Shield Configurations Research Articles

On Symmetry and Asymmetry in Nested Electromagnetic Shields

This work focuses on the study of shield systems consisting of nested enclosures. In the first step, using FDTD simulations and measurements in an anechoic chamber, we investigate the shielding effectiveness (SE) of the system of two nested rectangular enclosures in the frequency range of up to 3 GHz. It is shown for the first time that for a number of frequencies, the SE of the nested shields can be improved by 40–50 dB due to the asymmetric arrangement of the enclosures, their electrical connection, and the mutually perpendicular arrangement of the apertures. Next, we analyze the emissions from the electromagnetic radiation sources in the presence and absence of a nested shield system. The results show that a nested shield system may not attenuate the emission amplitude but increases it by more than 58 dB at the resonant frequencies of the enclosures. Then, we prove that a single enclosure can have a higher SE than the same enclosure as a part of a poorly designed nested shield system. The final part of the article formulates practical recommendations for the design of nested shield configurations.

Speaking with mask in the COVID-19 era: Multiclass machine learning classification of acoustic and perceptual parameters.

The intensive use of personal protective equipment often requires increasing voice intensity, with possible development of voice disorders. This paper exploits machine learning approaches to investigate the impact of different types of masks on sustained vowels /a/, /i/, and /u/ and the sequence /a'jw/ inside a standardized sentence. Both objective acoustical parameters and subjective ratings were used for statistical analysis, multiple comparisons, and in multivariate machine learning classification experiments. Significant differences were found between mask+shield configuration and no-mask and between mask and mask+shield conditions. Power spectral density decreases with statistical significance above 1.5 kHz when wearing masks. Subjective ratings confirmed increasing discomfort from no-mask condition to protective masks and shield. Machine learning techniques proved that masks alter voice production: in a multiclass experiment, random forest (RF) models were able to distinguish amongst seven masks conditions with up to 94% validation accuracy, separating masked from unmasked conditions with up to 100% validation accuracy and detecting the shield presence with up to 86% validation accuracy. Moreover, an RF classifier allowed distinguishing male from female subject in masked conditions with 100% validation accuracy. Combining acoustic and perceptual analysis represents a robust approach to characterize masks configurations and quantify the corresponding level of discomfort.

Impact study of beam losses in TRIUMF’s BL4N proton cave and ARIEL tunnel

As part of the ARIEL project, currently under construction at TRIUMF, a new proton beam line will be installed to transport up to 100 µA of nominal beam energy 480 MeV protons from the main cyclotron extraction port to an isotope separator on-line (ISOL) proton target station. This new beam line, approximately 80 m long, designated beam line 4-North (BL4N), will connect the cyclotron to the ARIEL facility via a tunnel. The proton beam line is designed for beam losses lower than 1 nAm−1 and will feature a collimator to remove the beam halo produced by large-angle scattering in the cyclotron extraction foil.The tunnel will be shared with an electron beam line with its own specific requirements for beam loss mitigation and machine protection, leading to another ISOL electron target station. The electron beam is generated by an e-linac with capacity for 500 kW beam power operation, but is ultimately expected to operate at 100 kW with losses not exceeding 20 nAm−1. After an initial stage of operation at 25 MeV the beam energy will be upgraded to 50 MeV.In this work, the effect of the beam losses, both chronic and catastrophic, in the tunnel and adjacent areas were studied. The FLUKA particle transport and interaction code was employed to estimate the impact of the combined proton and electron beam losses to the shielding, including as well the reflection of radiation from the target stations into the tunnel during ARIEL operation. This analysis resulted into a better assessment of the damage to equipment in the tunnel and the impact on maintenance due to activation of elements of the beam line. Maximum credible accidental scenarios were also detailed to validate the shielding configuration and the safety systems location.

