Transmission Cross Section Research Articles

Multiple semi-coherent particles strengthened ultra-fine-grained Al composites for neutron shielding materials

Neutron shielding materials face imbalanced behaviors among shielding, strength, and ductility properties. Based on the requirement of the high property shielding particles, a superior semi-coherent τ(Al4MgGd) phase was designed and predicted by cluster expansion (CE) method using density functional theory calculations. To realize its shielding property, the Powder Metallurgy-based routines (i.e., powder fabrication, spark plasma sintering, and hot extrusion techniques) are used to fabricate 6TiB2/Al-6Mg-5Gd (wt.%) composite with dispersed refined τ phases and homogenized TiB2 distribution. The atomic structure of ternary phase τ is examined by aberration-corrected high-angle annual dark-field (HAADF) scanning transmission electron microscope (STEM) and energy dispersive X-ray spectroscopy (EDXS) STEM experiments, which is well complied with the calculated compound (Al4MgGd). In detail, the τ(Al4MgGd) phase has a semi-coherent interface both with α-Al and TiB2, which is consistent with the prediction of interface relationships. With the optimized interfaces, the TiB2 and τ phases can effectively promote recrystallization and suppress grain growth, leading to the formation of ultra-fine grain structure. Then, the composite exhibits advanced shielding properties (Macroscopic transmission cross section ∼24.1 /cm, higher than 30 %B4C/Al) and optimized synergic mechanical properties (Ultimate tensile strength ∼506 MPa, elongation ∼12.9 %), which are far higher than available Al-based neutron shielding materials. Finally, the underlying strength-ductility mechanisms are discussed. Critically, the design and optimization of shielding particle interfaces are reliable strategies for developing novel structural-functional integrated materials.

Microstructural design to Al-6Mg-5Gd alloy for the unification of structural and neutron shielding properties

Design of composition and microstructure can effective improve the structural and neutron shielding properties of neutron shielding materials. Based on the shielding standard of 30%B4C/Al, an Al-6Mg-5Gd (wt%) alloy was designed by Shmakov-Yamamoto model and successfully fabricated by Powder Metallurgy-based routines (e.g., powder fabrication, spark plasma sintering and hot extrusion techniques). By the rapid solidification in the atomization process, the submicron cell structures were formed in powders. Due to the difference in the original powder size, the as-sintered alloys had heterogeneous microstructures, leading to the bimodal grain structures of as-extruded alloys. During these processes, the formation of nano-sized τ(C15) (Al4MgGd) phase in combination with its firstly observed transformation behavior showed the great impacts on microstructure evolutions. Therefore, the as-extruded alloy exhibited the superior yield strength (335±7 MPa), ultimate tensile strength (462±5 MPa) and elongation (10.2±0.3%). Through the neutron absorption test, the as-extruded alloy showed the comparable of macroscopic transmission cross section with 30%B4C/Al. In comparison with the available Al-based neutron shielding materials, our report exhibited the best unification of mechanical and functional properties. The underlying mechanisms for synergic strength-ductility behavior were discussed on the nano-sized phase strengthening, α-Al/τ interface modulation, and bimodal grain features. Critically, this work designed and studied a high-performance neutron shielding material, shedding light on the advanced structural-functional integrated materials.

Key Transmission Section Search Based on Graph Theory and PMU Data for Vulnerable Line Identification in Power System

Failure of vulnerable lines in the power system often results in tidal shifts, and triggering chain failures and their corresponding transmission sections are concentrated manifestations of the weak links in the power system. It is very important to identify the vulnerable lines and search the transmission section to prevent the chain faults as well as to analyze the stability of the power system. Aiming at the problems of inaccurate search of vulnerable lines, difficulties adapting to the complex and changing power system as well as wrong selection and omission of transmission section search in the existing references, this paper proposes an algorithm for searching vulnerable lines and their key transmission sections based on the graph theory and PMU (phasor measurement unit) data. First, the method combines with the graph theory and PMU data to construct the grid topology map. Second, the comprehensive indicators for screening vulnerable lines are proposed by fully considering the network topology and line capacity, which combines with power exchange efficiency and energy fluctuation probability. Third, the distance matrix in the Floyd algorithm is transformed into a unit group that can store more elements, which reduces the traversal times of the algorithm and improves computational efficiency. The fast localization of transmission cross sections associated with vulnerable lines is realized. Finally, the critical transmission cross sections are screened according to the line outage distribution factor and line safety margin. The IEEE 39-bus system is selected for simulation experiments, and the simulation results show that the key transmission section search method proposed in this paper can better adapt to the variable power grid and is faster and more accurate than the other common method.

