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
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
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
Experimental conditions High spin states of neutron-rich isotopes are populated by fusion-fission: 18 O (85 MeV) + 208 Pb 226 Th* FF1* + FF2* + <4-6n> 8 82 90 ~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
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
Fission fragments 100 Sn 132 Sn 78 Ni
Fission fragments 100 Sn 132 Sn 78 Ni
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
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
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 5/2 82 64 50 J.A. Pinston and G. Genevey, J. Phys. G: Nucl. Part. Phys. 30 (2004) R57-R82 Isomers in the A<130 Sn isotopes: - 10 + [(h 11/2 ) 2 ] and 7 - [(h 11/2 ) 1 (d 3/2 ) 1 ] in the even isotopes - 15 - [(h 11/2 ) -3 (d 3/2 ) -1 ] recently reported in 128 Sn [S. Pietri et al., PRC83, 044328 (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
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 1190-241 Shown here: 1190-557-241-782-639 in 120 Sn
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
New level schemes (odd Sn s)
New level schemes (even Sn s)
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)
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, 064310 (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!
B(E2) s and νh 11/2 filling 10 + : (h 11/2 ) 2 27/2 - : (h 11/2 ) 3 15 - : (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
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 119-126 Sn A.A. et al., Phys. Rev. C85, 054316 (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
Collaboration (Sn paper) 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
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