Volume 107, Issue 9-11 - Special Issue: International Year of the Periodic Table of Chemical Elements 2019

This brief introduction to the synthesis and chemistry of elements discovered since 1940 is focused primarily on Z=93–118. The goal of this work is not to simply catalogue the nuclear fusion reactions needed to prepare new elements, but rather to focus on the chemical and physical properties that these elements possess. These elements share a single common feature in that they all have large Z values, and thus have electronic structures that are significantly altered by both scalar relativistic effects and spin-orbit coupling. These effects scale nonlinearly with increasing Z and create unexpected deviations both across series and down groups of elements. The magnitude of these effects is large enough that orbital energies rearrange and mix in ways that complicate incomplete depictions of electronic structure that are based solely on electron repulsion. Thus, the primary aim of this review is to document the impact of relativistic effects on electronic structure and how this has altered not just our understanding of the chemistry of heavy elements, but has even created in the need to rearrange the Periodic Table itself.

Recent progress in the production of heavy nuclei far from stability and in the studies of nuclear and chemical properties of heavy actinides is briefly reviewed. Exotic nuclear decay properties including nuclear fission of heavy nuclei, measurements of first ionization potentials of heavy actinides, and redox studies of heavy actinides are described. Brief history of discovery of the transuranium elements is also presented.

The precise determination of atomic and nuclear properties such as masses, differential charge radii, nuclear spins, electromagnetic moments and the ionization potential of the actinides has been extended to the late actinides in recent years. In particular, laser spectroscopy and mass spectrometry have reached the region of heavy actinides that can only be produced only at accelerator facilities. The new results provide deeper insight into the impact of relativistic effects on the atomic structure and the evolution of nuclear shell effects around the deformed neutron shell closure at N  = 152. All these experimental activities have also opened the door to extend such measurements to the transactinide elements in the near future. This contribution summarizes recent achievements in Penning trap mass spectrometry and laser spectroscopy of the late actinides and addresses future perspectives.

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 6 th 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.

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.

Isotopes of transactinide elements have to be synthesized in nuclear reactions with light or heavy beam particles. The efficient production by neutron capture and subsequent β − decay as it is used for the production of isotopes of actinide elements up to fermium is no longer possible due to the lack of suitable target material. The content of this article is about the synthesis and the study of the decay properties of nuclei to which atomic, respectively proton numbers from Z = 104 to 118 could be unambiguously assigned by physical means. The results identified the reaction products as isotopes of new elements beyond the actinides, the transactinides. As such the elements received names given by the discovers ranging from rutherfordium for element 104 to oganesson for element 118 which completes the 7 th row of the Periodic Table of the Elements. Intensive heavy ion beams, sophisticated target technology, efficient electromagnetic ion separators, and sensitive detector arrays were the prerequisites for discovery of the elements from Z = 107 to 118 during the years from 1981 to 2013. The results and the techniques are described. Also given is a historical introduction into early experiments and the theoretical predictions for a possible existence of an island of stability located at the crossing of the next closed shells for the protons and neutrons beyond the doubly magic nucleus 208 Pb. The experimental results are compared with recent theoretical calculations on cross-sections and decay modes of these superheavy nuclei, respectively isotopes of superheavy elements. An outlook is given on further improvement of experimental facilities which will be needed for exploration of the extension and structure of the island of superheavy nuclei, in particular for searching for isotopes with longer half-lives predicted to be located in the south east and for isotopes of further new elements expected in the north-east direction of the island at the upper end of the chart of nuclei.