Measurements of the Neutron Total and Capture Cross Sections and Derivation of the Resonance Parameters of 181Ta

The neutron total and capture cross sections of 181Ta were measured at the Accurate Neutron-Nucleus Research Measurement Instrument of the Materials and Life Science Experimental Facility in the Japan Proton Accelerator Research Complex to improve the accuracy of the current resonance parameters. The total cross section was determined from the transmission measurement in the energy range from 0.2 to 150 eV. The capture cross section was derived from the capture yield using the pulse height weighting technique in the energy range from thermal to 150 eV. The thermal neutron capture cross section was measured as 21.3 ± 0.3 ( stat ) ± 0.6 ( sys ) b. The obtained transmission and capture cross section were simultaneously fitted using the resonance analysis code REFIT, and the resonance parameters for resonances below 150 eV were evaluated. The present resonance parameters were compared to reported measurements.

Classification of Transmission Modes through a Narrow Slot in a Thick Conducting Screen

This paper examines electromagnetic energy transmission through a narrow slot in a thick conducting plate when a plane wave is incident to the slot. The slot in the thick plate creates a waveguide structure. From the perspective of cutoff frequency, the transmission characteristics are classified into three modes. The transmission cavity resonance (TCR) mode in the range above the cutoff depends on the plate thickness, and peak transmission cross-sections (TCSs) appear periodically along the plate thickness, known as Fabry-Perot resonance. The near-cutoff resonance transmission (NCRT) mode depends on the slot length and plate thickness, and the maximum TCS appears only once as a slot length resonance (or transverse resonance). The peak TCS for the NCRT mode occurs with a thin plate thickness, which produces slot length resonance. The non-transmission cavity (NTC) mode is a non-transmission and non-resonance mode and is not propagated. All the maximum TCSs for the TCR and NCRT modes occur in parallel resonance. The analysis results show that the classification of the three transmission modes through the thick plate slot is effectively explained by the TCS and aperture impedance.

Zr92(n,γ) and ( n ,tot) measurements at the GELINA and n_TOF facilities

Background: Stellar nucleosynthesis of elements heavier than iron is driven by neutron capture processes. Zr92 is positioned at a strategic point along the slow nucleosynthesis path, given its proximity to the neutron magic number N=50 and its position at the matching region between the weak and main slow processes. Purpose: In parallel with recent improved astronomical data, the extraction of accurate Maxwellian averaged cross sections (MACSs) derived from a more complete and accurate set of resonance parameters should allow for a better understanding of the stellar conditions at which nucleosynthesis takes place. Methods: Transmission and capture cross section measurements using enriched Zr92 metallic samples were performed at the time-of flight facilities GELINA of JRC-Geel (BE) and n_TOF of CERN (CH). The neutron beam passing through the samples was investigated in transmission measurements at GELINA using a Li-glass scintillator. The γ rays emitted during the neutron capture reactions were detected by C6D6 detectors at both GELINA and n_TOF. Results: Resonance parameters of individual resonances up to 81 keV were extracted from a combined resonance shape analysis of experimental transmissions and capture yields. For the majority of the resonances the parity was determined from an analysis of the transmission data obtained with different sample thicknesses. Average resonance parameters were calculated. Conclusions: Maxwellian averaged cross sections were extracted from resonances observed up to 81 keV. The MACS for kT=30keV is fully consistent with experimental data reported in the literature. The MACSs for kT≲15keV are in good agreement with those derived from the ENDF/B-VIII.0 library and recommended in the KADoNiS database. For kT higher than 30 keV differences are observed. A comparison with MACSs obtained with the cross sections recommended in the JEFF-3.3 and JENDL-4.0 libraries shows discrepancies even for kT≲15keV.5 MoreReceived 21 February 2020Revised 7 January 2022Accepted 7 February 2022DOI:https://doi.org/10.1103/PhysRevC.105.025805Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasHydrostatic stellar nucleosynthesisNeutron physicsNuclear astrophysicsNuclear reactionsRadiative captureResonance reactionsProperties90 ≤ A ≤ 149TechniquesNuclear data analysis & compilationNuclear Physics

Resonance Transmission of Dual Plates with Narrow Small Slots due to Two Parallel Wires for Frequencies around 2 GHz

This paper presents the transmission cross-section (TCS) of a dual plate with narrow small slots when a plane wave is incident from the left half-space. Numerical results show that the TCS depends mainly on the plate spacing for a specified frequency. The TCS fluctuates with the plate spacing; the fluctuation period is approximately 0.5λ. When the plate spacing is larger than 0.5λ, the TCS reduces to 90% in the single plate case, and TCS enhancement is extremely difficult. However, when the plate spacing is less than 0.5λ, the TCS decreases gradually to approximately 36% in the single plate case, and TCS enhancement can be realized using two parallel wires. The analysis results show that resonance transmission is effectively obtained by the wires connected on the slots for a plate spacing within 0.5λ. Experimental measurements are presented to validate the theory.

