Shield Potential Research Articles

Structural, linear/nonlinear optical characteristics and radiation shielding effectiveness of Cu4O3/Cu2O dual-phase thin films: Influence of oxygen flow rate in reactive sputtering process

In the present work, we investigated the impact of oxygen flow rate on the structural, linear, and nonlinear optical characteristics while also evaluating the radiation shielding effectiveness during reactive radio frequency (rf) sputtering in the deposition of Cu4O3/Cu2O dual-phase thin films. Microstructural analysis revealed distinct changes with increased OFRs, switching from a Cu2O cubic structure phase to a Cu4O3 tetragonal structure phase. The XRD patterns revealed good crystallinity, and the crystallite size of the film reduced from 28 nm to 22 nm, and the microstrain exhibited an opposing trend as the oxygen flow rate increased. In contrast, investigating the optical properties of dual-phase Cu4O3 and Cu2O thin films using UV–Vis–NIR spectroscopy revealed intriguing trends in the absorbance spectra, absorption coefficient, and extension index. The apparent bandgap increases from 2.0 eV to 2.62 eV with increasing oxygen flow rates. In addition, nonlinear optical parameters, including the nonlinear refractive index n2 linear, nonlinear sensitivity (χ1 and χ3), and nonlinear absorption coefficient βc were calculated to demonstrate the applicability of these materials. The dual-phase structure of the films enhances their potential for effective radiation shielding. Our findings provide valuable insights into the design of properties of Cu4O3/Cu2O dual-phase thin films for applications ranging from photoelectric and nonlinear optical devices to radiation shielding effectiveness.

Lignin-Derived Lightweight Carbon Aerogels for Tunable Epsilon-Negative Response.

Electromagnetic (EM) metamaterials have garnered considerable attention due to their capacity to achieve negative parameters, significantly influencing the integration of natural materials with artificially structural media. The emergence of carbon aerogels (CAs) offers an opportunity to create lightweight EM metamaterials, notable for their promising EM shielding or absorption effects. This paper introduces an efficient, low-cost method for fabricating CAs without requiring stringent drying conditions. By finely tuning the ZnCl2/lignin ratio, the porosity is controlled in CAs. This control leads to an epsilon-negative response in the radio-frequency region, driven by the intrinsic plasmonic state of the 3D carbon network, as opposed to traditional periodic building blocks. This approach yields a tunable and weakly epsilon-negative response, reaching an order of magnitude of -103 under MHz frequencies. Equivalent circuit analysis highlights the inductive characteristics of CAs, correlating their significant dielectric loss at low frequencies. Additionally, EM simulations are performed to evaluate the distribution of the electric field vector in epsilon-negative CAs, showcasing their potential for effective EM shielding. The lignin-derived, lightweight CAs with their tunable epsilon-negative response hold promise for pioneering new directions in EM metamaterials and broadening their application in diverse extreme conditions.

Investigation of Partial Discharge Characteristics inside Vacuum Interrupter with Various Floating Shield Potentials

The reliable operation of vacuum circuit breakers (VCBs) plays an important role in the power system's reliability. The common cases which lead to the failure in the VCB are related to the loss of vacuum inside the vacuum interrupters (VIs). VIs commonly loses the vacuum with a higher leakage rate, resulting in a decrease in discharge voltage and partial discharge (PD) inside the VI which can lead to the eventual failure of the VCBs. Detecting vacuum leakage at the early stage became an important issue. In the prior study, vacuum failure was studied by detecting PD characteristics inside the VIs by regulating the different internal pressures. This study introduces a novel approach to investigating vacuum leakage within the VIs by detecting PD characteristics under various floating shield potentials to study the possibility of shield potential control on PD measurement. Comparing the experimental results measured at different internal pressures under various shield potentials, this study highlights the measurement of PD characteristics and the possibility of shield potential control on PD measurement. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

The Influence of Various Commonly Used Building Materials on the Shielding Effectiveness, Reflection and Absorption of the Electromagnetic Wave

