Chemical investigation of hassium (element 108)

Five decades of GSI superheavy element discoveries and chemical investigation

Superheavy element research has been a strong pillar of the research program at GSI Darmstadt since its foundation. Six new elements were discovered along with many new isotopes. Initial results on chemical properties of the heaviest elements were obtained that allowed for comparing their behavior with that of their lighter homologs and with theoretical predictions. Main achievements of the past five decades of superheavy element research at GSI are described along with an outlook into the future of superheavy element research in Darmstadt.

The influence of physical parameters on the in-situ metal carbonyl complex formation studied with the Fast On-line Reaction Apparatus (FORA)

The Fast On-line Reaction Apparatus (FORA) was used to investigate the influence of various reaction parameters onto the formation and transport of metal carbonyl complexes (MCCs) under single-atom chemistry conditions. FORA is based on a 252Cf-source producing short-lived Mo, Tc, Ru and Rh isotopes. Those are recoiling from the spontaneous fission source into a reaction chamber flushed with a gas-mixture containing CO. Upon contact with CO, fission products form volatile MCCs which are further transported by the gas stream to the detection setup, consisting of a charcoal trap mounted in front of a HPGe γ-detector. Depending on the reaction conditions, MCCs are formed and transported with different efficiencies. Using this setup, the impact of varying physical parameters like gas flow, gas pressure, kinetic energy of fission products upon entering the reaction chamber and temperature of the reaction chamber on the formation and transport yields of MCCs was investigated. Using a setup similar to FORA called Miss Piggy, various gas mixtures of CO with a selection of noble gases, as well as N2 and H2, were investigated with respect to their effect onto MCC formation and transport. Based on this measurements, optimized reaction conditions to maximize the synthesis and transport of MCCs are suggested. Explanations for the observed results supported by simulations are suggested as well.

Co-precipitation behaviour of single atoms of rutherfordium in basic solutions

All superheavy elements (SHEs), with atomic numbers (Z) ≥104, have been artificially synthesized one atom at a time and their chemical properties are largely unknown. Because these heavy nuclei have short lifetimes as well as extremely low production rates, chemical experiments need to be carried out on single atoms and have mostly been limited to adsorption and extraction. We have now investigated the precipitation properties of the SHE Rf (Z = 104). A co-precipitation method with samarium hydroxide had previously established that the co-precipitation behaviour of a range of elements reflected these elements' tendency to form hydroxide precipitates and/or ammine complex ions. Here we investigated co-precipitation of Rf in basic solutions containing NH₃ or NaOH. Comparisons between the behaviour of Rf with that of Zr and Hf (lighter homologues of Rf) and actinide Th (a pseudo-homologue of Rf) showed that Rf does not coordinate strongly with NH₃, but forms a hydroxide (co)precipitate that is expected to be Rf(OH)₄.

The periodic table and the physics that drives it

Mendeleev's introduction of the periodic table of elements is one of the most important milestones in the history of chemistry, as it brought order into the known chemical and physical behaviour of the elements. The periodic table can be seen as parallel to the Standard Model in particle physics, in which the elementary particles known today can be ordered according to their intrinsic properties. The underlying fundamental theory to describe the interactions between particles comes from quantum theory or, more specifically, from quantum field theory and its inherent symmetries. In the periodic table, the elements are placed into a certain period and group based on electronic configurations that originate from the Pauli and Aufbau principles for the electrons surrounding a positively charged nucleus. This order enables us to approximately predict the chemical and physical properties of elements. Apparent anomalies can arise from relativistic effects, partial-screening phenomena (of type lanthanide contraction) and the compact size of the first shell of every l-value. Further, ambiguities in electron configurations and the breakdown of assigning a dominant configuration, owing to configuration mixing and dense spectra for the heaviest elements in the periodic table. For the short-lived transactinides, the nuclear stability becomes an important factor in chemical studies. Nuclear stability, decay rates, spectra and reaction cross sections are also important for predicting the astrophysical origin of the elements, including the production of the heavy elements beyond iron in supernova explosions or neutron-star mergers. In this Perspective, we critically analyse the periodic table of elements and the current status of theoretical predictions and origins for the heaviest elements, which combine both quantum chemistry and physics.

