Multilayer Shield Research Articles

Gravity Probe B gyroscope readout system

We describe the Gravity Probe B London-moment readout system successfully used on-orbit to measure two gyroscope spin axis drift rates predicted by general relativity. The system couples the magnetic signal of a spinning niobium-coated rotor into a low noise superconducting quantum interference device. We describe the multi-layered magnetic shield needed to attenuate external fields that would otherwise degrade readout performance. We discuss the ∼35 nrad/yr drift rate sensitivity that was achieved on-orbit.

Layer-splitting technique for testing the recursive scheme for multilayer shields gamma ray buildup factors

This study illustrates the implementation of the newly suggested layer-splitting testing technique. This technique is introduced in order to be implemented in examining suggested formalisms for the recursive scheme (or iterative scheme). The recursive scheme is a concept used in treating and producing the gamma ray buildup factors in the case of multilayer shields. The layer-splitting technique simply enforces the scheme to treat a single layer of one material as two separated layers with similar characteristics. Thus it subjects the scheme to an abnormal definition of the multilayer shield that will test its performance in treating the successive layers. Thus, it will act as a method of verification for the approximations and assumptions taken in consideration.A simple formalism was suggested for the recursive scheme then the splitting technique was implemented on it. The results of implementing both the suggested formalism and the splitting technique are then illustrated and discussed. Throughout this study, cubic polynomial fitting functions were used to generate the data of buildup factors for the basic single-media that constitute the multilayer shields understudy. This study is limited to the cases of multiple shields consisting of repeated consecutive thin layers of lead–water and iron–water shields for 1MeV gamma rays.The produced results of the buildup factor values through the implementation of the suggested formalism showed good consistency with the Monte Carlo simulation results of Lin and Jiang work. In the implementation of the introduced technique, the deviation caused by the splitting of the layers in the multilayer shields understudy did not reach extreme limits and remains well below 16%. The proposed formalism showed good stability with the introduced changes, at least within the frame of this study. The implementation of the layer splitting technique was easy and it can be conducted on many other formalisms of the recursive approach.

Reducing shield thickness and backscattered radiation using a multilayered shield for 6–10 MeV electron beams.

Intraoral and external electron shields used in radiotherapy are designed to minimize radiation exposure to non-treatment tissue. Sites where shields are used include but are not limited to, the treatment of lips, cheeks and ears whilst shielding the underlying oral cavity, tongue, gingival or temporal region. A commonly known and published effect, concerns the enhancement in dose that can occur on the beam side on an electron shield caused by an increase in electron backscatter radiation. In this work a lead shield has been designed incorporating copper, aluminium and wax in a step down filter arrangement to minimise backscatter whilst minimizing overall shield thickness for better clinical setup and ease of use. For electron beams ranging from 6 to 10 MeV, a standard shield design of 4 mm lead, 0.6 mm copper, 1.0 mm aluminium and 1.5 mm wax (3.1 mm added filtration, 7.1 mm total thickness) provided adequate backscatter and transmission reduction to match a standard 4.5 mm lead and 10 mm wax (total thickness 14.5 mm) electron shield. Dose enhancement values of no more than 10 % were measured utilising this shield design with a 50 % reduction in shield thickness. The thinner shield will not only allow easier patient set up but should be tolerated better by patients when mucosal reactions occur as they place less physical pressure on these sites during treatment due to their smaller size.

Design of Light Multi-layered Shields for Use in Diagnostic Radiology and Nuclear Medicine via MCNP5 Monte Carlo Code

Introduction Lead-based shields are the most widely used attenuators in X-ray and gamma ray fields. The heavy weight, toxicity and corrosion of lead have led researchers towards the development of non-lead shields. Materials and Methods The purpose of this study was to design multi-layered shields for protection against X-rays and gamma rays in diagnostic radiology and nuclear medicine. In this study, cubic slabs composed of several materials with high atomic numbers, i.e., lead, barium, bismuth, gadolinium, tin and tungsten, were simulated, using MCNP5 Monte Carlo code. Cubic slabs (30×30×0.05 cm3) were simulated at a 50 cm distance from the point photon source. The X-ray spectra of 80 kVp and 120 kVp were obtained, using IPEM Report 78. The photon flux following the use of each shield was obtained inside cubic tally cells (1×1×0.5 cm3) at a 5 cm distance from the shields. The photon attenuation properties of multi-layered shields (i.e., two, three, four and five layers), composed of non-lead radiation materials, were also obtained via Monte Carlo simulations. Results Among different shield designs proposed in this study, the three-layered shield, composed of tungsten, bismuth and gadolinium, showed the most significant attenuation properties in radiology, with acceptable shielding at 140 keV energy in nuclear medicine. Conclusion According to the results, materials with k-edges equal to energies common to diagnostic radiology can be proper substitutes for lead shields.

