Passive Shielding Research Articles

Signal Integrity Assessment of GNRFET-Based Ternary Logic for Multi Layered GNR Interconnects with Dielectric Insertion

In this paper, signal integrity assessment is carried out for graphene nanoribbon field effect transistor (GNRFET) based ternary logic with dielectric inserted multi-layered GNR (MLGNR) interconnects. The analyses are carried out for crosstalk effects and eye diagrams with and without shielding lines. In this paper firstly, it is observed that the dielectric inserted MLGNR interconnects show better than copper (Cu) and multiwall carbon nanotube (MWCNT) interconnects. Secondly, active shield technique is adopted, and observed that it exhibits better performance than without shield and passive shield techniques. Also, the power-delay product performance parameter is evaluated and envisaged that active shield technique outperforms passive technique. Further, the eye diagram analysis is carried out for different bit rates. The different performance analyses in the paper have been carried out for 10 nm technology node.

A Review of Magnetic Shielding Technology for Space Radiation

The space radiation environment outside the protection of the Earth’s magnetosphere is severe and difficult to shield against. The cumulative effective dose to astronauts on a typical Mars mission would likely introduce risk exceeding permissible limits for carcinogenesis without innovative strategies for radiation shielding. Damaging cardiovascular and central nervous system effects are also expected in these space environments. There are many potential options for advanced shielding and risk mitigation, but magnetic shielding using superconductors offers several distinct advantages including using the conditions in space to help maintain the superconductor’s critical temperature and lower mass compared to equivalent passive shielding materials. Despite these advantages, the development of magnetic shielding technology has remained primarily in conceptual stages since the introduction of the idea in 1961. Over the last several decades, magnetic shielding has experienced periods of high and low attention by the human spaceflight community, leading to computational tools with single-use or other limitations and a non-uniform distribution of publications on the topic over time. Within the context of technology development and the surrounding space policy environment, this paper reviews and summarizes the available literature on the application of active magnetic shielding for space radiation protection, identifies challenges, and highlights areas for future research.

Measurement and Analysis on Magnetic Field Influence of Substation for Magnetic Shielding Device

The residual magnetic field in a magnetic shielding device with a multilayer high permeability material (permalloy) structure can be obtained at the nanotesla (nT) level or even lower. At present, in the process of designing a magnetic shielding device, most of the external environmental magnetic field settings are set at the size of the Earth’s environmental magnetic field, but the instruments inside the magnetic shielding device need to be powered, the active compensation coil needs to be powered, and the degaussing coil of passive shielding layer needs to be powered, so substations need to be used around magnetic shielding devices. The magnetic field generated by the substation will affect the magnetic shielding device, so this paper analyzes and measures the magnetic field generated by the substation. Firstly, the finite element model of a substation is established, and the influence of different substations on the environmental magnetic field is analyzed by changing the power. Secondly, the test method of a substation environment magnetic field is determined. Finally, the site test was carried out to measure the influence of different power substations and different distances on the magnetic field, and its influence on the magnetic shielding device was analyzed, which provided an important basis for the construction of the magnetic shielding device.

Realization and Tests of Prototype Fluxgate Magnetic Sensors for the ITER Neutral Beam Injectors.

In the ITER neutral beam injectors (NBI), the presence of an external variable magnetic field generated by the ITER tokamak itself, could deflect the ion beam during acceleration and cause a loss of beam focusing. For this reason, the ion source, the accelerator and the neutralizer will be shielded from external magnetic field by means of a passive magnetic shield and a system of active correction and compensation coils (ACCC). The ACCC will operate in a feedback control loop and thus require the measurement of magnetic field inside the NBI vessel. Magnetic sensors for this application must be capable of measuring DC and slow variable magnetic fields, and be vacuum-compatible, radiation-hard and robust, since they will be subjected to neutron flux produced by fusion reactions in the tokamak and inaccessible for maintenance. This paper describes the realization and tests of fluxgate magnetic sensors prototypes specifically designed for this purpose before the installation in MITICA and ITER.

