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Chemical studies of the transactinide elements at JAEA

6th China-Japan Joint Nuclear Physics Symposium Shanghai, China, May 17, 2006. Chemical studies of the transactinide elements at JAEA. Y. Nagame Advanced Science Research Center Japan Atomic Energy Agency (JAEA). Z ≥ 104: transactinide elements superheavy elements.

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Chemical studies of the transactinide elements at JAEA

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  1. 6th China-Japan Joint Nuclear Physics Symposium Shanghai, China, May 17, 2006 Chemical studies of the transactinide elements at JAEA Y. Nagame Advanced Science Research Center Japan Atomic Energy Agency (JAEA)

  2. Z ≥ 104: transactinide elements superheavy elements Periodic table of the elements

  3. Heavy element nuclear chemistry at JAEA • Chemical properties of the transactinide • elements (Z 104) • - Liquid-phase chemistry of Rf and Db • 2. Nuclear properties of heavy nuclei (Z 100) • - a-g spectroscopy of No (Z = 102) and • Rf (Z = 104) • 3. Nuclear fission of heavy nuclei (Z 100) • - Fission modes in heavy nuclei

  4. Contents Introduction Chemical studies of the transactinide elements  Relativistic effects in chemical properties of heavy elements  Atom-at-a-time chemistry Chemical studies of element 104 (Rf) at JAEA  Production of Rf  Characteristic chemical properties of Rf based on an atom-at-a-time scale  Fluoride complex formation of Rf 3.Conclusion

  5. Introduction Chemical studies of the transactinide elements Objectives: 1.Basic chemical properties  ionic charge, radius, redox potential, complex formation, volatility, etc. Architecture of the Periodic table of the elements  Periodicities of the chemical properties 3.Relativistic effects in chemical properties

  6. Relativistic effects (1) General: increase of the mass with increasing velocity At heavy elements: Increasing nuclear charge plays as the “accelerator” of the velocity of electrons.  Electrons near the nucleus are attracted closer to the nucleus and move there with high velocity.  mass increase of the inner electrons and the contraction of the inner electron orbitals (Bohr radius)  Direct relativistic effects

  7. Relativistic effects (2)  Electrons further away from the nucleus are better screened from the nuclear charge by the inner electrons and consequently the orbitals of the outer electrons expand.  Indirect relativistic effects It is expected that transactinide elements would show a drastic rearrangement of electrons in their atomic ground states, and as the electron configuration is responsible for the chemical behavior of elements, such relativistic effects can lead to surprising chemical properties. Increasing deviations from the periodicity of chemical properties based on extrapolation from lighter homologues in the Periodic table are predicted.

  8. Atom-at-a-time chemistry The transactinide elements must be produced at accelerators using reactions of heavy-ion beams with heavy target materials. Because of the short half-lives and the low production rates of the transactinide nuclides, each atom produced decays before a new atom is synthesized. Any chemistry to be performed must be done on an "atom-at-a-time" basis. Rapid, very efficient and selective chemical procedures are indispensable to isolate desired transactinides.  Repetitive experiments

  9. 2. Chemical studies of rutherfordium (Rf, Z = 104) at JAEA

  10. Experimental approach to Rf chemistry Increasing deviations from the periodicity of the chemical properties based on extrapolations from the lighter homologues are predicted. Experimental approach should involve detailed comparison of the chemical properties of the transactinides with those of their lighter homologues under identical conditions. We have investigated the chemical properties of Rf together with the lighter homologues Zr and Hf under the same on-line experiments.

  11. Schematic flow of the experiment He cooling gas 248Cm target 248Cm(18O,5n)261Rf (T1/2 = 78 S) 248Cm: 610 mg/cm2 18O6+: 300 pnA at JAEA tandem accelerator 18O beam Beam stop HAVAR window 2.0 mg/cm2 Gas-jet Recoils Chemistry Lab. Collection AIDA apparatus Dissolution & Complex formation Miniaturized liquid chromatography Sample preparation a-particle measurement Cyclic, 80 s

  12. He/KCl gas-jet AIDA (Automated Ion-exchangeseparation apparatus coupled with theDetection system for Alpha-spectroscopy) Signal out Pulse motors 8 vacuum chambers 600 mm2 PIPS detectors Preamp. Air cylinder ARCA Eluent bottles Micro-columns He gas heater Halogen lamp Ta disk reservoir Sampling table Cyclic discontinuous column chromatographic separation Automated detection of a-particles