MONTE-CARLO (MC) ANALYSIS OF BORATED MATERIALS FOR NEUTRON SHIELDING APPLICATIONS

Neutron shielding is of utmost importance in radiation environments such as nuclear reactors and particle accelerators and in fields such as health physics. In this work, the percentages of neutrons stopped by shields comprising of boron minerals (HDPE/B2O3, Epoxy/Priceite, Epoxy/Colemanite, Epoxy/Kernite) in their composition against neutron radiation of different energies is investigated using two separate MC simulations. Different layer combinations of epoxy based borated shielding materials with HDPE sheets were then simulated to find the optimum shielding configuration. In addition, radioactivation studies were carried out for these designs. The most suitable design was found to be the layered setup of the HDPE sheet and the epoxy/colemanite composite sheet for mixed neutron energies (

The hourly wind-bias-adjusted precipitation data set from the Environment and Climate Change Canada automated surface observation network (2001–2019)

Abstract. The measurement of precipitation in the Environment and Climate Change Canada (ECCC) surface network is a crucial component for climate and weather monitoring, flood and water resource forecasting, numerical weather prediction, and many other applications that impact the health and safety of Canadians. Through the late 1990s and early 2000s, the ECCC surface network modernization resulted in a shift from manual to automated precipitation measurements. Although many advantages to automation are realized, such as enhanced capabilities for monitoring in remote locations and a higher frequency of observations at lower cost, the increased reliance on automated precipitation gauges has also resulted in additional challenges, especially with data quality and homogenization. The automated weighing precipitation gauges used in the ECCC operational network have an increased propensity for wind-induced undercatch of solid precipitation. One outcome of the World Meteorological Organization (WMO) Solid Precipitation Intercomparison Experiment (SPICE) was the development of transfer functions for the adjustment of high-frequency solid precipitation measurements made with gauge/wind shield configurations used in the ECCC surface network. Using the SPICE universal transfer function (UTF), hourly precipitation measurements from 397 ECCC automated climate stations were retroactively adjusted for wind undercatch. The data format, quality control, and adjustment procedures are described here. The hourly adjusted data set (2001–2019; version v2019UTF) is available via the ECCC data catalogue at https://doi.org/10.18164/6b90d130-4e73-422a-9374-07a2437d7e52 (ECCC, 2021). A basic spatial impact assessment shows that the highest relative total precipitation adjustments occur in the Arctic, where solid precipitation has an overall higher annual occurrence ratio. The highest adjustments for solid precipitation are shared by the Arctic, Southern Prairies, and the coastal Maritimes, where stations tend to be more exposed and snowfall events occur at higher wind speeds.

Identification of radiopure tungsten for low background applications

In this article we explore the availability of radiopure tungsten and its potential as high density shield material for low background applications. For compact shield designs, conventionally, lead is used. Metallic tungsten and tungsten pseudo-alloys reach higher densities up to 19.3 g cm−3 and do not exhibit a significant 210Pb activity, which is a typical intrinsic contamination in lead. Within several γ-ray screening campaigns we were able to identify tungsten samples with activities similar or better than 1 mBq kg−1 in 232Th, 40K, 60Co and the second part of the 238U decay chain. In cooperation with a manufacturer we further reduced a persisting contamination in the first part of the 238U decay chain by a factor of ∼2.5 down to (305 ± 30) mBq kg−1. With Monte Carlo simulations, the construction of prototype tungsten-based setups and dedicated measurements, the shield capability of tungsten in comparison to lead was extensively studied. Specifically, the impact of cosmogenic radiation on the background at shallow depth was investigated. We showed that a 6%–40% reduction (depending on the exact shield configuration) in the muon-induced neutron fluence is achievable by replacing lead with an equivalent amount of tungsten regarding the suppression of external γ-radiation. Overall, many benefits using tungsten especially for low energy applications below a few 100 keV are found. The pseudo-tungsten alloy presented in this work paves the way for several applications especially regarding background suppression in particle and astroparticle physics search programs.

