Multilayer Shield Research Articles

Long-term corrosion protection of reinforcing bars via a self-responsive coating incorporating ZrP functional fillers

The conventional coating of reinforcing bars exhibits inadequate anti-corrosion efficacy stemming from a non-specific, blind protection mechanism, poses a threat to the durability of concrete. We devised a novel self-responsive functional filler, L-arginine (LA) intercalated zirconium phosphate (LCZrP), synthesized via an intercalation reaction. This innovative filler was seamlessly integrated into an epoxy (EP) resin matrix, yielding a smart anticorrosive coating that harmoniously combines active and passive corrosion protection strategies. The integration of LCZrP within the coating matrix serves a trifecta of purposes: it extends the corrosion propagation path, effectively disperses nanofiller agglomeration, and enhances interfacial adhesion with the epoxy coating. Critically, the controlled release of corrosion inhibitors from the interlayer further fortifies the coating's resistance to corrosion, imparting a multi-layered protective shield. After enduring a 60-day immersion in a simulated concrete pore solution, the LCZrP/EP coating demonstrated exceptional durability, maintaining a low-frequency impedance modulus value consistently within the range of 4.27×1010 to 5.12×1010 Ω·cm2, marking a remarkable 34-fold enhancement over the performance of the epoxy coating alone. This breakthrough underscores the LCZrP/EP coating's potential as a groundbreaking solution for reinforcing bar protection in concrete, harnessing the complementary strengths of epoxy resin's physical barrier, the impermeability of two-dimensional lamellar structures, and the proactive release of corrosion inhibitors to forge a robust, multi-faceted passivation layer.

Mass Optimization of a Multilayered Shield for Transportable Microreactors

The ability to easily transport microreactors is a major selling point for deploying microreactors to remote areas. However, this creates a unique shielding challenge, especially when the microreactor is being shipped after irradiation. A traditional reactor configuration utilizes a separate biological shield and pressure vessel to meet radiological shielding and pressure needs. The limited space available for transportable microreactors for both shielding and pressure vessels requires a revised assessment of separating out the biological shield and pressure vessel. To address these concerns, we examine a nuclear-grade sandwich composite (NGSC) that combines the reactor pressure vessel and biological shielding functions into a single component. Through a series of optimization problems for both transportation and operational use cases, the NGSC is able to minimize dose, minimize the vessel cost, and ensure that weight requirements are met for transportation. Initial results show that using a tungsten-tetraboride cermet in the first two layers of a six-layer NGSC provides adequate shielding for both use cases. These results show promise that an NGSC has enough overlap between operational and transportation cases to help reduce the design space for future analysis and assessment.

Design and implementation of a high-performance miniaturized multi-layer magnetic shielding spherical shell with minimal pores based on target magnetic field

Achieving the spin-exchange relaxation-free (SERF) state in atomic comagnetometers (ACMs) necessitates a stable and weak magnetic environment. This paper presents the design of a miniaturized permalloy magnetic shielding spherical shell (MSSS) with minimal apertures, tailored to meet these requirements. By employing a combination of analytical solutions and finite element analysis (FEA), we achieved superior magnetic shielding while maintaining a compact form factor. The analytical solution for the shielding factor indicated that a four-layer permalloy sphere shell with optimized air gaps was necessary. A numerical analysis model of the MSSS was developed and validated using COMSOL software, confirming the suitability of the air gaps. The size, shape, and orientation of the openings in the perforated sphere shell were meticulously designed and optimized to minimize residual magnetism. The optimal structure was fabricated, resulting in triaxial shielding factors of 47619, 52631, and 21739, meeting the anticipated requirements. A comparison of simulation results with experimental tests demonstrated the efficacy of the design methodology. This study has significant implications for ultra-sensitive magnetic field detection devices requiring weak magnetic field environments, such as atomic gyroscopes, magnetometers, atomic interferometers, and atomic clocks.

Analytical model and precise evaluation of multi-layer magnetic shielding performances considering ultra-weak magnetic properties

Regarding the vast difference between the design index and the actual performance of magnetic shielding devices, this paper proposes a novel method of using precise permeability under a specific weak magnetic field, aiming to improve the design accuracy of shielding performance. Firstly, the relative permeability of the permalloy is measured under the applied magnetic field from the geomagnetic field down to 1 nT. Next, the precise shielding coefficient formulas of the single- and double-layer spherical shells are derived. For the double-layer spherical shells, the deviation of remanence between considering the ultra-weak magnetic properties and using the constant permeability is 24.3%. This clarifies the necessity of considering the ultra-weak magnetic properties in multi-layer structures. Then, a new accurate method of the shielding coefficient for the finite-length magnetic shielding cylinder is proposed, with a deviation of less than 5%. Finally, this method has been validated again by remanence measurement of the three-layer magnetic shielding cylinders. The deviation between simulation and experiment is 4.03% when considering the ultra-weak magnetic properties. While using the constant permeability, the deviation is as high as 19.31%. Therefore, considering the ultra-weak magnetic properties in multi-layer structures can significantly improve the accuracy of the performance evaluation.

Origami multi-layer space shield for cylindrical space structure

The multidisciplinary space environment, encompassing orbital debris, cosmic radiation, and solar radiative heat, poses significant risks to spacecraft and astronauts, necessitating efficient and effective shielding solutions. A multi-layer shield with wide spacing has been proven to be an effective way to shield the spacecraft from space debris impact; however, due to the limited volume of the payload fairing, it was not feasible to apply a multi-layer shield to the spacecraft fuselage. Through the origami design, the shield maintains a compact form during launch and subsequently expands in outer space to enhance protection. Through geometric analysis, it has been confirmed that the deployable multi-layer space shield can occupy less space than conventional space shield structures while expanding into wider shield intervals and multiple layers. Through hypervelocity impact experiments, it was confirmed that as the bumper spacing of the multi-layer space shield expands, its ballistic performance becomes superior to conventional space structures. The deployable multi-layer space shield can reduce not only hypervelocity impacts but also solar radiative heat using the same mechanism as multi-layer insulation. Through cosmic radiation dose analysis, it has been confirmed that the multi-layer space shield is effective in cosmic radiation shielding compared to conventional space structures.

