Thorium Atoms Research Articles

Bis{µ-(2,2′-bipyridine-1κ2N,N′)-(6,6′-dicarbonyl-1κ2O,O′:2κO′)bis(N,N-diethylthioureato-2κS)}(acetato-1κO)(µ-acetato-1κO:2-κO′)(methanol-2κO)thoriumnickel

Reactions of 2,2′-bipyridine-6,6′-dicarbonyl-bis(N,N-diethylthiourea), H2Lbipy, with a mixture of thorium nitrate hydrate and nickel acetate hydrate in methanol with NEt3 as a supporting base yield brown single crystals of the bimetallic complex [ThNi(Lbipy)2(CH3COO)2(MeOH)]. Two 2,2′-bipyridine-centered bis(aroylthioureato) ligands connect the metal atoms in a way that the thorium atom is coordinated by two O,N,N,O donor atom sets, while the nickel atom establishes two S,O chelate rings in its equatorial coordination plane. The metal atoms are connected by a bridging acetato ligand, and their coordination spheres are completed by one methanol ligand (nickel) and a monodentate acetato ligand (thorium). A distorted octahedral coordination environment is established around the Ni2+ ion, while the Th4+ ion is in first approximation a 10-coordinate with a diffusely defined coordination polyhedron.

Gas-phase thorium molecules from laser ablation

Laser ablation is performed on an oxidized, roughly 35-year-old Th232 foil. The produced anionic and cationic molecules are investigated utilizing precision mass measurements by a multireflection time-of-flight mass spectrometer. Molecules with up to three thorium atoms are identified. This includes oxides ThnOx+ containing up to 2n−1 oxygen atoms and further species incorporating carbon or nitrogen. In addition, signals of U+, UO+, and the compound species ThUO2+ are found. Photoexcitation reveals selected molecules' dissociation patterns. The experimental findings are compared to density functional theory calculations. Published by the American Physical Society 2024

TWO-PHOTON RESONANCE MECHANISM OF OPTICAL PUMPING OF THE 8.3-eV ISOMER 229mTh IN NEUTRAL ATOMS

The possibility of refining the energy of the nuclear isomer 229mTh with the energy of 8.36 eV, the most likely candidate for the role of a nuclear frequency standard, using resonant optical pumping is discussed. Attention is focused on the broadening of theresonance in order toreduce scanning time. The proposed twophoton method uses radical broadening of the isomer line due to mixing with an electronic transition. This method is not burdened by cross-section reduction, in contrast with internal-conversion-based resonance broadening or intended extra-broadening of the spectral line of a scanning laser. In the case under consideration, it turns out to be two orders of magnitude more effective. It applies to both ionized and neutral thorium atoms. The realization of the method supposes excitation of both the nucleus and the electron shell in the final state.

LATTICE DYNAMICAL STUDY OF THORIUM SULPHIDE

Thorium sulfide (ThS) is a chemical compound composed of thorium and sulfur atoms, with the chemical formula ThS. It belongs to the class of sulfides. To understand the dimensional stability and thermal behaviour of thorium sulphide (ThS), a lattice dynamical research issued to investigate its vibrational characteristics. We study the density of states (DOS) and phonon dispersion in the 50–60 GHz frequency region using computational techniques. Important information about the stability of the ThS crystal structure are given by the phonon dispersion curves, namely the presence of imaginary phonon frequencies that point to dynamical stability. We identify the major modes of vibration and their contributions to the thermodynamic properties of ThS through studying the phonon density of states.Van der Waals' three-body force shell model is used in this study to theoretically investigate the lattice dynamical behaviour of (ThS...). Elastic constants, pressure derivatives, dispersion relation curve, combined density of states, equation of state, and specific ultrasonic properties of the ThS are among the parameters for which calculated values are gave.The stability of the structure and vibrational properties of thorium sulphide are now better known by lattice dynamical study, which provides the way to its effective application in a range of technological uses, from nuclear reactors to the production of creative materials. Keywords: lattice, dynamics, thermal, vibrational

Effect of fission products on the thermal conductivity of ThO2-A molecular dynamics study

