S. V. Shishkin

Chemical characterization of element 112

The heaviest elements to have been chemically characterized are seaborgium (element 106), bohrium (element 107) and hassium (element 108). All three behave according to their respective positions in groups 6, 7 and 8 of the periodic table, which arranges elements according to their outermost electrons and hence their chemical properties. However, the chemical characterization results are not trivial: relativistic effects on the electronic structure of the heaviest elements can strongly influence chemical properties. The next heavy element targeted for chemical characterization is element 112; its closed-shell electronic structure with a filled outer s orbital suggests that it may be particularly susceptible to strong deviations from the chemical property trends expected within group 12. Indeed, first experiments concluded that element 112 does not behave like its lighter homologue mercury. However, the production and identification methods used cast doubt on the validity of this result. Here we report a more reliable chemical characterization of element 112, involving the production of two atoms of 283112 through the alpha decay of the short-lived 287114 (which itself forms in the nuclear fusion reaction of 48Ca with 242Pu) and the adsorption of the two atoms on a gold surface. By directly comparing the adsorption characteristics of 283112 to that of mercury and the noble gas radon, we find that element 112 is very volatile and, unlike radon, reveals a metallic interaction with the gold surface. These adsorption characteristics establish element 112 as a typical element of group 12, and its successful production unambiguously establishes the approach to the island of stability of superheavy elements through 48Ca-induced nuclear fusion reactions with actinides.

Indication for a volatile element 114

Abstract Recently, the chemical investigation of element 112 revealed a highly volatile, noble metallic behaviour, as expected for the last group 12 member of the periodic table. The observed volatility and chemical inertness were ascribed to the growing influence of relativistic effects on the chemical properties of the heaviest elements with increasing nuclear charge. Here, we report for the first time on gas phase chemical experiments aiming at a determination of element 114 properties. This element was investigated using its isotopes 287114 and 288114 produced in the nuclear fusion reactions of 48Ca with 242Pu and 244Pu, respectively. Identification of three atoms of element 114 in thermochromatography experiments and their deposition pattern on a gold surface indicates that this element is at least as volatile as simultaneously investigated elements Hg, At, and element 112. This behaviour is rather unexpected for a typical metal of group 14.

Chemical procedure applied for the identification of Rf/Db produced in the 48Ca +243Am reaction

Summary A chemical separation procedure for Rf/Db is described which was applied to a long-lived decay product from the nuclear fusion reaction 48Ca+ 243Am. A 1.2 mg thick 243Am target was bombarded by 247 MeV 48Ca particles. The recoiling products were collected in a thick Cu catcher for about one day and then subjected to a chemical separation procedure that included an ion exchange from dilute HF solutions. Final samples were prepared on 30 μg/cm2 thick polyethylene (PE) foils and counted in 4π-geometry for α-particles and spontaneous fission (SF) coincidences. The detector arrays were surrounded by 3He detectors to also assay prompt neutrons. Decontamination factors from actinides of about 105 were achieved. Group 6 (W) to 14 (Pb) elements as models for their heavier homologues were shown to be separated from the Rf/Db fraction with more than 90%. In eight final samples, representing a total beam dose of 3.4 × 1018 particles, 15 SF events were detected. The decay pattern points to a single component with a half-life of ≈32h, which shows a chemical behavior similar to the lighter homologues of group 4 and 5 elements.

Ultra-pure 236Pu and 237Pu for environmental and biomedical research

Abstract Isotopically pure 236Pu (>99.999% by activity) has been produced by irradiating U (95% 235U) with 4He ions and refining the product by electromagnetic mass separation. Further developments in the production of 237Pu are also reported, giving material containing, by activity, only 3 × 10−6% 236Pu and probably only ∼ 10−5% 238Pu.

Adsorption interaction of astatine species with quartz and gold surfaces

Abstract The adsorption interaction of various astatine species with quartz and gold surfaces was investigated by gas chromatography methods. Due to variations of the redox potential of the carrier gas elemental astatine, astatine oxide and hypo-astatic acid have been produced. The identification of the astatine compounds is based on the analogy assumption to the gas phase chemistry of the closest homologues in group 17 of the periodic table, iodine and bromine. The deposition temperatures as well as enthalpies of adsorption have been determined for the astatine species. The enhancement of the metallic character within group 17 towards higher Z is clearly confirmed. Macroscopic properties (sublimation enthalpy) of previously unstudied AtO2 and HAtO were estimated. The determined data for elemental astatine were compared to available literature data. Based on the obtained experimental results possible designs of experiments for studying of chemical properties of the recently discovered element 117 can be suggested.

High-purity radionuclide production: material, construction, target chemistry for 26Al, 97Ru, 178W, 235Np, 236,237Pu

Abstract The work on isotopically pure 26 Al, 97 Ru, 178 W/ 178 Ta, 235 Np, 236 Pu and 237 Pu production was initiated because of intensive research on their applications in the biomedical field and environmental chemistry. The conditions for isotopically pure production have been investigated. This paper describes the data for the nuclear reactions of the radionuclide production, the different target designs and target chemistry procedures.

Production of 237Pu with high radiochemical purity

Abstract 237 Pu (half-life 45.3 d) is a valid metabolic tracer for the long-lived isotopes of plutonium, but its use in human subjects has previously been restricted by difficulties in producing it with acceptable isotopic purity. These difficulties have been overcome by applying mass-separation techniques to the impure product of irradiating 235 U with 25-MeV 4 He + ions.

Determination of gold in natural waters by neutron activation and γ-spectrometry after preconcentration with tributyl phosphate as solid extractant

Abstract A method for the preconcentration of gold in natural waters at the sampling site using tributyl phosphate as a solid extractant [Se(TBP)] was developed as a preliminary step prior to the determination of gold by neutron activation and γ-spectrometry. The SE(TBP) was saturated with gaseous chlorine for extracting all gold species. In batch experiments gold was quantitatively retained on the SE(TBP) in 10 min. After extraction and washing, the SE(TBP) was ashed or back-extracted. Gold was quantitatively eluted with hot, neutral 0.025 M thiourea. The gold content of residues of ashing or eluents after evaporation was determined by neutron activation and γ-spectrometry. The detection limit for the overall procedure was 0.2 ng 1 −1 . The efficiency was tested on ‘equilibrated’ solutions prepared from river water and tracer solutions of gold. For comparison, the gold content of natural water samples was determined using preconcentration on activated charcoal.

Ion-exchange separation of Zr and Hf microamounts in dilute HCl/HF solutions: A model system for chemical identification of Rf and study of its properties

A procedure was developed for selective separation of Group IV elements from Sr and Lu, followed by rapid separation of Zr and Hf by cation-exchange chromatography in dilute HCl/HF solutions. The possibility of using this procedure for chemical identification and determination of decay parameters of the new isotope 267Rf was demonstrated.

Production of high-purity26Al

Abstract26Al is a positron emitting radioisotope of aluminium and has a half-life of 7.16×105y. In addition to annihilation γ-rays of 511 keV, there are three high energy γ-rays 1129 (2.4%), 1809 (99.73%) and 2938 (0.27%) keV.26Al is the only radioisotope of aluminium available for radiochemical applications, the half-lives of the other aluminium isotopes are seconds and minutes. The usage of26Al is very important in the investigations of the metabolism of Al in human body (for example in Alzheimer disease studies) or as a tracer in radiochemical studies. But26Al is such a long-lived isotope that the task of producing it in tangible amounts is a very difficult one.