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A. Barzakh Petersburg Nuclear Physics Institute, Gatchina, Russia

Shape coexistence and charge radii in thallium, gold and astatine isotopes studied by in-source laser spectroscopy at RILIS-ISOLDE. A. Barzakh Petersburg Nuclear Physics Institute, Gatchina, Russia on behalf of ‘Astatine and Gold’ Collaboration. Astatine-Gold collaboration ( IS534).

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A. Barzakh Petersburg Nuclear Physics Institute, Gatchina, Russia

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  1. Shape coexistence and charge radii in thallium, gold and astatine isotopes studied by in-source laser spectroscopy at RILIS-ISOLDE A. Barzakh Petersburg Nuclear Physics Institute, Gatchina, Russia on behalf of ‘Astatine and Gold’ Collaboration

  2. Astatine-Gold collaboration (IS534) University of York, United Kingdom A. N. Andreyev, V. Truesdale RILIS and ISOLDE, Geneva, Switzerland S. Rothe, B. A. Marsh, A. M. Sjodin, T. C. Cocolios, V. N. Fedosseev M. D. Seliverstov Institut für Physik, Johannes Gutenberg-Universität Mainz, Mainz, Germany S. Raeder, K. D. A. Wendt University of the West of Scotland, United Kingdom X. Derkx, V. Liberati, J. Lane, K. Sandhu Instituut voor Kern- en Stralingsfysica, K.U. Leuven, Leuven, Belgium L. Ghys, C. Van Beveren, E. Rapisarda, D. Pauwels, D. Radulov, Yu. Kudryavtsev, M. Huyse, P. Van Duppen Comenius University, Bratislava, Slovakia S. Antalic, Z. Kalaninova PNPI, Gatchina, Russian Federation A. Barzakh, D. V. Fedorov, P. Molkanov University of Manchester, UK K. Lynch, I. Straschnov... MR-TOF@ISOLTRAP team K.Blaum, C. Borgmann, F. Herfurth, M.Kowalska, S.Kreim, D.Lunney, V.Manea, D.Neidherr, M.Rosenbusch, L. Schweikhard, F. Wienholtz, R. Wolf, K. Zuber.

  3. Outlook • Resonance Ionization Laser Ion Source (RILIS) at ISOLDE • IS and hfs measurements for the long chain of At isotopes • “Back to sphericity” in the lightest Au isotopes • Conclusions all results are preliminary!

  4. Laser Ion Source at ISOLDE Isotope/isomer shift A,Z A-1,Z • Isotope shift (IS), hyperfine structure (HFS) measurements: The wavelength of the narrow-band laser is scanned across the chosen transition. The photoion current at the collector of the mass separator increases at the resonance. • Detection of photoion current by measuring FC current, a//g or ToF spectra while scanning the frequency Target Hot Cavity Extractor Ion Source Mass separation Laser beams 60 kV Experiments Reaction products (neutral) Protons Ions Target material

  5. RILIS upgrade CVL to Nd:Yag Green Beams 90 W @ 532 nm UV beam 18 W @ 355 nm 10kHz rep rate 6 - 8 ns pulses

  6. RILIS upgrade Dye+Ti:Sa system 3 Ti:Sa lasers: 5 GHz linewidth Up to 5 W output power 680 – 1030 nm (fund.) 35 ns pulse length Since the two systems can be used either independently or in combination,there exists far greater flexibility for switching from one ionization scheme to another or rapidly changing the scanning step. Laser ion source at ISOLDE Nd:YAG lasers Dye lasers Ti:Sa lasers

  7. Detection: Windmill System at ISOLDE A. Andreyev et al., PRL 105, 252502 (2010) MINIBALL Ge cluster Si Annular Si Annular Si pure 50 keV beam from RILIS+ISOLDE Si a ff 50 keV beam from ISOLDE ff C-foil C-foils 20 mg/cm2 Si detectors • The WM technique requires waiting for the decay of the isotope (usually, α-decay). Not practical for long-lived or stable isotopes (or for β-decaying). • Setup: Si detectors from both sides of the C-foil • Large geometrical efficiency (up to 80%) • 2 fold fission fragment coincidences • ff-γ, γ-α, γ-γ, etc coincidences

