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Production and Chemistry of Transactinide Elements

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Production and Chemistry of Transactinide Elements Journal of Nuclear and Radiochemical Sciences, Vol. 6, No. 3, pp. 205-210, 2005 Production and Chemistry of Transactinide Elements Y. Nagame* Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan Received: July 31, 2005; In Final Form: September 30, 2005 Recent progress in production and chemistry of the transactinide elements, element 107 bohrium (Bh) and element 104 rutherfordium (Rf), is reviewed. First information on chemical properties of Bh was obtained in gas chro- matographic experiments on an atom-at-a-time basis. Chemical separation and characterization of 6 atoms of 267Bh produced in the bombardment of a 249Bk target with 22Ne beams are outlined. Aqueous chemistry of Rf being performed at JAERI (Japan Atomic Energy Research Institute) is briefly summarized. On-line anion- exchange experiments in acidic solutions on 261Rf produced in the 248Cm(18O,5n) reaction were conducted with a rapid ion-exchange separation apparatus. Characteristic anion-exchange behavior of Rf is discussed. 1. Introduction Chemical experiments with the transactinide elements are generally divided into the following 4 basic steps; i) synthesis According to the actinide concept,1 the 5f electron series ends of transactinide nuclides, ii) rapid transport of the synthesized with element 103, lawrencium (Lr), and a new 6d electron tran- nuclides to chemical separation apparatuses, iii) fast chemical sition series is predicted to begin with element 104, rutherford- isolation of a desired nuclide and preparation of a sample suit- ium (Rf). The elements with atomic numbers Z ≥ 104 are called able for nuclear spectroscopy, and iv) detection of nuclides transactinide elements or recently called superheavy elements.2 through their characteristic decay properties. Due to short half- The currently known transactinide elements, elements 104 lives and low production rates of the transactinide nuclides, through 112, are placed in the periodic table under their lighter each atom produced decays before a new atom is synthesized. homologues in the 5d electron series, Hf to Hg. Elements from This means that any chemistry to be performed must be done 113 to 118 except for 117 synthesized by Oganessian et al.3, 4 on an “atom-at-a-time” basis.2, 9, 10 Thus, rapid and very efficient would be in the successive 7p electron series (see Figure 1). radiochemical procedures must be devised. Recent comprehen- Studies of chemical properties of the transactinide elements sive reviews on the chemistry of the transactinide elements are offer unique opportunities to obtain information about trends in found in References 2, 9, and 10. the periodic table of the elements at the limits of nuclear stabil- The first successful chemical isolation and identification of ity and to assess the magnitude of the influence of relativistic Bh was accomplished in an experiment at the Philips cyclotron effects on chemical properties. From calculations of electron of PSI (Paul Sherrer Institute) by Eichler et al.11 The result configurations of heavier elements, it is predicted that sudden clearly indicated that the volatile bohrium oxychloride complex changes in the structure of electron shells may appear due to behaved like a typical member of group 7 of the periodic table relativistic effects which originate from the increasingly strong of the elements. From recent systematic studies of the anion- Coulomb field of a highly charged atomic nucleus.5 Therefore, exchange behavior of Rf, it was found that Rf is a member of it is expected that heavier elements show a drastic rearrange- the group 4 elements,12 although unexpected chemical behavior ment of electrons in their atomic ground states, and as electron of Rf was observed in the fluoride complex formation.13 configurations are responsible for chemical behavior of ele- In this paper, chemical studies on gas chromatographic ments, such relativistic effects can lead to surprising chemical behavior of Bh at PSI and aqueous chemistry of Rf at JAERI properties. Increasing deviations from the periodicity of chemi- are outlined. cal properties based on extrapolation from lighter homologues 2, 6−8 in the periodic table