K-shell Research Articles

Detailed analysis of banded chorus gap formation by an electron shell distribution

In a recent paper [K. Min, Phys. Plasmas 30, 012904 (2023)], the formation of the banded chorus with a gap in intensity at half the electron cyclotron frequency (Ωe/2) is demonstrated by particle-in-cell simulations including an isotropic shell distribution at an intermediate energy. This follow-up study focuses on the phase space density (PSD) hill formation process and its role in the chorus wave damping at the gap. We first show that phase-trapped particles closely follow single wave characteristics in momentum space. This means that the formation of either PSD hole or hill is primarily determined by the temperature anisotropy, T⊥/T‖, of an initial distribution function. The critical value of T⊥/T‖ increases (decreases) for a higher (lower) resonant frequency. We then revisit the recent banded chorus simulations to investigate how the presence of an isotropic shell distribution self-consistently affects chorus wave evolution at the gap. Initially, with an increasing wave frequency, more and more shell electrons get trapped and a PSD hill is formed. The enhanced PSD hill counteracts wave growth driven by phase-trapped anisotropic electrons and subsequently reduces wave amplitude. The weakened wave self-consistently feeds back to the particle trapping, ultimately suppressing both the PSD hole and hill. By the time the wave frequency reaches about 0.45Ωe, the gyro-phase structure of the electron distribution becomes much less organized. In some cases, however, the wave growth at the upstream source region can be strong enough that waves still manage to go through the gap frequency, suggesting that additional process(es) should likely be accompanied.

Origin of medium-range atomic correlation in simple liquids: Density wave theory

The atomic pair-distribution function of simple liquid and glass shows exponentially decaying oscillations beyond the first peak, representing the medium-range order (MRO). The structural coherence length that characterizes the exponential decay increases with decreasing temperature and freezes at the glass transition. Conventionally, the structure of liquid and glass is elucidated by focusing on a center atom and its neighboring atom shell characterized by the short-range order (SRO) and describing the global structure in terms of overlapping local clusters of atoms as building units. However, this local bottom-up approach fails to explain the strong drive to form the MRO, which is different in nature from the SRO. We propose to add an alternative top-down approach based upon the density wave theory. In this approach, one starts with a high-density gas state and seeks to minimize the global potential energy in reciprocal space through density waves using the pseudopotential. The local bottom-up and global top-down driving forces are not mutually compatible, and the competition and compromise between them result in a final structure with the MRO. This even-handed approach provides a more intuitive explanation of the structure of simple liquid and glass.

Achieving strength-ductility synergy in metallic glasses via electric current-enhanced structural fluctuations

Structural applications of metallic glasses are limited by their room-temperature brittleness and strain-softening, associated with the extreme localization of plastic flow in shear bands. Herein, we alleviate this dilemma by the structural fluctuation induced by electric currents, achieving simultaneous improvement of strengths, compression plasticity, and strain hardening capacity. The electric current enhances the structural fluctuations at the atomic scale, introducing more soft zones while densifying their surroundings, which differs from previously reported rejuvenation strategies. This unique structural pattern featuring soft zones surrounded by hard zones leads to extensive sprouts and interactions of shear bands, capturing substantial atoms to participate in the deformation. The plausible mechanism behind the electric current-influenced dynamic evolution of amorphous clusters is proposed. Electric current introduces interatomic electrostatic forces between shell atoms of amorphous clusters through charge transfer. This force decreases the coordination of Zr- and Cu-centered clusters and increases the Al-centered icosahedra in the glassy matrix. Differential evolution of clusters under electric currents enhances atomic structural fluctuations and originates from the cohesion mechanism determined by electron distribution. These findings are suggestive of vanishing room-temperature brittleness and shed atomic-scale light on modulations of the structure and properties of metallic glasses by electric currents.