Relativity in the electronic structure of the heaviest elements and its influence on periodicities in properties

Theoretical chemical studies demonstrated crucial importance of relativistic effects in the physics and chemistry of superheavy elements (SHEs). Performed, with many of them, in a close link to the experimental research, those investigations have shown that relativistic effects determine periodicities in physical and chemical properties of the elements in the chemical groups and rows of the Periodic Table beyond the 6th one. They could, however, also lead to some deviations from the established trends, so that the predictive power of the Periodic Table in this area may be lost. Results of those studies are overviewed here, with comparison to the recent experimental investigations.

Production and study of chemical properties of superheavy elements

Some highlight examples on the study of production and chemical properties of heaviest elements carried out mostly at GSI Darmstadt are presented. They focus on the production of some of the heaviest known elements (114Fl, 115Mc, and 117Mc), studies of non-fusion reactions, and on chemical studies of 114Fl. This is the heaviest element, for which chemical studies have been performed to date.

The study of rhenium pentacarbonyl complexes using single-atom chemistry in the gas phase

A gas-phase chemical study of rhenium carbonyls was carried out using short-lived radioisotopes produced at a heavy-ion accelerator. The Re isotopes produced in the nuclear reactions of natGd(23Na,xn)172-177Re were pre-separated with a gas-filled recoil ion separator and their carbonyls were synthesized in a mixture of inert gas and carbon monoxide. Using a low temperature isothermal chromatography apparatus, the adsorption enthalpies of Re carbonyls were derived to be ΔHads = -42 ± 2 kJ mol-1 on a Teflon® surface by fitting the external chromatograms with a Monte Carlo simulation program. A chemical yield of 25% relative to that of the transport yield for Re by a He/KCl gas-jet was achieved. The laser-ablation time-of-flight mass-spectrometric technique was employed to identify the species of Re carbonyls produced in the gas phase. The most stable species was deduced to be Re(CO)5 based on the mass-spectrometric analysis as well as quantum chemistry calculations.

The periodic table – an experimenter’s guide to transactinide chemistry

The fundamental principles of the periodic table guide the research and development of the challenging experiments with transactinide elements. This guidance is elucidated together with experimental results from gas phase chemical studies of the transactinide elements with the atomic numbers 104–108 and 112–114. Some deduced chemical properties of these superheavy elements are presented here in conjunction with trends established by the periodic table. Finally, prospects are presented for further chemical investigations of transactinides based on trends in the periodic table.

Diversity of Chemical Bonding and Oxidation States in MS4 Molecules of Group 8 Elements

The geometric and electronic ground-state structures of 30 isomers of six MS₄ molecules (M=Group 8 metals Fe, Ru, Os, Hs, Sm, and Pu) have been studied by using quantum-chemical density functional theory and correlated wavefunction approaches. The MS₄ species were compared to analogous MO₄ species recently investigated (W. Huang, W.-H. Xu, W. H. E. Schwarz, J. Li, Inorg. Chem. 2016, 55, 4616). A metal oxidation state (MOS) with a high value of eight appeared in the low-spin singlet T_d geometric species (Os,Hs)S₄ and (Ru,Os,Hs)O₄ , whereas a low MOS of two appeared in the high-spin septet D_2d species Fe(S₂ )₂ and (slightly excited) metastable Fe(O₂ )₂ . The ground states of all other molecules had intermediate MOS values, with S^2- , S₂^2- , S₂^1- (and O^2- , O^1- , O₂^2- , O₂^1- ) ligands bonded by ionic, covalent, and correlative contributions. The known tendencies toward lower MOS on going from oxides to sulfides, from Hs to Os to Ru, and from Pu to Sm, and the specific behavior of Fe, were found to arise from the different atomic orbital energies and radii of the (n-1)p core and (n-1)d and (n-2)f valence shells of the metal atoms in row n of the periodic table. The comparative results of the electronic and geometric structures of the MO₄ and MS₄ species provides insight into the periodicity of oxidation states and bonding.

On the Highest Oxidation States of Metal Elements in MO4 Molecules (M = Fe, Ru, Os, Hs, Sm, and Pu)

Metal tetraoxygen molecules (MO4, M = Fe, Ru, Os, Hs, Sm, Pu) of all metal atoms M with eight valence electrons are theoretically studied using density functional and correlated wave function approaches. The heavier d-block elements Ru, Os, Hs are confirmed to form stable tetraoxides of Td symmetry in (1)A1 electronic states with empty metal d(0) valence shell and closed-shell O(2-) ligands, while the 3d-, 4f-, and 5f-elements Fe, Sm, and Pu prefer partial occupation of their valence shells and peroxide or superoxide ligands at lower symmetry structures with various spin couplings. The different geometric and electronic structures and chemical bonding types of the six iso-stoichiometric species are explained in terms of atomic orbital energies and orbital radii. The variations found here contribute to our general understanding of the periodic trends of oxidation states across the periodic table.