are consequently predicted. It would 2. Production of Transactinide Elements be no longer possible to deduce detailed chemical properties of the transactinide elements simply from the position of the peri- Longer-lived transactinide nuclides required in chemical odic table. experiments exit in the neutron-rich region of the chart of nuclides and they are produced in so-called hot fusion reac- 1 18 18 19 22 26 1 2 tions of such beams as O, F, Ne, and Mg with actinides H He 2 13 14 15 16 17 244 248 249 3 4 5 6 7 8 9 10 targets of Pu, Cm, Bk, and so on. The produced trans- Li Be B C N O F Ne 11 12 13 14 15 16 17 18 actinide nuclides must be identified by measurement of their Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si PS Cl Ar 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 decay or by that of their known daughter nuclei with unambigu- KCa Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 ous detection techniques. Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 A schematic representation of a typical experimental set-up Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 87 88 89 104 105 106 107 108 109 110 111 112 113 114 115 116 118 Fr Ra Ac Rf Db Sg Bh Hs Mt Ds Rg 112113 114 115 116 118 for the production of transactinide nuclides is shown in Figure 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 2 where the target and recoil chamber for the production of La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 261 248 2 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 Rf at JAERI are depicted. A Cm target of 610 µg/cm Ac Th Pa UNp Pu Am Cm Bk Cf Es Fm Md No Lr thickness prepared by electrodeposition of Cm(NO3)3 from iso- Figure 1. Periodic table of the elements. propyl alcohol onto 2.4 mg/cm2 thick beryllium backing foil is bombarded by 18O beams delivered from the JAERI tandem *Corresponding author. E-mail: [email protected]. accelerator. The 18O6+ beam passes through 2.0-mg/cm2 FAX: +81-29-282-5927. HAVAR entrance window foil, 0.09 mg/cm2 He cooling gas © 2005 The Japan Society of Nuclear and Radiochemical Sciences Published on Web 12/28/2005 206 J. Nucl. Radiochem. Sci., Vol. 6, No. 3, 2005 Nagame He cooling gas 248Cm target on Be backing gas-jet outlet 18O beam water cooled beam stop gas-jet inlet HAVAR (He/KCl aerosols) window foil recoils chemistry 2.0 mg/cm2 laboratory Figure 2. Schematic diagram of a target recoil chamber arrangement with a gas-jet system. and the beryllium target backing, and it finally enters the 248Cm target material. The reaction products recoiling out of the tar- Figure 3. Schematic view of the Bh gas-chromatographic experi- get are thermalized in a volume of He gas (≈ 1 bar) which is ment. Courtesy of H. W. Gäggeler. loaded with potassium chloride (KCl) aerosols generated by sublimation from the surface of KCl powder at 640 ˚C. The T : 75 ℃ 150 ℃ 180 ℃ products attached to the aerosols are swept out of the recoil isothermal chamber with the He gas flow (2.0 L/min) and are transported Beam dose: 1.00 × 1018 1.00 × 1018 1.02 × 1018 through a Teflon-capillary (length 20 m, inner diameter 2.0 mm) by a He/KCl gas-jet system to a chemistry laboratory. Element no decay The reactions and the expected production rates of the trans- 267Bh 267Bh 267Bh 267Bh 267Bh 267Bh 107 chains actinide nuclides used for chemical studies are summarized in detected 2 8.81 MeV 8.85 MeV 8.72 MeV 8.84 MeV 8.91 MeV 8.81 MeV Table 1. Assuming the typical values of 800 µg/cm for the 24.5 s 34.4 s 2.9 s 26.7 s 10.5 s 18.4 s target thickness and the beam intensity of 3 × 1012 s−1, one can anticipate the production rates, for example, to be 4 atoms per 105 263Db 263Db 263Db 263Db 263Db 263Db minute for Rf and a 1 atom per hour for Bh. SF SF 8.40 MeV 8.35 MeV 8.37 MeV SF 21.1 s 98.9 s 29.9 s 73.4 s 0.8 s 16.3 s 3. Gas-phase Chemistry of Element 107, Bohrium (Bh) 103 82 MeV 46 MeV 259Lr 101 + 86 MeV 8.41 MeV Figure 3 shows the schematic of the experiment for the gas- 14.6 s phase chemistry of Bh.11 A target of 670 µg/cm2 249Bk covered with a layer of 159Tb (100 µg/cm2) was bombarded for about 4 Figure 4. Decay chains attributed to the decay of 267Bh. The weeks with 22Ne beams at a beam energy of 119 MeV to pro- observed α-particle and spontaneous fission decay energies and the duce 267Bh in the reaction 249Bk(22Ne,4n).
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