Double-layer Shield Research Articles

Source Terms and Attenuation Lengths for Estimating Shielding Requirements or Dose Analyses of Proton Therapy Accelerators

Proton therapy accelerators in the energy range of 100-300 MeV could potentially produce intense secondary radiation, which must be carefully evaluated and shielded for the purpose of radiation safety in a densely populated hospital. Monte Carlo simulations are generally the most accurate method for accelerator shielding design. However, simplified approaches such as the commonly used point-source line-of-sight model are usually preferable on many practical occasions, especially for scoping shielding design or quick sensitivity studies. This work provides a set of reliable shielding data with reasonable coverage of common target and shielding materials for 100-300 MeV proton accelerators. The shielding data, including source terms and attenuation lengths, were derived from a consistent curve fitting process of a number of depth-dose distributions within the shield, which were systematically calculated by using MCNPX for various beam-target shield configurations. The general characteristics and qualities of this data set are presented. Possible applications in cases of single- and double-layer shielding are considered and demonstrated.

The effects of 8-arm-PEG-catechol/heparin shielding system and immunosuppressive drug, FK506 on the survival of intraportally allotransplanted islets

This study proposed a double-layer shielding method of using 8-arm-PEG-catechol (PEG8) and N-hydroxysuccinimidyl-linked unfractionated heparin (UFH–NHS) for the prevention of instant blood-mediated inflammatory reaction (IBMIR) and immune reactions against transplanted pancreatic islets. The surface of islet was evenly covered by PEG8 and UFH–NHS. Both viability and functionality of islets were evaluated in vitro, and the anti-coagulation effect of conjugated heparin on the islet surface was also evaluated. The inhibition effects of PEG8/UFH double-layer shielding system on immune reactions and IBMIR induced by transplanted islets were evaluated in an allograft model. When pancreatic islets of Sprague–Dawley (SD) rats were transplanted in the liver of F344 rats, the mean survival time (MST) of PEG8/UFH double-layer shielded islets (6.8 ± 1.6 days) was statistically increased, compared to that of unmodified islets (3.6 ± 1.1 days). Furthermore, when 0.5 mg/kg of FK506 was daily administered, the MST of double-layer shielded islet (15.0 ± 2.1 days) was increased by two-fold, compared to that of unmodified islets treated with the same dose of FK506 (8.0 ± 2.4 days). Therefore, a newly developed strategy of combining the PEG8/UFH double-layer shielding system with FK506 would certainly be effective for preventing immune activation and IBMIR against allotransplanted islets.

Investigation of Models of Grid-Like Shields Subjected to Lightning Electromagnetic Field: Experiments in the Frequency Domain

In this paper, frequency-domain measurements of magnetic and electric field shielding effectiveness of grid-like spatial shield models exposed to lightning action are presented. Scaled experimental models of nearby and direct lightning strikes are proposed. Models of single-layer and double-layer wire shields of two different mesh widths are examined. Differences between the shielding effectiveness of magnetic and electric fields are discussed. The measurement results are compared to the results of numerical simulations.

Synthesis of titanium nitride thin films deposited by a new shielded arc ion plating

Thin films of titanium nitride (TiN) were deposited on stainless steel substrates by a modified deposition technique, double-layered shielded arc ion plating with vicarious circular holes (DL-SAIP). The results show that the TiN film with the distance of 10mm between the double-layered shield plates had the least droplets. The deposition rate of the films prepared with the new technique was more homogeneous than that of all the other shielded arc ion plating. The film/substrate adhesion and microhardness values of the TiN films were higher than 40N and 18GPa, respectively. Thus such TiN thin films can be expected in applications.

Design considerations to affect on shielding effectiveness for conductive enclosure

The main section of this paper has mentioned to design considerations for conductive enclosure. Firstly, shielding effectiveness is investigated for various shielded enclosures. Also, amount of increase in shielding effectiveness is obtained by double layer shields. Next, the influence of apertures and its equivalent rectangular slot are explained. Shielding effectiveness is analyzed for shielded enclosure with waveguide slot, empty shielded enclosure and shielded enclosure with substrate, separately.

