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High-seniority states in spherical nuclei: Triple pair breaking in tin isotopes

High-seniority states in spherical nuclei: Triple pair breaking in tin isotopes. Alain Astier, CSNSM Orsay, France. Outline :. Introduction Experimental conditions Fusion-fission reactions Detection (fragments and γ ’s) & Data analysis Sn results and discussion

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High-seniority states in spherical nuclei: Triple pair breaking in tin isotopes

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  1. High-seniority states in spherical nuclei: Triple pair breaking in tin isotopes Alain Astier, CSNSM Orsay, France Outline: Introduction Experimental conditions Fusion-fission reactions Detection (fragments and γ’s) & Data analysis Sn results and discussion New high-spin states identified New isomeric states revealed → B(E2)’s Shell-Model calculations Up to 3 neutron pairs broken in the νh11/2 orbit Conclusion & Perspectives

  2. J.A. Pinston and G. Genevey, J. Phys. G: Nucl. Part. Phys. 30 (2004) R57-R82 82 50 Introduction: Nuclear structure of the A<132Sn isotopes at high spin h11/2 High-spin structure of the n-rich Sn isotopes: - Very low number of involved configurations - Spherical configurations (Z=50) - Ideal for testing the two-body matrix elements of the residual interactions d3/2 s1/2 64 g7/2 d5/2 n Isomers in the A<130Sn isotopes: - 10+ [(h11/2)2] and 7- [(h11/2)1 (d3/2)1] in the even isotopes - 15- [(h11/2)-3 (d3/2)-1] recently reported in 128Sn [S. Pietri et al., PRC83, 044328 (2011)] - 23/2+ [(h11/2)2 (d3/2)1] and 27/2- [(h11/2)3] in the odd isotopes Higher spins in Sn isotopes expected by breaking more neutron pairs Several experimental challenges: - Production of these (moderately)-rich Sn isotopes at high-spin - Detection of the de-excitation of the high-spin states through long-lived isomers

  3. ~150 nuclei produced Symmetric fission around Z=45 EUROBALL 239 Ge (+BGO shield) eph~ 8.5% Experimental conditions High spin states of neutron-rich isotopes are populated by fusion-fission: 18O (85 MeV) + 208Pb → 226Th* →FF1* + FF2* + <4-6n> 88290 Energy of 85 MeV for 18O beam chosen in order to induce a “cold” fission σf ~ 100 mb, Ibeam ~ 5 pnA, ~ 104 fissions/s in the target Thick Pb target (100 mg/cm2)  low-lying γ-rays emitted by stopped nuclei ~ 4x109 events with fold ≥ 3

  4. 132Sn 78Ni Fission fragments → 50Sn +40Zr 18O + 208Pb 12C + 238U → 50Sn +48Cd 100Sn

  5. Gates: 2 γ’s of 104Mo Experimental tools 1) γ-coincidences: unambiguous individual identification and assignmentthanks to coincidences between complementary fragments Ex : reaction 18O + 208Pb → 226Th* :115,116,117,118,119Cdpartners of 104Mo 882904842 Counts Energy (keV)

  6. Ge2 Ge1 I0 E1 I1 E2 I2 Multipolarities of (E1,E2) transitionsdetermined from W(q) 3) Time measurements I0 I1 T1/2 can be extracted from the time spectrumTac(E2)-Tac(E1) I2 E1 T1/2 E2 Useful range for isomers: 10 ns < T1/2 < 300 ns Experimental tools 2) Angular correlations E1 q E2

  7. → Lots of unknown (and ~prompt!) transitions, belonging to the Sn complementary fragments High-spin states in Sn isotopes 118Cd – 118Cd (Sn partners in the12C+238U data set) 118Cd – 1190 keV → New cascades established in several Sn isotopes Shown here: 1190-557-241-782-639 in 120Sn 1190 - 241

  8. High-spin states in Sn isotopes → 126Sn 124Sn → 124Sn → 123Sn → 122Sn Confirmation from the coincidence with the Zr isotopes in the (18O+208Pb) data set → 121Sn → 120Sn