People spend two-thirds of their time in buildings. Building materials are, therefore, natural shielding for us. Many studies describe the shielding effect of non-building materials. This study evaluates the shielding effectiveness (SE) of electromagnetic fields for various building materials over a frequency range of 1 GHz to 9 GHz. Measurements of SE, reflection (R), and calculated absorption (A) were conducted to determine the shielding properties of mineral wool (MW), hardened polystyrene (PT), extruded polystyrene (PE), polyurethane board (PUR), brick wall (BW), brick wall filled with mineral wool (BW-MW), and concrete wall. The results demonstrate that MW, PT, PE, and PUR exhibit low SE and R, indicating minimal shielding capabilities, with absorption values that do not significantly deviate from the level of measurement uncertainty. Conversely, BW, BW-MW, and concrete wall materials exhibit high SE, with notably increased absorption at higher frequencies, highlighting their potential for effective EMI shielding. Particularly, the concrete wall presents the highest absorption values, making it a superior choice for shielding applications. Reflection trends revealed a plateau for BW in the 6 GHz to 9 GHz range, indicating a frequency-dependent behavior of shielding mechanisms. This study underscores the importance of balancing reflective and absorptive properties in shielding materials and suggests that composite materials may offer enhanced performance. The findings of this research provide guidance for the selection and design of shielding materials in environments with a frequency spectrum of electromagnetic frequencies from 1 GHz to 9 GHz.

Influence of the vapor shield potential control on the post-arc sheath development in vacuum interrupters

In tank-type multi-break vacuum circuit breakers (VCBs) and gas-insulated switchgear (GIS), the non-uniform distribution of vapor shield potential in the vacuum interrupters impacts the post-arc process significantly. To explore the effect of the vapor shield potential on the development of the post-arc sheath, a particle-in-cell model with shield potential control is proposed to obtain two-dimensional distributions of post-arc particles. Based on the synthetic test circuit and probe array, the test platform of the post-arc characteristic diagnostic is set up to verify the influence of vapor shield potential distribution on the post-arc sheath. The extinguishing process of the vacuum arc is also observed by the high-speed CMOS camera. Simulation and experimental results show that at shield potential of 0.5 transient recovery voltage, the post-arc sheath develops most rapidly and the distribution of cathode spots is the most uniform. These findings can provide valuable insights for the design of vacuum interrupters and the control of shield potential in tank-type GIS.

Asymmetric and Flexible Ag-MXene/ANFs Composite Papers for Electromagnetic Shielding and Thermal Management.

Lightweight, flexible, and electrically conductive thin films with high electromagnetic interference (EMI) shielding effectiveness and excellent thermal management capability are ideal for portable and flexible electronic devices. Herein, the asymmetric and multilayered structure Ag-MXene/ANFs composite papers (AMAGM) were fabricated based on Ag-MXene hybrids and aramid nanofibers (ANFs) via a self-reduction and alternating vacuum-assisted filtration process. The resultant AMAGM composite papers exhibit high electrical conductivity of 248,120 S m-1, excellent mechanical properties with tensile strength of 124.21 MPa and fracture strain of 4.98%, superior EMI shielding effectiveness (62 dB), ultra-high EMI SE/t (11,923 dB cm2 g-1) and outstanding EMI SE reliability as high as 96.1% even after 5000 cycles of bending deformation benefiting from the unique structure and the 3D network at a thickness of 34 μm. Asymmetric structures play an important role in regulating reflection and absorption of electromagnetic waves. In addition, the multifunctional nanocomposite papers reveal outstanding thermal management performances such as ultrafast thermal response, high heating temperatures at low operation voltage, and high heating stability. The results indicate that the AMAGM composite papers have excellent potential for high-integration electromagnetic shielding, wearable electronics, artificial intelligence, and high-performance heating devices.