English

The effective linear attenuation coefficients and build-up factors for single shield of Al, Fe, Pb, and for multi-layer shield of Al-Pb, Al-Fe, Fe-Pb, Al-Fe-Pb as a function of shield thickness, atomic number, and order of the materials composing the shield are investigated for two photon energies of 0.662 MeV and 1.25 MeV. Two derived practical formulas to calculate the effective attenuation coefficient and build-up factor for multilayer shields are used. It is noticed that changing the order of the materials among the shield has no significant effect on the experimental result. Measurement agrees well with the trend of the suggested formulas for calculating the effective attenuation coefficient and the buildup factor. The linear attenuation coefficient is observed to have a strange dependency with the atomic number and photon energy. For single layer shield, the attenuation coefficient increases with decreasing atomic number at low photon energy and increasing with increasing atomic number at high photon energy.

Особенности процесса склеивания многослойного клееного щита пва клеями

Особенности процесса склеивания многослойного клееного щита пва клеями

Application prospects of multilayer film shields for space equipment protection against constant magnetic fields

Protection of scientific equipment aboard spacecrafts against both natural and artificial constant magnetic fields is an urgent problem. Multilayer film electromagnetic shields produced by electrodeposition showed high shielding efficiency during laboratory tests. To test their application prospects under conditions of real space flights, a “Nanomag” scintillation telescope was developed and fabricated. Laboratory tests which demonstrated its operability at magnetic field induction to 4 mT are presented in this paper.

Pre-particle filtration and moisture control by efficient purging in various inlet and outlet of a 450 mm wafer front-opening unified pod

The trend toward narrower line width in semiconductor manufacturing has made contamination control more and more important. The presence of moisture in wafer containers, such as front opening unified pods (FOUP), can lead to the native oxide residues growth, metal corrosion, and thin film cracking on wafer surfaces. Accordingly, decreasing contamination methods and improving factory efficiency are continuously researched. Single or multi-layer particulate shields on top of wafers in FOUPs may be used to prevent pollutant accumulation. In addition, point-of-use (POU) filtration may also been used to control particle contamination in FOUPs during wafer transformation and storage. The demand for stricter filtration led to the usage of 0.10 and 0.20 µm membranes to control the contamination. However, with the introduction of finer membranes end users may have concerns about deleterious remainders on wafers from undergoing filtration. There are a total of 25 pieces of wafers in the FOUP and the arrangement is from the bottom (wafer No. 1) to the top (wafer No. 25) with arising manner. Purging FOUPs to expel moisture vapors with Clean Dry Air (CDA) is one of the most popular methods.There was no previous research for investigating the purge performance on new-generation 450mm FOUPs. This research aims to study main factors influencing the performance of the purge system on 450mm FOUPs, including moisture concentration, CDA flow rate, and filter pressure.

Multilayer passive shielding of scintillation detectors based on BGO, NaI(Tl), and stilbene crystals operating in intense neutron fields with an energy of 14.1 MeV

We discuss the issues related to choosing the optimum type of passive shielding of scintillation detectors based on BGO, NaI(Tl), and stilbene crystals from the direct penetration of neutron radiation with an energy of 14.1 MeV that was emitted isotropically into a solid angle of 4π. A series of experimental measurements of the count-rate suppression factor that may be obtained for the indicated detectors through the use of various shielding filters comprising iron, lead, and borated polyethylene layers with a total thickness not exceeding 50 cm are conducted.

Mathematical formulation for transparency and maximum scattering from bilayer MTM-coated PEC cylinders

In this paper, a novel formulation interval to design multilayer metamaterial (MTM) radar absorbers and shields in cylindrical structure is presented. In this proposed approach, the interaction of electromagnetic waves by an infinitely long perfect conducting cylinder coated with bilayer MTM is investigated. Transparency and maximum scattering conditions for the structure, under a normally uniform plane wave with transverse electric, transverse magnetic and circular polarizations, are mathematically extracted by using small argument forms of Bessel and Hankel functions. In transparency, the capability of radars is dissipated by the full transmission of the incident waves back to the direction from which they were radiated. On the other hand, scattering maximization by diffuse reflection and making chaff, confuses the radars in target detection. Theoretical formulations are verified by COMSOL which is full wave software. However, our formulations are proved for electrically small cylinders, but simulation results show that they are useful for cylinders with dimensions compared to the wavelength.

Multilayer film shields for the protection of PMT from constant magnetic field.