The Simons Observatory: Magnetic Shielding Measurements for the Universal Multiplexing Module

The Simons Observatory (SO) includes four telescopes that will measure the temperature and polarization of the cosmic microwave background using over 60,000 highly sensitive transition-edge bolometers (TES). These multichroic TES bolometers are read out by a microwave RF SQUID multiplexing system with a multiplexing factor of 910. Given that both TESes and SQUIDs are susceptible to magnetic field pickup and that it is hard to predict how they will respond to such fields, it is important to characterize the magnetic response of these systems empirically. This information can then be used to limit spurious signals by informing magnetic shielding designs for the detectors and readout. This paper focuses on measurements of magnetic pickup with different magnetic shielding configurations for the SO universal multiplexing module (UMM), which contains the SQUIDs, associated resonators, and TES bias circuit. The magnetic pickup of a prototype UMM was tested under three shielding configurations: no shielding (copper packaging), aluminum packaging for the UMM, and a tin/lead-plated shield surrounding the entire dilution refrigerator 100 mK cold stage. The measurements show that the aluminum packaging outperforms the copper packaging by a shielding factor of 8-10, and adding the tin/lead-plated 1K shield further increases the relative shielding factor in the aluminum configuration by 1-2 orders of magnitude.

An Investigation of Magnetic Field Influence in Underground High Voltage Cable Shields

Magnetic fields and the shielding efficiency of the shields of underground high voltage cables are studied in this paper regarding several shielding configurations and materials. Shielding efficiency and magnetic fields are computed for shields with the same mesh but from different shielding materials, such as aluminum, ferrite, metal, and steel. In order to get the best shield configuration depending on the source characteristics and the material, a conducting ferromagnetic region with various thickness values is considered as shielding. A finite element model is introduced to investigate the influence of the parameters of magnetic fields and the shielding efficiency of underground high voltage cables. Furthermore, the reduction of the magnetic fields with or without shieldings is also presented. The developed method is performed with the magnetic vector potential formulations and validated on a practical problem.

Monte Carlo Codes for Neutron Buildup Factors

The point-kernel method is a widely used practical tool for gamma-ray shielding calculations. However, application of that method for neutron transport simulations is very limited. The accuracy of the method strongly depends on the accuracy of buildup factors used in the calculations. Buildup factors are usually obtained using appropriate computer codes, either based on discrete ordinates transport method or Monte Carlo approach. Since these codes put strong demands on computer resources, they are applied on a limited number of shielding configurations and an attempt is made to use these results and formulate an empirical expression for buildup factors estimation. Due to high physical complexity of neutron transport through shielding material it is very hard to perform parameterisation in order to establish adequate empirical formula. Existing formulas are very limited and are usually applicable to a narrow neutron energy range for few commonly used shielding materials, mostly in monolayer configuration. Recently, a new approach has been proposed for determination of gamma ray buildup factors for mono-layer, as well as multi-layer shielding configurations covering a wide gamma ray energy range. The new regression model is based on support vector machines learning technique, which has theoretical background in statistical learning theory. Development of named regression model required a large number of experimental data obtained by Monte Carlo computer code. More than 7000 Monte Carlo runs were required. Due to physical complexity neutron transport is likely to require even more experimental data in order to generate a model of reasonable accuracy. Therefore, the choice of appropriate Monte Carlo code is a very important question. One has to take into account the accuracy as well as the time required for input preparation and running the code. What also has to be considered is the possibility of the code to be incorporated in an algorithm for automated generation of experimental data. In this paper three Monte Carlo codes are analysed, namely SCALE4.4 code package (SAS3 sequence), SCALE6.0 code package (MAVRIC sequence), and MCNP5. Two simple experimental setups based on a point isotropic source in spherical and slab-like shield are modelled, and the codes are examined on previously mentioned issues. The comparison results show that each one of the examined codes has potential to be used for neutron buildup factor model generation. However, some aspects of their utilization require further analysis prior to final selection.