Chemistry of the superheavy elements

The quest for superheavy elements (SHEs) is driven by the desire to find and explore one of the extreme limits of existence of matter. These elements exist solely due to their nuclear shell stabilization. All 15 presently 'known' SHEs (11 are officially 'discovered' and named) up to element 118 are short-lived and are man-made atom-at-a-time in heavy ion induced nuclear reactions. They are identical to the transactinide elements located in the seventh period of the periodic table beginning with rutherfordium (element 104), dubnium (element 105) and seaborgium (element 106) in groups 4, 5 and 6, respectively. Their chemical properties are often surprising and unexpected from simple extrapolations. After hassium (element 108), chemistry has now reached copernicium (element 112) and flerovium (element 114). For the later ones, the focus is on questions of their metallic or possibly noble gas-like character originating from interplay of most pronounced relativistic effects and electron-shell effects. SHEs provide unique opportunities to get insights into the influence of strong relativistic effects on the atomic electrons and to probe 'relativistically' influenced chemical properties and the architecture of the periodic table at its farthest reach. In addition, they establish a test bench to challenge the validity and predictive power of modern fully relativistic quantum chemical models.

Theoretical predictions of properties and volatility of chlorides and oxychlorides of group-4 elements. II. Adsorption of tetrachlorides and oxydichlorides of Zr, Hf, and Rf on neutral and modified surfaces

With the aim to interpret results of gas-phase chromatography experiments on volatility of group-4 tetrachlorides and oxychlorides including those of Rf, adsorption enthalpies of these species on neutral, and modified quartz surfaces were estimated on the basis of relativistic, two-component Density Functional Theory calculations of MCl4, MOCl2, MCl6(-), and MOCl4(2) with the use of adsorption models. Several mechanisms of adsorption were considered. In the case of physisorption of MCl4, the trend in the adsorption energy in the group should be Zr > Hf > Rf, so that the volatility should change in the opposite direction. The latter trend complies with the one in the sublimation enthalpies, ΔH(sub), of the Zr and Hf tetrachlorides, i.e., Zr < Hf. On the basis of a correlation between these quantities, ΔH(sub)(RfCl4) was predicted as 104.2 kJ/mol. The energy of physisorption of MOCl2 on quartz should increase in the group, Zr < Hf < Rf, as defined by increasing dipole moments of these molecules along the series. In the case of adsorption of MCl4 on quartz by chemical forces, formation of the MOCl2 or MOCl4(2-) complexes on the surface can take place, so that the sequence in the adsorption energy should be Zr > Hf > Rf, as defined by the complex formation energies. In the case of adsorption of MCl4 on a chlorinated quartz surface, formation of the MCl6(2-) surface complexes can occur, so that the trend in the adsorption strength should be Zr ≤ Hf < Rf. All the predicted sequences, showing a smooth change of the adsorption energy in the group, are in disagreement with the reversed trend Zr ≈ Rf < Hf, observed in the "one-atom-at-a-time" gas-phase chromatography experiments. Thus, currently no theoretical explanation can be found for the experimental observations.

Superheavy element flerovium (element 114) is a volatile metal

The electron shell structure of superheavy elements, i.e., elements with atomic number Z ≥ 104, is influenced by strong relativistic effects caused by the high Z. Early atomic calculations on element 112 (copernicium, Cn) and element 114 (flerovium, Fl) having closed and quasi-closed electron shell configurations of 6d(10)7s(2) and 6d(10)7s(2)7p1/2(2), respectively, predicted them to be noble-gas-like due to very strong relativistic effects on the 7s and 7p1/2 valence orbitals. Recent fully relativistic calculations studying Cn and Fl in different environments suggest them to be less reactive compared to their lighter homologues in the groups, but still exhibiting a metallic character. Experimental gas-solid chromatography studies on Cn have, indeed, revealed a metal-metal bond formation with Au. In contrast to this, for Fl, the formation of a weak bond upon physisorption on a Au surface was inferred from first experiments. Here, we report on a gas-solid chromatography study of the adsorption of Fl on a Au surface. Fl was produced in the nuclear fusion reaction (244)Pu((48)Ca, 3-4n)(288,289)Fl and was isolated in-flight from the primary (48)Ca beam in a physical recoil separator. The adsorption behavior of Fl, its nuclear α-decay product Cn, their lighter homologues in groups 14 and 12, i.e., Pb and Hg, and the noble gas Rn were studied simultaneously by isothermal gas chromatography and thermochromatography. Two Fl atoms were detected. They adsorbed on a Au surface at room temperature in the first, isothermal part, but not as readily as Pb and Hg. The observed adsorption behavior of Fl points to a higher inertness compared to its nearest homologue in the group, Pb. However, the measured lower limit for the adsorption enthalpy of Fl on a Au surface points to the formation of a metal-metal bond of Fl with Au. Fl is the least reactive element in the group, but still a metal.