Aramid nanofiber assisted preparation of 3D-oriented graphite/silicone composite slices with high through-plane thermal conductivity and efficient electromagnetic interference shielding

High-performance electromagnetic interference (EMI) shielding materials with outstanding thermal transfer ability are urgently needed for modern electronics. Here, efficient 3D-oriented graphite/silicone EMI shielding composite slices with high through-plane thermal conductivity were prepared through the construction of 3D-oriented graphite skeletons followed by incorporation of silicone and cutting. The flaky graphite was utilized as functional fillers, and an ultra-low addition of aramid nanofibers (ANFs) was conducted to construct the supporting frameworks to maintain the structure of 3D-oriented graphite skeletons. The strategy of constructing of 3D-oriented graphite skeletons before incorporating of silicone facilitated the forming of efficient electrically conductive network and thermal transfer pathway in the prepared composite slices. The differences in thermal, electrical and EMI shielding properties that originated from the orientation of interconnected flaky graphite were systematically studied. As a result, the composite slices show significant enhancements of EMI SE of 65.28 dB in X-band, 76.62 dB in Ka-band and through-plane thermal conductivity of 10.53 W m−1 K−1 at the graphite fraction of 32.68 vol%. Additionally, the composite slices exhibit a good near-field (NF) shielding performance at the frequency range of 1–9 GHz. The composite slices reveal substantial potential for advanced EMI shielding and thermal management applications.

Janus-inspired flexible cellulose nanofiber-assisted MXene/Silver nanowire papers with fascinating mechanical properties for efficient electromagnetic interference shielding

MXene-based nanocomposites are highly desirable for electromagnetic interference (EMI) shielding applications. However, it is crucial but challenging to obtain an excellent trade-off between mechanical properties and EMI performances. Herein, inspired by Janus structure, flexible cellulose nanofiber-assisted MXene/silver nanowires (CNF-MXene/AgNWs) papers (CMAPs) are developed by a scalable sequential self-assembly plus a hot-pressing strategy. The ingenious introduction of highly conductive AgNWs into MXene forms a complementary leaf-like nanostructure, synergistically constructing highly effective conductive frameworks. Contributed by the designed Janus architecture, high-performance CNF substrate, and extensive hydrogen-bonding interactions, the resultant Janus CMAPs (J-CMAPs) with a low MXene/AgNWs addition of 30 wt% possess a high electrical conductivity (1066.85 S/cm), excellent mechanical strength (224.04 MPa) and modulus (9.98 GPa), exceptional EMI shielding effectiveness of 43.65 dB, and record-high EMI SE/t of 16788.51 dB cm−1 and SSE/t of 10543.18 dB cm2 g−1 with a reflection-dominant shielding mechanism, successfully achieving an outstanding balance between mechanical properties and EMI shielding performances. More importantly, high frequency structure simulator (HFSS) simulation in the frequency domain is further conducted to intuitively comprehend the attenuation process of electromagnetic waves and shield mechanism, verifying fascinating EMI shielding performances. Besides, the Janus paper also presents desirable Joule heating performances at low input voltage, short response time (<10 s), and superb heating stability and long-term steady reliability. We believe that the J-CMAPs demonstrate the great potential and advantage for advanced EMI shielding and portable thermal management applications.

Self-Limited ultraviolet laser sintering of liquid metal particles for μm-Thick flexible electronics devices

Lightweight, deformable and highly conductive conductors are rather appealing in flexible electronics devices such as electromagnetic interference (EMI) shielding films; however, the most commonly used metallic foils or carbon nanomaterials suffer from critical limitation of either film thickness or electrical conductivity. Herein, we present a facile approach to rapidly fabricate sintered liquid metal submicron particles (LMSPs) films in combination spray-coating with direct nanosecond ultraviolet (UV) laser sintering. High conductive, μm-thick sintered LMSPs films were prepared owing to the self-limited penetration depth of UV laser, and their sheet resistances are easily tuned at least seven orders of magnitude by the laser processing parameters. A calculated parametric map upon particle diameter and laser fluence whether or not a liquid metal particle is ruptured has been obtained and it is quite well in accordance to the experiment results. Such laser-sintered LMSPs films are finally utilized to fabricate shielding films with superior EMI shielding effectiveness (SE) of ∼33 dB and specific EMI SE over thickness (SSE/t) of ∼27500 dB•cm2•g−1, and flexible electromagnetic metamaterials with a high absorption above 99.9 % at resonance frequency of 12.9 GHz and 14.3 GHz, showing their high potential for flexible EMI shielding and electromagnetic wave absorption applications.