Thermal conductivity (k), as an important thermal property of nuclear fuels, would be deteriorated due to fission products. Therefore, to investigate the effect of fission products on the thermal conductivity of nuclear fuels is essential. Two typical fission products: Xe and Kr with 0–2 % concentration are considered in this work. The lattice constants (L) of ThO2 increase due to fission products at all testing temperatures. The extent of increase in L due to Xe interstitials is the maximum. The fission products significantly reduce the thermal conductivity of ThO2. The extent of reduction in thermal conductivity of ThO2 by the defects follows the trend Xe (interstitials) > Xe (substitutional defects) > Kr (substitutional defects) > Kr (interstitials). Finally, the full-filled Xe/Kr bubble has a nearly identical thermal conductivity as an empty void or half-filled Xe/Kr bubble. The underlying reason may be that the thorium atoms have a lower mobility than uranium atoms. These calculated values can be used to predict the thermal properties of the irradiated ThO2.

Insights into ThB40: Stability, Electronic Structure, and Interaction.

The interaction between nonmetal and metal atoms has attracted great interest in the development of organometallic compounds and their promising applications. In this study, we explored the interaction between boron and thorium atoms, based on the stable B40Th coordination compound, by employing density functional theory calculations. We elucidated the stability and geometries of the B40Th coordination compound and revealed the electron transfer from the metal atom Th to B40, which is evidenced by the natural bond orbital calculations. This electron transfer is attributed to the electron-withdrawing character of the boron atom and results in clear electrostatic interaction. Additionally, bond critical analysis and bond order calculations show obvious covalent characters between the metal and nonmetal atoms. The IR spectrum was simulated to give detailed information to identify this targeted compound in future experiments. This study is expected to enhance the understanding of metal-nonmetal interactions and provides useful information for constructing new organometallic compounds based on actinium metal atoms.

Actinide-Actinide Bonding: Electron Delocalisation and σ-Aromaticity in the Tri-Thorium Cluster [{Th(η8 -C8 H8 )(μ-Cl)2 }3 K2

The tri-thorium cluster [{Th(η8 -C8 H8 )(μ3 -Cl)2 }3 {K(THF)2 }2 ]∞ (Nature 2021, 598, 72-75) was reported to feature intriguing σ-aromatic bonding between the thorium atoms, a mode of metal-metal bonding unique in the actinide series. However, the presence of this bonding motif has since been challenged by others. Here, we computationally explore electron delocalisation in a molecular cluster fragment of [{Th(η8 -C8 H8 )(μ3 -Cl)2 }3 {K(THF)2 }2 ]∞ and examine its responses to an applied magnetic field using a variety of methods. We also discuss the importance of the choice of basis set for the Th atoms and issues regarding locating QTAIM bond critical points. When taken together, the computed data consistently suggest the presence of delocalised Th-Th bonding and Th3 σ-aromaticity.

Adsorption properties of black phosphorene for actinides U, Th, and Pu: A first‐principles study

AbstractDensity functional theory (DFT) calculations were carried out in this work to systematically investigate the adsorption properties of monolayer black phosphorene (BP) for actinide uranium (U), thorium (Th), and plutonium (Pu) atoms. More specifically, the linear response method was used and the HubbardUvalues of 2.97 and 2.61 eV were fitted describing the strong lattice point Coulomb interactions of the U and Pu 5forbitals, respectively. From the DFT + Ucalculations, it was demonstrated that the U, Th, and Pu atoms can be favorably adsorbed on the hollow sites of the BP surface, with an adsorption energy of 3.48, 4.93, and 0.98 eV, respectively. By analyzing the electronic structure, charge transfer, and highest occupied molecular orbital, it was revealed that the U and Th adatoms can induce the generation of impurity states within the band gap of BP and stabilize their adsorption by strongp‐dcoupling with the phosphorus atoms. In addition, from the electron–phonon coupling calculations, it was revealed that the temperature for the stable adsorption of the U and Th adatoms can reach as high as 500 and 673 K. By using the adsorption rate equation, the critical temperature for the adsorption–desorption transition of U and Pu adatoms was estimated to be 632 and 185 K, respectively, while the Th adatom did not tend to desorb. Our results clearly indicate that BP is an ideal adsorption and separation material for actinides with promising potential applications, such as uranium extraction from seawater.

