Nuclear Analysis最新文献

Two-dimensional (2D) non-van der Waals hematene has increasingly attracted attention in the applications of photocatalysis, spintronic devices, and magnetic storage media. Mechanical properties as well as magnetic and electronic properties tuned via strain in two-dimensional non-van der Waals Fe-terminated (hematene-1) and O-terminated hematene (hematene-2) have been systematically studied using the first principles density functional theory. The stress-strain relationships for 2D hematene-1 and hematene-2 demonstrate the influence of biaxial strain is larger than that of uniaxial strain, and under uniaxial strain, the stress-strain relationships transform from the isotropic and linear elastic behavior under small strain to the anisotropic and nonlinear response under large strain. For hematene-1 under uniaxial and biaxial strain and hematene-2 under biaxial strain, the magnetic moments of Fe1 and Fe2 atoms increase monotonically with applied strain, while for hematene-2 under uniaxial strain, the magnetic moment of Fe1 atom first decreases and then increases with applied strain, and the case is opposite for Fe2 atom. For hematene-1, the band gap decreases with increasing strain from −10% to 7%, while for hematene-2 under uniaxial strain, the spin up band gap decreases with increasing strain, and the case is opposite for the spin down band gap. The present work not only provides a basic understanding of the mechanical properties of 2D hematene but also demonstrates its magnetic and electronic properties tuned by strain engineering for the potential possibility in both spintronic and catalytic applications.

Porous CeO₂ has been of great interest recently, due to its great catalytic efficiency in splitting CO₂ into CO and O₂. Porous CeO₂ microspheres are the key to scaling up such reactions in the fluidized-bed solar thermochemical reactors. In this paper, we report the processing and CO₂ splitting performance of porous ceria microspheres. To fabricate the porous ceria microspheres, homogenous cerium-based sol-gel precursors were synthesized from cerium acetate. The acrylamide (AM) was used as both solidification and pore-generation agent. The polymerization of acrylamide facilitated the conversion of liquid droplets to solid gel microspheres. The optimal AM content was around 20 wt%, ensuring both sufficient porosity and the integrity of the ceria microspheres after thermal decomposition. After heat treatment at 1500 °C for 1 h, porous CeO₂ microspheres were obtained, with an average diameter of ∼800 μm and surface area of 2.9 m²/g. These microspheres had high porosity and good sphericity. The CO₂ splitting performances of these microspheres were characterized using thermogravimetric analysis (TGA). During the thermal cycles between 1000 and 1400 °C, the O₂ yield of porous ceria microspheres was 49 μmol/g, and the CO yield was 88 μmol/g. Compared with porous ceria granules of particle size of ∼800 μm, the porous ceria microspheres exhibited higher O₂ and CO production yields. After thermochemical cycles, the microspheres were not sintered together, and the surface area was slightly reduced to 2.7 m²/g.

A method combining particle-induced X-ray emission spectrometry (PIXE) and elastic backscattering spectrometry (EBS) was used to calibrate the PIXE system at Peking University. The selected thin standard samples were typically 50 μg/cm² and the thicknesses of two thick standard samples are 3 mm. The calibration of PIXE system was divided into the calibration curve measurement of thin standard samples and the external standard method of thick standard samples. Both thin and thick samples cover the commonly used PIXE X-ray energy range 1.4–18.0 keV. GUPIXWIN introduces an Instrument factor H to describe the calibration process. It is found that the measured H(Z) curve can be approximated as a Z-independent line with an average value of $3.30\times {10}^{-4}$. The deviation of multiple measurements of a single element is between 0.42% and 4.75%. For thick samples, the incident particles are protons and ³He⁺, a H value of $\left(4.97\pm 0.01\right)\times {10}^{-4}$ was obtained.

The nanostructured Er₂O₃ thin films implanted by Helium (He) were prepared by magnetron sputtering under different He partial pressure. The creep properties of the Er₂O₃ films under different temperatures ranging from ambient temperature to 450 °C were investigated systematically by nanoindentation measurements. The morphology and microstructure of the films were determined by a scanning electron microscope (SEM) and an X-ray diffractometer (XRD), respectively. The effects of He on the creep properties of the Er₂O₃ film were discussed by using a slope ($d\dot{\epsilon }/d\sigma$) of the creep rate stress curve at the steady-state creep stage. The results show that the crystallinity of the films became weak with the He partial pressure. Furthermore, the implanting He has a strong impact on the creep resistance of the Er₂O₃ thin films.

The transparency of scintillator screen has always been an important factor restricting the imaging performance. Here we present an innovative strategy, by combining the gel glass with GOS:Tb, F, we fabricated GOS:Tb, F/gel glass scintillation screen for effectively improvement of transmittance. The transmittance of the scintillator screen is ≥ 55% in the visible region. Thereafter, the relationship between the luminescence properties of the scintillator screen and the X-ray voltage and current is discussed in detail. In addition, the resolution of the scintillator screen under X-ray is 10 lp/mm, which may provide a promising application strategy in X-ray imaging.