A new ultra low-level HPGe activity counting setup in the Felsenkeller shallow-underground laboratory

A new ultra low-level counting setup has been installed in the shallow-underground laboratory Felsenkeller in Dresden, Germany. It includes a high-purity germanium detector (HPGe) of 163% relative efficiency within passive and active shields. The passive shield consists of 45 m rock overburden (140 meters water equivalent), 40 cm of low-activity concrete, and a lead and copper castle enclosed by an anti-radon box. The passive shielding alone is found to reduce the background rate to rates comparable to other shallow-underground laboratories. An additional active veto is given by five large plastic scintillation panels surrounding the setup. It further reduces the background rate by more than one order of magnitude down to 116(1) kg−1d−1 in an energy interval of [40 keV;2700 keV]. This low background rate is unprecedented for shallow-underground laboratories and close to deep underground laboratories.

Study of a Double-layer Passive Magnetic Shielding System for Electric Vehicle WPT

Study of a Double-layer Passive Magnetic Shielding System for Electric Vehicle WPT

Performance of the SABRE detector module in a purely passive shielding

We present here a characterization of the low background NaI(Tl) crystal NaI-33 based on a period of almost one year of data taking (891 kgtimes days exposure) in a detector configuration with no use of organic scintillator veto. This remarkably radio-pure crystal already showed a low background in the SABRE Proof-of-Principle (PoP) detector, in the low energy region of interest (1–6 keV) for the search of dark matter interaction via the annual modulation signature. As the vetoable background components, such as ^{40}K, are here sub-dominant, we reassembled the PoP setup with a fully passive shielding. We upgraded the selection of events based on a Boosted Decision Tree algorithm that rejects most of the PMT-induced noise while retaining scintillation signals with > 90% efficiency in 1–6 keV. We find an average background of 1.39 ± 0.02 counts/day/kg/keV in the region of interest and a spectrum consistent with data previously acquired in the PoP setup, where the external veto background suppression was in place. Our background model indicates that the dominant background component is due to decays of ^{210}Pb, only partly residing in the crystal itself. The other location of ^{210}Pb is the reflector foil that wraps the crystal. We now proceed to design the experimental setup for the physics phase of the SABRE North detector, based on an array of similar crystals, using a low radioactivity PTFE reflector and further improving the passive shielding strategy, in compliance with the new safety and environmental requirements of Laboratori Nazionali del Gran Sasso.

Shielding effectiveness of different polymers and low-density hydrides in a combined radiation shield for crewed interplanetary space missions

Exposure to Galactic cosmic rays (GCR) and solar particle events (SPE) has been identified as one of the critical barriers for long term space missions that impose both immediate and delayed health hazards on the astronauts. There are two types of protective shields available namely active and passive shields, and combining these two shields can be a useful strategy. The study aims to present the effectiveness of a combined radiation shield containing an active toroidal shield with a layer of passive shield made of different polymers or low-density hydrides. The active shield is capable of deflecting protons (Z < 1) with energies below 700 MeV/n and for Alpha, and Fe ions (Z > 1) it can deflect up to 200 MeV/n and 175MeV/n respectively. The shielding effectiveness of polymers and hydrides with different thicknesses was investigated with Monte Carlo simulations performed by means of Geant4/MULASSIS. The shielding properties were studied using proton, alpha, and Fe ions with energies of 1 GeV/n. Nuclear stopping power and Fast Neutron Removal Cross Section (FNRCS) were calculated using SRIM and PHY-X/PSD. For the 20 gm/cm2 thick layer made of polymers, the reduction of dose equivalent for proton, alpha, and Fe ion of 1GeV/n are 5.44%, 54.34%, and 63.76% respectively and in the case of Low-density Hydrides with the same dimension, the rates are 4.12%, 55.3%, and 76.88%. Low-density hydrides demonstrated better radiation shielding capability than the polymers. The results are compared with OLTARIS for GCR spectra of 2010 solar minimum. The downsides of this type of shield are also briefly covered.

Simple and active magnetic-field stabilization for cold atom experiments.

Cold atom experiments usually need a controllable and low-noise bias magnetic field to provide a quantization axis. Most labs need home-made stabilization of the field according to the actual setup, as commercially available power supply cannot directly satisfy their requirements. Here, by measuring the field fluctuations and active feedback modulating current supply of the applied magnetic field, we successfully demonstrate a field of 10.58G with a stability to the level of 2.8 × 10-7 in a duration of 5min. The root mean square noise is reduced to 0.05 mG, compared to the noise of 1.3 mG without stabilization. The coherence time of the magnetic-field sensitive transition between the rubidium ground states F=1,mF=-1 and 1,0, as measured by Rabi oscillation, is extended to 19.2ms from the unstabilized value of 1.3ms. This result is long enough for most experiments on quantum simulation and precision measurement. As our system has no passive magnetic shielding and additional compensation coils, it is highly simple and compact to provide the stable magnetic field and would be adapted to various applications with cold atoms.