The interplay of d and f orbitals in the chemistry of the early actinides: High spin versus low spin

Early actinides lie at the borderline between d- and f-block elements. Here we describe the coordination capabilities of thorium featuring characteristics from both blocks. Thus analysis of the recently synthesized monoanion [Cp3Th]− indicates a diamagnetic singlet d2f0 ground state for the central thorium(II) atom. In this species the trigonal (Cp3)3− ligand system provides a strong ligand field for the thorium d-orbitals accounting for the low spin of this system. This differs from the high spin unambiguous f-element analogue, [Cp3U]−. For the d0f0 thorium(IV) complex (η8-C8H8)2Th both π→d and π→f forward bonding is observed, where a comparison with (η8-C8H8)2U is given. This indicates that a borderline element such as thorium can exhibit either d- or f-block character according to the surrounding ligand field.

Chemical bonding between thorium and novel BN nanomaterials

We study the nature of chemical bonding of the thorium atom with novel BN-based nanomaterials: fullerenes B30N30, B12N8, B8N12, and the BN analog of coronene—B12N12H12, used as a representative molecular fragment of the two dimensional hexagonal BN-sheet. Our ab initio calculations are performed within the dispersion-corrected density functional approach with a hybrid exchange-correlation potential. The smallest 20-atom BN-fullerenes B12N8, B8N12 proposed by us are shown to be stable and should be observable experimentally. Thorium is found at the center of these structures pushing the outer shell of atoms farther away. The shape of the B12N8-cage in Th@B12N8 is conserved, while the shape of the B8N12 molecule in Th@B8N12 is largely deformed. The initially planar structure of B12N12H12 in the presence of thorium becomes corrugated, demonstrating pronounced off-plane displacements under the thorium atom. Other four-valent metals (Ti, Zr, and Hf) also cause off-plane displacements of B and N atoms albeit to a much smaller scale. In the 60-atom fullerene B30N30, which is the BN analog of C60, two conformations of Th@B30N30 are found: one is with thorium facing the hexagon with one B–B and one N–N covalent bonds and a second, lying 0.79 eV higher, with thorium close to the center of pentagon with one B–B covalent bond.

Влияние формы электродов на оптическое излучение плазмы кототкодугового разряда высокого давления в ксеноне

A short-arc high-pressure xenon discharge with a thoriated tungsten cathode (this is the reason for the presence of thorium atoms in the discharge gap) is investigated depending on the shape of the electrode surface. Based on the previously developed model, the electrokinetic characteristics and optical radiation of the plasma are calculated. It is shown that the shape of the electrode surface (the shape of the anode surface is considered in more detail) strongly affects, first of all, the electric field in the discharge gap, which, in turn, determines the plasma temperature and the spatial distributions of thorium atoms and charged particles (thorium and xenon ions). The resulting change in the electrokinetic characteristics significantly affects the optical radiation of the plasma, allowing the choice of the shape of the electrode surface to obtain the prevalence of radiation in the ultraviolet, visible, or infrared regions of the spectrum.

Thorium-thorium bonding marks actinide milestone

Bonds between actinide elements are extremely rare, with barely a handful identified in fleeting or exotic circumstances. Researchers have now created a fully fledged crystalline complex containing thorium-thorium bonds, synthesized and isolated under ordinary experimental conditions ( Nature 2021, DOI: 10.1038/s41586-021-03888-3 ). Stephen T. Liddle of the University of Manchester and colleagues made the new compound by combining a thorium precursor with a tetrasilyl cyclobutadiene dianion—a powerful reducing agent. This formed a complex containing a cluster of three thorium atoms flanked by cyclooctatetraenyl ligands and bridging chlorides. The dark-blue crystals decompose slowly at room temperature but remain stable at –35 °C. The researchers compared crystal structure data and spectroscopy and magnetic measurements with quantum chemical calculations and determined that the thorium cluster contains a three-center two-electron bond and that these delocalized electrons are σ aromatic. “It’s pretty much the last thing that anyone expected,” Liddle says. “It underlines to me

Theoretical insight into actinide monometallofullerene Th@C74 with four-electron-transfer characteristics