Link Budget Analysis with Laser Energy for Time Transfer Using the Ajisai Satellite

Two-way Laser Time Transfer (TLTT) using the Ajisai satellite has been considered as a more accurate and stable time transfer technique than existing methods; TLTT requires the kHz laser pulses to decrease the systematic restrictions for TLTT realization. However, because of the low energy of the kHz laser pulses as well as the low cross section due to the small size of the Ajisai reflecting mirror, the link budget is an important issue to establish the TLTT link between two ground stations. In this study, the TLTT link budget is investigated to find the optimal laser pulse energy via analysis of geometric effects using 30 days of orbital data of the Ajisai satellite from 29 March 2021 within a ground network consisting of four stations located in three countries. The geometric configuration reduces the TLTT link budget by three orders of magnitude due to free space loss, atmospheric transmission, and effective cross section; then, the pulse energy is required to be much higher than laser ranging to the Ajisai satellite. It is shown from the simulation that a few tens of mJ level of pulse energy at the transmitting station is quite enough for TLTT realization.

Self-consistent quantum field theory for the characterization of complex random media by short laser pulses

We present a quantum field theoretical method for the characterization of disordered complex media with short laser pulses in an optical coherence tomography setup (OCT). We solve this scheme of coherent transport in space and time with weighted essentially nonoscillatory methods (WENO). WENO is preferentially used for the determination of highly nonlinear and discontinuous processes including interference effects and phase transitions like Anderson localization of light. The theory determines spatiotemporal characteristics of the scattering mean free path and the transmission cross section that are directly measurable in time-of-flight (ToF) and pump-probe experiments. The results are a measure of the coherence of multiple scattering photons in passive as well as in optically soft random media. Our theoretical results of ToF are instructive in spectral regions where material characteristics such as the scattering mean free path and the diffusion coefficient are methodologically almost insensitive to gain or absorption and to higher-order nonlinear effects. Our method is applicable to OCT and other advanced spectroscopy setups including samples of strongly scattering mono- and polydisperse complex nano- and microresonators.

Automatic Identification and Importance Evaluation Technology of Power Transmission Section

In theory, the cross section is the minimum cut set in the network. For the actual power grid, the transmission cross section is a collection of transmission lines between different regions, which is mainly used for power transmission to achieve the purpose of generating load balance. In this paper, a power grid zoning algorithm is proposed based on the topological structure characteristics and current operation state of the power grid, and the key transmission sections can be directly obtained without depending on the calculation of safety and stability margin. A practical system state partition model and key section sorting method are introduced, and a set of automatic identification method flow of key transmission sections of the system is established by searching for electrical betweenness. The importance of the transmission section is quantitatively evaluated from three angles: the margin from the stability limit, the hub position in the current power flow state, and the impact on the power grid after the power cut-off. The evaluation results can be used as a Reference for decision-making in the planning and reconstruction of the transmission section, safety monitoring, protection configuration, etc.

도체 평판에서 소형 개구의 투과 단면적

Transmission cross section(TCS) is described analytically as 2 Gλ2/4π irrespective of the aperture shapes for various transmission resonant apertures, such as small ridged circular or H-shaped, U-shaped, or Jerusalem cross-shaped apertures in an infinite thin conducting plane. The proposed expression is validated by comparison with the numerical results obtained from the method of moments(MOM). The TCS characteristics of the transmission resonant cavity structure in a thick conducting plane are also studied and the equivalence between the two small aperture structures is reported from the viewpoint of transmission efficiency.