Active EMI Suppression System for a 50 mT Unshielded Portable MRI Scanner.

Passive shielding is usually applied to block electro-magnetic interference (EMI) for portable very-low field MRI scanners, but it goes against the mobility of the scanners. Here, the reference channel-based active EMI suppression (AES) system was proposed to discard them. Different from the existing studies, this work started with analyzing the interference transmission paths and discovered that the human body coupling was the main path. Then, the "ring-" shaped EMI receiving coil designed here together with the electrocardiograph (ECG) electrode patch were used to suppress the human-body-coupled interferences. For the first time, the periphery data of the k-spaces of the RF coil and the EMI detectors were utilized to calculate the transfer factors in multiple frequency bands by using the least square method. The reference EMI signals were transferred to the interferences in the MR signal by multiplying the transfer factors in each frequency band, and the denoised MR signal could be obtained by subtracting the transferred reference EMI signals. The prototype of the AES system was applied to a 50 mT unshielded portable MRI scanner. The in-vivo experiments indicated that the interference suppression rate of the AES system equipped with the "ring-" shaped EMI receiving coil could reach 96.8%. Meanwhile, the SNR of the images after interference suppression by the AES system equipped with both types of detectors was 97.2% of that of the images scanned inside the shielded room. The proposed AES system ensures that the portable MRI scanner works normally in unshielded environment. Our study provides a solution to make portable MRI scanners truly movable.

Status of the Jiangmen Underground Neutrino Observatory

The Jiangmen Underground Neutrino observatory (JUNO) experiment uses a large liquid scintillator detector to detect electron antineutrinos issued from nuclear reactors at a distance of 53 km. Its main goal is to determine the neutrino mass hierarchy and precisely measure some of the oscillation parameters. The detector will be located 700 m underground and will consist of 20 ktons of liquid scintillator contained in a 35 m diameter acrylic sphere, instrumented with 17612 (20-inch) and 25600 (3-inch) photomultiplier tubes (PMT), respectively. It will achieve an unprecedented 3% energy resolution (at 1 MeV). The objective is to detect 100000 events after 6 years of data taking. Two independent veto systems are foreseen to reduce the different backgrounds. A 40 kton ultrapure water Cherenkov pool instrumented with 2400 20-inch PMTs surrounds the central detector. It will tag events coming from outside the neutrino target. It will also act as a passive shielding for neutrons and gammas. In addition, a muon tracker will be installed on top of the detector (top muon veto) in order to tag cosmic muons and validate the muon track reconstruction.

Radionuclide activity in cryoconite from glaciers of the Central Caucasus, Russia

This work presents the results of a study of radionuclide activity in cryoconite from glacier and glacial soil of the Central Caucasus. Cryoconite were sampled from the surface of the Garabashi glacier, and soil samples were taken from the humus horizon of periglacial mountain forest-meadow soil. Measurements were performed with low-background germanium gamma spectrometers located inside a passive shield consisting of ∼20 cm of copper, ∼15 cm of lead, and ∼8 cm of borated polyethylene. The specific activity of radionuclides (Be-7, K-40, Th-232, U-235, U-238, Cs-137) was established. It was revealed that all measured spectra contain γ-lines from decays of K-40, decay chains of U-238, U-235 and Th-232. In addition, the spectra of cryoconite samples from the Garabashi glacier show a 477.6 keV line from the decay of the cosmogenic isotope Be-7, and in the soil sample a 661.7 keV line from the radionuclide Cs-137. No radionuclide Be-7 was detected in the mountain forest-meadow soil. Radionuclide Cs-137 is present in the soil sample, while in cryoconite, is not detected. Radioisotope activities in the Garabashi glacier cryoconite, except for the cosmogenic isotope Be-7, do not differ significantly in terms of mass, i.e., the content of K-40, U-238, U-235 and Th-232 in them is approximately the same. The activity of all the studied radionuclides in the soil sample compared to cryoconite samples is lower, although the differences are not significant, except for Th-232, whose activity in soil is almost two times lower.

