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Nuclear fission of heavy (actinide) nuclei results predominantly in asymmetric mass splits 1 . Without quantum shell effects, which can give extra binding energy to their mass-asymmetric shapes, these nuclei would fission symmetrically. The strongest shell effects appear in spherical nuclei, such as the spherical ‘doubly magic’ (that is, both its atomic and neutron numbers are ‘magic’ numbers) nucleus 132 Sn, which contains 50 protons and 82 neutrons. However, a systematic study of fission 2 has shown that heavy fission fragments have atomic numbers distributed around Z  = 52 to Z  = 56, indicating that the strong shell effects in 132 Sn are not the only factor affecting actinide fission. Reconciling the strong spherical shell effects at Z  = 50 with the different Z values of fission fragments observed in nature has been a longstanding puzzle 3 . Here we show that the final mass asymmetry of the fragments is also determined by the extra stability provided by octupole (pear-shaped) deformations, which have been recently confirmed experimentally around 144 Ba ( Z  = 56) 4 , 5 , one of very few nuclei with shell-stabilized octupole deformation 6 . Using a quantum many-body model of superfluid fission dynamics 7 , we find that heavy fission fragments are produced predominantly with 52 to 56 protons, which is associated with substantial octupole deformation acquired on the way to fission. These octupole shapes, which favour asymmetric fission, are induced by deformed shells at Z  = 52 and Z  = 56. By contrast, spherical magic nuclei are very resistant to octupole deformation, which hinders their production as fission fragments. These findings may explain surprising observations of asymmetric fission in nuclei lighter than lead 8 . Quantum many-body calculations of superfluid fission dynamics reveal that heavy fragments from asymmetric fission of actinides are associated with considerable octupole (pear-shaped) deformation acquired on the way to fission.

The first reference on this rapidly growing topic provides an essential up-to-date guide to current and emerging trends.A group of international experts has been carefully selected by the editors to cover all the central aspects, with a focus on molecular species while also including industrial applications.

Evaluation of covariance for JENDL was virtually started after the release of JENDL-3.2. The covariance data were obtained for 16 nuclides and compiled to the JENDL-3.2 Covariance File. At the time of the JENDL-4.0 development, covariances were much enhanced especially for actinides; covariance data were given for 99 nuclides in total. The latest version JENDL-5 includes covariance data for 105 nuclides by adding new evaluations for light nuclides and structure materials. An overview of the covariance evaluation for JENDL is presented.

A U L III-edge X-ray absorption spectroscopic investigation of UVI interactions with minor cement minerals, ettringite and hydro­talcite, is reported. The study is supplemented by 27Al magic angle scattering nuclear magnetic resonance spectroscopy, X-ray diffraction and geochemical modelling. Portland cement based grouts used for radioactive waste immobilization contain high replacement levels of supplementary cementitious materials, including blast-furnace slag and fly ash. The minerals formed upon hydration of these cements may have capacity for binding actinide elements present in radioactive waste. In this work, the minerals ettringite (Ca6Al2(SO4)3(OH)12·26H2O) and hydro­talcite (Mg6Al2(OH)16CO3·4H2O) were selected to investigate the importance of minor cement hydrate phases in sequestering and immobilizing UVI from radioactive waste streams. U L III-edge X-ray absorption spectroscopy (XAS) was used to probe the UVI coordination environment in contact with these minerals. For the first time, solid-state 27Al magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy was applied to probe the Al coordination environment in these UVI-contacted minerals and make inferences on the UVI coordination, in conjunction with the X-ray spectroscopy analyses. The U L III-edge XAS analysis of the UVI-contacted ettringite phases found them to be similar (>∼70%) to the uranyl oxyhydroxides present in a mixed becquerelite/metaschoepite mineral. Fitting of the EXAFS region, in combination with 27Al NMR analysis, indicated that a disordered Ca- or Al-bearing UVI secondary phase also formed. For the UVI-contacted hydro­talcite phases, the XAS and 27Al NMR data were interpreted as being similar to uranyl carbonate, that was likely Mg-containing.

