1 / 26

Moving along Z=82, beyond the doubly-magic 208 Pb nucleus

Moving along Z=82, beyond the doubly-magic 208 Pb nucleus. G.Benzoni INFN sezione di Milano. Outline: physics motivations reaction mechanism experimental details data analysis Selection of nuclei of interest preliminary results and comparison with shell model calculations. 208 Pb.

fauna
Télécharger la présentation

Moving along Z=82, beyond the doubly-magic 208 Pb nucleus

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Moving along Z=82, beyond the doubly-magic 208Pb nucleus G.Benzoni INFN sezione di Milano • Outline: • physics motivations • reaction mechanism • experimental details • data analysis • Selection of nuclei of interest • preliminary results and comparison with shell model calculations

  2. 208Pb N/Z~1.0– 1.6 N/Z~3.0 Study shell structure along Z=82 What is the shell structure of neutron-rich Pb nuclei? Evolution of shell structure: Measurement of the E(2+), E(4+) and B(E2)

  3. Search for exotic Pb isotopes “east of 208Pb” stable Excited states Isomeric states Need to test stability of shell structure N=126, Z=82 region Indications of a weakening of Z=82 when approaching drip-line Drip-line is far away and not at all possible to approach TAG: long-living isomeric states

  4. What can isomers tell us?! ns Years T1/2(isomer) is “long” decay is hindered EXPERIMENTAL: • mere existence! • properties: E*, I(ħ), T1/2 • decay mode(s) • intermediate levels: E*, Iħ, lifetimes,... THEORY: • single-particle energies • configurations • interaction strengths • deformation • ... • “FUTURE”: • Coulomb excitation of isomers • interaction cross section gives radii • fusion-evaporation using isomeric beams

  5. Search for exotic Pb isotopes “east of 208Pb” Up to date information on heavy Pb following Pfutzner exp. @ GSI: Populated up to 215Pb but g infos only on 212Pb Predicted Presence of isomers involving high-j orbitals νg9/2, νi11/2, νj15/2 GSI • 5x106 pps • 2 HPGe detectors (Effγ=1%) • 350 ions implanted Neutron-rich lead isotopes known up to 212Pb M. Pfutzner PLB444 (1998) 32.

  6. Beta-decay lifetimes • Experimental β-decay data needed around 208Pb to validate theoretical models. • Predictions might differ by orders of magnitude. • β-lifetimes needed for r-process calculations. • Last lifetime measured for 215Pb I.N. Borzov PRC67, 025802 (2003)

  7. Experimental approach: 238U fragmentation at 1 GeV/u allows to reach heavy Pb isotopes with reasonable cross section (212Pb up to 220Pb). Epax The GSI UNILAC-SIS accelerator system combined with the FRS and RISING setup provide a UNIQUE worldwide facility to populate and study the neutron-rich lead isotopes. Abrabla M. Pfutzner PLB444 (1998) 32.

  8. Ablation (evaporation) abrasion Production mechanism: relativistic fragmentation pre-fragment • production of nuclei ranging from beam species to H • vfragment ≈ vbeam • short flight time chance to study short living nuclei • Cold fragmentation: fragments with N similar to the beam, but with several protons stripped

  9. Experimental details: Experiment performed at the end of September 2009 5 days data taking Beam current 1-2 x 109 pps (238U 1GeV/u) 3 FRS settings: 205Pb : ID confirmation 215-217Pb: “production” settings: populated nuclei ranging from 212-218Pb GSI-FRS Br-DE-Br method

  10. 91+ 2.5 g/cm2 Be 92+ 238U 90+ 238U 1GeV/u 212Pb Deg. S1: 2.4 g/cm2 S2 position MONOCHROMATIC Deg S2: 758 mg/cm2 Experimental details: charge states of primary beam (A/Q)212Pb == (A/Q)238U Intermediate focal plane. Mocadi simulation (cross section not included) E215Pb= 650 MeV/u after S1 deg

  11. Active Stopper 9 DSSSD 5cm x 5cm 2TPC [XS4] SCI41[TOF] 2x MUSIC [Z1,Z2] Deg S4: ~2.4 g/cm2 2TPC [XS2] SCI21 [TOF] 15 Cluster (105 HPGe crystals) εg = 9-14% (1.3-0.6 MeV) Flash mult. = 4-5 crystals dead Experimental details: RISING stopped beam array FRS detectors SCI42 implantation SCI43 veto 238U 1GeV/u

  12. RISING Stopped Beam set-up 24 12

  13. start Veto The active stopper Active stopper: 3x3 DSSSD 5cm x 5cm Logarithmic preamplifiers – position – implantation-decay correlation – energy (implantation/decay) Implant GeV scale Beta decay MeV scale Implantation-gamma correlation for isomers: Implantation trigger Beta-gamma correlation for implanted nuclei: Beta-decay trigger

  14. Z Heavy products Pb Fission fragments A/Q Where is 215Pb ??? Fission fragments+high Z products  ID very complicated

  15. 215Pb_sett DQ=-1 DQ=0 DQ=-2 Z DQ=+1 Br1 - Br2 Charge state selection • Formation of many charge states owing to interactions with materials • Isotope identification is complicated • Need to disentangle nuclei that change their charge state after S2 deg. (Br)Ta-S2 – (Br)S2-S4