• Th@D 3 h (14246)-C 74 is theoretically revealed to be the most predominant candidate for the first time. • Four-electron transfer from thorium atom to D 3 h (14246)-C 74 carbon cage is theoretically confirmed. • Even with same electron-transfer as Sc 2 C 2 @ C 74 , significant difference on both stabilities and interaction mechanisms of Th/U @ C 74 is analyzed. • A strong covalent interaction between thorium atom and C 74 carbon cage exists. The stabilization performance of Th@C 74 series have been determined by using density functional theory methods combined with statistical thermodynamic analyses. Results indicate that the only isolated pentagon rule satisfied isomer Th@ D 3 h (14246)-C 74 possesses excellent thermodynamic stabilities. The frontier molecular orbital analysis demonstrates that four-electron-transfer from metal to D 3 h (14246)-C 74 cage occurs. Further interaction mechanisms of the X@C 74 (X = Th, U, Sc 2 C 2 ) revealed that, besides of electron-transfer, the interaction between metal and pentagon adjacency plays also an important factor determining relative stabilities of C 74 endohedral metallofullerenes. The covalent interactions between inner metals and C 74 cage should not be neglected.

Crystal stabilities and electronic properties of thorium silicide under ambient conditions and high pressures from a first-principles study

The thorium compounds are prospective candidates for the next generation nuclear materials. Using the first-principles and particle swarm optimization methods, we have investigated structures and physical properties of four atomic ratios of thorium and silicon hybrids under various ranges from ambient pressure to 200 GPa. A series of new phases have been predicted and thermodynamics, mechanical stabilities, elastic properties, electronic properties and chemical bonds of all the stable structures have been studied in details. Furthermore, we utilize potential energy surface to investigate the vibration property of Si2 dimer in Th3Si2. The result indicates that the Si2 dimer in Th3Si2 compound have the similar vibration property as a free standing Si2. This also means the silicon atoms do not have a strong interaction with thorium atoms in thorium silicide.

Local electrochemical deposition of thorium-229 targets and excitation of isomeric state by electron beam

The results of the study of local formation of thin-film coatings based on thorium oxide on SiO2/Si(111) surfaces by electrochemical deposition. It is shown that as a result of electrochemical deposition of thorium atoms from an acetone solution of Th(NO3)4 with the presence of water on the silicon surface, local formation of thorium compounds occurs. Chemical analysis of the composition of the samples obtained by XPS showed the presence of compounds based on thorium, silicon, oxygen and carbon. It is shown that annealing for 6 hours at 600? C in the atmosphere leads to the departure of carbon, and the formed film consists only of thorium and oxygen. It is shown that such a system can be promising for further studies of the nuclear low-lying isomer transition in the 229Th isotope under electron beam irradiation. The method of excitation of isomeric thorium-229 nuclei by irradiation of a solid-state target based on thorium silicate with an electron beam is considered. The process of generating secondary electrons with a significant increase in the multiplication coefficient for electrons with energies in the range from 1 keV to 25 keV is considered. The values of the output function of isomeric nuclei and the excitation cross section of an isomeric transition in inelastic scattering are obtained on the basis of numerical modeling and theoretical estimation.

Charge Properties of Thorium Implanted in Silicon Oxide

A study of thorium atoms implanted in silicon oxide was carried out within the density functional theory method. The charge properties of Th in the ThO2:nSiO2 and Th:nSiO2 compounds, where Th acts as an interstitial and substitutional impurity in cristobalite, have been studied. Geometric optimization of structures is carried out with allowance for electron-electron interactions, self-consistent distribution of electron density is investigated, and Bader effective charges are estimated.

Local Electrochemical Deposition of Nuclear Materials as a Method for Creating Miniature Solid-State Targets for Precision Measurements

The results of a study of the local formation of thorium oxide-based coatings on the SiO2/Si (111) surface during electrochemical deposition are presented. It was experimentally found that as a result of electrochemical deposition of thorium atoms from an acetone solution of Th(NO3)4 with the presence of water on the silicon surface, local formation of thorium compounds occurs. The results of the analysis of the chemical composition of the surface by the method of local XPS analysis show that these compounds are those based on thorium, silicon, oxygen, and carbon. After annealing for 6 h at 600°C in atmosphere, carbon completely disappears, and the formed cluster film seemingly consists only of thorium and oxygen. It is shown that this system is promising for future research on nuclear low-lying isomeric transition in the 229Th isotope under electron beam irradiation.

The Application of HEXS and HERFD XANES for Accurate Structural Characterisation of Actinide Nanomaterials: The Case of ThO2.