Shed light on new growth pattern in rapid solidified Ta metal: MD simulation, DFT calculation and CALYPSO search

Aiming at the micro-structures of rapid solidified Ta system under cooling rate of 1×1010 K/s, the lowest-energy and meta-stable geometric structure of Tan (n = 19–30) clusters are systematically investigated via MD simulation, DFT calculation and CALYPSO search. It is revealed that the ground-state geometric structure of free Ta clusters plays a significant role in determining its solidified atomic structures and evolution laws in the early stage of nucleation. We explained why the hexagonal close packed (hcp) atomic clusters (Ta22) dominate the solid state of Ta when cooled at a rate of 1 × 1010 K/s. And found that the coexistence of slightly distorted icosahedral (Ta13) and hcp clusters (Ta22) at 300 K is due to the high energy stability of free Ta26–C2v (B) cluster. The larger size of Ta clusters with a perfect closed-shell geometric structure plays a key role in energetic effects, as demonstrated by their thermodynamic stability in terms of binding energy. Additionally, electronic structure stability is achieved when there are fewer electrons on the Fermi level (N(EF)), resulting in Ta atomic clusters that exhibit higher energetic stability and lower chemical activity. Our analysis of the interaction between different atoms in Ta clusters revealed that stronger electronic interactions of central(c)-central(c) and central(c)-shell(s) atoms contribute to the higher energy and chemical stability. Finally, we provide insights into understanding the growth patterns of nucleation in liquid metals through an examination of geometric and electronic structures of free Ta cluster.

Mediating Photochemical Reaction Rates at Lewis Acidic Rare Earths by Selective Energy Loss to 4f-Electron States.

Manifesting chemical differences in individual rare earth (RE) element complexes is challenging due to the similar sizes of the tripositive cations and the corelike 4f shell. We disclose a new strategy for differentiating between similarly sized Dy3+ and Y3+ ions through a tailored photochemical reaction of their isostructural complexes in which the f-electron states of Dy3+ act as an energy sink. Complexes RE(hfac)3(NMMO)2 (RE = Dy (2-Dy) and Y (2-Y), hfac = hexafluoroacetylacetonate, and NMMO = N-methylmorpholine-N-oxide) showed variable rates of oxygen atom transfer (OAT) to triphenylphosphine under ultraviolet (UV) irradiation, as monitored by 1H and 19F NMR spectroscopies. Ultrafast transient absorption spectroscopy (TAS) identified the excited state(s) responsible for the photochemical OAT reaction or lack thereof. Competing sensitization pathways leading to excited-state deactivation in 2-Dy through energy transfer to the 4f electron manifold ultimately slows the OAT reaction at this metal cation. The measured rate differences between the open-shell Dy3+ and closed-shell Y3+ complexes demonstrate that using established principles of 4f ion sensitization may deliver new, selective modalities for differentiating the RE elements that do not depend on cation size.

Enhanced treatment of azo dyes in wastewater using heat-activated persulfate with micro-nano bubble aeration

Azo dyes-containing wastewater can lead to environmental issues and pose threats to public health. The efficient degradation of azo dyes with novel and potent techniques, remains a challenge. This study presented an innovative utilization of micro-nano bubble aeration technology to improve the treatment of Rhodamine B through heat-activated persulfate oxidation. Through single factor experiments, the impacts of persulfate concentration, temperature, initial Rhodamine B concentration, and pH values were systematically explored on the degradation of Rhodamine B in heat-activated persulfate oxidation. The removal rate of Rhodamine B was 94.53% optimized by Response surface optimization method. The reaction rate was in the range of 0.0109–0.0528 min−1, governed by pseudo-first-order kinetics. By applying the Arrhenius equation, the activation energy was determined to be 14.06 KJmol−1. Furthermore, properties of micro-nano bubbles and their synergistic coefficient were investigated in heat-activated persulfate oxidation. Quenching tests revealed the predominance of sulfate radicals, and full wavelength scanning facilitated an in-depth investigation of the reaction mechanism. Additionally, a proposed electron shell structure elucidated the decomposition process of Rhodamine B. Therefore, the implementation of micro-nano bubble aeration technology based on heat-activated persulfate oxidation, held the promise as an efficient and effective approach for the treatment of printing and dyeing wastewater.

EXAFS study of the local environment of lead and iron sorbed onto volcanic ash

This work focuses on the EXAFS investigation of the local environment of lead and iron sorbed onto volcanic ash materials previously studied using XANES technique. Different compounds found in the composition of volcanic ash were used as the models in the EXAFS fitting procedure of the experimental EXAFS spectra collected at the Fe K edge and Pb L3 edge in the Fe- and Pb-sorbed volcanic ash samples. The results showed two types of interactions involving in the adsorption process of both samples. The first is related to iron or lead absorber with oxygen atoms in the first coordination shell. The second interaction occurred between the absorbers (Fe or Pb) and the backscatters (Fe or Pb) in the second shell. The local environment of the iron-sorbed element may have a cubic geometry with different crystallographic sites related to oxygen and iron atoms. On the other hand, the lead-sorbed element may be in orthorhombic geometry with different sites related to oxygen atoms and lead atoms. The adsorption mechanisms involved in the process of iron and lead sorption are ion exchange with probable chemisorption for iron and microprecipitation for lead.