Influence of rare-earth ions on the radiation protection ability of some optical glasses containing Bi2O3 and SiO2

ObjectiveThis study probed the gamma ray shielding functionality of some rare earth doped bismuth-silicate glasses (BS). The mass attenuation coefficient MAC of pure BS (BS-Pure) and those with 2.5 mol% of Bi2O3 substituted with CeO2 (BS-Ce), Nd2O3 (BS-Nd), Sm2O3 (BS-Sm), and Eu2O3 (BS-Eu) was estimated. MethodThe experimental values of glass density and molar volume were systematically used to evaluate the radiation shielding properties of the studied optical glasses. The MAC was computed for photon energies between 0.015 and 15 MeV by employing Monte Carlo simulation and Phy-X software. MAC values were then used to extract all the other related parameters. ResultsMAC computed via the two approached agrees well within 1.9%. MAC of the glasses fluctuates between 0.041 and 100.044 cm2g−1 for BS-Pure; 0.041 – 98.725 cm2g−1 for BS-Ce; 0.041 – 99.249 cm2g−1 for BS-Nd; 0.04 – 99.335 cm2g−1 for BS-Sm; and 0.041 – 99.061 cm2g−1 for BS-Eu. Also, the effective atomic number of the glasses were within the range of 38.707–81.874 for BS-Pure, 38.397–81.509 for BS-Ce, 38.377–81.366 for BS-Nd, 38.402–81.366 for BS-Sm and 38.414–81.368 for BS-Eu. ConclusionCompared to traditional photon shields such as concrete, RS-360 commercial glasses, recently investigated heavy glasses, polymer and rocks, the BS-X glasses displayed superior shielding potential. The BS-X glasses thus could function well in gamma radiation shielding technology.

Smart membrane absorbing electromagnetic waves based on polyvinyl chloride/graphene composites

The rapid proliferation and intensive use of electronic devices have led to an increase in electronic pollution, such as electronic noise, electromagnetic interference (EMI), and radiofrequency interference (RFI), which cause malfunctions of electronic devices. The emergence of flexible polymer composites has a remarkable potential for electromagnetic shielding depending on their unique characteristics, such as their electrical, thermal, mechanical, and magnetic properties, which are very useful for suppressing electromagnetic noise. Graphene (G) and its composites can serve as better shielding materials against these interferences due to their lightweight and high corrosion resistance. Researchers are still grappling with the need for flexible and scalable smart composite materials to prevent radioactive pollution from electronic devices. The inclusion of next-generation graphene (G) conductive fillers loaded with polyvinyl chloride (PVC) /graphene is the subject of our current research (G). Due to the absorption-dominated shielding process, the composite has an extraordinarily low percolation threshold and a high shielding efficiency (SE) against electromagnetic interference (EMI).The distribution and dispersion patterns of graphene particles in the matrix phase were validated by SEM electron micrographs. The composite, which contains just 40% graphene by weight, has an EMI SE value of 26 dB in the frequency range of 10 to 15 GHz and is only 2 mm thick.In this case, we believe that promoting a scalable and industrially viable G/PVC composite, which is a novel and strong candidate in the burgeoning field of high-stress electromagnetic shielding applications in the future, is the best option.

The influence of Gd2O3 on shielding, thermal and luminescence properties of WO3–Gd2O3–B2O3 glass for radiation shielding and detection material

The physical, structural, optical, shielding, thermal and luminescence properties of WO3-Gd2O3–B2O3 glasses were studied in this work. The effect of WO3 replacement by Gd2O3 on radiation shielding and radiation detection potential was evaluated. The glass density increases with increasing Gd2O3 concentration and the maximum value is 5.97 g/cm3. The FTIR and XRD result confirm that the trigonal BO3, tetrahedral BO4 and tungsten complex are the main chemical groups and coorperate into the amorphous structure of glass. The optical absorption spectra exhibit the absorbance of glasses in ultraviolet and visible light region. The shielding parameters of glasses, such as mass attenuation coefficient, effective atomic number, electron density and half value layer, were investigated theoretically and experimentally. They perform a small degradation of shielding property by increasing Gd2O3 content. There is no obvious dependence of Gd2O3 concentration on glass thermal conductivity and expansion. The strong photoluminescence of [WO6]6- group with 524 nm occurred under its charge transfer excitation and under the energy transfer from excited Gd3+ ion. In the radioluminescence, WGB glasses emitted the visible light with 562 nm based on the mixed emission from [WO6]6- group and oxygen vacancy. The glass possesses the X-ray detection efficiency around 18.65% of BGO crystal. The WO3–Gd2O3–B2O3 glass with 17.5 and 27.5 mol% of Gd2O3 is a promising γ-ray shielding material at room temperature and high temperature circumstance, respectively and one with 25 mol% of Gd2O3 owns the attractive potential for the X-ray radiation detection applications.