The neutralization of acidic solutions containing U (IV) and Ce (III) at room temperature in glove box atmosphere and in the presence of dithionite results in coprecipitation of these elements as amorphous solid solutions Ce x U 1– x O 2± y . The solubilities of the precipitates with different mole fractions ( x ) of Ce(OH) 3 ( x = 0.01 or 0.1) were determined in 1  M NaClO 4 solutions between pH 2.2 and 12.8 under reducing conditions. The solids were investigated by a variety of methods (chemical analysis, SEM-EDX, XRD, XPS, XAS) to determine the nature of the solid solutions formed, their composition and the valence state of Ce and U. X-ray photoelectron spectroscopy confirmed the oxidation states of the solids both before and after the equilibration as Ce (III) and U (IV). The amorphous coprecipitates reached equilibrium relatively fast (∼1 week). The release of Ce from the coprecipitates was totally dominated by the release of uranium over the whole pH range. The Ce concentrations decrease slightly with the decrease of Ce content in the solid, suggesting that Ce x U 1– x O 2± y solids behave thermodynamically as solid solutions. The concentrations of U in equilibrium with the coprecipitate were in excellent agreement with the solubility of UO 2 (s) under reducing conditions reported in the literature. The conditional solubility product of Ce(OH) 3 from the coprecipitate was several orders of magnitude (∼4 in the near neutral pH range and ∼18 in the acidic range) lower than that of pure Ce(OH) 3 (s). The activities and activity coefficients of Ce(OH) 3 (s) in the coprecipitate were also estimated. Activity coefficients are much less than 1, indicating that the mixing of Ce(OH) 3 with UO 2 is highly favorable.

Our knowledge of actinide chemical bonds lags far behind our understanding of the bonding regimes of any other series of elements. This is a major issue given the technological as well as fundamental importance of f -block elements. Some key chemical differences between actinides and lanthanides—and between different actinides—can be ascribed to minor differences in covalency, that is, the degree to which electrons are shared between the f -block element and coordinated ligands. Yet there are almost no direct measures of such covalency for actinides. Here we report the first pulsed electron paramagnetic resonance spectra of actinide compounds. We apply the hyperfine sublevel correlation technique to quantify the electron-spin density at ligand nuclei (via the weak hyperfine interactions) in molecular thorium( III ) and uranium( III ) species and therefore the extent of covalency. Such information will be important in developing our understanding of the chemical bonding, and therefore the reactivity, of actinides. Covalency in actinide–­ligand bonding is poorly understood compared to that in other parts of the periodic table due to the lack of experimental data. Here, pulsed electron paramagnetic resonance methods are used to directly measure the electron spin densities at coordinated ligands in molecular thorium and uranium complexes.

Partitioning of americium from lanthanides (Ln) present in used nuclear fuel plays a key role in the sustainable development of nuclear energy 1 – 3 . This task is extremely challenging because thermodynamically stable Am(III) and Ln(III) ions have nearly identical ionic radii and coordination chemistry. Oxidization of Am(III) to Am(VI) produces AmO 2 2+ ions distinct with Ln(III) ions, which has the potential to facilitate separations in principle. However, the rapid reduction of Am(VI) back to Am(III) by radiolysis products and organic reagents required for the traditional separation protocols including solvent and solid extractions hampers practical redox-based separations. Herein, we report a nanoscale polyoxometalate (POM) cluster with a vacancy site compatible with the selective coordination of hexavalent actinides ( 238 U, 237 Np, 242 Pu and 243 Am) over trivalent lanthanides in nitric acid media. To our knowledge, this cluster is the most stable Am(VI) species in aqueous media observed so far. Ultrafiltration-based separation of nanoscale Am(VI)-POM clusters from hydrated lanthanide ions by commercially available, fine-pored membranes enables the development of a once-through americium/lanthanide separation strategy that is highly efficient and rapid, does not involve any organic components and requires minimal energy input. A new strategy to separate radioactive americium from lanthanides based on complexation with polyoxometalates and ultrafiltration technique is highly efficient and rapid, does not involve any organic components and requires minimal energy input.