The structural characterisation of actinide nanoparticles (NPs) is of primary importance and hard to achieve, especially for non‐homogeneous samples with NPs less than 3 nm. By combining high‐energy X‐ray scattering (HEXS) and high‐energy‐resolution fluorescence‐detected X‐ray absorption near‐edge structure (HERFD XANES) analysis, we have characterised for the first time both the short‐ and medium‐range order of ThO2 NPs obtained by chemical precipitation. By using this methodology, a novel insight into the structures of NPs at different stages of their formation has been achieved. The pair distribution function revealed a high concentration of ThO2 small units similar to thorium hexamer clusters mixed with 1 nm ThO2 NPs in the initial steps of formation. Drying the precipitates at around 150 °C promoted the recrystallisation of the smallest units into more thermodynamically stable ThO2 NPs. HERFD XANES analysis at the thorium M4 edge, a direct probe for f states, showed variations that we have correlated with the breakdown of the local symmetry around the thorium atoms, which most likely concerns surface atoms. Together, HEXS and HERFD XANES are a powerful methodology for investigating actinide NPs and their formation mechanism.

Density Functional Theory Study of Oxygen Adsorption and Dissociation on Lower Miller Index Surfaces of ThN

Thorium nitride (ThN), a promising metallic nuclear fuel with higher actinide density and higher thermal conductivity, is investigated as a candidate nuclear fuel for the next generation of reactors. In this article, a systematic investigation of the adsorption mechanism of molecular (O2) and dissociated oxygen (O–O) for several configurations, on clean ThN (100), (110), and (111) surfaces, was performed using the density functional theory calculations. To elucidate the interfacial interaction of ThN with O2, an extensive examination of the relaxed adsorption structures, adsorption energies, electronic structure, changes in bond lengths, and the Bader charge transfer were conducted. The energetics and the most stable adsorption configurations of O2 at higher coverages are also reported. The results obtained indicate that the (100) surface is the most stable with a surface energy of 0.98 J/m2, followed by (111) and (110) with an energy of 1.68 J/m2 and 1.77 J/m2 respectively. The relaxed adsorption structures revealed that O2 has a stronger affinity for the thorium (Th) atom than the nitrogen (N) atom. The calculated interatomic bond distances of the Th–O bond was found to be consistent with the measured bond length of thorium oxide (ThO2), indicating the formation of the thorium oxide layer on the surface of ThN. Among all the different configurations considered on the (100) surface, only the O2 molecule placed at the Th–N bridge site has undergone spontaneous dissociation, whereas, in the case of (111) surface, the O2 molecule placed at the bridge site and the side-on Th site has undergone spontaneous dissociation. However, the O2 molecule adsorbed on the (110) surfaces of ThN requires activation energy for dissociation to occur. These observations in ThN surfaces are in stark contrast with the previously reported cases of uranium nitride (UN) and α-U (001), where all the configurations have undergone a spontaneous dissociation. Oxidation behavior of ThN is a critical issue that needs to be understood before researchers can push for its use in commercial reactors. In line with this thought, a molecular-level understanding of the surface chemistry of ThN in an oxygen environment is expected to provide information on the oxidation mechanisms.

Chemical bonding between thorium atoms and a carbon hexagon in carbon nanomaterials.

We explore the unusual nature of chemical bonding of thorium atoms with a ring of six carbon atoms (hexagon) in novel carbon materials. Our ab initio calculations of Th-based metallofullerenes (Th@C60 and Th@C20) and Th bound to benzene or coronene at the Hartree-Fock level with the second order perturbation (MP2) correction accounting for the van der Waals interactions demonstrate that the optimal position of the thorium atom is where it faces the center of a hexagon and is located at a distance of 2.01-2.07 Å from the center. For Th encapsulated in C60 it is found at 2.01 Å, whereas the other local energy minima are shifted to larger energies (0.22 eV and higher). Inside C60 the highest local minimum at 1.17 eV is observed when Th faces the center of the five member carbon ring (pentagon). Based on our calculations for Th with benzene and coronene where the global minimum for Th corresponds to its position at 2.05 Å (benzene) or 2.02 Å (coronene) from the hexagon center, we conclude that a well pronounced minimum is likely to be present in graphene and in a single wall carbon nanotube. The ground state of Th is singlet, and other high spin states (triplet and quintet) lie higher in energy (>1.62 eV). We discuss a potential use of carbon nanomaterials with the 229Th isotope having its nuclear transition in the optical range, for metrological purposes.