The EURO-GANEX process was developed for co-separating transuranium elements from irradiated nuclear fuels. A hot flow-sheet trial was performed in a counter-current centrifugal contactor setup, using a genuine high active feed solution. Irradiated mixed (carbide, nitride) U 80 Pu 20 fast reactor fuel containing 20 % Pu was thermally treated to oxidise it to the oxide form which was then dissolved in HNO 3 . From this solution uranium was separated to >99.9 % in a primary solvent extraction cycle using 1.0 mol/L DEHiBA ( N , N -di(2-ethylhexyl)isobutyramide in TPH (hydrogenated tetrapropene) as the organic phase. The raffinate solution from this process, containing 10 g/L Pu, was further processed in a second cycle of solvent extraction. In this EURO-GANEX flow-sheet, TRU and fission product lanthanides were firstly co-extracted into a solvent composed of 0.2 mol/L TODGA (N , N , N ′, N ′-tetra- n -octyl diglycolamide) and 0.5 mol/L DMDOHEMA ( N , N ′-dimethyl- N , N ′-dioctyl-2-(2-hexyloxy-ethyl) malonamide) dissolved in Exxsol D80, separating them from most other fission and corrosion products. Subsequently, the TRU were selectively stripped from the collected loaded solvent using a solution containing 0.055 mol/L SO 3 -Ph-BTP (2,6-bis(5,6-di(3-sulphophenyl)-1,2,4-triazin-3-yl)pyridine tetrasodium salt) and 1 mol/L AHA (acetohydroxamic acid) in 0.5 mol/L HNO 3 ; lanthanides were finally stripped using 0.01 mol/L HNO 3 . Approximately 99.9 % of the TRU and less than 0.1 % of the lanthanides were found in the product solution, which also contained the major fractions of Zr and Mo.

Separation of trivalent actinide (An) and lanthanide (Ln) elements is one of the burning topics in the back end of the nuclear fuel cycle due to the similarity in their chemical behaviour. A significant amount of research is being carried out worldwide to develop suitable ligands for the separation of the trivalent actinides and lanthanides. Some of the research groups are engaged in continuous improvement of the di-ethylene-triamine-penta acetic acid (DTPA) based Ln/An separation method, whereas extensive research is going on for the development of the lipophilic and hydrophilic ‘N’ donor heteropolycyclic ligands as the actinide selective ligand. A number of ‘S’ donor ligands are also explored for the Ln/An separation. In the present review, we made an attempt to highlight various separation processes based on soft donor ligands developed for Ln/An separations. Beside the conventional solvent extraction processes, separation possibilities membrane based and solid phase extraction techniques are evaluated for the Ln/An separation and are compiled in the present review.

Developing necessary reprocessing techniques to meet the remarkable increase of spent nuclear fuels (SNFs) is crucial for the sustainable development of nuclear energy. This review summarizes recent research progresses related to the SNF reprocessing in China, with an emphasis on actinides separation over lanthanides through three different techniques, hydrometallurgical reprocessing, pyrometallurgical processes, and selective crystallization based separation. Some future perspectives with respect to advanced actinide separation are also given.

The Fukushima Daiichi Nuclear Power Station, which is owned by the Tokyo Electric Power Company, was damaged by the great earthquake and tsunami on March 11, 2011, and serious contamination due to radioactive nuclides occurred. To investigate the waste management methodologies, contaminated materials were radiochemically analyzed. This paper reviews the analytical data concerning actinide elements. Contaminated water has accumulated in the basement of the reactor and other buildings, and actinide nuclides have been detected in this water. Actinides first get dissolved into the water inside the primary containment vessel, and then their concentration in the water decreases to a certain level with further flow. The contaminated water is chemically decontaminated; however, the actinide concentration does not decrease with time. This suggests that the actinides are continuously being supplied by the damaged fuel via slow dissolution. The dissolved transuranic (TRU) nuclides are recovered in the precipitate via a chemical treatment and are mostly removed from the water. Pu, Am, and Cm were detected in the topsoil at the site and appear to originate from the damaged fuel, whereas the detected U originates from natural sources. TRU nuclides slowly move in soil to deeper layers. The contamination of the rubble is nonuniform, and actinides are detected as well as fission products. Inside the reactor building of unit #2, the TRU nuclide concentration is comparatively higher near the boundary of the primary containment vessel, which experienced a fault during the accident. As for the vegetation, TRU nuclides were only found in fallen leaves near the reactor buildings.

This review highlights recent data on the complexation of Pa(V) with inorganic (fluoride and sulphate) and organic (oxalate, nitrilotriacetate, diethylenetriaminepentaacetate) ligands in solution. New thermodynamic parameters relative to the complexation of Pa(V) with sulphate are presented. The review also includes gas phase and theoretical studies focused on the interaction of Pa(V) in the dioxo and oxo forms with water.