  9. Q - D Q - Q Q - Q Q - D Q - Q Q - Q Q - Q Q - Q High-spin states in Sn isotopes Angular correlations (O+Pb reaction)

  10. New level schemes (odd Sn’s)

  11. New level schemes (even Sn’s)

  12. Euroball-SAPhIR experiment (thin target) SAPhIR: 32 photovoltaic cells, eff~45% inside the Euroball target chamber Fission fragments stopped in SAPhIR: isomeric decay at rest (no Doppler!) Useful range for lifetime measurements: 50 ns < T1/2 < 1 μs Study of the 12C+238U reaction, using a thin (0.14 mg/cm2) 12C target

  13. SAPhIR events Detection of delayed γrays by Euroball in the range [50 ns - 1 μs] delayedγ-γmatrix Gate 241 keV (120Sn+122Sn) → new isomer (15-) in 120Sn and 122Sn! from delayedγ-γ-t events Gate 253 keV (120Sn) (122Sn) Gate 264 keV

  14. Even-A Sn isotopes Odd-A Sn isotopes Summary of the new information obtained in Sn isotopes at high spin How can we interpret these states?

  15. even odd Theoretical knowledge: the π(h11/2)ncase From R.D. Lawson, Z. Phys. A 303, 51 (1981) Residual interactions taken from the experimental spectrum of 148Dy (n=2). Seniority is conserved. For n=6 (i.e. πh11/2 midoccupation): 16+ → 14+1 is forbidden (same seniority) 16+ → 14+2 is allowed!  T1/2 (16+, n=6) < T1/2 (16+, n=4) Unfortunately no experimental data available for states with seniority ν=4,5,6…

  16. Shell-model results ANTOINE code, see K. Sieja et al., PRC79, 064310 (2009) for calculation details h6 h5d1 h4d2 + h4d1s1 h6d1 h4 h5 h4d1 h3d1 h3 h2 h2d1 h1d1 (6 holes in 132Sn) (7 holes in 132Sn )

  17. Even-A Sn isotopes Odd-A Sn isotopes Experimental ν(h11/2)nstates with n=1,2,3,4,5,6 in the A<132Sn isotopes h6d1 h5d1 h6? h4 h4d1 h3d1 h5 h3 h2d1 h2 h1d1 The 18+ state (from h6) is not yrast: h4d2 or h4d1s1 are “cheaper”! → 18+ (h6) not observed Blocking of the odd neutron in d3/2 → Seniority-6 state (h6) observed!

  18. B(E2)’s andνh11/2 filling 10+: (h11/2)2 27/2-: (h11/2)3 15-: (h11/2)3(d3/2)1 Same behaviors of the 3 series Half-filling at A=123 (N=73)  Confirmation of the 15- configuration

  19. Conclusions & Perspectives Fusion-fission  an efficient γ-spectrometer: a powerful tool to produce and study high-spin states of neutron-rich isotopes The SAPhIR-Euroball coupling, with the thin-target reaction, was very useful  Major improvement of 8 Sn level schemes Reference: “High-spin states with seniority ν=4,5, and 6 in 119-126Sn” A.A. et al., Phys. Rev. C85, 054316 (2012) (20th paper reporting results of the O+Pb experiment!!!)  Tins are all the same!  Shell-Model works very well  Seniority-6 states identified for the first time Perspectives Soon: high spins of Te isotopes same neutrons, “only” 2 protons more… End 2012: EXOGAM@ILL campaigns thermal neutrons on 235U/241Pu thick targets

  20. Collaboration A. Astier, M.-G. Porquet, I. Deloncle, CSNSM, IN2P3-CNRS/Université Paris-Sud, 91405 Orsay, France Ch. Theisen, M. Houry, R. Lucas CEA Saclay, IRFU/SPhN, 91191 Gif-sur-Yvette Cedex, France D. Verney IPNO, IN2P3-CNRS/Université Paris-Sud, 91406 Orsay, France F. Azaiez, D. Curien, O. Dorvaux, G. Duchêne, B.J.P. Gall, M. Rousseau IPHC, IN2P3-CNRS/Université Louis Pasteur, 67037 Strasbourg Cedex 2, France G. Barreau CENBG, IN2P3-CNRS/Université Bordeaux I, 33175 Gradignan, France N. Redon, O. Stézowski IPNL, IN2P3-CNRS/Université Claude Bernard, 69622 Villeurbanne Cedex, France

  21. Thank you for your attention!

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