  8. Detection: MR-TOF MS at ISOLDE Multi-reflection time-of-flight mass separator (MR-TOF MS) ~1000 revolutions, ~35 ms, m/Δm ~ 105 • MR-TOF MS is not limited by decay scheme or long half-lives • MR-TOF MS offers a way to separate background for direct single-ion detection usingMCP (time scale: tens of ms). R. N. Wolf et al., Nucl. Instr. and Meth. A 686, 82-90 (2012), S. Kreim et al., INTC-P-299, IS 518 (2011)

  9. Shape coexistence and charge radii in Pb region Po: ISOLDE, PRL106, 052503 (2011) T. Cocolios et al. Pb: ISOLDE, PRL98, 112502 (2007)H. De Witte et al. 85At? Tl: IS511 ISOLDE and IRIS (Gatchina) ?

  10. Photoionization scheme for the radioactive element At IP 532 nm 795 nm 216 nm Optimal photoionization scheme. Narrow band lasers can be used for the 1st and 2nd transitions At 6p48p(?), J=3/2 6p47s, J=3/2 6p5, J=3/2 • ISOLDE + TRIUMF, Canada: • Many new atomic levels were found • Transition strengths were measured • For the first time the ionization potential was measured

  11. Astatine HFS spectra IP 532 nm 795 nm 216 nm 1st step scanning is better for δ<r2> extraction 2nd step scanning is better for hfs analysis (Q and μ determination)

  12. IS534October 2012:Charge radii of At isotopes WM FC WM MR-TOF MS

  13. October 2012:IS534 experiment at ISOLDE – Au isotopes autoionizing state IP 674.1 nm 306.6 nm 267.7 nm Au ionization scheme

  14. IS534: Charge Radii of Au isotopes, ISOLDE 2012 level ordering for Au isomers at A=178 was determined in dedicated ISOLTRAP measurements • Deformation jump toward less deformed shapes in the light Au isotopes • Shape coexistence in 178Au (large deformation difference between 2 states) • Shape staggering near 181Au and 178Au

  15. Confirmed prediction: “return to sphericity” in Au new results J.L.Wood, E.E. Zganjar, C. De Coster, K. Heyde, Nucl.Phys. A 651 (1999) 323

  16. Summary: Charge Radii in Pb region ? ? • Astatine seems to follow Po δ<r2> trend (“early onset of deformation”) • Intruder isomer shift in 197At (shape coexistence, similar to Tl nuclei) • “Back to sphericity” in the lightest Au isotopes • Pronounced odd-even staggering (A=181,178) and shape coexistence (A=178) in Au isotopic chain

  17. Conclusions • IS’s and hfs’s for 10 At isotopes (isomers) were measured for two transitions, 216 nmand 795 nm, The fast switching between these modes of scanning provides much more flexibility to experiment and gives more reliable and complementary data for analysis (especially for atoms without known spectroscopic information). • MR-TOF mass separator was used for photo-ions detection for the first time. This method seems to be indispensable for measurements with great surface ionized background and for long lived isotopes with great yield and/or absence of alpha decay mode. • Using WM installation for photo-ions detection gives the possibility to obtain wealth of additional nuclear spectroscopic information (decay schemes, spin and parity assignment etc.) without supplementary time requirement. • Coordinated (ISOLDE&IRIS) program for Tl isotopes investigation enabled us to use both installation more efficiently. • Very interesting results for At and Au isotopes by IS/hfs measurements were obtained: “inverse jump of deformation”, unexpected spin assignments, shape isomers etc. The study of shape coexistence in the lead region will be continued: to go further for Au’s, to fill the gaps and go further for At’s (ISOLDE), to investigate Bi isotopes (IRIS), etc.