Neutron total cross section calculation within the framework of quasi-harmonic approximation

The accuracy of neutron scattering cross sections is the gauge for the realistic outcome of a neutron transport simulation. To improve the traditional harmonic physics model used in such simulations, we revisit the slow neutron transport theory in crystalline materials and aim to develop a unified model that has good performance for neutron transport problems in crystals in a wide range of temperatures and pressures. The quasi-harmonic approximation (QHA) correlates phonon evolution explicitly with unit cell volume. Therefore, it is capable of evaluating a variety of material properties at finite temperatures. In this work, we show numerically that it is a very effective tool for our application as well. Within the framework of QHA, we calculate the temperature dependent characteristics of phonons in three elemental crystals, namely Be, Mg and Al. Based on the obtained results, our calculated neutron total cross sections agree closely with experimental transmission cross sections in a large temperature range below the melting point. We show that as the harmonic cross section model ignores the effects of phonon softening in these crystals, it underestimates the total inelastic cross sections at high temperatures. In the case of Al, we observe that such underestimation is up to 7% at room temperature. In addition, we study the phonon–phonon scatterings in Al. We observe that the cross section is insensitive to the finite phonon lifetimes even at 800 K.

Approximate Transmission Coefficients in Heavy Ion Fusion

In this paper we revisit the one-dimensional tunnelling problem. We consider different approximations for the transmission through the Coulomb barrier in heavy ion collisions at near-barrier energies. First, we discuss approximations of the barrier shape by functional forms where the transmission coefficient is known analytically. Then, we consider Kemble's approximation for the transmission coefficient. We show how this approximation can be extended to above-barrier energies by performing the analytical continuation of the radial coordinate to the complex plane. We investigate the validity of the different approximations considered in this paper by comparing their predictions for transmission coefficients and cross sections of three heavy ion systems with the corresponding quantum mechanical results.

A Proposal to Improve the Standard on the Shielding Effectiveness Measurements of Materials and Gaskets in a Reverberation Chamber

In this paper, a reexamined estimate of the test fixture validation factor (TFVF) of fixtures for shielding effectiveness (SE) measurements in a reverberation chamber is shown. The fundamental conditions for the applicability of the model shown here are a large aperture between the chambers, whose transmission cross section is well approximated by the geometrical optics, and an isolation between the chambers greater than or equal to 10 dB, as specified in this paper. The model is applicable for both nonmarginal and marginal SE values; but, in the latter case, the requested isolation between the two chambers has to be met with no sample in the aperture. For nonmarginal SE values, the conditions requested for the applicability of the model are practically the same as those requested in the standard IEC 61000-4-21. The model is applicable to SE measurements of gaskets as well. The results show that the TFVF used in the standard procedure IEC 61000-4-21 has to be updated to achieve more accurate measurements of SE in light of the studies conducted on this topic. We give such an update in this study.

Magnons Heat Transfer and Magnons Scattering in Magnetic Sandwich Lattices: Application to Fe/Gd(5)/Fe System

A model calculation is presented for the coherent magnon transmission and thermal transport at ferromagnetic nanojunction boundaries. The system consists of a Gd ultrathin film sandwiched between two Fe semi-infinite ferromagnetically ordered crystals. The dynamic of the system is analyzed using the equations of motion for the spin precession amplitudes on the lattice sites, valid for the range of temperatures of interest. The coherent transmission and reflection cross sections at the nanojunction boundary are calculated using the matching method. These calculations are presented for arbitrary directions on the boundary, for all accessible frequencies in the propagating bands, at variable temperatures and for a given thicknesses of the ultrathin nanojunction, with no externally applied magnetic field. The model is applied in particular to the Fe/Gd(5)/Fe system with a ferromagnetic Gd nanojunction. Our model yields the total integrated coherent thermal conductivity due to coherent magnons transmission via the sandwiched five Gd spin layers of the nanojunction. It elucidates, in particular, the dependence of the coherent magnons transmission and thermal transport in relation to the spatially inhomogeneous magnetic order of the atomic planes of the nanojunction for a given thickness.

The design of a novel neutron shielding B4C/Al composite containing Gd

Equivalent amount of B (BEq) can be used to evaluate the thermal neutron shielding property of materials. Based on the calculation of BEq, a novel boron carbide and gadolinium particles reinforced Al composite (15%B4C+1%Gd)/Al was designed. The composite was successfully prepared by vacuum hot pressing method. The B4C particles and Gd phase were homogeneously distributed in the Al matrix. The Monte Carlo Particle transport program MCNP simulation and thermal neutron shielding tests demonstrated that the (15%B4C+1%Gd)/Al composite definitely had an almost equivalent neutron shielding property as the 30%B4C/Al composite, which in turn proved the accuracy of the design. The macroscopic transmission cross section (Σ) of (15%B4C+1%Gd)/Al composite was as high as 21.3cm−1, which was better than that of 30%B4C/Al composite. Tension tests indicated that by decreasing B4C content, the elongation of the composite reached as much as 9%. The addition of Gd can replace a part of B4C content in the composite, which can increase the plasticity of the composite, and keep the neutron shielding property simultaneously.