Since the early 40s when the first research related to the development of the atomic bomb began for the Manhattan Project, actinides (An) and their association with the use of nuclear energy for civil applications, such as in the generation of electricity, have been a constant source of interest and fear. In 1962, the first Society of Toxicology (SOT), led by H. Hodge, was established at the University of Rochester (USA). It was commissioned as part of the Manhattan Project to assess the impact of nuclear weapons production on workers’ health. As a result of this initiative, the retention and excretion rates of radioactive heavy metals, their physiological impact in the event of acute exposure and their main biological targets were assessed. In this context, the scientific community began to focus on the role of proteins in the transportation and in vivo accumulation of An. The first studies focused on the identification of these proteins. Thereafter, the continuous development of physico-chemical characterization techniques has made it possible to go further and specify the modes of interaction with proteins from both a thermodynamic and structural point of view, as well as from the point of view of their biological activity. This article reviews the work performed in this area since the Manhattan Project. It is divided into three parts: first, the identification of the most affine proteins; second, the study of the affinity and structure of protein-An complexes; and third, the impact of actinide ligation on protein conformation and function.

A survey of the positron-emitting radionuclides over the whole mass range of the Periodic Table of Elements was carried out. As already known, positrons are preferably emitted from light mass neutron deficient radionuclides. Their emission from heavier mass nuclides is rather rare. The applications of positron annihilation in three areas, namely materials research, plant physiology and medical diagnosis, are reported. The methods of production of positron emitters are discussed, with emphasis on radionuclides presently attracting more attention in theranostics and multimodal imaging. Some future perspectives of radionuclide development technologies are considered.

Halogen radioisotopes have a variety of physical half-lives which are suitable for probing a wide variety of pharmacokinetic processes. Compared with other radiohalogens, relatively little work has been done with radiochlorine. However, high specific activity radioisotopes of chlorine are available from low energy cyclotron production in quantities suitable for positron emission tomography (PET) and fundamental research. In particular, the sole radioisotope of chlorine which may be used for PET imaging, 34m Cl, has achieved a state of development that permits imaging in clinical settings though sparse research effort has been focused on this isotope over the last 40 years. Additionally, the other longer-lived radioisotopes of chlorine will likely continue to show utility for more traditional radiotracer studies and chemistry development.

The halogens bromine and iodine have similar chemical properties and undergo similar reactions due to their closeness in Group 17 of the periodic chart. There are a number of bromine and iodine radionuclides that have properties useful for diagnosis and therapy of human diseases. The emission properties of radiobromine and radioiodine nuclides with half-lives longer than 1 h are summarized along with properties that make radionuclides useful in PET/SPECT imaging and β/Auger therapy, such that the reader can assess which of the radionuclides might be useful for medical applications. An overview of chemical approaches that have been used to radiolabel molecules with radiobromine and radioiodine nuclides is provided with examples. Further, references to a large variety of different organ/cancer-targeting agents utilizing the radiolabeling approaches described are provided.

The use of α-emitting radionuclides in targeted alpha therapy (TAT) holds great potential for treatment of human diseases, such as cancer, due to the short pathlength and high potency of the α particle, which can localize damage to targeted cells while minimizing effects to healthy surrounding tissues. In this review several potential α-emitting radionuclides having emission properties applicable to TAT are discussed from a radiochemical point of view. Overviews of production, radiochemical separation and chelation aspects relative to developing TAT radiopharmaceuticals are provided for the α-emitting radionuclides (and their generator systems) 211 At, 224 Ra/ 212 Pb/ 212 Bi, 225 Ac/ 213 Bi, 227 Th/ 223 Ra, 230 U/ 226 Th, 149 Tb and 255 Fm.

Diagnostic and therapeutic nuclear medicine relies heavily on radiometal nuclides. The most widely used and well-known radionuclide is technetium-99m ( 99m Tc), which has dominated diagnostic nuclear medicine since the advent of the 99 Mo/ 99m Tc generator in the 1960s. Since that time, many more radiometals have been developed and incorporated into potential radiopharmaceuticals. One critical aspect of radiometal-containing radiopharmaceuticals is their stability under in vivo conditions. The chelator that is coordinated to the radiometal is a key factor in determining radiometal complex stability. The chelators that have shown the most promise and are under investigation in the development of diagnostic and therapeutic radiopharmaceuticals over the last 5 years are discussed in this review.