  13. Excitation function of 248Cm(18O, 5n)261Rf Maximum production cross section : ~ 13 nb at 94-MeV 18O Production rate： ~ 2 atoms per minute

  14. Fluoride complex formation M4+ + nF-⇄ MF4+nn- (M=Zr, Hf, and Rf) Fluoride anion (F-)strongly coordinates with metal cations.  Formation of strong ionic bonds is expected Electrostatic interaction between M4+ andF-  charge density, ionic radius, etc. Fast reaction kinetics of the fluoride complex formation Ion-exchange chromatographic behavior of Rf, Zr, and Hf in hydrofluoric acid (HF) solution

  15. Anion-exchange behavior of Rf, Zr, and Hf in HF 4226 cycles of anion-exchange experiments  266 a events form 261Rf and 257No, 25 a-a correlations Column size: 1.6 mm i.d.  7.0 mm Column size: 1.0 mm i.d.  3.5 mm

  16. Kd vs. [HF2-] HF ⇄ H+ + F- HF + F-⇄HF2- Rn-MF4+n +nHF2-⇄nR-HF2+ MF4+nn-(M=Rf, Hf and Zr), R: resin [M]r [M]aq [Rn-MF4+n ] [MF4+n n–] [R-HF2 ]n [HF2–]n [R-HF2 ]n [MF4+n n–] [Rn-MF4+n ] [HF2–]n = = Kd = K = log Kd = C- nlog[HF2-] slope = charge state of the metal complex

  17. Conclusion Large difference in the fluoride complex formation of Rf and the lighter homologues Zr and Hf  Fluoride complex formation: Rf < Zr ≈ Hf According to the HSAB (Hard and Soft Acids and Bases) concept, the fluoride anion is a hard anion and interacts stronger with (hard) small cations. Thus, a weaker fluoride complex formation of Rf as compared to those of Zr and Hf would be reasonable if the size of the Rf4+ ion is larger than those of Zr4+ and Hf4+ as predicted with relativistic molecular calculations. Zr4+ : 0.072 nm Hf4+ : 0.071 nm Rf4+ : 0.079 nm (prediction)

  18. JAERI- M. Asai, M. Hirata, S. Ichikawa, T. Ichikawa, Y. Ishii, I. Nishinaka, T. K. Sato, H. Tome, A. Toyoshima, K. Tsukada, and T. Yaita RIKEN - H. Haba Osaka Univ. - H. Hasegawa, Y. Kitamoto, K. Matsuo, D. Saika, W. Sato, A. Shinohara, and Y. Tani Niigata Univ. - S. Goto, T. Hirai, H. Kudo, M. Ito, S. Ono, and J. Saito Tokyo Metropolitan Univ. - H. Nakahara and Y. Oura Univ. Tsukuba - K. Akiyama and K. Sueki Kanazawa Univ. - H. Kikunaga, N. Kinoshita, and A. Yokoyama Univ. Tokushima - M. Sakama GSI - W. Brüchle, V. Pershina, and M. Schädel Univ. Mainz - J. V. Kratz Acknowledgement

  19. Kd vs. [NO3]- in HF/HNO3 HF ⇄ H+ + F- (HF + F-⇄ HF2-) HNO3⇄ H+ +NO3- Zr, Hf: slope = -2 [MF6]2- (M=Zr, Hf) [F-] = 3 x 10-3 M Rf: slope = -2 [RfF6]2- closed (on-line) open (off-line) log Kd = C - nlog[NO3-] Rn-MF4+n + nNO3-⇄nR-NO3 + MF4+nn- : n = -2

  20. Kd vs. [F-] in HF/HNO3 MF5- MF62-RfF5- RfF62- Rf (on-line) Zr (off-line) Hf (off-line) HF2- counter ion 3x10-3 M Formation of [MF6]2-: Zr  Hf > Rf

  21. Energy levels of the valence ns and (n-1)d electrons rel: relativistic nr: non-relativistic

  22. Radial wave functions of valence orbitals for Rf J A E R I Contraction of orbitals Rf 5f non-rel rel Rf 6s 1 Rf 6p Rf 6d radial density rR(r) 0 spin-orbit coupling -1 0 2 4 0 2 4 distance(a.u.)