A Theory of Alternative Methods for Measurements of Absorption Cross Section and Antenna Radiation Efficiency Using Nested and Contiguous Reverberation Chambers

Average ACS can be measured in a reverberation chamber; however, the existing technique determines a value that includes the effects of the radiation efficiencies of the antennas used in the measurement. Correcting for these necessitates further complex measurements. Here, we present the theory of an alternative measurement methodology using two nested or contiguous reverberation chambers which is free from errors caused by the radiation efficiencies of the antennas. The new method is based on the theoretical average transmission cross sections (TCS) of circular holes in a metal plate between the two chambers. In fact, the method can be viewed as an accurate transfer calibration measurement between TCS and ACS that is independent of both the chamber and antenna characteristics. Further, since the existing method of measuring ACS includes the effects of the radiation efficiencies of the antennas, a comparison of the ACS of a reference object, measured using both the existing and new methods, also provides an alternative method of determining radiation antenna efficiency. Measurement uncertainties for both alternative measurement methods—ACS and antenna radiation efficiency—are also derived.

Microcavity enhanced directional transmission through a subwavelength plasmonic slit.

We show numerically that a compact structure, consisting of multiple optical microcavities at both the entrance and exit sides of a subwavelength plasmonic slit, can lead to greatly enhanced directional transmission through the slit. The microcavities can increase the reflectivity at both sides of the slit, and therefore the resonant transmission enhancement. In addition, the microcavities can greatly improve the impedance matching, and therefore the coupling between free-space waves and the slit mode. An optimized structure with two microcavities on both the entrance and exit sides of the slit leads to ~16 times larger transmission cross section per unit angle in the normal direction compared to the optimized reference slit without microcavities. We also show numerically that the operation frequency range for high emission in the normal direction is broad.

Spin Wave Transmission by Spin Impurities in a Quasi-1D Heisenberg Ferromagnetic Tubular Structure

This paper introduces a theoretical study to investigate, at a low temperature, the spin wave propagation and total magnon transmission via atomic substitution sites in a quasi-1D Heisenberg ferromagnetic tubular structure. The model system consists of four ordered ferromagnetic atomic chains, arranged in the space of a parallel manner two to two and containing a finite number of substitution sites, considered as spin impurities. The model is supported on a non-magnetic substrate and considered otherwise free from magnetic interactions with its environment. To describe the dynamics of the tubular structure, we used the theoretical matching procedure. The total transmission and reflection cross sections at the boundary containing the substitution sites are calculated and analyzed as a function of the incident frequency per propagating mode of the perfect quasi-1D tubular structure. The impurity observables are numerically calculated for different cases of softening and hardening to investigate how the local dynamics can respond to changes in the microscopic environment on the perturbed domain. Our results show the interferences between incident spin modes and the localized spin states of the substitution sites. The observe effects are induced by the modification of boundary magnetic exchange values and spin intensity of the impurity sites of the system. The results yield, also, an understanding for the relationship between the coherent magnon transmission and the position of the substitution spin sites in the studied structure.

Mapping of transmission spectrum between plasmonic and nonplasmonic single slits II: nonresonant transmission

In our previous work, the similarity in resonant transmission properties for plasmonic and nonplasmonic 2D single slits can be realized by mapping their resonant wavelengths through waveguide dispersion. To further extend the mapping for nonresonant condition, complex reflection and transmission coefficients at the end faces of a semi-infinite slit are analyzed to reconstruct the whole transmission spectra. The complex reflection coefficients are found to be similar at the same effective wavelength for both the plasmonic and nonplasmonic cases. The spectrum reconstructed by a Fabry–Perot model matches the transmission spectrum of a nonplasmonic slit and can be transformed into that of a plasmonic case by wavelength stretching with plasmonic waveguide dispersion. The transmission cross section is bounded by λ/(πd). Width-dependent redshifts of the transmission spectrum are associated with effective capacitances at the slit end faces. The same mapping method applies for a single slit with substrate or periodic structure. Furthermore, the optical property of a plasmonic slit can be achieved by a nonplasmonic slit via dimensional scaling. The focusing lens effect of a plasmonic slit array can be mimicked by a nonplasmonic slit array with dimensional scaling. The unified transmission properties of plasmonic and nonplasmonic 2D single slits can simplify the design of slit structures for plasmonic applications.