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Nuclear collectivity and shape evolution in exotic nuclei

Nuclear collectivity and shape evolution in exotic nuclei

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Nuclear collectivity and shape evolution in exotic nuclei

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  1. Nuclear collectivity and shape evolution in exotic nuclei Wolfram KORTEN CEA Saclay DSM/IRFU/SPhN

  2. Oblate Prolate M. Girod, CEA Bruyères-le-Châtel Shapes and shells in exotic nuclei Quadrupole deformationof the nuclear ground states • Dominance of prolate ground state shapes over most of the nuclear chart • Islands of oblate nucleiand shape coexistence (N~Z, A~100, …) • Erosion of shell gapsleads to (strongly) deformed nucleiat N=20, 28 and 40

  3. Evolution of collectivity around N=40 • Persistence of N=40 sub-shell closure beyond 68Ni ? •  correlations stronger than N=40 gap for Z28 • increased collectivity with filling of g9/2 • Previous experimental results: • Coulomb excitation of 78-82Ge at ORNL / HRIBF E. Padilla-Rodal et al., PRL 94, 122501 (2005) • Coulomb excitation of 74-80Zn at CERN / ISOLDE J. Van de Walle et al., PRL 99, 142501 (2007) J. Van de Walle et al., PRC 79, 014309 (2009) • New experimental approach • Lifetime measurements after MNT/DIC • B(E2) in Fe  EXOGAM/VAMOS at GANIL • B(E2) in Zn  AGATA/PRISME at LNL Z=28 N=50 N=40

  4. Mf If Ii Experimental methods: Coulomb excitation • Coulomb excitation of 74-80Zn at CERN / ISOLDE • AZnon 108Pd/120Snat ≈2.8 MeV/u • integral measurement • excitation probability via normalization to target • one observable: (2+), two unknowns: B(E2), Qs J. Van de Walle et al., PRL 99, 142501 (2007) 74Zn two unknowns: • B(E2; 0+ 2+) • Qs(2+) 20 ps = 0 ! 25 ps 28.5 ps J. Van de Walle et al., PRC 79, 014309 (2009)

  5. Collectivity in neutron-rich nuclei around N=40 Recoil-Distance Doppler-shift (RDDS) lifetime measurements in nuclei produced by multi-nucleon transfer or deep-inelastic reactions Z=28 N=50 N=40 -2p : 62Fe 74Zn -2p+2n: 64Fe 76Zn 238U + 64Ni @ 6.5 MeV/u VAMOS + EXOGAM 76Ge + 238U @ 7.6 MeV/u PRISMA + AGATA Demo.

  6. 3x135° 1x180° 45° Q Q D v1 v2 Mg 5x90° drift chamber: x,y Se-D: trigger, t1 drift chamber: x,y ionisation chamber: E silicon wall: E, t2 RDDS experiment in inverse kinematics at VAMOS 64Ni 238U, 6.5 MeV/u 64Fe

  7. bbef ~10% baft ~ 8.5% E’g Eg Eg E’g The Recoil-Distance Doppler-Shift technique Differential RDDS technique combined with deep-inelastic (or multi-nucleon transfer) reactions was pioneered at LNL using the CLARA-PRISMA set-up J. Valiente-Dobón et al., PRL 102 (2009) 242502

  8. 64Fe Lifetimes in neutron-rich Fe isotopes 64Fe 62Fe 238U + 64Ni @ 6.5 MeV/u J. Ljungval et al., PRC C 81, 061301(R) (2010)

  9. Collectivity in neutron-rich Fe isotopes d5/2 66Fe 50 g9/2 40 p1/2 f5/2  Importance of neutron g9/2 (and d5/2) intruder orbitals p3/2 28 f7/2 p n J. Ljungval et al., PRC C 81, 061301(R) (2010) W. Rotheret al., PRL 106, 022502 (2011)

  10. Collectivity in neutron-rich nuclei around N=40 Lifetime measurements in neutron-rich Fe and Co isotopes Z=28 N=50 N=40 -1p : 63Co -1p+2n: 65Co 238U + 64Ni @ 6.5 MeV/u VAMOS + EXOGAM

  11. Structure of odd-mass Co isotopes Fe and Ni Core coupled states ? Structure of the ground state ?

  12. Lifetime measurement in 63,65Co “Fe-like” 3/2-7/2- transition • Direct lifetime • extraction possible • T1/2=15.4 ± 1.8 ps • B(E2)= 3.71 ± 0.43 W.u A. Dijon et al., PRC 83, 064321 (2011)

  13. Lifetime measurement in 63,65Co “Fe-like” 3/2-7/2- transition • Direct lifetime • extraction possible • T1/2=15.4 ± 1.8 ps • B(E2)= 3.71 ± 0.43 W.u “Ni-like”9/2-7/2- transition • lifetime extraction • requires selection in • excitation energy • T1/2=0.9 ± 0.4 ps • B(E2)= 12.2 ±5.4 W.u A. Dijon et al., PRC 83, 064321 (2011)

  14. Collectivity in neutron-rich nuclei around N=40 Lifetime measurements in neutron-rich Zn and Co isotopes Z=28 N=50 N=40 -2p : 74Zn -2p+2n: 76Zn 76Ge + 238U @ 7.6 MeV/u PRISMA + AGATA Demo.