High-performance and robust dual-function electrochromic device for dynamic thermal regulation and electromagnetic interference shielding

• A dual-function EC device with dynamic thermal regulation and EMI shielding simultaneously is first constructed. • The doping mechanism and EC mechanism of PANI are discussed in detail. • This flexible device exhibits excellent EMI shielding, thermal regulation and the high stability under mechanical stimulus. High-performance devices with the electromagnetic interference (EMI) shielding and dynamic thermal regulation performances are highly desirable for modern integrated electronic and telecommunication systems in areas such as aerospace, communication equipment, and smart electronics. Herein, the dual-function electrochromic (EC) device is fabricated using the polyaniline (PANI) film as the infrared (IR) EC layer, the polymethyl methacrylate (PMMA) gel polymer as the electrolyte and the MXene/PANI/poly vinylidene fluoride (PVDF)/Au (MPPA) film as the EMI shielding layer. The device exhibits a superior EMI shielding effectiveness (SE) of 36.5 dB at 11.6 GHz, benefiting from the highly efficient conductive porous structure, as well as excellent dynamic thermal regulation performances by manipulating emittance (emittance modulation of 0.39 at 8–14 μm), which could also achieve the dynamic heating or cooling of the practical object. Moreover, the performances of the device show no obvious degradation even under 650 cycles bending and 500 cycles twisting, indicating the high robustness. These results indicate that the dual-function device has promising potential for high-performance EMI shielding and thermal management applications.

Appraisal of new density coefficient on integrated-nanoparticles concrete in nuclear protection

Abstract The most important material for shielding is concrete in nuclear facilities which performance can be improved by addition some Nanoparticles (NP) at the various concentrations. Nanoparticles, which have a distinctive potential for bio-radiation and shielding of nuclear reactors, are used in many areas due to their special characteristics, which lead to an improvement in the mechanical properties and the pore structure of the concrete shield. The aim of this research was to initiate a novel coefficient (n), experiment to theory density ratio for integrated NP at different nanoparticle concentrations (xnano), established upon purely mathematical viewpoints and some appropriate physical objectives.

Clogging Potential of Earth-Pressure Balance Shield Driven Tunnels

Background: Nowadays, the construction of urban tunnels for rapid transportation in metropolises is necessary. Since these tunnels are excavated at low depths, they are often associated with different problems and hazards. Some of them can reduce the efficiency of the tunnel boring machines and sometimes will stop the project. Among these problems the clogging can cause problems at the cutter head, in the chamber, and in other sections where the material transference occurs. Objective: The main purpose of this paper is to evaluate and determine the risk of clogging in the tunneling boring machine in Line 6 of the Tehran Metro. It includes stations: Amirkabir, Shohada Square, Emam Hossein Square and Sayyadeh Shirazi. This phenomenon induces an adhesion of the shield with the soil, increasing the necessary shear forces and it can eventually leads to the project interruption. Methods: Due to the fact that the criterion for the behavior of fine soils against moisture is Atterberg Limits, therefore, Atterberg Limits and the water content were utilized. For this purpose, the new method proposed by Hollman and Thewes (2013) was used. In this study, in addition to the Atterberg limits, the amount of free water resulting from the machine and from the underground water inflow was included in the calculations. Results: It was found that the water content should be increased carefully as the soil is very sensitive to this parameter. An increase of 15% of the water content permits to reduce the risk of clogging. If the added free water amount 15%, the probability of clogging becomes high. Whereas, in case where the added free water amount reaches 20%, the risk of clogging decreases significantly. Conclusion: According to the performed assessments, it was found that critical areas for the clogging aspect are both the cutter head and the chamber. The sensitivity of the soil is very important to the free water amount. Therefore, due to the behavior of sticky and plastic of clay soils against increasing water, it is necessary to determine the percentage of allowable water used in mechanized excavation projects.

