Presentation on theme: "Chemical studies of the transactinide elements at JAEA Y. Nagame Advanced Science Research Center Japan Atomic Energy Agency (JAEA) 6th China-Japan Joint."— Presentation transcript:
Chemical studies of the transactinide elements at JAEA Y. Nagame Advanced Science Research Center Japan Atomic Energy Agency (JAEA) 6th China-Japan Joint Nuclear Physics Symposium Shanghai, China, May 17, 2006
Periodic table of the elements Z ≥ 104: transactinide elements superheavy elements
Heavy element nuclear chemistry at JAEA 1.Chemical properties of the transactinide elements (Z 104) - Liquid-phase chemistry of Rf and Db 2. Nuclear properties of heavy nuclei (Z 100) - spectroscopy of No (Z = 102) and Rf (Z = 104) 3. Nuclear fission of heavy nuclei (Z 100) - Fission modes in heavy nuclei
Contents 1.Introduction Chemical studies of the transactinide elements Relativistic effects in chemical properties of heavy elements Atom-at-a-time chemistry 2.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
1.Introduction Objectives: 1. Basic chemical properties ionic charge, radius, redox potential, complex formation, volatility, etc. 2.Architecture of the Periodic table of the elements Periodicities of the chemical properties 3. Relativistic effects in chemical properties Chemical studies of the transactinide elements
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
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.
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
2. Chemical studies of rutherfordium (Rf, Z = 104) at JAEA
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.
Schematic flow of the experiment Collection Dissolution & Complex formation He cooling gas 18 O beam HAVAR window 2.0 mg/cm Cm target Beam stop Recoils Gas-jet Miniaturized liquid chromatography Sample preparation -particle measurement Cyclic, 80 s AIDA apparatus 248 Cm( 18 O,5n) 261 Rf (T 1/2 = 78 S) 248 Cm: 610 g/cm 2 18 O 6+ : 300 pnA at JAEA tandem accelerator Chemistry Lab.
Eluent bottles Ta disk reservoir Micro-columns He gas heater Halogen lamp Sampling table Air cylinder Pulse motors Signal out 8 vacuum chambers 600 mm 2 PIPS detectors Preamp. He/KCl gas-jet AIDA (Automated Ion-exchange separation apparatus coupled with the Detection system for Alpha- spectroscopy) Cyclic discontinuous column chromatographic separation Automated detection of -particles ARCA
Excitation function of 248 Cm( 18 O, 5n) 261 Rf Maximum production cross section : ~ 13 nb at 94-MeV 18 O Production rate ： ~ 2 atoms per minute
Fluoride complex formation M 4+ + nF - ⇄ MF 4+n n- (M=Zr, Hf, and Rf) Fluoride anion (F - ) strongly coordinates with metal cations. Formation of strong ionic bonds is expected Electrostatic interaction between M 4+ and F - 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
Anion-exchange behavior of Rf, Zr, and Hf in HF Column size: 1.0 mm i.d. 3.5 mmColumn size: 1.6 mm i.d. 7.0 mm 4226 cycles of anion-exchange experiments 266 events form 261 Rf and 257 No, 25 correlations
R n -MF 4+n + n HF 2 - ⇄ n R-HF 2 + MF 4+n n- (M=Rf, Hf and Zr), R: resin K d vs. [HF 2 - ] HF ⇄ H + + F - HF + F - ⇄ HF 2 - HF ⇄ H + + F - HF + F - ⇄ HF 2 - log K d = C - n log[HF 2 - ] [R-HF 2 ] n [MF 4+n n– ] [R n -MF 4+n ] [HF 2 – ] n K = [M] r [M] aq [R n -MF 4+n ] [MF 4+n n– ] [R-HF 2 ] n [HF 2 – ] n = = K d = slope = charge state of the metal complex
Conclusion fluoride complex formation of Rf 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 Rf 4+ ion is larger than those of Zr 4+ and Hf 4+ as predicted with relativistic molecular calculations. Zr 4+ : nm Hf 4+ : nm Rf 4+ : nm (prediction)
Acknowledgement 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
K d vs. [NO 3 ] - in HF/HNO 3 R n -MF 4+n + n NO 3 - ⇄ n R-NO 3 + MF 4+n n- : n = -2 Rf: slope = -2 [RfF 6 ] 2- Zr, Hf: slope = -2 [MF 6 ] 2- (M=Zr, Hf) closed (on-line) open (off-line) [F - ] = 3 x M HF ⇄ H + + F - (HF + F - ⇄ HF 2 - ) HNO 3 ⇄ H + + NO 3 - HF ⇄ H + + F - (HF + F - ⇄ HF 2 - ) HNO 3 ⇄ H + + NO 3 - log K d = C - n log[NO 3 - ]