Adsorption interaction of carrier-free thallium species with gold and quartz surfaces

The adsorption interactions of thallium and its compounds with gold and quartz surfaces were investigated. Carrier-free amounts of thallium were produced in nuclear fusion reactions of alpha particles with thick gold targets. The method chosen for the studies was gas thermochromatography and varying the redox potential of the carrier gases. It was observed that thallium is extremely sensitive to trace amounts of oxygen and water, and can even be oxidized by the hydroxyl groups located on the quartz surface. The experiments on a quartz surface with O2, He, H2 gas in addition with water revealed the formation and deposition of only one thallium species – TlOH. The adsorption enthalpy was determined to be Δ H SiO2 ads(TlOH) = −134 ± 5 kJ mol−1. A series of experiments using gold as stationary surface and different carrier gases resulted in the detection of two thallium species – metallic Tl (H2 as carrier gas) and TlOH (O2, O2+H2O and H2+H2O as pure carrier gas or carrier gas mixture) with Δ H Au ads(Tl) = −270 ± 10 kJ mol− and Δ H Au ads(TlOH) = −146 ± 3 kJ mol−1. These data demonstrate a weak interaction of TlOH with both quartz and gold surfaces. The data represent important information for the design of future experiments with the heavier homologue of Tl in group 13 of the periodic table – element 113 (E113).

Prediction of the thermal release of transactinide elements (112 ≤ Z ≤ 116) from metals

Metallic catcher foils have been investigated on their thermal release capabilities for future superheavy element studies. These catcher materials shall serve as connection between production and chemical investigation of superheavy elements (SHE) at vacuum conditions. The diffusion constants and activation energies of diffusion have been extrapolated for various catcher materials using an atomic volume based model. Release rates can now be estimated for predefined experimental conditions using the determined diffusion values. The potential release behavior of the volatile SHE Cn (E112), E113, Fl (E114), E115, and Lv (E116) from polycrystalline, metallic foils of Ni, Y, Zr, Nb, Mo, Hf, Ta, and W is predicted. Example calculations showed that Zr is the best suited material in terms of on-line release efficiency and long-term operation stability. If higher temperatures up to 2773 K are applicable, tungsten is suggested to be the material of choice for such experiments.

Nuclear structure and reaction studies near doubly magic 270Hs

Fast on-line gas chemical separations of Hs (hassium, element 108) in the form of HsO4 were applied to investigate the reactions 26Mg + 248Cm and 36S + 238U. In an experiment at the gas-filled separator DGFRS the reaction 48Ca + 226Ra was studied. In all cases the product of complete nuclear fusion is 274Hs*. For the first time, the new nuclide 270Hs was produced in the 4n evaporation channel and its decay properties investigated. The nuclide 270Hs was predicted by microscopic-macroscopic calculations to be a deformed doubly magic nucleus and its decay properties are therefore of special interest to theory. Also, much more detailed information was gained on the decay of 269Hs and its daughters, which led to a new assignment of decay properties of the daughter nuclides 265Sg and 261Rf. There is evidence fo r isomeric states in 265Sg and 261Rf, while 266Sg is not an alpha-particle emitter as believed previously, but decays by spontaneous fission (SF) with a rather short half-life. Also, interesting features of the used reaction 26Mg + 248Cm led to the discovery of the nucleus 271Hs in the same experiments. An investigation of the influence of the Q-value on the fusion reaction in relation to the location of the fusion barrier showed, that the high binding energy of 48Ca largely compensates for the lower fusion probability compared to more asymmetric reactions, while 36S is not as promising as a projectile.