Hybrid Shielding for Hypervelocity Impact of Orbital Debris on Unmanned Spacecraft

The passive shielding of space craft structures is critical due to the increase in demand for lightweight protection, which is required to counter the damaging effects of micro-meteoroid orbital debris (MMOD) on unmanned spacecraft, which have steeply increased in recent years. Research on hypervelocity impact (HVI) led to the development of shield configurations such as the conventional Whipple shield, which consists of two plates separated by a stand-off distance to allow for the fragmentation and dispersion of the debris from the impact. Variations in the Whipple shield have been proposed, where additional layers are included for increased energy dissipation efficiency. In this work, the authors develop, validate and test a numerical model of an orthogonally loaded hybrid Whipple shield, incorporating an aluminium honeycomb core, orientated with hexagonal tubes perpendicular to the direction of proposed debris travel, to mitigate the well-known channelling effect. The debris threat is an A2024-T3 projectile, impacting the structure at a velocity of 6.5 km/s. The proposed model is validated with experimental observations of the debris spread at half-angle and the efficiency of the proposed topology is assessed against a conventional two-plate A2024-T3 shield. The honeycomb core cell density, its position relative to the point of impact, the thickness of the honeycomb shell, and the material of the honeycomb are thoroughly analysed. A hybrid honeycomb structure concept is proposed, which provides a highly efficient alternative to a standard Whipple shield design, without significantly compromising the weight of the structure. The obtained results clearly show that the hybrid Whipple shield exhibits significantly increased the kinetic energy dissipation of the debris from the impactor and shield front plate, with an increase in the dissipated kinetic energy that can reach 86.8% relative to the conventional shield.

QADCGPIC–M: A point kernel shielding code with features for handling bulk shields up to 100 mean free path and stratified shielding configurations

Salient modifications and validations performed on a Point Kernel method based code QADCGPIC, which are important for optimizing shield design is presented in the paper. The geometric progression method based build–up factors (BUFs) for penetration depths of medium up to 100 mean free path is incorporated into the modified QADCGPIC–M code. Further improvement to the code is made by incorporating the modified Kalos’ formula of double layer gamma ray exposure build–up factor (DBUF) for the shielding materials used in the design of nuclear and radiological facilities. The modified code is validated by estimating the BUFs, DBUFs, and gamma dose rates at the exit of the shield with Monte Carlo simulation for various shielding configurations of lead, tungsten, iron, and concrete and published values. The validation exercise indicates a good agreement between the computed values by different methods. The incorporation of geometric progression fitting formula and modified Kalos’ formula into the QADCGPIC–M code increases the ability of the code to handle bulk shielding and optimization of thicknesses of double layered shielding configurations.

Effectiveness of Electrostatic Shielding in High-Frequency Electromagnetic Induction Soil Sensing.

High-frequency electromagnetic induction (HFEMI) sensors, operating in the frequency range from 300 kHz to 30 MHz, have been proposed for the measurement of soil electrical conductivity and dielectric permittivity that are related to the physical and chemical properties of soil. Because of the high-frequency operation, the capacitive coupling between the sensor transmitter and receiver coils is comparable to inductive coupling, creating the need for electrostatic shielding. The remnant capacitive coupling after the implementation of shielding can lead to significant difficulties in the sensor signal interpretation, because both coupling mechanisms are highly dependent on the geometry of the HFEMI sensor and applied shield. In this paper, we introduce the discussion on the relationship between the sensor geometry, shielding and the coupling mechanisms for HFEMI soil sensing. We theoretically and experimentally evaluate a typical HFEMI sensor and its shielding in the frequency range of up to 20 MHz and propose a method for evaluating the effectiveness of a shield configuration. In the case study, we experimentally analyze the HFEMI sensor above a saline solution for two shield configurations. The results agree well with the results of a finite element method analysis.

Low-Frequency Magnetic Shielding of Planar Screens: Effects of Loop Radius and Loop-to-Loop Distance

For the magnetic shielding configuration of both emitting and receiving loops placed coaxially on either side of a planar screen, we investigate the effects of loop radius and loop-to-loop distance on shielding effectiveness by numerically solving the accurate integral expression. The results are in good agreement with finite element simulations and experimental results. Simple and reliable approximate formulas are also proposed for pure conductive screens and pure magnetic screens, respectively. It is shown that the effects are obvious when the loop-to-loop distance is smaller than the loop radius. Also, conductive screens and magnetic screens exhibit opposite and competing shielding effectiveness evolution behaviors. In addition, in the case of conductive screens with a smaller receiving loop compared to the emitting loop, the shielded loop-to-loop mutual inductance does not always decrease with the increase of the loop-to-loop distance but peaks at a distance between the screen thickness and half of the emitting loop radius.

