[en] Full text: The multiple probable oxidisation states of actinide elements can lead to their molecular anions to result in complicated yield patterns from a Cs+ sputter ion source. For actinides AMS, two methods can be practiced in order to concentrate the yields into just one or two anion species. The present common practice has been to deprive the availability of oxygen in the sputter targets, so that the mono-oxide anions are produced with good or applicable ionization efficiencies. However, this method requires the typical 860-type Cs+ sputter ion sources to be operated with relatively high Cs+ fluxes, a condition that not all such sources in use can be operated with a lasting stability. On the contrary, with low Cs+ fluxes, good or applicable ionization efficiencies can also be achieved for producing element-specific poly-atomic oxide, oxyfluoride, or fluoride anions of actinides, if the sputter targets are aided with dominantly oxidizing or fluorinating matrices. We describe a systematic study of such phenomena using ZnO and FeF₃ to form the respective oxidizing and fluorinating matrices. It was found that using element-specific polyatomic atomic fluoride anions and FeOxHy+FeF₃ sputter targets, not only all rare actinides could be measured with low detection limits matching those by mono-oxides, but also with the available ionization efficiencies fully utilized within a shorter time. In addition: sample chemistry is simplified without the need for high temperature calcination; the lack of triply charged hydride ions and mono-isotopic fluorine help in achieving better ²³⁶U/²³⁸U abundance sensitivity using just one large analyzing magnet in the high energy system of AMS; scatter interferences of ²³²ThF₆- to ²³¹PaF₆- detection, and ²³⁸UF₄- to ²³⁷NpF₄- and ²³⁹PuF₄- detection, are naturally lower by an order of magnitude because Th and U molecular anions are concentrated into ThF₅- and UF⁵-; and finally, measurement background is two orders of magnitude less sensitive to any long-lasting ion source memories. In conclusion, the use of element-specific poly-atomic fluoride anions and FeOxHy+FeF₃ sputter targets is a viable alternative approach to actinides AMS, especially when low-output Cs+ sputter ion sources are used.

[en] Full text: The cesium-sputter negative-ion source is a fundamental component of accelerator mass spectrometry studies. Improvements in ion current and output emittance allow for higher precision measurements and potential for new applications. The High Voltage Engineering Europa SO-110C ion source has been modeled using Integrated Engineering Software’s Lorentz 2E ion trajectory simulation software. This software includes the mutual space charge interactions between the incoming cesium ions from their production in the ionizer and the outgoing negative ion beam from the target (cathode). Simulations examined the effects of changing the geometry of various source components, electrode potentials, ion currents, position of the target and negative ion mass. The simulations demonstrated that, as the cesium current is increased, the cesium beam broadens by its own space charge repulsion. This affects its focusing and distribution on the sample material. It is important that the cesium cover the outer proportions of the sample well for best usage of the material and stability of the outgoing negative ion beam. Changes in geometry and electrode potentials can mitigate this effect. Informed by these simulations, experiments at the A.E. Lalonde Accelerator Mass Spectrometry Laboratory (Lalonde) recessed the target in incremental 1 mm steps (targets were translated away from the ionizer along the axis of symmetry). Custom target bases were machined to facilitate these recesses without the need to modify the target pressing procedure. The abundant isotopes were measured using the post-accelerator offset Faraday Cups and rare isotopes at the gas ionization detector to compare outputs at various settings. These tests were first run at routine ¹⁴C measurement settings (6 kV target-ionizer potential difference, 115°C cesium oven temperature) on graphite blanks. At these settings, a target recess of 1 mm gave the most stable output with the highest usage of sample material. A second experiment, using targets made from a ¹⁰Be standard, expanded this study by increasing the cesium oven temperature (and hence cesium current) incrementally from 130-140°C, while also varying the target-ionizer potential difference (4-11 kV). This multi-dimensional study gave several promising settings, resulting in the most precise measurement of ¹⁰Be performed to date at Lalonde. A demonstration of key simulations and a comparison with experimental results will be presented.