Effectiveness of Kevlar and water-soaked hygienic wipes in a combined radiation shield for manned long termed space missions

Exposure to Galactic cosmic rays (GCR) and solar particle events (SPE) in long term space missions, astronauts will experience both immediate and delayed impacts. To confront space radiation active and passive shielding approaches are available and deploying a suitable coupling of these two shields can be a good solution. This paper presents a combined radiation shield comprising an active toroidal shield with an additional 10 cm layer of a passive shield made of Kevlar or Water-soaked hygienic wipes (WSHW). The active shield can deflect protons with energy around 575 MeV, and it can deflect higher Z particles (Alpha, Fe) up to 190 MeV/n. The shielding effectiveness of Kevlar and Water-soaked hygienic wipes was investigated with Monte Carlo simulations. The shielding properties were studied using proton, alpha, and Fe ions with energies of 1 GeV/n. WSHW has shown greater radiation shielding efficiency than Kevlar. For Kevlar, the rate of total absorbed dose reduction for proton, alpha, and Fe ion is 3.47%, 43.36%, and 44.53% respectively and for WSHW, the rate is 4.2%, 45.13%, and 59.87% respectively. Results are also compared with Polyethylene (PE). The shortcomings of this form of shield are also briefly covered as well.

Accuracy Assessment of Simplified Computation of Active and Passive Magnetic Shielding for Optically Pumped Magnetometers

A low residual environmental magnetic field is required for the proper operation of most optically pumped magnetometers (OPMs). This is achieved using a combination of passive and active magnetic shielding. Passive magnetic shielding often uses multiple layers of highly permeable materials. A realistic two-layer magnetically shielded room (MSR) for biomagnetic measurements is numerically studied using the finite element method. A measured B-H characteristic of Mumetal is used, which is linearly extrapolated from the Rayleigh region (RR) into the low magnetic field range. This extension of the magnetization curve yields no significant differences compared to using a constant permeability value for the low magnetic field range. Furthermore, we model the MSR with only one shield and apply a simple analytical method of images (MOI). The MOI yields on average a 100-fold reduction in computation time. The relative difference of the magnetic flux density computed with MOI and finite element method (FEM) is smaller than < 1% at the center of a spherical region of interest (ROI) with a radius of 0.3 m desired from the point of magnetoencephalography (MEG) using OPMs. The achieved accuracy of the MOI makes it suitable for the optimization of active shielding coils.

Dose Attenuation in Innovative Shielding Materials for Radiation Protection in Space: Measurements and Simulations.

Galactic cosmic rays (GCR) are among the main deterrents to manned space exploration. Currently, the most realistic way to reduce the dangers caused by GCR to acceptable levels is passive shielding. Light materials guarantee the strongest dose attenuation per unit mass. High-density polyethylene is considered the gold standard for radiation protection in space. Nevertheless, accelerator-based experimental campaigns already showed the advantages of more hydrogen-rich innovative shielding materials such as lithium hydride. The experimental campaigns of this work focused on the absorbed dose attenuation properties of lithium-based hydrides chemically stabilized with a paraffin matrix. Such materials were compared to pure lithium-based hydrides, polyethylene, structural materials such as spacecraft aluminum alloys and lithium batteries, and in situ shielding materials such as Moon regolith and its main components silicon and silicon dioxide. The experimental results were compared to simulations performed with PHITS, FLUKA, and Geant4, which are among the most used Monte Carlo codes for radiation protection in space. The simulations showed systematic differences and highlighted the pressing need for reliable nuclear cross-section models.

Comparative Analysis of Crosstalk Effects in Dielectric Inserted Horizontal andVertical Multi-layer GNR Interconnects for Ternary Logic System

In this work, the performance of copper (Cu), dielectric inserted horizontal graphene nanoribbon (Di-HGNR) interconnect and dielectric inserted vertical graphene nanoribbon (Di-VGNR) interconnects are investigated using active shielding and passive shielding techniques. However, the analysis is carried out by adapting driver-interconnect-load system. This analysis considers the interconnect length from 500 to 2000 μm for 10 nm technology node. Further, the crosstalk induced effects on various interconnect structures are examined. It is envisaged that Di-VGNR exhibits lowest propagation delay compared to Cu and Di-HGNR. Further, the in-phase and out-phase crosstalk delay among the coupled interconnect lines is determined. It is investigated that active shielded Di-VGNR has least crosstalk induced delay compared to other interconnect structures considered in this study. Therefore, Di-VGNR interconnects outperforms Cu and Di-HGNR and are best suited for future VLSI interconnects.