  23. Production of 261Rf 248Cm(18O,5n)261Rf (78 s), 18O6+ beam: 300 pnA He Cooling Gas 248Cm target: 610 mg/cm2 248Cm Target on Be Backing Gas-jet Outlet 18O Beam Water Cooled Beam Stop Gas-jet Inlet (He/KCl) HAVAR Window 2.0 mg/cm2 Recoils Wheel Rotation Si PIN Photodiodes Catcher Foil 120 mg/cm2, 20 mm i.d. MANON: Measurement system for Alpha-particle and spontaneous fissioN events ON-line

  24. Production rates of transactinide nuclides used for chemistry study

  25. Times 1 2 3 4 5 6 7 8 ：　　　　　　　　　　　 　： ：　　　　　　　　　　 　　： Atom-at-a-time-chemistry “Single atom” “Classical” Phase 1 Phase 2 Phase1 Phase 2 Activity 1>>Activity 2 Probability 1>>Probability 2

  26. Anion-exchange procedure in HF with AIDA 1. Collection of 261Rf and 169Hf for 125 s 2. Dissolution with 240 mL of 1.9 M - 13.9 M HF and feed onto the column at 740 mL/min 3. 210 mL of 4.0 M HCl at 1.0 mL/min AIX column: MCI GEL CA08Y resin (20 mm) 1.6 mm i.d.  7.0 mm (1.0 mm i.d.  3.5 mm) Fraction 1 (A1) Fraction 2 (A2) Adsorption probability = 100 A2 / (A1 + A2) 169Hf : elution behavior and chemical yields (~ 60%) 85Zr and 169Hf from Ge/Gd target

  27. Anion-exchangein HF + + + + R2-RfF6 + 2HF2- ⇔ 2R-HF2 + RfF62- Anion-exchange resin HF solution Adsorption on resin HF  H+ + F- HF + F- HF2- r HF2- r N r HF2- r N r RfF62- exchanger Anion-exchange between RfF62- and HF2- r r N HF2- r r HF2- N r RfF62-

  28. Automated Ion exchange separation apparatus coupled with the Detection system for Alpha spectroscopy (AIDA)

  29. Anion-exchange procedures for Rf and the homologues, Zr and Hf in HF Front view Side view AIDA He/KCl Jet in 1.9–13.9 M HF 240–260 μL Eluent in Collection site 4 M HCl 200–210 μL Gas out Slider Magazine 2nd fraction Sample 1st fraction α/γ-spectroscopy 5 cm Ta disk Magazine 20 micro-columns, MCI GEL CA08Y, 22 mm 1.6 mmΦ x 7.0 mm or 1.0 mmΦ x 3.5 mm Schädel et al. RCA48(1989)171.

  30. Ionic radii of the group-4 elements (M4+) Actinide contraction: The radii of the actinide ions (An3+) are observed to decrease with increasing positive charge of the nucleus. This contraction is a consequence of the addition of successive electrons to an inner f electron shell, so that the imperfect screening of the increasing nuclear charge by the additional f electron results in a contraction of the outer or valence orbital.

  31. Charge state n of an anion MF4+nn–(M4+ = Rf, Zr and Hf) Assuming that the adsorption equilibrium of an ion MF4+n n– can be represented by the equation, Rn-MF4+n + nHF2– ⇔ nR-HF2 + MF4+n n– (where R represents the resin), one obtains the mass action constant [R-HF2 ]n [MF4+n n–] [Rn-MF4+n ] [HF2–]n K = . The distribution coefficient Kd is expressed as [M]r [M]aq [Rn-MF4+n ] [MF4+n n–] [R-HF2 ]n [HF2–]n 1 K Kd = = = . For tracer solutions, the following simplification will be assumed using the constant c [R-HF2]n = c . Thus, the following equation is deduced [R-HF2 ]n K log Kd = log - nlog [HF2–] ≈ c - nlog [HF2–].

  32.  Chemical experiments on Rf should be conducted together with the homologues under strictly identical conditions. Simultaneous production of Rf, Zr and Hf Target recoil chamber + gas-jet transport system 248Cm(18O,5n)261Rf (78 s) + Gd(18O,xn)169Hf (3.24 min) natGe(18O,5n)85Zr (7.86 min) + Gd(18O,xn)169Hf (3.24 min) 248Cm target: 610 mg/cm2 18O6+ beam: 300 pnA He Cooling Gas 248Cm Target on Be Backing Gas-jet Outlet 18O Beam Water Cooled Beam Stop Gas-jet Inlet (He/KCl) HAVAR Window 2.0 mg/cm2 Recoils Rapid Chemical Separation Apparatus AIDA

  33. Anion-exchange behavior of Rf, Zr and Hf in HCl Adsorption of Rf is similar to those of Zr and Hf. - typical behavior of the group-4 element

  34. Upper part of the chart of nuclides

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