Relativistic electronic structure studies on the heaviest elements

Spectacular developments in relativistic quantum theory and computational algorithms in the last two decades allowed for accurate predictions of properties of the heaviest elements and their experimental behaviour. The most recent works in this area of investigations are overviewed. Preference is given to those related to experimental research. The role of relativistic effects is elucidated.

Gas chemical properties of heaviest elements

Chemical studies at the upper end of the periodic table have reached atomic number 114. Recent experiments aiming at investigating chemical properties of elements Cn, 113, and 114 are summarized. Though partly preliminary, all these elements behave as expected: due to the filled 6d 10 shell, they do not behave like transition metals anymore, as observed for the lighter transactinides. They exhibit a volatile behavior as expected for 7s and 7p elements. On the other hand, due to the extremely low signal to noise ratio in detectors used to identify separated products highest precaution on identifying single atoms is mandatory. As an example, published early attempts to synthesize Cn and to perform chemical studies with this element that could not be confirmed in later studies are summarized.

Synthesis of superheavy elements by cold fusion

The new elements from Z = 107 to 112 were synthesized in cold fusion reactions based on targets of lead and bismuth. The principle physical concepts are presented which led to the application of this reaction type in search experiments for new elements. Described are the technical developments from early mechanical devices to experiments with recoil separators. An overview is given of present experiments which use cold fusion for systematic studies and synthesis of new isotopes. Perspectives are also presented for the application of cold fusion reactions in synthesis of elements beyond element 113, the so far heaviest element produced in a cold fusion reaction. Further, the transition of hot fusion to cold fusion is pointed out, which occurs in reactions for synthesis of elements near Z = 126 using actinide targets and beams of neutron rich isotopes of elements from iron to germanium.

Aqueous-phase chemistry of the transactinides

The experimental techniques developed to perform rapid chemical separations of the heaviest elements in the aqueous phase are presented. In general, these include transport of the nuclear reaction products to a separation device by the gas-jet technique and dissolution in an aqueous solution containing inorganic ligands for complex formation. The complexes are chemically characterized by a partition method which can be liquid–liquid extraction, ion-exchange- or reversed-phase extraction chromatography. The separated fractions are quickly evaporated to dryness for the preparation of samples for α-particle spectroscopy. Comments are given on the special situation in which chemistry has to be studied with single atoms. Theoretical predictions of chemical properties are compared to the presently known chemical behaviour of rutherfordium, Rf (element 104), dubnium, Db (element 105), seaborgium, Sg (element 106), and hassium, Hs (element 108) and to that of their lighter homologs in the Periodic Table in order to assess the role of relativistic effects in the chemistry of the heaviest elements.

Gas chromatography of indium in macroscopic and carrier-free amounts using quartz and gold as stationary phases

The chemical investigation of E113 is likely to become soon feasible. The determination of chemical properties of carrier-free amounts of the lighter homologues of element 113, especially indium and thallium, allows designing experimental set-ups and selecting experimental conditions suitable for performing these studies. Here, we present investigations of the interaction of indium species with quartz and gold surfaces. Deposition temperatures as well as enthalpies of adsorption were determined for indium T dep=739±20 °C (−ΔH ads(In)=227±10 kJ mol−1) and for indium hydroxide T dep=250±20 °C (−ΔH ads(InOH)= 124±10 kJ mol−1) respectively, on quartz. In case of adsorption of indium on a gold surface only a lower limit of the deposition temperature was established T dep>980 °C (−ΔH ads(In)≥315±10 kJ mol−1). Investigations of macroscopic amounts of indium in thermosublimation experiments at similar experimental conditions were instrumental to establish a tentative speciation of the observed indium species.

Development of a SISAK extraction system for chemical studies of element 108, hassium

A liquid–liquid extraction system suitable for studies of chemical properties of Hs (element 108), in the form of HsO4, was developed using γ-emitting isotopes of its homologue Os. The system is targeted for the fast on-line extraction system SISAK, which operates in a continuous manner and is suitable for liquid-phase studies of transactinide elements. The distribution of OsO4 between various dilute NaOH solutions and toluene was studied. Both batch and SISAK on-line experiments were performed to develop an appropriate system. From analysis of the extraction curves equilibrium constants for the formation of the presumed complexes, Na[OsO4(OH)] and Na2[OsO4(OH)2], were obtained: K 1=(1±0.5)×104 and K 2=12±8, respectively. The SISAK system includes a liquid-scintillation detection system for α measurements. Due to quenching effects it is not possible to perform direct measurement of the aqueous phase α´s. Therefore, a two-stage extraction method that provides an indirect measurement of the activity in the aqueous phase was developed as part of the proposed system for Hs: Acidification of the raffinate from the first stage result in recovery of OsO4, which is highly extractable into toluene. The yield of extraction in the second step, from 0.01 M NaOH solution after acidification with H2SO4 solution, was (90±3) %.