Photomultiplier tubes (PMTs) are widely used in physical experiments as well as in applied devices. PMTs are sensitive to magnetic field, so creation of effective magnetic shields for their protection is very important. In this paper, the results of measurements of shielding effectiveness of multilayer film magnetic shields on PMT-85 are presented. Shields were formed by alternating layers of a material with high magnetic permeability (Ni-Fe) and high electric conductivity-Cu. The maximum number of bilayers reached 45. It is shown that in weak magnetic fields up to 0.5 mT, the output signal amplitude from PMT-85 does not change for all used multilayer shields. In strong magnetic field of 2-4 mT, the output signal amplitude decrease with 10%-40% depending from the number of layers in the shield. The Pulse distribution of PMT-85 in magnetic field 0.2-4 mT slightly changed in the range 1.1%-1.3% for the case when the number of layers do not exceed 10 and practically did not change for a shield with 45 double layers.

Application Prospects of Multilayer Film Shields for Space Research Instrumentation

We have studied the magnetic properties of multilayer film cylindrical configuration shields (MFS) based on NiFe / Cu. The studied samples were prepared by electrode position. MFS were constituted by alternating layers of NiFe and Cu, deposited on an aluminum cylinder with diameter of 4cm, length of 13cm and 0.5cm thickness. The thickness of each ferromagnetic layer varied from 10 to 150μm, and the thickness of Cu layers was 5μm. Five-samples in which the number of ferromagnetic layers varied from 3 to 45 and copper – from 2 to 44 were tested. The best shielding efficiency was achieved at the maximum number of layers and comprised about 102. Permalloy multilayer foil shield at the same total thickness has several times less efficiency in comparison with MFS. The description of a prototype of the charged particles telescope for space application is presented. Results of its testing regarding sensitivity to the constant magnetic field are described.

Effect of the Nature of the Layer of Conductive Polymer Composite on the Effectiveness of a Multi-Layer Electromagnetic Shielding

The purpose of this communication is to study the effect of the nature of the polymer layer on the electromagnetic shielding effectiveness of a multilayer organic based composite material. Our work is divided into two parts. In the first part, we set different layer thicknesses and the frequency is varied. In the second part, we set the frequency and do vary the nature of the polymer layer and the thickness of the different layers. The different results obtained we show that the efficiency is strongly influenced by the nature of the polymer layer.

Small-size railgun of mm-size solid bodies for hypervelocity material testing

The shielding of spacecraft and satellites from the impacts of space debris particles of millimeter size is an important problem in space industry and exploration. As a rule, these particles have irregular shapes; therefore, their impact leads to different consequences from the impact of spherical particles. The goal of our study was to reveal specific features in the hypervelocity impact of cubic impactors on thin metal and polymer plates (elements of multilayer spacecraft and satellite shielding, which is known as the “Whipple shield”).

Numerical and experimental development of multilayer magnetic shields

In this paper a detailed description of different passive shields for Extremely Low Frequency (ELF) applications is presented. The first part of the paper analyzes ferromagnetic and conductive materials by means of simulations and measurements. This step is mainly devoted to the identification of physical characteristics such as the relative permeability of the analyzed ferromagnetic materials. All the simulations are performed with a standard Finite Element (FE) code assuming linear behavior of the tested materials. The results are then used in the design of many shielding configurations and, finally, three different multilayer shield compositions are tested and presented. The second part of this paper outlines guidelines to assure a good shielding efficiency in the actual installation of a multilayer shield. The orientation of the shield as well as the possible decay of the shielding performance due to the discontinuity among the different slabs is investigated by means of experimental measurements. It is observed that the conductive part of the multilayer shield has to be faced to the source to have better performance. Moreover, it is important to assure the electrical conduction between the separate slabs. In this paper the conduction among different plates is conveniently obtained connecting them by straight bars of aluminum. In the third part of the paper the multilayer shield is tested under actual working conditions. A MV/LV substation was reproduced in the laboratory using a 630kVA transformer working at its rated power. Several configurations were tested and the most significant results are presented. It is highlighted that, if the proper layout is not employed, the performance of the actual shield can be very different from the one of the material.

Thermal FEA for Alcator C-Mod Advanced Outer Divertor

An advanced outer divertor is being developed for Alcator C-Mod to study reactor fuel (tritium) retention and plasma wall material interaction physics at reactor temperatures with high power long-pulse discharges. The divertor will be operated at controlled temperature of 600 °C. To achieve this goal, the divertor will be structurally and electrically continuous along the toroidal direction, requiring it to expand radially as temperature increases. This paper describes the thermal finite element analysis (FEA) and results of the outer divertor. There are four aspects, with focus on the A-Frame assembly. First of all, a one twentieth module of the full divertor is composed of divertor tiles, tile mounting plate, heaters, divertor gusset, A-Frame support, spherical bearings, bracket, halo current shunt, vessel gusset, and so on. By adjusting the power of each of the seven toroidal divertor heaters, the tiles achieve a uniform temperature poloidally with toroidal temperature variation within allowables. The temperature of each component is evaluated, and results are used to support the design changes. Second, radiation simulation on multilayer radiation shields behind divertor plate is presented. Third, radiation simulation of the diverter heater itself is done to understand more details of heat transfer from the heater to the surrounding tiles and support plates. Finally, thermal analysis is completed with a model including a tile and its mounting plate, to predict the effect of plasma heat load on divertor tiles. All the thermal FEA was performed with COMSOL, a commercial FEA software.