[en] Adsorption of Pb"2"+ ion by a tartrate intercalated MgAl layered double hydroxides (MgAl-TA LDHs) was studied. The adsorption isotherms and kinetics were investigated as a function of various experimental parameters using batch adsorption experiments. The results indicated that the adsorption isotherm was well described by Sips model. The kinetic adsorption data were fitted well to the pseudo-second-order kinetic equation. The adsorption of Pb"2"+ was controlled mainly by the chemical process combined with intraparticle diffusion. Parameters of adsorption thermodynamic suggested that the interaction of Pb"2"+ adsorbed by MgAl-TA LDHs adsorbents was thermodynamically spontaneous and endothermic.

[en] Let X be a projective smooth holomorphic Poisson surface, in other words, whose anti-canonical bundle is effective. We show that moduli spaces of certain Bridgeland stable objects on X are smooth. Moreover, we construct Poisson structures on these moduli spaces.

[en] It is anticipated that accelerator mass spectrometry (AMS) assay of actinides, in particular ²³⁶U and ²³³U in uranium and ²²⁹Th and ²³⁰Th in thorium, will become valuable for identifying the previous human use of such materials. A discussion is included concerning the possibility of using ²³⁶U as a thermal neutron monitor having an integration period of up to 100 million years using AMS to fragment all molecular interferences. Using the detection of ²³⁶U/²³⁸U at levels below 10^-13 as a design goal, a description is provided of the geometry of a proposed broad-range precision AMS spectrometer that includes a 3 MV terminal tandem accelerator and a terminal gas stripper. The elimination of interfering molecular ambiguities and backgrounds is discussed. A post-acceleration stripping procedure for M/Q ambiguity elimination is presented. A novel acceleration and fragmentation protocol is also described where molecular fragmentation is carried out at ground, outside of the tandem, rather than by stripper fragmentation at high voltage. It is shown that this new procedure simplifies AMS especially for heavy elements and leads to the possibility of using smaller tandems and analysis components. Multiple scattering during terminal charge changing is considered together with its effects upon accuracy and efficiency. (orig.)

[en] Field grading composite dielectrics with good nonlinear electrical properties can function as smart materials for electrical field control in a high-voltage apparatus. Besides the well-documented nonlinear conducting behavior, the field-dependent effective permittivity of field grading composites were also reported; however, in-depth research on the mechanism and influencing factors of this nonlinear permittivity are absent. This paper theoretically discusses the origin of the nonlinear effective permittivity, and the mechanism is illustrated through the waveform analysis of the nonlinear response of ZnO microvaristor/silicone rubber composites under a pure AC field. The field-dependent effective permittivity and loss property of the ZnO composites are measured by a dielectric spectrometer in both DC and AC fields under different frequencies. Through comparison of measurement results and theoretical models, the influence of the filler concentration, frequency, and time domain characteristics of the applied field on the nonlinear permittivity of the field grading composites are well explained. This paper provides insight into the nonlinear permittivity of field grading composites, and will be helpful for further tuning the performance of field grading composites. (paper)

[en] The necessity to use negative ions for injection into AMS systems which use tandem accelerators has, from its beginning, led to the use of molecular anions (negative ions) to inject the analyte atom. This strategy is required for those elements, typically metals, which have weak binding of an electron to the neutral atom and so produce very low (nA or less) beams from a sputter source. Early work used oxide beams, for example BeO [1], and oxides continue to be commonly used. While oxides provide stable target materials and beams, they are electrically insulating, so require mixing with a conducting binder. They also require powerful ion sources to generate usable currents and the presence of 3 oxygen isotopes can, in some cases, cause ambiguities in the beam that is mass-selected for injections. In 2009, Zhao et al. [2] published the results of an extensive investigation of molecular anions using fluorine, covering much of the periodic table. Not only is fluorine a mono-isotopic element, but the binding properties of molecular fluorine anions show a stoichiometric relationship which can provide useful isobar discrimination.