  18. For p-s transition (as 216 nm transition in At) the assumption MSMS=(0±1)·MNMS is commonly used F(At) is calculated with the assumption of MSMS=0 from the condition that δ<r2>124, 122 is equal to the “parabola” value at Z=85

  19. King plot for 216 nm and 795 nm lines in At 197m 207 197g 198g 198m 217 F216/F795(At)=-2.26(8) compare with F256/F843(Po)=-2.241(7) for similar transitions in Po Isotope shift δA,A’: Δσ for different transitions should lie on a straight line with a slope Fλ1/ Fλ2

  20. Isomer selectivity for 197,198At Isomer selectivity enables to measure masses of 197g,198gAt at ISOLTRAP and receive nuclear spectroscopic information for pure g.s.

  21. Isomer selectivity for 178Au Isomer selectivity enables to measure masses of 178g,178mAt at ISOLTRAP and therefore to establish level ordering

  22. F’2=1 Jf=1/2 F’2 F’1 F’1=0 I=1/2 0—>0 transition is forbidden! F2 F2=1 Ji=1/2 F1 F1=0 Only 3 rather than usual 4 lines will be seen in the hfs spectra of isotopes with I=1/2

  23. IS534: Hyperfine Structure Scans for 177,179Au 179Au (WM) 177Au (WM) Number of peaks and their intensities ratio fix ground state spins of 177,179Au: I=1/2 179Au 3/2+ calculated 179Au 1/2+ calculated

  24. Why is 1/2+1/2+181Tl177Au a decay hindered? HF>3 I=3/2 m~1.6mN , pure sph. 3s1/2, (as in the heavier Tl’s) 1/2+ m~1.1mN , (preliminary) mixed/def/triaxial 3s1/2,/d3/2 1/2+ Plot from A.Andreyev et al., PRC 80, 024302 (2009)

  25. Additional atomic spectroscopic information for Astatine IP 532 nm F’2=2 Jf=3/2 F’2=3 795 nm Jf=5/2 F’1=1 F’1=2 216 nm F2=2 F2=2 Ji=3/2 Ji=3/2 F1=1 F1=1 58805 cm-1, J=3/2 or 5/2 J=3/2 J=3/2 I=1/2 The number of peaks (4 rather than 3) unambiguously point to J=3/2 for 58805 cm-1 atomic state in At

  26. Hyperfine structure anomaly for Au isotopes

  27. King plot for 276 nm and 535 nm lines in Tl

  28. Charge Radii of Tl isotopes, ISOLDE & IRIS (Gatchina) Long chain (N from 102 to 116) of the (intruder) isomeric states with the deformation markedly greater than the deformation of g.s. (shape coexistence). Previously known isomeric chain is extended for both sides (N>112, N<106). For the first time the great isomer shift was found for odd-odd nuclei also (A=186, 184).

  29. Comparison of relative δ<r2> for Pb and Tl nuclei For the sake of clarity, only the results for the even-neutron nuclei are presented. The corresponding picture for odd-neutron nuclei is quite similar. The Tl radii perfectly follow the pattern of the Pb radii even below the midshell at N = 104 where the well known pronounced deviation from this behavior, connected with the onset of permanent prolate deformation, was found for the adjacent Hg (Z = 80) and Au (Z = 79) nuclei.

  30. Magnetic moments for Tl nuclei Newly measured magnetic moments for Tl isotopes at and below the midshell (N≤104) perfectly follow the trends for heavier Tl isotopes with the same spin.

  31. Isomer shift for intruder states in Tl nuclei The most striking finding is the unexpected growth of the isomer shift between ground (1/2+) and isomeric (intruder) states (9/2-) in odd Tl nuclei. All calculations predicted that the difference in deformation (i.e., isomer shift) between g.s. and m.s. is nearly constant or even decreases after A=187.

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