Measurement of low-energy Compton and neutron scattering in Si CCDs for dark matter searches

For optimal sensitivity to low-mass dark matter candidates experiments like DAMIC-M employ skipper charged-coupled devices (CCDs) with detection threshold of just a few ionization charges. Ionization signals from small-angle Compton scatters of environmental \gammaγ-rays, an important component of the background in dark matter searches, must thus be characterized down to OO(10 eV) energy. Using a ^{241}241Am \gammaγ-ray source, we report a precise measurement of scattering on Si atomic shell electrons in a skipper CCD with single-electron resolution. Notable differences are observed between data and theoretical expectations in the L-shell energy region (<150 eV). We also present preliminary data from a skipper CCD exposed to low-energy neutrons (<24 keV) from a ^{124}124Sb^99Be photoneutron source, demonstrating a measurement of the nuclear recoil ionization efficiency in Si down to few ionization charges.

The Dependence of X-Ray Attenuation Parameters of (Al, Cu, And Zr) Metals on their Atomic Number

This paper studied X-ray attenuation in metals (Al-13, Cu-29, Zr-40). X-ray energy of 17 keV of kα line of molybdenum was directed to metal bars with 0.05 cm thickness. These three metals have differences in their atomic numbers and electronic distributions in the electronic shells; aluminium (Al-13) was chosen as the low atomic number, copper (Cu-29), and zirconium (Zr-40) as the high atomic number. The linear and mass attenuation coefficients, atomic and electronic cross-sections, and electron density for X-ray attenuation through each element were determined experimentally. The results explained a new idea to describe X-ray scattering: the effect of valance and bound electron (electron distribution) of the metals. The metal with more bound electrons in its outermost shell scattered more radiation for a specific range of energy, even though the metal has a less atomic number.

Search for Light Dark Matter with Ionization Signals in the PandaX-4T Experiment.

We report the search results of light dark matter through its interactions with shell electrons and nuclei, using the commissioning data from the PandaX-4T liquid xenon detector. Low energy events are selected to have an ionization-only signal between 60 to 200 photoelectrons, corresponding to a mean nuclear recoil energy from 0.77 to 2.54keV and electronic recoil energy from 0.07 to 0.23keV. With an effective exposure of 0.55 tonne·year, we set the most stringent limits within a mass range from 40 MeV/c^{2} to 10 GeV/c^{2} for pointlike dark matter-electron interaction, 100 MeV/c^{2} to 10 GeV/c^{2} for dark matter-electron interaction via a light mediator, and 3.2 to 4 GeV/c^{2} for dark matter-nucleon spin-independent interaction. For DM interaction with electrons, our limits are closing in on the parameter space predicted by the freeze-in and freeze-out mechanisms in the early Universe.

Revisiting the stable structures of gold clusters: Au n (n = 16–25) by artificial neural network potential

Identifying the stable structures of gold (Au) clusters is a huge challenge in cluster science. In this work, we have searched the ground-state structures of neutral Au n (n = 16–25) clusters using the potential of an artificial neural network (ANN) trained with density functional theory (DFT) data. Compared with the DFT data, the root mean square error of binding energy predicted by the ANN potential is about 8.66 meV/atom. Applying the ANN potential to search the ground-state structures by comprehensive genetic algorithm, we have found several new candidates of Au18, Au22, and Au23, which have not been previously reported. Au18 has a hollow cage structure, whereas Au22 and Au23 are flat cage structures. From the electronic analysis, we elucidate the stability mechanism of the newly found structures that are associated with the electronic shell closure of superatomic orbitals. Additonally, we also clarified how to clean a database to train an efficient ANN potential in detail. Overall, this work proves that applying machine learning to the description of atomic interactions can accelerate the search of ground-state structures of clusters and help to find new candidates for stable cluster structures.