  16. DQ=0 Z Br1 - Br2 Pb Application of charge state selection Z A/Q Z Clear ID plot, well resolved A/Q

  17. 206Hg 209Tl 212Pb 215Bi 210Hg 213Tl 216Pb 219Bi 215Pb setting with DQ=0, g information for: Z A/Q

  18. Isomers in ms range found in all measured even Pbs, 212-218Pb Example of Eg vs. Time matrix to identify long-living isomers 214Pb Energy (keV) Projection on Energy axis PRELIMINARY 185 339 Time (25 ns) 834 Energy (keV)

  19. Preliminary results: Pb chain T1/2 = 5.0 (3) μs 212Pb 6+ -> 4+: 160 keV 4+ -> 2+: 312 keV 2+ -> 0+: 805 keV T1/2 = 5.9 (1) μs 214Pb 4+ -> 2+: 341 keV 6+ -> 4+: 170 keV 2+ -> 0+: 834 keV T1/2=0.40 (1) μs 216Pb 6+ -> 4+: 160 keV 4+ -> 2+: 401 keV 2+ -> 0+: 887 keV

  20. 6+ -> 4+: 160 keV T1/2 = 5.0 (3) μs 4+ -> 2+: 312 keV 2+ -> 0+: 805 keV 212Pb comparison btw us and M.Pfutzner... narrower slits to cut primary beam and heavier nuclei (increased beam intensity) Higher g efficieny (~10%) Number of isotopes ~ 100 Number of isotopes:350 PRELIMINARY

  21. X 8+ 8+ X The experimental levels and the seniority scheme The 8+ isomer is a seniority isomer, involving neutrons in the 2g9/2 216Pb 212Pb 214Pb 210Pb

  22. S.p. energies (MeV) N=184 Shells -1.40 3d3/2 -1.45 2g7/2 4s1/2 -1.90 3d5/2 -2.37 -2.51 1j15/2 N=7 major shell -3.16 1i11/2 2g9/2 -3.94 N=126 The valence space in the Kuo-Herling interaction 208Pb is a doubly-magic nucleus (Z=82, N=126). For neutron-rich Lead isotopes, the N=6 major shell is involved PRC 43, 602 (1992)

  23. Shell model calculations with K-H Calculations with Antoine code and K-H interaction 218Pb 216Pb 210Pb 212Pb 214Pb th. exp. th. exp. th. exp th. exp. th.

  24. 210Hg isomer 208Hg PRC 80, 061302(R) Change in structure ? Preliminar! 210Hg 642 keV 663 keV 546 keV Energy (keV)

  25. Resume: • recente exp. to study heay Pb isotopes with 238U fragmentation reactions • preliminary results on Pb chain up to 216Pb • Preliminary comparison with shell model calculations confirming 8+ isomer is a seniority isomers • Still to do • study other charge states • detailed study of isomers in species (Hg, Tl, Bi,Po) • study short/long living isomers with other TDC signals • extract isomeric ratios • study beta decay • ......... (suggestions ???)

  26. Collaboration: ~70 people and 18 institutions G. Benzoni, J.J. Valiente-Dobon, A. Gottardo,R. Nicolini. A. Bracco, F.C.L. Crespi,F. Camera, A. Corsi, S. Leoni, B. Million, O. Wieland, G.de Angelis, D.R. Napoli, E. Sahin,S.Lunardi,R.Menegazzo, D. Mengoni, F. Recchia, P. Boutachkov, L. Cortes, C. Domingo-Prado,F. Farinon, H. Geissel, J. Gerl,N. Goel, M. Gorska, J. Grebosz, E. Gregor, T.Haberman,I. Kojouharov, N. Kurz, C. Nociforo, S. Pietri, A. Prochazka, W.Prokopowicz, H. Schaffner,A. Sharma, H. Weick, H-J.Wollersheim, A.M. Bruce, A.M. Denis Bacelar, A. Algora,A. Gadea, M. Pf¨utzner, Zs. Podolyak, N. Al-Dahan, N. Alkhomashi, M. Bowry, M. Bunce,A. Deo, G.F. Farrelly, M.W. Reed, P.H. Regan, T.P.D. Swan, P.M. Walker, K. Eppinger,S. Klupp, K. Steger, J. Alcantara Nunez, Y. Ayyad, J. Benlliure, E. Casarejos,R. Janik,B. Sitar, P. Strmen, I. Szarka, M. Doncel, S.Mandal, D. Siwal, F. Naqvi,T. Pissulla,D. Rudolph,R. Hoischen,P.R.P. Allegro, R.V.Ribas,Zs. Dombradi Universita’ degli Studi e INFN sezione di Milano, Milano, I; INFN-LNL, Legnaro (Pd), I; Universita’ di Padova e INFN sezione di Padova, Padova, I; University of the West of Scotland, Paisley, UK; GSI, Darmstadt, D; Univ. Of Brighton, Brighton, UK; IFIC, Valencia, E; University of Warsaw, Warsaw, Pl; Universiy of Surrey, Guildford, UK; TU Munich, Munich, D; University of Santiago de Compostela, Santiago de Compostela, E; Comenius University, Bratislava, Sk; Univ. Of Salamanca, Salamanca, E; Univ. of Delhi, Delhi, IND; IKP Koeln, Koeln, D; Lund University, Lund, S; Univ. Of Sao Paulo, Sao Paulo, Br; ATOMKI, Debrecen, H.

More Related