Thermal analysis of coupled vapor-cooling-shield insulation for liquid hydrogen-oxygen pair storage

The long-term storage of liquid hydrogen (LH2)-liquid oxygen (LO2) pair with extremely low heat leakage is essential for future deep space exploration. Vapor-cooled shield (VCS) is considered an effective insulation structure that can significantly reduce the heat penetration into the LH2 tanks, however it is relatively ineffective for the LO2 tanks. Novel coupled VCS insulation schemes for LH2-LO2 bundled tanks were proposed to achieve optimal performance not only for the LH2 but also for the LO2 tanks. A thermodynamic model had been developed and validated by experiments. The optimal VCS location, the temperature profile within the insulation, the heat leakage reduction contributed by the VCS, and the thermal performance versus scheme structural mass had been parametrically investigated. A comparison indicated that the proposed single integrated shield configuration can reduce the heat flux of the LH2 and the LO2 tanks by 64.0% and 54.8%, respectively compared with the non-VCS structure. In addition, the results also confirmed that zero boil-off storage of LO2 can be achieved by only utilizing the exhausted hydrogen vapor, with no need for an extra cryocooler.

Analytical and experimental studies on 245 kV gas insulated surge arrester

The voltage distribution across gas insulated surge arrester (GISA) is highly non-uniform as compared to conventional porcelain-clad surge arresters. The aim of the present paper is to optimize design of grading shield in such a way that the non-uniformity voltage factor across GISA must be less than ±10%. To achieve this order of non-uniformity factors, special grading shields like window based cylindrical and conical shields are proposed. In the present paper, 245 kV GISA model has been considered to analyze voltage distribution across the metal-oxide (MO) blocks. The electrostatic field and voltage distribution analyses are carried out on surge arrester by considering various shield configurations using numerical techniques. Further, design of shield and development is verified by performing dielectric duties on GISA assembly without MO blocks as per IEC 62,271–203. The lightning and switching impulse discharge current tests were carried out on the developed 245 kV GISA residual voltages were recorded. These voltage levels for above discharge currents are found to be in the order of 2.8 – 3.2 p. u. and are at acceptable levels as per IEC 60,099–4. Finally, protection level or V-I characteristics of GISA is established by measuring residual voltages for the entire current range.

Development of real-time measurement system for emission and absorption of visible light during heavy gamma-ray irradiation

A system for the real-time measurement of the visible light emission from and absorption by a material in an intense gamma-ray field was developed. A white light-emitting diode produces a visible light beam that passes through an irradiated specimen and is measured by an ultraviolet–visible spectrophotometer through a long glass optical fiber accompanied with a Pb shielding configuration. A video camera provides real-time visual observation of the gradual change in the color state of the irradiated specimens. In order to study the formation of silver nanoparticles in detail, blue color dye was added to the radiolytic medium and its color change was examined as a function of irradiation dose to observe the interaction among radiation-introduced radicals in water, generated silver nanoparticles, and dye molecules. A mutual impact between the formation of silver nanoparticles and the deformation of the dye during gamma radiolysis are experimentally clarified. The combination of direct visual observation and optical absorption measurement is expected to provide powerful clues for elucidating various phenomena caused by irradiation effects.

Space radiation electrostatic shielding scaling laws: Beam-like and isotropic angular distributions