Stability constants and enthalpies of N-methylethylenediamine-N,N′,N'-triacetic acid (MEDTA, denoted as H₃L) complexes with uranyl were measured using potentiometry and microcalorimetry, I = 1.0 mol L⁻¹ NaClO₄ solution at 25 °C. Thermodynamic analyses revealed three U(VI)/MEDTA complexes: UO₂(HL), UO₂L⁻, and UO₂(OH)L²⁻. The results showed that the complex formation of UO₂L⁻ (UO₂²⁺ ​+ ​L³⁻ = UO₂L⁻) is endothermic and driven solely by entropy. MEDTA in the UO₂L⁻ complex is a tetradentate and coordinates with U(VI) along the ethylenediamine backbone. Stability constant of mononuclear uranyl complex with MEDTA (UO₂L⁻) is lower than UO₂²⁺/EDDA complex but higher than UO₂²⁺/HEDTA complex, indicating that dangling acetate arm of MEDTA or hydroxyethyl group of HEDTA would lower the stability.

Nanosecond laser irradiation damage of optical films is one of the main factors to limit the output power when the high power solid laser system is used to drive inertial confinement nuclear fusion. In this review, taking SiO₂ and HfO₂ antireflection films as examples, the physical mechanisms of nanosecond laser irradiation damage of optical films were summarized from two aspects, i.e., numerical simulation studies and experimental investigations, including thermal melting damage, stress damage and plasma damage during irradiation. Based on the current research and difficulties in the field of irradiation damage of optical films, a brief outlook is given here, which may be helpful to improve the output power and operation stability of laser fusion devices in the future.

In a deep geological repository system, the presence of clay colloids in the geological disposal medium is considered to be a potential factor promoting nuclide migration. In this study, Gaomiaozi bentonite colloid (GMZC) was extracted using the gravity sedimentation method, and its interaction with U(VI) at neutral pH was studied. Small angle X-ray scattering (SAXS), X-ray photoelectron spectroscopy (XPS), dynamic light scattering, and other characterizations methods were used to analyze and observe the microstructure and agglomeration morphology of the bentonite colloidal particles before and after the reaction with U(VI) at the macro-meso-microscopic level. The XPS results indicate that the U(VI) reacted with the Si–O and Al–O on the GMZC particle surfaces at room temperature, and the hydrolyzed product of the U(VI) covered the colloidal surfaces in the neutral water environment, resulting in a decrease in the absolute zeta potential (from ∼31 mV to ∼19 mV). The hydrodynamic diameter of the colloidal particles did not change significantly (∼336 nm–∼360 nm), but the small-angle scattering data revealed that the fractal dimension was larger after the reaction (∼2.8–∼3.1), indicating particle agglomeration. About 14% of the GMZC particles were precipitated after reacting with the U(VI). When the temperature was increased to 55 °C and 85 °C, the precipitation did not change significantly, but the fractal dimension of the mixed system increased (from ∼3.1 to ∼3.6), and the d₀₀₁ peak was not observed in the SAXS results. When the temperature was decreased by 25 °C, the hydrodynamic diameter of the zeta potential and SAXS image both returned to the level before the temperature increase, indicating that the unstable change in the colloidal system caused by the temperature increase was reversible.

The binding strengths of ligand 2,2ʹ-bipyridine-6-carboxylate (BiPCA) and 1,10-phenanthroline-2-carboxylate (PhenCA) with trivalent actinides (An) like Am(III) and Cm(III), and lanthanides (Ln) like Nd(III), Sm(III), and Eu(III) were investigated by solvent extraction, potentiometry, and crystallography. Both ligands exhibit good actinides selectivity over lanthanides and radius selectivity for intragroup Ln(III) or An(III). In comparison, PhenCA is more prominent than BiPCA in these capabilities. Single crystal structures of the Nd(III)/Eu(III) with BiPCA and PhenCA illustrate that BiPCA, as well as PhenCA, is tridentate and chelates with Nd(III)/Eu(III) by two aromatic N-donors and a carboxyl O-donor. PhenCA exhibits shorter coordination bonds to the central atom than BiPCA, in agreement with the fact that in solution PhenCA behaves stronger binding strength than BiPCA to the same lanthanide cation. However, for the lanthanide complexes with the same ligand, no regular trend of the coordination bonds has been observed between Nd(III) and Eu(III).

With the development of pulsed spallation sources of neutrons in recent years has come the possibility to generate intense beams of higher energy than possible at reactor sources. This has enabled neutron total scattering methods to develop significantly for studies across a wide range of application areas. In this article we will review the background theory for analysis of total scattering in terms of the pair distribution function, we will review modern facilities and instrumentation, we will describe a range of analysis methods, and finally we will present a number of examples of recent work that illustrate many of the ideas discussed here.