A Two-Level Genetic Algorithm for Electromagnetic Optimization

Optimizing complex engineering problems may demand large computational efforts because of the use of numerical models. Global optimization can be established through the use of evolutionary algorithms, but may demand a prohibitive amount of computational time. In order to reduce the computational time, we incorporate in the global optimization procedures a physics-based fast coarse model. This paper presents a two-level genetic algorithm (2LGA) for electromagnetic optimization. This algorithm employs the global convergence properties of the genetic algorithm, where acceleration of the optimization results from the fast computations of the coarse model (low level) and where accuracy is guaranteed by using a limited number of fine model (high level) evaluations. Using the coarse model, we iteratively build surrogate models (intermediate levels) where metamodels produce surrogate models which approximate the fine model. The proposed algorithm comprises internal parameters which are self-tunable. We applied the 2LGA to the optimization of an algebraic test function, to the optimization of a die press model (TEAM Workshop Problem 25) and to the optimization of an octangular double-layered electromagnetic shield. The results show that the 2LGA is converging to the optimal solutions as the traditional genetic algorithm and that the acceleration is dependent on the accuracy of the low level. An acceleration factor of more than two can be achieved.

Optimization of an Octangular Double-Layered Shield Using Multiple Forward Models

A large computational effort is required in order to design an octangular double-layered shield that can be modeled by a 3-D numerical model only. Indeed, the conventional optimization methods minimize a cost function by many evaluations of this 3-D model. To reduce the CPU time, an optimization technique is developed-based on sequential quadratic programming-that takes advantage of two other models that are faster but less accurate than the 3-D FEM: a 2-D FEM and an analytical model.

Reduction of Lightning-Induced Magnetic Fields and Voltages Inside Struck Double-Layer Grid-Like Shields

This paper presents a numerical analysis of the reduction of lightning-induced magnetic fields and voltages inside double-layer grid-like spatial shields typically used in reinforced concrete buildings, e.g., nuclear power plants. The calculations are performed with the CONCEPT computer code, which solves Maxwell's equations using the method of moments in the frequency domain. The computer code is extended with the well-known transmission line model (TL-model) in order to simulate direct lightning strikes. The structure under study comprises a cubic cage of 2 m side length having single- or double-layer grid-like spatial shields with square meshes of 0.25 m width. Three lightning-channel attachment points are considered at the cage roof, namely, the center, the midedge, and the corner. The simulated lightning currents are the positive, the negative first, and the negative subsequent strokes at lightning protection level I (LPL I) according to the international standard series IEC 62305. The computed quantities comprise the currents through some selected wires of the grid-like spatial shields, the magnetic fields, the magnetic-field derivatives, and the induced voltage across a typical installation loop inside the shield. The results of the single-layer shield are compared to those of the double-layer one to evaluate the additional reduction of the latter shield.

Extended Theory on the Inductance Calculation ofPlanar Spiral Windings Including the Effectof Double-Layer Electromagnetic Shield

Recent progress on wireless planar battery charging platform highlights a requirement that the platform must be shielded underneath so that the electromagnetic (EM) flux will not leak through the bottom of the charging platform. The presence of the EM shield will inevitably alter the flux distribution and thus the inductance of the planar windings. In this paper, a theory of inductance calculation of spiral windings is extended to determine the inductance of planar spiral windings shielded by a double-layer planar EM shield which consists of a layer of soft magnetic material and a layer of conductive material. With the generalized equations, the impedance of the planar spiral windings on double-layer shielding substrate and the optimal thickness of shielding materials can be calculated accurately without using time-consuming finite-element method. Therefore, the influence of the double-layer electromagnetic shield on the inductance of the planar spiral windings can be analyzed. Simulations and measurements have been carried out for several shielding plates with different permeability, conductivity, and thickness. Both of the simulations and measurements of the winding inductance agree well with the extended theory.