  15. Lifetime measurement in neutron-rich Ni, Cu and Zn isotopes AGATA experiment performed in June 2010 at the LNL using multi-nucleon transfer reaction (76Ge + 238U) Spokespersons: A. Goergen (Saclay), M. Doncel (U. Salamanca), E. Sahin (LNL)

  16. Quadrupole Dipole MCP X-Y, time 6.5 m (TOF) MWPPAC AGATA IC X-Y, time E,E Angular range: -30º to 140º The PRISMA spectrometer at LNL

  17. Particle identification with PRISMA Z identification Charge state determination and selection Mass separation (all distances together)

  18. Lifetime experiments with AGATA at PRISMA Multi-nucleon transfer reactions in direct kinematics: 76Ge+238U Recoil-Distance Doppler Shift (RDDS) experiments  differential plunger 76Ge beam (577 MeV, 0.3pnA) 238U target (1.4 mg/cm2) Ta backing (1.2mg/cm2) Nbdegrader (4 mg/cm2) 50-70 khZGe singles rate

  19. v RDDS with EXOGAM vs. AGATA Demonstrator Exogam AGATA Demo. GEANT 4 simulation and AGATA tracking (J. Ljungvall) peak separation for all angles 6 times more counts for same peak separation AD at 14cm 180 detector at 11 cm 135 detectors at 14.5 cm

  20. RDDS spectra of neutron-rich Zn isotopes C. Louchart et al, to be published

  21. RDDS analysis: Differential Decay Curve method 100 mm • and • v = 30 mm/ps 200 mm 500 mm 1000 mm 1900 mm C. Louchart et al, to be published

  22. RDDS analysis: Differential Decay Curve method

  23. Collectivity in neutron-rich Zn isotopes References: [1] J.K. Tuli, Nucl. Data Sheets 103 (2004) 389 [2] B. Prytychenko arXiv:1102.3365v2 (2011) [3] D. Muecher et al., PRC 79 (2009) 054310 [4] S. Leenhardtet al., EPJ A 14 (2002) 1 [5] J. Van de Walle et al., PRC79 (2009) 014309 [6] M. Niikura et al., PRC (2012) in press [7] E. Clement, priv. comm. Quadrupole moment Q(2+) of 74Zn 20 ps 25 ps 28.5 ps Preference for oblate shape of 74Zn C. Louchart et al, to be published

  24. Quadrupole collectivity of 74Zn J.-P. Delaroche et al, PRC 81, 014303 (2010) M. Honma et al, PRC 80, 064323 (2009) 74Zn From lifetime experiment M. Niikura et al. arXiv : 1105.4072v1 (2011) HFB D1S J. Van de Walle et al, PRL 99, 142501 (2007) J.-P. Delaroche et al, PRC 81, 014303 (2010) M. Honma et al, PRC 80, 064323 (2009) 74Zn • Q(2+) >0 indicates “oblate” shape • not supported by the shell model • nor the HFB D1S calculation • B(E2) in accordance with shell model • and HFB D1S calculation

  25. Collectivity in neutron-rich Zn isotopes • Maximum of collectivity at N~42 • B(E2; 2+ 0+) values in agreement with previous measurements • lower B(E2; 4+2+) values with • minimum at N=44 • Discrepancy for t(4+)in 74Zn with previous (Coulomb excitation) measurement 70Zn: D. Mücher et al. PRC 79 054310 (2009) 74Zn: J. Van de Walle et al. PRC 79 014309 (2009)

  26. Collectivity in neutron-rich Zn isotopes • B(E2; 2+->0+) values are in agreement with shell model calculations • Beyond mean field calculation over estimate the collectivity in particular for • B(E2; 4+->2+) values • Shell model calculations do not reproduce the trend of the systematics for B(E2; 4+->2+) values

  27. Collectivity in neutron-rich Zn isotopes R(E2) <1 for all Zn isotopes (except 70Zn at N=40) similar to Ca and (partially) Cr isotopes, but different from Ti (Z=22)

  28. Collectivity in neutron-rich nuclei around N=40 Lifetime measurement in neutron-rich Zn and Cu isotopes Z=28 N=50 N=40 -3p-2n : 71Cu -3p:73Cu 76Ge + 238U @ 7.6 MeV/u PRISMA + AGATA Demo.