Energy Spectrum of β Electrons in Neutrinoless Double-β Decay Including the Excitation of the Electron Shell of Atoms

Double-β decay is accompanied with a high probability by the excitation of the electron shell of the daughter atom; as a result, the energy carried away by β electrons decreases. The mean value and standard deviation of the excitation energy of the electron shell of the daughter atom in the double-β decay of germaniumhave been determined within the Thomas–Fermi and relativistic Dirac–Hartree–Fock methods. Using the estimates thus obtained, a two-parameter model of the energy spectrum of β electrons in the neutrinoless mode has been developed including the redistribution of the reaction energy between the decay products. The shift of the total energy of β electrons does not exceed 50 eV with a probability of 90%. However, the mean excitation energy is ~400 eV, i.e., an order of magnitude higher, whereas the standard deviation is ~2900 eV, which is apparently due to a significant contribution from inner electron levels to the energy characteristics of the process. The distortion of the shape of the peak of the 0ν2β decay should be taken into account when analyzing the data of detectors with a resolution of ~100 eV or higher.

Kβ to Kα X-ray intensity ratio and K–L vacancy transfer probability of Mn following electron capture decay

Kα and Kβ X-rays of Mn following electron capture (EC) decay of 55Fe were detected using Amptek XR-100 T-CdTe X-ray detector spectrometer. Measured Kα and Kβ X-ray intensities of Mn were used to determine the Kβ to Kα intensity ratio and total K–L total vacancy transfer probability. These values were compared with the theoretical, semiempirical, and others’ experimental values obtained via EC decay as well as photoionization. The X-ray intensity ratio of Mn was found to be higher by 1.5% from the relativistic Hartree-Slater theoretical value. This deviation may be attributed to the exchange interactions occurring between the 3p and 3d shell electrons as well as the recoil effect of the nucleus due to neutrino emission.

Energy Spectrum of β Electrons in Neutrinoless Double-β Decay Including the Excitation of the Electron Shell of Atoms

Double-β decay is accompanied with a high probability by the excitation of the electron shell of the daughter atom; as a result, the energy carried away by β electrons decreases. The mean value and standard deviation of the excitation energy of the electron shell of the daughter atom in the double-β decay of germanium _{{32}}^{{76}}{text{Ge}} to ;_{{34}}^{{76}}{text{Se}}text{*} + ;2{{beta }^{ - }}( + 2{{bar {nu }}_{e}}) have been determined within the Thomas–Fermi and relativistic Dirac–Hartree–Fock methods. Using the estimates thus obtained, a two-parameter model of the energy spectrum of β electrons in the neutrinoless mode has been developed including the redistribution of the reaction energy between the decay products. The shift of the total energy of β electrons does not exceed 50 eV with a probability of 90%. However, the mean excitation energy is ~400 eV, i.e., an order of magnitude higher, whereas the standard deviation is ~2900 eV, which is apparently due to a significant contribution from inner electron levels to the energy characteristics of the process. The distortion of the shape of the peak of the 0ν2β decay should be taken into account when analyzing the data of detectors with a resolution of ~100 eV or higher.

Systematic study of the stopping power of the lanthanides

In the last decade, lanthanides have become the subject of multiple studies due to their importance in technological applications. This paper aims to systematically study the energy loss per unit length of protons on the 15 lanthanides, from lanthanum to lutetium. We investigate the stopping power cross sections by considering the influence of the relativistic atomic structure, namely the description of the $4f$ electrons, the number of electrons in the valence shells, and the electronic screening of the same or close subshells. The electronic stopping model considers separate contributions from bound and valence electrons. We employ a many-electron model for the former and a combination of perturbative and nonperturbative free-electron gas approaches for the latter. Our stopping results for the lanthanide series cover an extended energy range from very low to the MeV region. We compare them with measurements and other theoretical (dpass, casp) and semiempirical (srim) methods. Our results agree with most experimental data, even the recent values around the maximum for gadolinium. We implement Lindhard's scaling for the stopping number for all the data available of the 15 targets. Lindhard scaling for the stopping number includes all the data for the 15 targets. The present paper cast doubts on certain data sets, which should affect srim's description of lanthanides, such as La, Nd, Dy, and Tb. We call attention to the scarcity of measurements in the low and intermediate ranges, and we suggest experimental efforts to shed light on the stopping power of these relevant targets.