Study on the Leakage Fields Prediction of a Static Ferromagnetic Shield in Consideration of Hysteresis and Residual Strain of Shielding Materials

A new approach for an estimation of a static ferromagnetic shielding effectiveness is proposed and verified considering the magnetic hysteresis of shielding materials. The measured leakage field of the shielding enclosure corresponds to the results of the finite element method (FEM) analysis when the permeability used for the calculation takes into consideration the effect of coercivity as a parameter representing the hysteresis of the shielding material. The effects of both permeability and coercivity on the leakage fields are discussed with regard to the magnetic properties of the shielding materials by using FEM analysis. The maximum leakage field, a figure of merit of the shielding efficacy, is determined by the coercivity of the material used for the shield. An increase in the leakage field caused by the deterioration of the soft magnetic properties is also discussed from the viewpoint of the effect of the residual strain induced during the assembly and installation of the shielding system. A double-layer shielding technique is effective in reducing the leakage field especially when it is feared that the shields are strained.

Ballistic resistance of double-layered armor plates

In this paper, the ballistic resistance of double-layered steel shields against projectile impact at the sub-ordnance velocity is evaluated using finite element simulations. Four types of projectiles of different weight and nose shapes are considered, while armor shields consist of two layers of different materials. In a previous study of the same authors, it was shown that a double-layered shield of the same metal was able to improve the ballistic limit by 7.0–25.0% under impact by a flat-nose projectile, compared to a monolithic plate of the same weight. Under impact by a conical-nose projectile, a double-layered shield is almost as capable as a monolithic plate. The present paper extends the analysis to double-layered shields with various metallic material combinations. The study reveals that the best configuration is the upper layer of high ductility and low strength material and the lower layer of low ductility and high strength material. This configuration results in some 25% gain in the ballistic limit under moderate detrimental impact. This research helps clarify the long standing issue of the ballistic resistance of the multi-layered armor configuration.

Protection performance of double-layered metal shields against projectile impact

Protection performance of double-layered metal shields against projectile impact

Detection of Metal Contaminants in Food Using High Tc SQUIDs Magnetometer

A PC controlled food contaminant detection system for practical use was designed and constructed. The system we have developed is the High-Tc SQUID based system, which is covered with waterproof stainless steel plates and acceptable to HACCP (Hazard Analysis and Critical Control Point) program. The outer dimension of the system is 1500L mm x 477W mm x 1445H mm and the acceptable object size is 200W mm x 80H mm. This system employed a double-layered permeable metallic shield with thickness of 1 mm as a magnetically shielded box. The distribution of the magnetic field in the box was simulated by FEM; the gap between each shield layer was optimized before fabrication. Then the shielding factor of 732 in Z-component was achieved. This value is good enough to operate the system in a factory. As a result, we successfully detected a steel ball as small as 0.3 mm in diameter with a distance of 75 mm.

A food contaminant detection system based onhigh-Tc SQUIDs

We have designed and constructed a computer controlledfood contaminant detection system for practical use, based onhigh-Tc SQUID detectors. The system, which features waterproof stainless steelconstruction, is acceptable under the HACCP (Hazard Analysis and CriticalControl Point) programme guidelines. The outer dimensions of the system are1500 mm length × 477 mm width × 1445 mm height, and it can acceptobjects up to 200 mm wide × 80 mm high. An automatic liquid nitrogen filling system was installed in the standardmodel. This system employed a double-layered permeable metallic shield with athickness of 1 mm as a magnetically shielded box. The distribution of themagnetic field in the box was simulated by FEM; the gap between eachshield layer was optimized before fabrication. A shielding factor of 732 in theZ-component was achieved. This value is high enough to safely operate the system in anon-laboratory environment, i.e., a factory. During testing, we successfully detected a steelcontaminant as small as 0.3 mm in diameter at a distance of 75 mm.

An iterative method for calculating gamma-ray build-up factors in multi-layer shields

Point kernel codes that simulate gamma-ray transport often use build-up factors to take scattered photons into account. This study introduces a new method, for computing multi-layer shield build-up factors. This method, based on an empirical formula for calculating double-layer shield build-up factors, is iterative. For an N-layer shield, each iteration of the method treats the first and the second layer of the shield. It replaces these layers by a single equivalent layer composed of an appropriate material and, hence, it turns the N-layer shield into an (N - 1)-layer shield. In order to determine the equivalent layer of an appropriate material, a neural network approach is developed: some neural networks trained on a large set of various configurations provide the equivalent material for any double-layer configuration. The method is implemented into MERCURE-6.3 straight-line attenuation code and is validated by comparison between MERCURE-6.3 results and reference data for one-dimensional geometries. Reference data obtained from transport calculations performed using the Sn transport code TWODANT. The comparisons prove the accuracy and sturdiness of the method.