Name and symbol of the element with atomic number 112 (IUPAC Recommendations 2010)

A joint IUPAC/IUPAP Working Party (JWP) has confirmed the discovery of the element with atomic number 112. In accord with IUPAC procedures, the discoverers proposed a name, copernicium, and symbol, Cn, for the element. The IUPAC Inorganic Chemistry Division Committee recommended this proposal for acceptance, and it has now been approved by the IUPAC Bureau as delegated to act by the IUPAC Council meeting on 12 August 2007.

Predictions of adsorption behaviour of the heaviest elements in a comparative study from the electronic structure calculations

Thermodynamics of adsorption of gaseous species on the surface of a gas chromatography column is considered using the knowledge of the electronic structure of the adsorbate. Relevant equations based on a model of mobile adsorption are offered to predict the adsorption temperature, T ads, of a heavy-element (or its compound) with respect to T ads of its lighter homolog (or the same type of compound). A case of adsorption of OsO4 and HsO4 on an inert (quartz or silicon nitride) surface of a chromatography column is taken, as an example. The influence of various properties of the adsorbate, such as molecular weight and size, on T ads is analyzed to show that those factors should not be ignored in intentionally accurate predictions of T ads. A comparison of the desorption constants of OsO4 and HsO4 obtained with the use of the calculated spectroscopic properties shows that HsO4 should be significantly more volatile than OsO4, mainly due to the entropy factor.

Thermochromatographic studies of mercury and radon on transition metal surfaces

In preparation for the experimental investigation of chemical properties of element 112 model studies were conducted based on the assumed similarity of element 112 to either the noble gas Rn or the transition metal Hg, its supposed lighter homologue in group 12. The adsorption behavior of elemental Hg on the transition metals Ag, Au, Ni, Pd, and Pt were investigated experimentally by off-line gas thermochromatography. The deduced adsorption data of Hg were compared with new values calculated using the Eichler–Miedema model. The observed sequence of increasing Hg-metal-interactions for Ag < Ni < Au < Pd < Pt confirms the predicted trend. The only exception was Pd, on which Hg was calculated to adsorb at a higher temperature than on Pt. Difficulties to obtain reproducible clean surfaces of Ag, Ni, Pd, and Pt led to the choice of Au as the best metal surface suitable to adsorb Hg.

For fast on-line gas thermochromatography studies on metallic surfaces a new set-up was developed based on the In-situ Volatilization and On-line detection technique (IVO). This set-up was tested in on-line thermochromatographic investigations with short-lived Hg isotopes and 219Rn, using Au or Pd as stationary surfaces. An overall efficiency of about 60% and a transportation time less than 25 s was determined for this newly designed IVO. A separation factor of more than 106 was estimated for non-volatile species.

Evidence for the formation of sodium hassate(VIII)

Hassium, element 108, was produced in the fusion reaction between26Mg and248Cm. The hassium recoils were oxidizedin-situto a highly volatile oxide, presumably HsO4, and were transported in a mixture of He and O2to a deposition and detection system. The latter consisted of 16 silicon PIN-photodiodes facing a layer of NaOH, which served, in the presence of a certain partial pressure of water in the transport gas, as reactive surface for the deposition of the volatile tetroxides. Six correlated α-decay chains of Hs were detected in the first 5 detectors centred around detection position 3. In analogy to OsO4, which forms Na2[OsO4(OH)2], an osmate(VIII), with aqueous NaOH, HsO4presumably was deposited as Na2[HsO4(OH)2], a hassate(VIII).

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

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.