Ultraflexible and Mechanically Strong Double-Layered Aramid Nanofiber-Ti3C2Tx MXene/Silver Nanowire Nanocomposite Papers for High-Performance Electromagnetic Interference Shielding.

High-performance electromagnetic interference (EMI) shielding materials with ultraflexibility, outstanding mechanical properties, and superior EMI shielding performances are highly desirable for modern integrated electronic and telecommunication systems in areas such as aerospace, military, artificial intelligence, and smart and wearable electronics. Herein, ultraflexible and mechanically strong aramid nanofiber-Ti3C2Tx MXene/silver nanowire (ANF-MXene/AgNW) nanocomposite papers with double-layered structures are fabricated via the facile two-step vacuum-assisted filtration followed by hot-pressing approach. The resultant double-layered nanocomposite papers with a low MXene/AgNW content of 20 wt % exhibit an excellent electrical conductivity of 922.0 S·cm-1, outstanding mechanical properties with a tensile strength of 235.9 MPa and fracture strain of 24.8%, superior EMI shielding effectiveness (EMI SE) of 48.1 dB, and high EMI SE/t of 10 688.9 dB·cm-1, benefiting from the highly efficient double-layered structures, high-performance ANF substrate, and extensive hydrogen-bonding interactions. Particularly, the nanocomposite papers show a maximum electrical conductivity of 3725.6 S·cm-1 and EMI SE of ∼80 dB at a MXene/AgNW content of 80 wt % with an absorption-dominant shielding mechanism owing to the massive ohmic losses in the highly conductive MXene/AgNW layer, multiple internal reflections between Ti3C2Tx MXene nanosheets and polarization relaxation of localized defects, and abundant terminal groups. Compared with the homogeneously blended ones, the double-layered nanocomposite papers possess greater advantages in electrical, mechanical, and EMI shielding performances. Moreover, the multifunctional double-layered nanocomposite papers exhibit excellent thermal management performances such as high Joule heating temperature at low supplied voltages, rapid response time, sufficient heating stability, and reliability. The results indicate that the double-layered nanocomposite papers have excellent potential for high-performance EMI shielding and thermal management applications in aerospace, military, artificial intelligence, and smart and wearable electronics.

The influence of clay addition in fly ash concrete mixture for nuclear shielding

The disposal of ashes from power plants has caused health issues and reduce the air quality of the surrounding areas. The ashes have a potential to be used in construction of concrete mixture as partial replacement for cement. This research studies the potential fly ash and clay mixture (FAC) as a nuclear shielding material in concrete mixture. The raw materials and the testing were all done in Agensi Nuklear Malaysia. All concrete mixtures had a constant water/cement ratio of 0.266. The hardened concrete mixtures were tested for compressive strength. Scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and small angle neutron microscopy (SANS) are used to characterize the properties of the mixtures. The results suggested that mixture of FAC concrete with 10% of clay addition showing good potential for nuclear shielding compared to other ratios.

Appraisal of new density coefficient on integrated-nanoparticles concrete in nuclear protection

Abstract The most important material for shielding is concrete in nuclear facilities which performance can be improved by addition some Nanoparticles (NP) at the various concentrations. Nanoparticles, which have a distinctive potential for bio-radiation and shielding of nuclear reactors, are used in many areas due to their special characteristics, which lead to an improvement in the mechanical properties and the pore structure of the concrete shield. The aim of this research was to initiate a novel coefficient (n), experiment to theory density ratio for integrated NP at different nanoparticle concentrations (xnano), established upon purely mathematical viewpoints and some appropriate physical objectives.