Improvement of MERCURE-6’s General Formalism for Calculating Gamma-Ray Buildup Factors in Multilayer Shields

This study proposes an improvement of the general formalism for calculating gamma-ray buildup factors in multilayer shields developed by Assad et al. The main modification concerns the treatment of the double-layer shield formed by the two first layers of a multilayer shield. Instead of replacing the double-layer shield with an equivalent thickness of the layer of the second material, the improved general formalism replaces it with a single-layer shield made of an appropriate material. The determination of the appropriate material is implemented into MERCURE-6.1 thanks to neural networks trained on a large set of various configurations.One-dimensional comparisons with the TWODANT transport Sn code shows the accuracy of the new formalism for shields composed of three and five layers. Indeed, for three-layer shields with an infinitesimal second layer and for multilayer shields composed of numerous thin layers (more than 15), MERCURE-6.1 matches the reference data quite well. The MERCURE-6.1 ability to solve three-dimensional realistic cases is highlighted by comparisons to the TRIPOLI-4 and MCNP-4C Monte Carlo codes.

On simple methods for calculating elf shielding of infinite planar shields

Simple approximate methods are developed and described for calculating the extremely low-frequency magnetic-shielding effectiveness for single- and double-layer infinite planar shields. In addition, exact expressions are given and "nearly exact" expressions are derived. Each expression has been compared to the exact expression in order to determine the range of parameters over which it is valid. Each approximate expression can be calculated rapidly and has a simple physical interpretation that leads to physical insight into the shielding process.

Calculation of gamma-ray buildup factors for two-layered shields made of water, concrete and iron and application of approximating formula

Gamma-ray buildup factors that are the basic data for the point kernel calculations were calculated up to 40 mean free path (mfp) for double-layered shields consisting of water, concrete and iron by the EGS4 code using a special splitting technique at gamma-ray energies of 0.1, 0.3, 0.6, 1, 3, 6 and 10 MeV. The assumed shields were 40 mfp monolayer, 5 mfp first layer +35 mfp second layer, 10 mfp first layer +30 mfp second layer and 20 mfp first layer +20 mfp second layer of these materials. All the possible combinations of single- and double-layered shields made up of two materials from water, concrete and iron were assumed in the calculations. The calculated data were parameterized by an empirical formula based on the transmission matrix method of recently proposed by the authors. The formula reproduced very well the reference data in all cases, except for those at 0.1 MeV where the small disagreement is now under investigation.

High Tc SQUID sensor system for non-destructive evaluation

Magnetic field mapping measurements were performed using commercial high- T c superconducting quantum interference device (SQUID) sensors. The sensors are incorporated in a fully computerized scanning system and were found to be operative only when encased inside a double-layer mu-metal shield. This allowed us to measure signals of the order of 0.5 nT. In all cases, the field map obtained was consistent with the theoretically expected images. In measurements with two samples, the relative orientation and center-to-center separation of the samples could be easily deduced from the field map. Surface flaw detection of unglazed ceramic tiles under an externally applied magnetic field is also discussed.

A New Approximating Formula for Calculating Gamma-Ray Buildup Factors in Multilayer Shields

This study proposes a new approximating formula for calculating gamma-ray buildup factors in multilayer shields. The formula combines the buildup factors of single-layer shields with products and quotients. The feasibility of the formula for reproducing the buildup factors was tested by using point isotropic buildup factors calculated with the SN1D discrete ordinates code as reference data. The dose buildup factors of single-, double-, and multilayer shields composed of water, aluminum, iron, and lead were calculated for a spherical geometry in the energy range between 10 MeV and 40 keV and for total thicknesses of up to 30 mean free paths. The calculation of the buildup factors takes into account the bound electron effect of Compton scattering (incoherent scattering), the coherent scattering, the pair production, and the secondary sources of bremsstrahlung and fluorescence.The tests have shown that the approximating formula reproduces the reference data of double-layer shields very well for most cases. With the same parameters and with a new physical consideration that takes into account in a global way the degradation of the gamma-ray energy spectrum, the buildup factors of three- and five-layer shields were also very well reproduced.