G. A. Bozhikov

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.

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.

Isolation of radionuclides from thorium targets irradiated with 300-MeV protons

Procedures were developed for isolation and separation of radionuclides from a thorium target irradiated with 300-MeV protons. A large set of radionuclides, including those of heavy elements (225,226Ac, 223,224,225Ra, 230U, 230Pa), were obtained. A perspective scheme was suggested for separation of radionuclides from irradiated thorium.

Cyclotron production and radiochemical purification of 88,89Zr via α-particle induced reactions on natural strontium

The radionuclides (88)Zr and (89)Zr have been produced by cyclotron irradiation of (nat)SrO with 35 MeV α-particles at a beam current of 15 μA. The thick source production yield of (89)Zr is ~3.1 MBq μA(-1) h(-1). A two-step radiochemical purification utilising anion-exchange chromatography in hydrochloric and hydrofluoric acids has been developed to separate (88,89)Zr from the target material, natural strontium, the target substrate, aluminium, and long-lived (88)Y.

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.

Coprecipitation of Ti, Zr, and Hf as Rf homologs with La fluoride from solutions of hydrofluoric acid

The discovery of relatively longer halflives of transactinides ( T1/2 ~ 1.3 h) and (T 1/2 ~ 29 h) offers new approaches for the study of chemical properties of Rf and Db in solutions. This work examines the effects that the pH of a solution, HF concentration, the concentration of proper ions in the solution, the presence of foreign multivalent ions in the solution, and the contact time of liquid and solid phases have on the coprecipitation of radioisotopes of group�4 elements Ti, Zr, and Hf with fluoride La. The morphology of the solid phase was studied using electron microscopy methods (SEM and TEM); an Xray phase analysis of the obtained solid phases was performed. It was inferred that the fluoride forms of Zr and Hf cocrystallize with LaF3. The possibilities of using coprecipitation for examining the influence that the rela� tivistic effects have on the chemical properties of Rf and Db were discussed.

Use of a nanostructured material for separation of 238U and 237U produced by the photonuclear reaction 238U(γ, n)237U

Abstract237U was produced by the reaction 238U(γ, n) on an electron accelerator, MT-25 microtron, at the Flerov Laboratory of Nuclear Reactions. For the separation of 237U and [238U, the recoil nuclei were collected by a nanostructured material, hydrated manganese dioxide (of the cryptomelane type), in the solid-solid system. From fission products, 237U was separated by ion exchange. The specific activity of the resulting 237U was 4.5 × 109 Bq (mg 238U)-1, with the content of radioactive impurities of ≤10-6 Bq Bq-1. The chemical yield of 237U was 80%.

Sorption of U(VI) with soil from the region of location of the Novi Khan radioactive waste repository in Bulgaria

Sorption of U(VI) with soil from the region of location of the radioactive waste repository was studied. The radionuclide 237U produced by the photonuclear reaction 238U(γ, n)237U on an electron accelerator, MT-25 microtron (FLNR, JINR), was used as tracer. The U(VI) speciation in solution at various U concentrations was calculated in the range pH 1–7 using the Speciation program.

Anion Exchange Behavior Of Ti, Zr, Hf, Nb And Ta As Homologues Of Rf And Db In Mixed HF--Acetone Solutions

We studied in detail the sorption behavior of Ti, Zr, Hf, Nb and Ta on AG 1 anion exchange resin in HF‐acetone mixed solutions as a function of organic cosolvent and acid concentrations. Anion exchange behavior was found to be strongly acetone concentration dependent. The distribution coefficients of Ti, Zr, Hf and Nb increased and those of Ta decreased with increasing content of acetone in HF solutions. With increasing HF concentration anion exchange equilibrium analysis indicated the formation of fluoride complexes of group 4 elements with charge‐3 and Ta—‐2. For Nb the slope of‐2 increased up to‐5. Optimal conditions for separation of the elements using AIX chromatography were found. Group 4 elements formed MF73− (M = Ti, Zr, Hf) complexes whose sorption decreased Ti>Hf>Zr in reverse order of complex stability. This fact is of particular interest for studying ion exchange behavior of Rf compared to Ti. The advantages of studying chemical properties of Rf and Db in aqueous HF solutions mixed with organi...