Homogenous electrocatalytic water reduction with formation of dihydrogen is demonstrated with a trisaryloxide U(III) complex, for which the catalytic cycle was elucidated and found to involve rare terminal U( iv )–OH and U( v )=O complexes. A uranium compound with catalytic activity Karsten Meyer and colleagues report the first example of electrocatalytic reduction of H 2 O to H 2 using a molecular uranium ( III ) coordination complex. The catalytic nature of this reaction is unusual, since the bonding strength of the uranyl (O=U( IV )=O) motif means that most uranium complexes react irreversibly with water to form uranyl-based species, rather than participating in reversible oxidation/reduction reactions inherent to the recovery of catalysts. The catalytic cycle is shown to involve a rare terminal U( IV )-OH complex. The possibility of developing uranium-based catalysts could be relevant to nuclear waste management strategies, as the mildly radioactive and depleted uranium produced as waste by the nuclear power industry could be a valuable resource. Depleted uranium is a mildly radioactive waste product that is stockpiled worldwide. The chemical reactivity of uranium complexes is well documented, including the stoichiometric activation of small molecules of biological and industrial interest such as H 2 O, CO 2 , CO, or N 2 (refs 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ), but catalytic transformations with actinides remain underexplored in comparison to transition-metal catalysis 12 , 13 , 14 . For reduction of water to H 2 , complexes of low-valent uranium show the highest potential, but are known to react violently and uncontrollably forming stable bridging oxo or uranyl species 15 . As a result, only a few oxidations of uranium with water have been reported so far; all stoichiometric 2 , 3 , 16 , 17 . Catalytic H 2 production, however, requires the reductive recovery of the catalyst via a challenging cleavage of the uranium-bound oxygen-containing ligand. Here we report the electrocatalytic water reduction observed with a trisaryloxide U( iii ) complex [(( Ad,Me ArO) 3 mes)U] (refs 18 and 19 )—the first homogeneous uranium catalyst for H 2 production from H 2 O. The catalytic cycle involves rare terminal U( iv )–OH and U( v )=O complexes, which have been isolated, characterized, and proven to be integral parts of the catalytic mechanism. The recognition of uranium compounds as potentially useful catalysts suggests new applications for such light actinides. The development of uranium-based catalysts provides new perspectives on nuclear waste management strategies, by suggesting that mildly radioactive depleted uranium—an abundant waste product of the nuclear power industry—could be a valuable resource.

Chemists have spent over a hundred years trying to make ambient temperature/pressure catalytic systems that can convert atmospheric dinitrogen into ammonia or directly into amines. A handful of successful d-block metal catalysts have been developed in recent years, but even binding of dinitrogen to an f-block metal cation is extremely rare. Here we report f-block complexes that can catalyse the reduction and functionalization of molecular dinitrogen, including the catalytic conversion of molecular dinitrogen to a secondary silylamine. Simple bridging ligands assemble two actinide metal cations into narrow dinuclear metallacycles that can trap the diatom while electrons from an externally bound group 1 metal, and protons or silanes, are added, enabling dinitrogen to be functionalized with modest but catalytic yields of six equivalents of secondary silylamine per molecule at ambient temperature and pressure.Metallacycles formed from two large, under-coordinated actinide MIV cations and two rigid arene-bridged aryloxide ligands are capable of binding dinitrogen inside their cavity. These f-block complexes can catalyse the reduction and functionalization of dinitrogen as well as the catalytic conversion of molecular dinitrogen to a secondary silylamine.

The Moon has a magmatic and thermal history that is distinct from that of the terrestrial planets 1 . Radioisotope dating of lunar samples suggests that most lunar basaltic magmatism ceased by around 2.9–2.8 billion years ago (Ga) 2 , 3 , although younger basalts between 3 Ga and 1 Ga have been suggested by crater-counting chronology, which has large uncertainties owing to the lack of returned samples for calibration 4 , 5 . Here we report a precise lead–lead age of 2,030 ± 4 million years ago for basalt clasts returned by the Chang’e-5 mission, and a 238 U/ 204 Pb ratio ( µ value) 6 of about 680 for a source that evolved through two stages of differentiation. This is the youngest crystallization age reported so far for lunar basalts by radiometric dating, extending the duration of lunar volcanism by approximately 800–900 million years. The µ value of the Chang’e-5 basalt mantle source is within the range of low-titanium and high-titanium basalts from Apollo sites ( µ value of about 300–1,000), but notably lower than those of potassium, rare-earth elements and phosphorus (KREEP) and high-aluminium basalts 7 ( µ value of about 2,600–3,700), indicating that the Chang’e-5 basalts were produced by melting of a KREEP-poor source. This age provides a pivotal calibration point for crater-counting chronology in the inner Solar System and provides insight on the volcanic and thermal history of the Moon. Basalt samples returned from the Moon by the Chang’e-5 mission are revealed to be two billion years old by radioisotopic dating, providing insight on the volcanic history of the Moon.