Sulfate complexation of element 104, Rf, in H2SO4/HNO3 mixed solution

Chemical characterization of heavy actinides and light transactinides - Experimental achievements at JAEA

The chemical characterization of the heaviest elements at the farthest reach of the periodic table (PT) and the classification of these elements in the PT are undoubtedly crucial and challenging subjects in chemical and physical sciences. The elucidation of the influence of relativistic effects on their outermost electronic configuration is also a critical and fascinating aspect. However, the heaviest elements with atomic numbers Z ≳ 100 must be produced at accelerators using nuclear reactions of heavy ions and target materials. Therefore, production rates for these elements are low, and their half-lives are as short as a few seconds to a few minutes; they are usually available in a quantity of only a few atoms at a time. Here, we review some highlighted studies on heavy actinide and light transactinide chemical characterization performed at the Japan Atomic Energy Agency tandem accelerator facility. We discuss briefly the prospects for future studies of the heaviest elements.

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.

From SRAFAP to ARCA and AIDA – developments and implementation of automated aqueous-phase rapid chemistry apparatuses for heavy actinides and transactinides

The development of automated rapid chemistry techniques and their application for batch-wise, chromatographic separations of heavy elements in the liquid-phase are outlined. Starting in the mid-1970s with manually performed separations using pressurized liquid-chromatography techniques, this development led to the first version of the Automated Rapid Chemistry Apparatus, ARCA, in the early 1980s. After a breakthrough to a much higher level of automation and miniaturization, the new apparatus ARCA II was built in the late 1980s. Based on it, the Automated Ion-exchange separation apparatus coupled with the Detection system for Alpha spectroscopy, AIDA, became operational in the late 1990s. In the context of technical and technological advancements, this article discusses the successful application of these instruments for (i) the search for superheavy elements, (ii) cross section measurements of actinide elements produced in multi-nucleon transfer reactions with actinide targets, (iii) chemical separation and characterization of the heavy actinides mendelevium, Md, and lawrencium, Lr, and (iv) studies of the transactinide elements rutherfordium, Rf, dubnium, Db, and seaborgium, Sg. Details of the separations are outlined together with the big advancements made over time and the limitations reached. For the transactinide elements, examples are given for their observed chemical behavior; often affected by an interplay between hydrolysis and complex formation. Influenced by relativistic effects, chemical properties of these elements sometimes deviated from those of their lighter homologs in the Periodic Table.

Observation of the chemical reaction equilibria of element 104, rutherfordium: solid-liquid extraction of Rf, Zr, Hf and Th with Aliquat 336 resin from HCl

We successfully observed the equilibrium state of the chemical reactions for superheavy elements on a one-atom-at-a-time scale; we investigated the time dependence of the extraction behaviour of element 104, Rf. The distribution coefficient of Rf in 9 M HCl was found to be higher than those of its homologous elements, probably due to differences in the chloride complexation of Rf.

Coprecipitation experiment with Sm hydroxide using a multitracer produced by nuclear spallation reaction: A tool for chemical studies with superheavy elements

To establish a new methodology for superheavy element chemistry, the coprecipitation behaviors of 34 elements with samarium hydroxide were investigated using multitracer produced by a spallation of Ta. The chemical reactions were rapidly equilibrated within 10s for many elements. In addition, these elements exhibited individual coprecipitation behaviors, and the behaviors were qualitatively related to their hydroxide precipitation behaviors. It was demonstrated that the ammine and hydroxide complex formations of superheavy elements could be investigated using the established method.