Structure microscopy of an atom in high magneto-optical medium based on transmission and reflection spectra

A five level atomic medium driving by probe and standing waves control fields having dielectric function $$\epsilon _r$$ and permeability function $$\mu _r$$ is placed in a cavity of dielectric function $$\epsilon _1$$ . The permittivity and permeability functions are directly related to the reflection and transmission spectra of the medium. The reflection and transmission spectra of the medium provide information about internal structure and properties of the atom. A central peak/depth is reported in the reflection and transmission spectra, which corresponds to the nuclear region of an atom. Around the central peak/depth regions, circular ring type patterns in the reflection and transmission spectra are reported. These ring type patterns exhibit atomic shells of the atoms. The theoretical investigation of internal structure microscopy of an atom have potential applications in nano-lithography and atoms trapping. Our proposed model might be helpful for increasing the capability of optical microscopy and atoms imaging.

Detection of Electron Paramagnetic Resonance Spectra of Optically Induced Carriers with the Properties of the Effective Mass in the WS2 Transition Metal Dichalcogenide

The spin properties of transition metal dichalcogenides are of interest for applications in spintronics. Anisotropic electron paramagnetic resonance spectra in a WS2 single crystal under optical excitation have been detected. These spectra assumingly belong to localized carriers near the valence band and reflect features of the 5d shell of the crystal. It has been shown that the g-factor for the magnetic field perpendicular to the c‑axis of the crystal (in-plane magnetic field) is larger than that for the magnetic field parallel to the c‑axis (perpendicular to the layer plane), which can provide information on the type of the 5d function. The discussed center is most likely described by the wavefunction, which can be associated with the valence band of the crystal.

Obrazovanie i raspad avtoionizatsionnykh sostoyaniy - osnovnoy mekhanizm neuprugikh poter' pri stolknoveniyakh atomov keV-energiy

It has been shown that the formation of autoionization states makes the dominant contribution to inelastic energy loss and to ionization in keV atomic collisions, i.e., at velocities lower than the velocities of atomic electrons. Scaling laws have been proposed to calculate the cross sections for the formation of vacancies in inner K and L electron shells of colliding atoms. A model has been proposed to relate ionization processes and the observed inelastic energy losses. Auger transitions in a short-lived quasimolecule formed by two atoms approaching each other have been studied. The nature of the continuous component in electron spectra emitted in collisions has been determined. It has been shown that the excitation of autoionization states determines the stopping cross sections for keV atoms in matter.

Radioactive decays of stored highly charged ions

Decay properties known in neutral atoms can be altered significantly if all or most bound electrons are removed. Straightforwardly, in fully-ionised nuclei, the decay channels involving electrons are simply disabled. Also decay modes, that are hindered or completely blocked in neutral atoms, may, respectively, become dominant or open up in highly charged ions. Few-electron ions are by themselves clean systems with well-defined quantum numbers, in which the interactions within the remaining electrons can either be excluded or treated precisely, thereby allowing for investigations of the influence of atomic shell on nuclear decay properties. Violent stellar environments characterised by high temperatures and densities lead to high ionisation degrees of nuclides involved in nucleosynthesis processes. In spite of the rich motivation for studying radioactive decays of highly charged ions, intensive measurements became possible only after heavy-ion storage rings coupled to radioactive-ion beam facilities became available. Presented here is a compact review of the relevant experimental techniques and experiments.

Giant NLO response and ultraviolet transparency of superalakalis decorated C6O6Li6 complexes; a DFT perspective

Materials having nonlinear optical (NLO) properties are the demand of optics and optoelectronics fields because of their widespread applications. Keeping in view the applications of NLO materials, some new superalkalis doped C6O6Li6 complexes are introduced in this study having remarkable NLO response. Thermodynamic stability of nonlinear optical materials (NLO) is prime requirement of experimentalists for practical applications. All the considered complexes have high thermodynamic stability. Furthermore, these superalkali doped complexes reveal fabulous electronic properties. Superalkalis shift their outer shell electrons towards the C6O6Li6 nanocluster, which act as diffuse excess electrons. The HOMO-LUMO gaps (H-L Egap) of superalkali doped complexes are effectively reduced due to shifting of electrons that reveals their conducting properties. NBO charge analysis confirmed electron charge transfer from superalkalis to C6O6Li6 surface. Linear and NLO properties of these complexes are estimated from first order polarizability (α o) and hyperpolarizability (β o) parameters. Among all complexes, C6O6Li6.K3O has the highest first hyperpolarizability (β o = 6.02 × 105 au). TD-DFT analysis confirmed the ultraviolet transparency of doped complexes. Two level model is used to rationalize the trend of first hyperpolarizability and the internal factors responsible for the enhancement of NLO response.