Attempts to chemically investigate element 112

Two experiments aiming at the chemical investigation of element 112 produced in the heavy ion induced nuclear fusion reaction of 48Ca with 238U were performed at the Gesellschaft für Schwerionenforschung (GSI), Darmstadt, Germany. Both experiments were designed to determine the adsorption enthalpy of element 112 on a gold surface using a thermochromatography setup. The temperature range covered in the thermochromatography experiments allowed the adsorption of Hg at about 35 °C and of Rn at about -180 °C. Reports from the Flerov Laboratory for Nuclear Reactions (FLNR), Dubna, Russia claim production of a 5-min spontaneous fission (SF) activity assigned to 283112 for the 238U(48Ca,3n) 283112 reaction. Hence, Experiment I was designed to detect spontaneously fissioning (SF) isotopes of element 112 with half-lives (t 1/2) longer than about 20 s. 11 high-energy events were detected. 7 events exhibit a deposition pattern resembling a chromatographic peak in the vicinity of Rn deposition. However, the energy of the events observed in Experiment I was lower than expected for a SF-decay of 283112. Therefore, these events could not be unambiguously attributed to the decay of 283112. In contradiction with earlier publications newer reports from FLNR Dubna claim that 283112 decays by α-particle emission (E α = 9.5 MeV) with t 1/2 = 4 s followed by a SF-decay of 279Ds (t 1/2 = 0.2 s). Therefore, Experiment II was designed to be sensitive to both claimed decay properties of 283112. However, during this experiment neither short α-SF correlations nor SF coincidences were detected. The conclusion is that 283112 was not unambiguously detected, neither in Experiment I nor in Experiment II.

Theoretical investigations of the reactivity of MO4 and the electronic structure of Na2[MO4(OH)2], where M=Ru, Os, and Hs (element 108)

Fully relativistic, four-component, density functional theory calculations (4c-DFT) were performed for [MO4(OH)2]2- and Na2[MO4(OH)2], where M=Ru, Os, and Hs. The electronic structure of the Hs complex ion was shown to be similar to that of the Os complex ion, though [HsO4(OH)2]2- should be more covalent than the lighter congeners in group 8, by analogy with MO4. The calculations of the free energy change, Δ G r, of the [MO4(OH)2]2- and Na2[MO4(OH)2] formation reactions from the volatile tetroxides and NaOH have shown that HsO4 should be slightly less reactive than OsO4, with the difference in ΔG r being less than 52 kJ/mol. In the experimental study of the deposition of OsO4 and HsO4 on the surface of NaOH in the presence of water, such a difference in reactivity has not yet been clearly revealed. The anionic complex of Ru(VIII) was found to be much less stable than those of Os and Hs. Also, Delta;G r for the formation of [RuO4(OH)2]2- from RuO4 was found to be ∼300 kJ/mol more positive than ΔG r for analogous reactions of Os and Hs, which explains why the Ru(VIII) complex is not known. The ionic radii, IR(Hs8+)=0.454 Å for CN=4, IR(Os8+) = 0.49 Å and IR(Hs8+) = 0.54 Å for CN=6, have been obtained on the basis of the calculations of bond lengths in MO4, as well as via a correlation between R max of the outer np obitals and IR of the 5d and 6d elements, respectively.

Discovery of the element with atomic number 112 (IUPAC Technical Report)

The IUPAC/IUPAP Joint Working Party (JWP) on the priority of claims to the discovery of new elements has reviewed the relevant literature pertaining to several claims. In accordance with the criteria for the discovery of elements previously established by the 1992 IUPAC/IUPAP Transfermium Working Group (TWG), and reiterated by the 1999 and 2003 IUPAC/IUPAP JWPs, it was determined that the 1996 and 2002 claims by the Hofmann et al. research collaborations for the discovery of the element with atomic number 112 at Gesellschaft für Schwerionenforschung (GSI) share in the fulfillment of those criteria. A synopsis of Z = 112 experiments and related efforts is presented. A subsequent report will address identification of higher-Z elements including those of odd atomic number.

Observation of the 3n evaporation channel in the complete hot-fusion reaction 26Mg + 248Cm leading to the new superheavy nuclide 271Hs

The analysis of a large body of heavy ion fusion reaction data with medium-heavy projectiles (6 < or = Z < or = 18) and actinide targets suggests a disappearance of the 3n exit channel with increasing atomic number of the projectile. Here, we report a measurement of the excitation function of the reaction (248)Cm ((26)Mg,xn)(274-x)Hs and the observation of the new nuclide (271)Hs produced in the 3n evaporation channel at a beam energy well below the Bass fusion barrier with a cross section comparable to the maxima of the 4n and 5n channels. This indicates the possible discovery of new neutron-rich transactinide nuclei using relatively light heavy ion beams of the most neutron-rich stable isotopes and actinide targets.