K d vs. [F - ] in HF/HNO 3 MF 5 - MF 6 2- RfF 5 - RfF 6 2- HF 2 - counter ion 3x10 -3 M Rf (on-line) Zr (off-line) Hf (off-line) Rf (on-line) Zr (off-line) Hf (off-line) Formation of [MF 6 ] 2- : Zr Hf > Rf
Energy levels of the valence ns and (n-1)d electrons rel: relativistic nr: non-relativistic
non-relrel distance(a.u.) radial density rR(r) JAERI spin-orbit coupling Rf 5f Rf 6s Rf 6d Contraction of orbitals Rf 6p Radial wave functions of valence orbitals for Rf
18 O Beam 248 Cm Target on Be Backing HAVAR Window 2.0 mg/cm 2 Gas-jet Outlet Gas-jet Inlet (He/KCl) Water Cooled Beam Stop He Cooling Gas Recoils 248 Cm( 18 O,5n) 261 Rf (78 s), 18 O 6+ beam: 300 pnA 248 Cm target: 610 g/cm 2 MANON: Measurement system for Alpha-particle and spontaneous fissioN events ON-line Si PIN Photodiodes Catcher Foil 120 mg/cm 2, 20 mm i.d. Wheel Rotation Production of 261 Rf
Production rates of transactinide nuclides used for chemistry study
Atom-at-a-time-chemistry Times ： ： “Classical” “Single atom” Phase 2Phase1 Activity 1 >> Activity 2 Phase 1Phase 2 Probability 1 >> Probability 2
Anion-exchange procedure in HF with AIDA 1. Collection of 261 Rf and 169 Hf for 125 s 2. Dissolution with 240 L of 1.9 M M HF and feed onto the column at 740 L/min AIX column: MCI GEL CA08Y resin (20 m) 1.6 mm i.d. 7.0 mm (1.0 mm i.d. 3.5 mm) L of 4.0 M HCl at 1.0 mL/min Fraction 1 (A 1 ) Fraction 2 (A 2 ) Adsorption probability = 100 A 2 / (A 1 + A 2 ) 169 Hf : elution behavior and chemical yields (~ 60%) 85 Zr and 169 Hf from Ge/Gd target
N + + HF 2 - RfF 6 2- HF 2 - R 2 -RfF 6 + 2HF 2 - ⇔ 2R-HF 2 + RfF 6 2- HF solution Anion-exchange resin RfF 6 2- r N HF 2 - Anion-exchange between RfF 6 2- and HF 2 - r r r r r r r r Adsorption on resin exchanger N + + N r HF H + + F - HF + F - HF 2 - HF H + + F - HF + F - HF 2 - Anion-exchange in HF
Automated Ion exchange separation apparatus coupled with the Detection system for Alpha spectroscopy (AIDA)
AIDA He/KCl Jet in Slider Eluent in Collection site Sample 5 cm Magazine 20 micro-columns, MCI GEL CA08Y, 22 m 1.6 mmΦ x 7.0 mm or 1.0 mmΦ x 3.5 mm Anion-exchange procedures for Rf and the homologues, Zr and Hf in HF the homologues, Zr and Hf in HF 4 M HCl 200–210 μL Gas out Magazine 1.9–13.9 M HF 240–260 μL α/γ-spectroscopy 1 st fraction 2 nd fraction Front viewSide view Ta disk Schädel et al. RCA 48(1989)171.
Actinide contraction: The radii of the actinide ions (An 3+ ) 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. Ionic radii of the group-4 elements (M 4+ )
Assuming that the adsorption equilibrium of an ion MF 4+n n– can be represented by the equation, R n -MF 4+n + n HF 2 – ⇔ n R-HF 2 + MF 4+n n– (where R represents the resin), one obtains the mass action constant The distribution coefficient K d is expressed as Thus, the following equation is deduced For tracer solutions, the following simplification will be assumed using the constant c [R-HF 2 ] n = c. [R-HF 2 ] n [MF 4+n n– ] [R n -MF 4+n ] [HF 2 – ] n K = [M] r [M] aq K d = [R n -MF 4+n ] [MF 4+n n– ] == 1K1K [R-HF 2 ] n [HF 2 – ] n log K d = log [R-HF 2 ] n K - n log [HF 2 – ] ≈ c - n log [HF 2 – ]... Charge state n of an anion MF 4+n n– (M 4+ = Rf, Zr and Hf)
Simultaneous production of Rf, Zr and Hf 248 Cm target: 610 g/cm 2 18 O 6+ beam: 300 pnA 18 O Beam 248 Cm Target on Be Backing HAVAR Window 2.0 mg/cm 2 Gas-jet Outlet Gas-jet Inlet (He/KCl) Water Cooled Beam Stop He Cooling Gas Recoils Rapid Chemical Separation Apparatus AIDA Target recoil chamber + gas-jet transport system 248 Cm( 18 O,5n) 261 Rf (78 s) + Gd( 18 O,xn) 169 Hf (3.24 min) 248 Cm( 18 O,5n) 261 Rf (78 s) + Gd( 18 O,xn) 169 Hf (3.24 min) nat Ge( 18 O,5n) 85 Zr (7.86 min) + Gd( 18 O,xn) 169 Hf (3.24 min) nat Ge( 18 O,5n) 85 Zr (7.86 min) + Gd( 18 O,xn) 169 Hf (3.24 min) Chemical experiments on Rf should be conducted together with the homologues under strictly identical conditions.
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