The upgraded low-background germanium counting facility Gator for high-sensitivity γ-ray spectrometry

We describe the upgrade and performance of the high-purity germanium counting facility Gator, which is dedicated to low-background γ-ray spectrometry. Gator is operated at the Gran Sasso Underground Laboratory in Italy, at an average depth of 3600 meter water equivalent, and employed for material screening and selection in ultra-low background, rare-event search experiments in astroparticle physics. The detector is equipped with a passive shield made of layers of copper, lead and polyethylene, and the sample cavity is purged with gaseous nitrogen maintained at positive pressure for radon suppression. After upgrading its enclosure, the background rate is (82.0 ± 0.7) counts/(kg·day) in the energy region 100 keV to 2700 keV, a 20% reduction compared to the previously reported rate. We show the stability of various operation parameters as a function of time. We also summarize the sample analysis procedure, and demonstrate Gator's sensitivity by examining one material sample, a candidate photosensor for the DARWIN experiment.

Novel method of ancient pottery analysis based on radioactive isotope ratios: a pilot study

The proposed method has been applied to a multi-phased settlement complex and pottery manufacturing centre in Ostrowite in northern Poland. In this study the radioactive isotope ratios method has been applied to a set of ceramic pottery specimens from the same multi-layered archaeological site and probably produced from local raw material. The pilot radiometric research was based on: 24 Neolithic (5200–5000 BCE), 21 Early Iron Age (800–600 BCE), 4 Roman Period (100–400 CE), and 13 Middle Ages (1030–1320 CE) pottery fragments, and also 8 samples of local clay (glacial till) and 3 burned clay samples. The method shows the similarities within the ceramic material used to manufacture the pottery. The variations in the quantitative and qualitative compositions of the basic products (clay, silt, loam, sand, ash and organic admixtures) used in the preparation of the ceramic paste change the isotopic composition and activity ratios. Pottery from each ceramic manufacturing centre, based on the specific composition of the raw materials, have characteristic isotope ratios. Radioactive isotope ratios as fingerprints of ancient ceramic manufacturing centres have not yet been applied as an archaeometric method. In this study two isotope ratios have been selected and applied: 40K/228Ac and 226Ra/208Tl. All analysis have been done using gamma spectrometry system, with quality and quantity analysis of the spectrums. Low-background passive shield was used for obtain improvement of results quality. The pilot study confirms the grouping of isotope ratio results for each sample type, even in terms of similarities with the base clay material collected in this region.

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.

Development of an equipment for real-time continuous monitoring of alpha and beta radioactivity in river water

Different regulations require the monitoring of radioactivity in the environment (e.g., 2013/51/Euratom, Real Decreto 314/2016) to protect the environment and the population from abnormal radioactivity presence caused by natural reasons or discharges or accidents in nuclear installations. Nowadays, the monitoring of α- and β-emitting radionuclides is performed discontinuously in laboratories due to the difficulties in applying classical techniques to continuous measurements. This limits the number of samples that can be measured per day, produces high costs per analysis, and introduces a significant delay between the moment of contamination and when it is detected. Plastic scintillation microspheres (PSm) represent a new possibility for continuous measurements because water samples can flow through a bed of PSm connected to a pair of photomultipliers (PMTs), allowing continuous monitoring of the activity. This idea is the basis of the Waterrad detector, which can monitor radioactivity at environmental levels in river water. This paper describes the optimization of a detection cell containing PSm, a detection chamber as well as active and passive shielding. In its final set-up, the Waterrad detector presents a background signal of 0.23 (1) cps and detection efficiencies of 1.86(7)·10−5 cps·L·Bq−1 for 3H, 7.4(8)·10−3 cps·L·Bq−1 for 90Sr/90Y and 5.5(5)·10−3 cps·L·Bq−1 for 241Am. The detection limits in the optimum window for a counting time of 5 h were 490 Bq/L for 3H, 2.3 Bq/L for 90Sr/90Y and 3.0 Bq/L for 241Am. These values indicate that Waterrad can be used as an alarm detector for monitoring radioactivity in water at activity levels similar to those of environmental samples, making it suitable for water or waste surveillance involving a high frequency of measurements.