High-spin studies and nuclear structure in three semi-magic regions of the nuclide chart High-seniority states in Sn isotopes

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1 High-spin studies and nuclear structure in three semi-magic regions of the nuclide chart High-seniority states in Sn isotopes Outline: Alain Astier, CSNSM Orsay, France Motivations Experimental conditions & Data analysis The Sn region Physical context New high-spin states & New isomers Discussion: Up to 3 neutron pairs broken in the νh 11/2 orbit Conclusion & Perspectives Fifth International Workshop on Nuclear Fission and Fission--Product Spectroscopy, Caen, May 28-31, 2013

2 one High-spin studies and nuclear structure in three X semi-magic regions of the nuclide chart High-seniority states in Sn isotopes Outline: Alain Astier, CSNSM Orsay, France Motivations Experimental conditions & Data analysis The Sn region Physical context New high-spin states & New isomers Discussion: Up to 3 neutron pairs broken in the νh 11/2 orbit Conclusion & Perspectives Fifth International Workshop on Nuclear Fission and Fission--Product Spectroscopy, Caen, May 28-31, 2013

3 Motivation: Structure of neutron-rich isotopes from high-spin studies Goal: Synthesis of neutron-rich isotopes at high spins a Evolution of the nuclear structure far from stability Fusion-evaporation: n-deficient isotopes Two possibilities: Deep-inelastic collisions Fission And of course: Start from the most neutron-rich compound system Do not lose too many neutrons in the process Approach chosen in this work: Fission following a heavy-ion induced fusion (at low energy) Two reactions extensively studied: 18 O+ 208 Pb and 12 C+ 238 U Gamma spectroscopy

4 Experimental conditions High spin states of neutron-rich isotopes are populated by fusion-fission: 18 O (85 MeV) Pb 226 Th* FF1* + FF2* + <4-6n> ~150 nuclei produced Symmetric fission around Z=45 EUROBALL 239 Ge (+BGO shield) ε ph ~ 8.5% Energy of 85 MeV for 18 O beam chosen in order to induce a cold fission σ f ~ 100 mb, I beam ~ 5 pna, a ~ 10 4 fissions/s in the target Thick Pb target (100 mg/cm 2 ) a low-lying γ-rays emitted by stopped nuclei ~ 4x10 9 events with fold 3

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

6 Fission fragments 100 Sn 132 Sn 78 Ni

7 Fission fragments 100 Sn 132 Sn 78 Ni

8 Fission fragments 100 Sn 132 Sn 78 Ni Many new physical information obtained, in particular in 3 regions: N=50 isotones and around N=82 isotones Z=50 isotopes

9 Experimental tools 1) γ-coincidences: unambiguous individual identification and assignment thanks to coincidences between complementary fragments 2) Angular correlations I 0 I 1 I 2 E 1 E 2 E 1 E 2 θ Ge 1 Ge 2 Multipolarities of (E1,E2) transitions determined from W(θ) 3) Time measurements I 0 I 1 I 2 E 1 E 2 T 1/2 T 1/2 can be extracted from the time spectrum Tac(E 2 )-Tac(E 1 ) Useful range for isomers: 10 ns < T 1/2 < 300 ns

10 Nuclear structure of the A<132 Sn isotopes at high spin 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 h 11/2 d 3/2 s 1/2 g 7/2 d 5/ J.A. Pinston and G. Genevey, J. Phys. G: Nucl. Part. Phys. 30 (2004) R57-R82 Isomers in the A<130 Sn isotopes: [(h 11/2 ) 2 ] and 7 - [(h 11/2 ) 1 (d 3/2 ) 1 ] in the even isotopes [(h 11/2 ) -3 (d 3/2 ) -1 ] recently reported in 128 Sn [S. Pietri et al., PRC83, (2011)] - 23/2 + [(h 11/2 ) 2 (d 3/2 ) 1 ] and 27/2 - [(h 11/2 ) 3 ] in the odd isotopes ν 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

11 High-spin states in Sn isotopes 118 Cd 118 Cd (Sn partners in the 12 C+ 238 U data set) Lots of unknown (and ~prompt!) transitions, belonging to the Sn complementary fragments 118 Cd 1190 kev New cascades established in several Sn isotopes Shown here: in 120 Sn

12 High-spin states in Sn isotopes Assignment of all the new cascades to the right Sn isotopes: From the yield of the Cd complementary fragments present in each γ-γ (Sn-Sn) spectrum 126 Sn 124 Sn Angular correlations (O+Pb reaction) Q - D Q - Q Q - Q Q - D Q - Q Q - Q Q - Q Q - Q 123 Sn 122 Sn 121 Sn 120 Sn

13 New level schemes (odd Sn s)

14 New level schemes (even Sn s)

15 SAPhIR events Detection of delayed γ rays by Euroball in the range [50 ns - 1 µs] delayed γ-γ matrix Gate 241 kev ( 120 Sn+ 122 Sn) new isomer (15 - ) in 120 Sn and 122 Sn! T 1/2 obtained from delayed γ-γ-t events Gate 253 kev ( 120 Sn) Gate 264 kev ( 122 Sn)

16 Experimental ν(h 11/2 ) n states with n=1,2,3,4,5,6 in the A<132 Sn isotopes Even-A Sn isotopes Odd-A Sn isotopes h 6? h 5 d 1 h 6 d 1 h 4 h 3 d 1 h 5 h 4 d 1 h 2 h 1 d 1 h 3 h 2 d 1 SM calculations with ANTOINE code: (see K. Sieja et al., PRC79, (2009) for calculation details) The 18 + state (from h 6 ) is not yrast, h 4 d 2 or h 4 d 1 s 1 are cheaper! 18 + (h 6 ) not observed Blocking of the odd neutron in d 3/2 Seniority-6 state (h 6 ) observed!

17 B(E2) s and νh 11/2 filling 10 + : (h 11/2 ) 2 27/2 - : (h 11/2 ) : (h 11/2 ) 3 (d 3/2 ) 1 Same behaviors of the 3 series Half-filling at A=123 (N=73) a Confirmation of the 15 - configuration

18 Conclusions & Perspectives Fusion-fission an efficient γ-spectrometer: a very 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 F Major improvement of 8 Sn level schemes F Tins are all the same! F Shell-Model works very well F Seniority-6 states identified for the first time Perspectives Reference: High-spin states with seniority ν=4,5, and 6 in Sn A.A. et al., Phys. Rev. C85, (2012) (20 th paper reporting results of the O+Pb experiment!!!) Similar physics: high spins of Te isotopes (same neutrons, only 2 protons more ) Other experiments: EXOGAM@ILL campaigns (now) thermal neutrons on 235 U/ 241 Pu thick targets AGATA+VAMOS@GANIL (2014+) fusion-fission in inverse kinematics, thin targets 78 Ni

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

20 Thank you for your attention!