Perforation and penetration of aluminium target plates by armour piercing bullets

Experimental, analytical and numerical simulations were performed to study the ballistic resistance of 6061-T6 aluminium plates subjected to a normal impact of small calibre armour piercing bullets. Two types of bullets were used, steel and tungsten carbide core bullets. Three plate thicknesses, 101.6 mm, 76.2 mm and 25 mm, were considered. Bullets were impacted at ordnance velocity thus results range from deep penetration to complete perforation with residual velocity. Ballistic results, deformations of the plates and of the bullets are discussed and reproduced through numerical simulations using both LS-DYNA and ABAQUS solvers; analytical models by means of a cavity expansion approach are also used. Exploiting analytical and numerical models the ballistic behaviour of the two bullets on the three plates is discussed with emphasis on the capability of the models to reproduce the physical features of the phenomena. X-ray diffraction measurements for the residual stress patterns of the plate's surface were also performed on all of the plates both before and after the tests and the experimental measurements are compared with the numerical model results. A specific discussion about tungsten carbide core bullet behaviour is reported highlighting the importance of the sabot in the impact phenomena. Although the work focuses on monolithic plates, the results and discussion can be of interest for the design of optimised multilayer armour shields.

Experimental Study on the Behavior of a New Multilayer Shield against Hypervelocity Debris Impact

To protect the spacecraft from hypervelocity impact of the space debris, a new kind of multilayer shield laminated of aluminum layers and CFRP layers was designed and investigated. Three different shields with the same area density were manufactured, including single aluminum alloy layer, single CFRP layer, and multilayer of aluminum/CFRP. The hypervelocity impact experiment was carried, in which the hypervelocity projectile was launched by a two-stage light gas gun. To compare the hypervelocity impact behavior and evaluate the protection ability of the different shields, the area and depth of the projectile pits were analyzed. The experiments results show that the protection effect of the multilayer shield laminated of aluminum/CFRP layers is better than the single aluminum layer or the single CFRP layer, though they are in the same area density.

Experimental verification of numerical simulation of projectile impact on ballistic shields

Abstract In this work, the author presents experimental verification of numerical simulation of projectile impact on constructional shields. The experimental tests were performed at a unified test stand to investigate ballistic resistance of materials in field conditions. The stand was developed at the Polish Naval Academy in Gdynia, and then patented. The design of this test stand was based on construction of a ballistic pendulum, fitted to measure: impact force, turn angle of the ballistic pendulum x, impact velocity and residual velocity of the projectile. All the measurement data were transmitted to a digital oscilloscope and a personal computer. The ballistic velocity of the shield of VBL(R) - defined according to Recht’s and Ipson’s method, was compared with V BL(Z) and VBL(Z1) - determined according to the author’s method. Verification of numerically simulated ballistic velocity VRO versus the before-mentioned velocity was carried out at the 10GHMBA-E620T steel shields impacted by 12.7 mm type B- 32 projectiles. The introduced method can be used for determining ballistic thickness hBL and ballistic velocity VBL for both homogeneous plates as well as multi-layered constructional shields

Research on Preparation and Property of Alternating Multilayer Polymer Electromagnetic Shielding Materials

With the development of materials science and technology, performance and preparation of polymer materials becomes a hot topic. The heat resistance and corrosion resistance of Polymer material are strong and can be manufacture for composite materials. It is widely used in many areas. This paper adds metal shielding materials into polymer materials and uses layered coating technology. This paper treats metal mesh and PET film composite structure as in the electromagnetic shielding layer and prepares the alternating multilayer polymer electromagnetic shielding materials. This paper tests electronic shielding effect of the material. It mainly detects the shielding effect of pass rate, the decay rate, and the electromagnetic intensity of visible light. The result shows that the permeation rate of the materials for visible light is about 40%, and the attenuation effect is 85db. Multilayered metal shielding mesh shields 60% magnetic field strength and obtains good electromagnetic shielding effects. This paper tests the mechanical properties of the material through the polarizing microscope which proves that alternating multilayer polymer material has good continuity mechanical properties and high yield strength and heat resistance. It provides theoretical support for the development of the new type of electromagnetic shielding materials.