[en] The construction of a Z-scheme photocatalytic system is significant in realizing efficient water splitting for hydrogen (H${}_2$) evolution. Herein, a novel donor-acceptor covalent organic polymer (COP) is introduced to construct a COP-ZnIn${}_2$S${}_4$ (ZIS) heterostructure via in situ condensation reaction. The COP-ZIS heterostructure with platinum (Pt) as cocatalyst delivers a high hydrogen evolution rate of 5.04 mmol g${}^{-<!--\; ???\; -->1}$ h${}^{-<!--\; ???\; -->1}$, which is 16 and 3 times higher than ZIS and Pt/ZIS, respectively. The built-in field between the highest occupied molecular orbital of COP and the valence band (VB) of ZIS forms a Z-scheme heterostructure, realizing efficient charge separation. Based on density functional theory calculations, the porphyrin molecule in COP act as electron donor that provides compensating electrons to ZIS. The cocatalyst boosts the utilization of electrons in ZIS. The rate-limiting steps for H${}_2$ evolution with ZIS are overcome by improving charge separation with the Z-scheme heterostructure and speeding up the reaction with cocatalyst. Therefore, the COP-ZIS heterostructure with Pt exhibits optimized H${}_2$ evolution. This study will inspire to construct novel organic and inorganic Z-scheme photocatalysts for efficient green energy production. (© 2022 Wiley‐VCH GmbH)

[en] Full text: One of the most important tasks in the design and construction of ultra-low background experiments is the radioassay of the materials used. This requires the selection of the materials and enables the calculation of expected detector background. The ASTREA project (Accelerator mass spectrometry Survey of Trace Radionuclides for Experiments in Astroparticle physics) addresses AMS radioassay challenges for a few rare event experiments. Some examples are nEXO, which is searching for neutrinoless double beta decay; and NEWS-G and DarkSide, which are attempting to directly detect dark matter. This project, led by the André E. Lalonde AMS Laboratory (AEL-AMS) at the University of Ottawa, is performed in collaboration with Carleton University, Queens University and University of Alberta. The main focus of the project is screening Pb-210 in various detector construction materials, with emphasis on low background copper and high-performance polymers. We have studied the possibility of using 2 different materials for the AMS measurements: lead fluoride (PbF₂) and lead oxide (PbO) targets, producing respectively (PbF₃)- and (PbO₂)- ions on the LE side. In both cases, the ²¹⁰Pb/²⁰⁶Pb blank ratio is in the 1e-14–1e-13 range. Measurements on 1-2 g Kapton films have established upper limits in the range 850-2500 mBq/kg at 90% C.L. Future ASTREA activities will focus on the Pb-210 assay in acrylic, which is considered for future low background dark matter detectors. Previous best results, obtained in 2014 by γ-counting 2 kg of acrylic, have established an upper limit for the Pb-210 concentration of 0.3 mBq/kg. Our proposed method, using AMS, should provide a limit of detection in the 0.01-0.1 mBq/kg range. Other important study looks at the Pb-210 contamination in the electroformation process of the copper for the NEWS-G and nEXO detectors. For the Pb-210 concentration in the copper, we estimate a limit of detection in the 0.3-1.0 mBq/kg range.

[en] Xi'an Accelerator Mass Spectrometry (Xi'an-AMS) has been put into routine operation since August, 2006. The main instrument -3 MV accelerator mass spectrometer, has performed steadily and reliably. More than 2741 samples were analyzed, which included "1"4C, "1"0Be, "2"6Al and "1"2"9I. About 50% of the samples were submitted by the outside users. In addition, to further improve the performance and efficiency of the system, an insertion head of the ion source was redesigned and the control system was upgraded considerably, based on collaboration with High Voltage Engineer of Europe (HVEE). The measurement results show that the new source head runs more steadily and there is little memory effect on "1"4C measurement. (authors)