Current issues of search of gold placers in the south of Ukraine

The main gold ore territory of Ukraine is Ukrainian shield, mainly its central and eastern parts. Currently, the potential of Ukrainian shield is estimated at 2.4 thousand tons of gold. Gold ore deposits are insufficiently studied and not brought to development. The same can be said about the development of gold placers. But in the case of shallow deposits its study and development may be economically justified, it does not require large capital investments and allows to recoup costs in a short time. This is especially true given the extremely favorable situation on the world gold market in recent years. Erosion and denudation of native deposits certainly led to the formation of deposits of native placer gold in the sedimentary cover on the territory of the Ukrainian shield and its slopes. Significant amounts of geological information on the widespread distribution of placer gold in loose sediments, in the modern basins of the Dnieper, Southern Bug, Don, Black and Azov Sea shelf, have been accumulated. This corresponds to the location of indigenous sources of gold and the general direction of unloading of river systems. Previous geological studies in this area have revealed numerous manifestations of placer gold of various scales, but no industrial facilities have been recorded. Placer gold in the south of Ukraine is characterized by a high mass fraction of gold of small and thin size classes and significantly aleurite-clay composition of gold-bearing deposits. Such characteristics complicate the geological search and real assessment of gold-bearing objects and, provided that standard sampling and processing methods are used in geological works, lead to underestimation of the real gold content. Studies conducted on the most studied placer sites convincingly show that gold is lost when washing samples, even under careful control. And this is a typical situation for many objects (not only Ukrainian), which were studied using the standard method of extracting free gold by gravity. That is why there are reasonable doubts about the reliability and quality of the current assessment of placer gold deposits. In our opinion, the prospects for the search for loose gold on the Ukrainian shield and its slopes are significantly underestimated. The presence of indigenous sources with great resource potential and at the same time numerous known manifestations of different ages and scales of placer gold clearly indicate the possibility of the formation of placers with industrial characteristics in the sedimentary stratum of southern Ukraine. The use of modern technologies for the gold enrichment and extraction, high-precision analytical research and the favorable state of the world gold market force to urgently review the results of previous geological work. The problem of conducting new comprehensive research aimed at auditing the accumulated data, identifying, and studying of placer deposits namely with gold of small and thin size classes is becoming urgent. The result of such work should be the discovery and industrial development of gold placers, which can be the basis of gold production in Ukraine.

Magnetic shielding of a short thick GdBCO tube fabricated by the buffer aided top-seeded infiltration and growth method

Melt-textured (RE)Ba2Cu3O7 superconductors (where RE is a rare earth element like Y, Gd or Dy) have a significant potential for passive magnetic shielding. Their critical current density Jc, however, is not uniform throughout the sample and this fact needs to be taken account to design a large magnetic shield made of these materials. In this work, magnetic shielding properties have been investigated at 77 K in an axial magnetic field for short GdBCO tubes fabricated by the top-seeded infiltration and growth (TSIG). The tubes, having ∼10 mm thick walls, were studied with or without caps made of the same material. First, the shielding factor measured at several positions along the axis of the open tube was used to assess the non-uniformity of the shielding performance along the z axis. Second, four different configurations were brought when closing a tube with a disk, and their shielding performances were measured and compared. Third, we investigated the magnetic shielding efficiency for the tube closed with caps of different geometrical characteristics. The thickness of the cap used to close one side of the tube was shown to be an important parameter; experimental results showed that the same efficiency of a given cap could be obtained by stacking up two thinner caps with the same total height. Finally, the shielding behaviour of the open tube was modelled in order to investigate the flux penetration and to analyse the possible distribution of the critical current density Jc in the non-uniform GdBCO tube. The field dependence of the shielding factors measured at five elevations along the axis of the tube could be reproduced qualitatively by considering the GdBCO tube made of 3 layers, each of them with a constant Jc. This gives evidence that a simple model ignoring the field dependence of the critical current density can be used to reproduce the experimental magnetic shielding data. The model was also used to show the field penetration into the tube walls. These results are useful for getting better understanding of the properties of bulk superconductors synthesized by the TSIG process and to identify, in a non-destructive manner, which parts of the samples could be improved to obtain a good shielding performance.