  29. Experimental results: 71Cu M. Doncel et al, to be published

  30. Experimental results: 71Cu Shell-model calculations using the fpg valence space do not reproduce the B(E2) values for Cu isotopes. • I. Stefanescu et al., Phys. Rev. Lett 100 (2008) 112502 • N.A. Smirnova et al., Phys. Rev. C (2004) 044306 Inclusion of the neutron d5/2 orbital LNPS interaction: shell-model calculations using an enlarged valence space: pf-shell orbitals for protons and f5/2, p1/2, p3/2, g9/2 and d5/2 orbitals for neutrons. (3) K. Sieja et al., Private Communication.

  31. Experimental results: 71Cu Occupation numbers for neutrons and protons: Different character for the 7/2- excited states Different behavior of the proton p3/2 and f5/2 orbitals Inclusion of the neutron d5/2 orbital The inclusion of the neutron d5/2 orbital, which is the SU(3) partner of the g9/2 orbital, leads to an enhancement of the quadrupole contribution. B(E2) values are well reproduced taking into account this contribution not considered in previous shell-model calculations.

  32. 100Ru 102Ru 104Ru 106Ru 108Ru 96Mo 98Mo 100Mo 102Mo 104Mo 106Mo 108Mo 94Zr 96Zr 98Zr 100Zr 102Zr 104Zr 106Zr 92Sr 94Sr 96Sr 98Sr 100Sr 102Sr 104Sr 90Kr 92Kr 94Kr 96Kr 98Kr 100Kr 102Kr 90Se 92Se 94Se 96Se 98Se Shape evolution in the A~100 region • rapid shape changes and • shape coexistence expected • accessible with HIE-Isolde and SPIRAL-2

  33. 3x135° 1x180° Q Q D v1 v2 Mg 5x90° drift chamber: x,y Se-D: trigger, t1 drift chamber: x,y ionisation chamber: E silicon wall: E, t2 In-flight studies of fission fragments at GANIL pioneered by F. Farget et al. (see talk Fr morning) Fission fragment production/identification with VAMOS Gamma-ray detection with EXOGAM RDDS experimentusing plunger (spring 2011) New results for several neutron-rich nuclei 112Ru, 118Cd, many odd-mass isotopes 9Be 238U, 6.5 MeV/u 110Ru A. Shrivastava, F. Rejmund et al Phys. Rev. C80 091305(R) (2009) 110Ru

  34. Fission fragment distribution 9Be(238U,ff)X at 6.5 MeV/u

  35. Preliminary fission fragment gamma-ray spectra 2+ 2+ 2+ 4+ 100Zr 104Mo 110Ru t(I≥4+) 4+ 4+ 6+ 6+ 8+ 8+ 10+ 2+ 106Mo 2+ 4+ 102Zr t(I≥4+) 112Ru t(I≥4+) 4+ 2+ 4+ 6+ 6+ 8+ 8+ 2+ 114Ru t(I≥2+) 2+ 108Mo t(I≥4+) 9Be(238U,ff)X at 6.5 MeV/u 98-102Zr; 104-108Mo; 110-114Ru 114-118Pd; 118-122Cd 4+ 6+

  36. Summary and perspectives • Application of Recoil-Distance Doppler-Shift Method to • deep-inelastic andfusion-fission reactions is a powerful • tool to study (moderately) neutron-rich nuclei • Onset of collectivity in the Fe isotopes below 68Ni • starts already around N~38 and requires inclusion of • d3/2 orbital in shell model calculations • Neutron-rich Zn isotopes show tendency towards oblate • deformationin contrast to theoretical expectations; • B(E2) ratios of 4+and 2+decays are systematically < 1 • Perspective for strong progress when using RDDS technique • with AGATA@VAMOS (2014) and complementary Coulomb • excitation experiments using SPIRAL2 and HIE-Isolde

  37. Thank you

  38. Recent 72Zn measurement at GANIL 17.9(1.8) M. Niikura et al. Accepted PRC (2012) 18.2(1.4) C. Louchart et al. 5.9(7) C. Louchart et al. 33.6 μm (6+) 1153.3 (4+) 846.75 2+ 652.68 99 μm 0+ I. Celikovic et al. GANIL-VINCA

  39. Quadrupole moments in neutron-rich Zn nuclei Combined with results from ISOLDE Coulex RDDS lifetime measurement will yield quadrupole moments for 2+ states in 74,76Zn. • focus of ISOLDE experiment was on 80Zn • new Coulex measurement (~ 3 days) • improve precision for 74,76Zn significantly • obtain data for 72Zn (planned in summer 2012) J. Van de Walle et al., PRC 79, 014309 (2009)

  40. DSAM lifetime measurement in 72Zn

  41. All nuclei 20<Z<40 Non-magic nuclei 40<Z<80 vibrator rotor R.B. Cakirli et al. PRC 70, 047302 (2004) possible explanation as transition from seniority regime to collective motion ? J.J. Ressler et al. PRC 69, 034317 (2004)