei • Instability of 10He (Z = 2, N = 8) and 28O (Z = 8, N = 20) • Disappearance of neutron standard magic numbers N = 8 and N = 20 • Appearance of new neutron magic numbers N = 6 and N = 16 New doubly magic nuclei 8He (Z = 2, N = 6) and 24O (Z = 8, N = 16) (below neutron decay threshold no bound excited states) Adding +1 proton we obtain: Cores of halo nucleus 9Li (Z = 3, N = 6) and 25F (Z = 9, N = 16) halo nucleus 11Li (Z = 3, N = 8) and 27-31F (Z = 9, N = 18 – 22)

31. Doubly magic Nuclei – bases for Nuclear Halo’s or very Neutron-rich Nuclei?

33. Change of effective single particle energies in Si and O

34. Search for 33F

35. 8 16 20 24 24

37. Conclusions • Disappearance of doubly magic nuclei 10He and 28O • Changes in magic numbers near driplines - N=6,16 • New doubly magic nuclei near driplines -8He and 24O • Triton separation energy of odd Z nuclei shows the posibility of existence N=24 subshell in neutron-rich nuclei

38. Collaboration GANIL, Caen, France R.Anne, M.Lewitowicz, W.Mittig, F.de Oliveira, P.Roussel-Chomaz, H.Savajols, M.G.Saint-Laurent IPN, Orsay, France F.Azaiez, M.Belleguic, C.Donzaud, J.Duprat, D.Guillemaud-Mueller, S.Leenhardt, A.C.Mueller, F.Pougheon, J.E.Sauvestre, O.Sorlin, M. Stanoiu FLNR, JINR, Dubna, Russia Yu.Penionzhkevich, S.Lukyanov, Yu.Sobolev LPC, Caen, France N.L.Achouri, J.C.Angelique, S.Grevy, N.Orr NIPNE, Bucharest-Magurele, Romania C.Borcea, A.Buta, I. Stefan, F. Negoita, Atomki, Debrecen, Hungary Zs.Dombradi, D.Soher, J.Timar, NPI, ASCR, Řež, Czech Republic D.Baiborodin, J.Mrázek, G.Thiamová, J.Vincour, Z.D.

39. Thanks for your attention