Californium (Cf) is currently the heaviest element accessible above microgram quantities. Cf isotopes impose severe experimental challenges due to their scarcity and radiological hazards. Consequently, chemical secrets ranging from the accessibility of 5f / 6d valence orbitals to engage in bonding, the role of spin-orbit coupling in electronic structure, and reactivity patterns compared to other f-elements, remain locked. Organometallic molecules were foundational in elucidating periodicity and bonding trends across the periodic table, 1-3 with a 21 st century renaissance of organometallic thorium (Th) through plutonium (Pu) chemistry [4][5][6][7][8][9][10][11][12] , and to a smaller extent americium (Am) 13 , transforming chemical understanding. Yet, analogous curium (Cm) -Cf chemistry has lain dormant since the 1970s. Here, we revive air-/moisture-sensitive Cf chemistry through the synthesis and characterization of [Cf(C5Me4H)2Cl2K(OEt2)]n from two milligrams of 249 Cf. This bent metallocene motif, not previously structurally authenticated beyond uranium (U) 14,15 , contains the first crystallographically characterized Cf-C bond. Analysis suggests the Cf-C bond is largely ionic with a small covalent contribution.Lowered Cf 5f orbital energy vs. Dy 4f in the colourless, isoelectronic, and isostructural [Dy(C5Me4H)2Cl2K(OEt2)]n results in an orange Cf compound, contrasting with light green typically associated with Cf compounds [16][17][18][19][20][21][22] . MainThe first actinide (An) metallocene, uranocene, [U(C8H8)2], reported in 1968 2,23 , featured two aromatic (C8H8) 2rings sandwiching the U 4+ ion and demonstrated that non-actinyl molecules are capable bonding that is intermediate between covalent transition metals and ionic lanthanide ions 24 . Recent organometallic and nonaqueous Th and U chemistry has exploded 12 , redrawing the boundaries of known oxidation states 25 , multiplybonded molecular motifs 26 , small molecule reactivity 4 , and covalency/electronic structure trends 5,8,24,27 .Analogous advances with the heaviest available transuranium actinides are limited, although there are some, such as the deep red putative CfCp3, that contrasted with the light green of most other Cf compounds 22 . While several AnCp3 (An = Th, U -Cf) 6,9,22,28,29 molecules have been synthesized and/or examined by theory 30,31 , none have been authenticated beyond Pu 6,9,11 . Related bent Th and U metallocenes like [M(C5R5)2Xn] (X = anion; n = 1, 2) have played a major role in improving our understanding of actinide electronic structure and
Efficient predictive capabilities are essential for the actinide series since regulatory constraints for radioactive work, associated costs needed for specialized facilities, and the short half-lives of many actinides present great challenges in laboratory settings. Improved predictive accuracy is advantageous for numerous applications including the optimization and design of separation agents for nuclear fuel and waste. One limitation of calculations in support of these applications is that the large variations observed from predictions obtained with currently available methods can make comparisons across studies uncertain. Benchmarking currently available computational methodologies is essential to establish reliable practices across the community to guarantee an accurate physical description of the systems studied. To understand the performance of a variety of common theoretical methods, a systematic analysis of differences observed in the prediction of structural characteristics, electron withdrawing effects, and binding energies of [An(NO 3 )] 2+ (with An = Ac to Lr) in gas and aqueous phases is reported. Population analysis obtained with Mulliken and Löwdin reflect a large dependence on the level of theory of choice, whereas those obtained with natural bond orbital show larger consistency across methodologies. Predicted stability across the actinide series calculated with coupled cluster with perturbative doubles and triples at the triple ζ level is equivalent to the one obtained when extrapolated to the complete basis set limit. The ground state of [Fm(NO 3 )] 2+ and [Md(NO 3 )] 2+ is predicted to have an electronic structure corresponding to An III state in gas and An IV in aqueous phase, whereas the ground state of [An(NO 3 )] 2+ (with An = Ac to Es, Lr) presents an electronic structure corresponding to An IV in the gas and aqueous phase. The compounds studied with No in gas and aqueous phase present a preferred No III state, and the Lr compounds did not follow trends predicted for the rest of the actinide series, as previously observed in studies regarding its unusual electronic structure relative to its position in the periodic table.
Eu2+-activated strontium iodide is an excellent single crystal scintillator used for gamma-ray detection, and significant effort is currently focused on the development of large-scale crystal growth techniques. A new approach of molten-salt pumping or so-called melt aging was recently applied to optimize the crystal quality and scintillation performance. Nevertheless, a detailed understanding of the underlying mechanism of this technique is still lacking. The main purpose of this paper is to conduct an in-depth study of the interplay between microstructure, trap centers, and scintillation efficiency after melt aging treatment. Three SrI2:2 mol % Eu2+ single crystals with 16 mm diameter were grown using the Bridgman method under identical growth conditions with the exception of the melt aging time (e.g., 0, 24, and 72 h). Using energy-dispersive X-ray spectroscopy, it is found that the matrix composition of the finished crystal after melt aging treatment approaches the stoichiometric composition. The mechanism responsible for the formation of secondary phase inclusions in melt-aged SrI2:Eu2+ is discussed. Simultaneous improvement in light yield, energy resolution, scintillation decay-time and afterglow is achieved in melt-aged SrI2:Eu2+. The correlation between performance improvement and defect structure is addressed. The results of this paper lead to a better understanding of the effects of defect engineering in control and optimization of metal halide scintillators using the melt aging technique.
Triplet sets of replaceable graphite rod collector probes (CPs), each with collection surfaces on opposing faces and oriented normal to the magnetic field, were inserted at the outboard mid-plane of DIII-D to study divertor tungsten (W) transport in the Scrape-Off Layer (SOL). Each CP collects particles along field lines with different parallel sampling lengths (determined by the rod diameters and SOL transport) giving radial profiles from the main wall inward to R-Rsep ∼ 6 cm. The CPs were deployed in a first-of-a-kind experiment using two toroidal rings of distinguishable isotopically enriched, W-coated divertor tiles installed at 2 poloidal locations in the divertor. Post-mortem Rutherford backscatter spectrometry of the surface of the CPs provided areal density profiles of elemental W coverage. Higher W content was measured on the probe side facing along the field lines toward the inner target indicating higher concentration of W in the plasma upstream of the CP, even though the W-coated rings were in the outer target region of the divertor. Inductively coupled plasma mass spectroscopy validates the isotopic tracer technique through analysis of CPs exposed during L-mode discharges with the outer strike point on the isotopically enriched W coated-tile ring. The contribution from each divertor ring of W to the deposition profiles found on the mid-plane collector probes was able to be de-convoluted using a stable isotope mixing model. The results provided quantitative information on the W source and transport from specific poloidal locations within the lower divertor region.
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