Passive radiation shielding alone cannot provide adequate protection for astronauts on long-term, deep-space missions. High atomic number and energy (HZE) ions, and/or their secondaries, can penetrate any realistic mass shielding for long-term deep-space missions and cause damage to cells via direct energy deposition and/or through the production of secondary particles and fragmented nuclei. Active shielding, or the use of electromagnetic fields to deflect or stop incoming ions before reaching the spacecraft, has gained substantial attention over the last decade as a way to augment passive shielding. Recently, a mathematical relationship between a dimensionless scaling parameter characterizing the active shield and the incoming ion and a protected area formed on a downstream detector due to the deflection of HZE ions by the applied field was validated in Earth-based laboratory conditions. In the present work, the mathematical formulation is extended to relate electrostatic shielding efficacy with the ability to deflect positively charged ions with parameters relevant to space applications. Additionally, a modified scaling parameter is formulated to characterize the shielding efficacy of a “family” of electrostatic active shielding configurations for reducing flux density for a space-relevant isotropic source of energetic protons. The results of this study demonstrate a strong correlation among dimensionless scaling parameters and shielding efficacy metrics for space radiation-relevant HZE ions in beam and isotropic angular distributions. Furthermore, it establishes a framework for optimizing design of three-dimensional electrostatic shielding configurations to improve space radiation protection for astronauts on exploration-class missions.

Characterization of the non-ideal debris cloud in yaw hypervelocity impact by cylindrical projectile

This work revisits the classical hypervelocity impact problem of a cylindrical projectile impinging upon a thin plate at an attack angle. A methodology is described to identify the potentially dangerous fragments that can perforate the rear plate in a Whipple shield configuration. The attack angle is re-calculated based on the reported orthogonal view angles, followed by numerical modeling of the hypervelocity impact event using the SPH method in AUTODYN-3D, and the qualitative and quantitative post-processing of the debris cloud generated from the hypervelocity impact. The model predictions are compared to results from the experimental data from the literature for two different attack angles – they will be shown to be in good agreement. The concentrated area of dangerous fragments in the debris cloud is quantified in detail, and its damage mechanism to the rear plate is revealed. The majority of the projectile fragments are located inside the inner cone and the cross-wing of the debris cloud, where the latter bridge connecting the inner cone and the outer bubble, and they are defined according to their geometry shapes being as the components of the debris cloud. The accumulative effect of the two structures are shown to attribute to the potential damage in the rear plate. This work aims to help Whipple shield designers seeking a theoretical method to estimate the threat of yaw hypervelocity impact.

Reducing space radiation cancer risk with magnetic shielding

Interplanetary space radiation presents significant hazards to astronaut health and survival because it can cause both acute and chronic health effects including carcinogenesis. Mitigation of space radiation risks remains critical for enabling human missions beyond Earth orbit. Currently available options for space radiation shielding, such as water shielding, may not be sufficient at reducing space radiation dose and cancer risk to within current regulatory limits. Active magnetic shielding using superconductors has consistently been identified for further study due to its high potential benefit. In response, we have developed Monte Carlo models to determine the effectiveness of several of the latest magnetic shielding concepts, along with current passive shielding techniques, in terms of risk of exposure induced death. This was done for various Mars flyby mission profiles according to current space agency risk tolerance limits. Our study found that few shielding options were able to meet current risk tolerance limits without relying on astronauts of advanced age (>60 years). However, all of the magnetic shielding configurations provided substantial benefit in reducing space radiation cancer risk given high magnetic field strength (7 Tesla). With this information, space agencies can move towards engineering assessments of magnetic shielding technology and begin to advance the concept into a solution enabling interplanetary travel.

Optimization of a B[formula omitted]C/graphite composite energy degrader and its shielding for a proton therapy facility

Proton therapy is an advanced cancer treatment modality due to its ability to precisely deliver radiation doses to tumors using the Bragg peak effect. An energy degrader plays a vital role at a cyclotron-based proton therapy facility, as it provides a rapid, reliable, and reproducible method of setting the appropriate beam energy for radiotherapy. However, the protons undergo nuclear interactions with the matter in the degrader, leading to significant secondary particles causing a large ambient radiation dose nearby, creating severe risks for the facility operation. This study investigated the beam loss mechanism and the secondary particle generation in a B4C/graphite composite (BGC) energy degrader. Monte Carlo simulations were performed to ensure the shielding design’s reliability. Calculations showed that the BGC degrader had a higher beam transmission efficiency than a pure graphite degrader, while the secondary neutron yield was higher. An optimum shielding configuration can significantly reduce the radiation dose to an acceptable level for sensitive devices and maintenance staff.