Improved Common-Mode Leakage Current Measurement Method for Insulation Condition Monitoring in Distribution Grids

Common-mode (CM) leakage current is an essential insulation indicator for condition monitoring in distribution grids. However, online measurement of CM leakage current is a difficult task in the industry due to the disturbances of far larger load currents. To address this challenge, a novel CM leakage current measurement method based on multi-layer magnetic shield has been proposed in this paper. The analytical solution for the magnetic field around the shield is firstly derived and validated by finite element analysis. Comprehensive comparison with previous single-layer shield design is then conducted for a typical industrial case, proving that an improvement of about 46 dB can be achieved for CM leakage current measurement by the novel design. A sensor prototype has also been developed with optimized parameters and validated by experiments. The effectiveness of the proposed method is proved, with minor CM leakage current accurately extracted from load currents which are 3000 times larger.

Analysis and measurement of magnetic noise in multilayer magnetic shielding system combined with mu-metal and ferrite for atomic sensors

The multilayer magnetic shielding system is widely used in atomic sensors. However, for miniaturized atomic sensors with volume limitations, such as spin-exchange relaxation-free (SERF) gyroscopes, the remaining environmental magnetic interference and mu-metal magnetic noise will affect the sensitivity of atomic sensors. In this study, we establish a comprehensive magnetic noise calculation model for the magnetic shielding system of a SERF gyroscope, which considers the influence of the environmental magnetic noise on the magnetic shielding and the coupling effect between different layers. For suppressing magnetic noise of the magnetic shielding system, the property of different ferrites was measured and compared, then the particle swarm optimization is applied to design the magnetic shielding structure. Finally, the experimental device is established for measuring performances of the magnetic shielding system per and post optimization. By comparison, radial and axial magnetic noise post optimization are decreased by 37% and 22%, respectively.

Simulation and Design of Optimized Three-Layer Radiation Shielding to Protect Electronic Boards of Satellite Revolving in Geostationary Earth Orbit (GEO) Orbit against Proton Beams

The safety of electronic components used in aerospace systems against cosmic rays is one of the most important requirements in their design and construction (especially satellites). In this work, by calculating the dose caused by proton beams in geostationary Earth orbit (GEO) orbit using the MCNPX Monte Carlo code and the MULLASSIS code, the effect of different structures in the protection of cosmic rays has been evaluated. A multi-layer radiation shield composed of aluminum, water and polyethylene was designed and its performance was compared with shielding made of aluminum alone. The results show that the absorbed dose by the simulated protective layers has increased by 35.3% and 44.1% for two-layer (aluminum, polyethylene) and three-layer (aluminum, water, polyethylene) protection respectively, and it is effective in the protection of electronic components. In addition to that, by replacing the multi-layer shield instead of the conventional aluminum shield, the mass reduction percentage will be 38.88 and 39.69, respectively, for the two-layer and three-layer shield compared to the aluminum shield.

Genetic algorithm for multilayer shield optimization with a custom parallel computing architecture

This paper introduces a novel architecture for optimizing radiation shielding using a genetic algorithm with dynamic penalties and a custom parallel computing architecture. A practical example focuses on minimizing the Total Ionizing Dose for a silicon slab, considering only the layer number and the total thickness (additional constraints, e.g., cost and density, can be easily added). Genetic algorithm coupled with Geant4 simulations in a custom parallel computing architecture demonstrates convergence for the Total Ionizing Dose values. To address genetic algorithm issues (premature convergence, not perfectly fitted search parameters), a Total Ionizing Dose Database Vault object was introduced to enhance search speed (data persistence) and to preserve all solutions’ details independently. The Total Ionizing Dose Database Vault analysis highlights boron carbide as the best material for the first layer for neutron shielding and high-Z material (e.g., Tungsten) for the last layers to stop secondary gammas. A validation point between Geant4 and MCNP was conducted for specific simulation conditions. The advantages of the custom parallel computing architecture introduced here, are discussed in terms of resilience, scalability, autonomy, flexibility, and efficiency, with the benefit of saving computational time. The proposed genetic algorithm-based approach optimizes radiation shielding materials and configurations efficiently benefiting space exploration, medical devices, nuclear facilities, radioactive sources, and radiogenic devices.

Multilayer radiation shields for nuclear and radiological centers using free-lead materials and nanoparticles

We prepared two types of lead-free shielding materials consist of double and triple layered with different thicknesses and reported the radiation shielding performance of the developed concrete samples. The linear attenuation coefficient (LAC) of microcomposites was calculated theoretically by XCOM-software and compared with experimental results and less than 4 % difference was observed at all discussed energies. We measured the half and tenth value layers (HVL and TVL) of the single, double and triple layered samples and evaluated the radiation shielding efficiency (RSE) at different energies. The experimental data showed that the inclusion of nanoparticles into the composites reduced the TVL. The triple layered sample, composed of a 3 cm IM-2 layer, a 15 cm CON-2 layer, and a 2 cm IM-2 layer, exhibited exceptional radiation shielding performance, with an RSE of 97.5 % at 0.662 MeV, and an RSE of approximately 92 % for energies greater than 1 MeV. Comparing our samples to pure lead, we found that our double and triple layered samples could replace lead in practical applications, with the triple layer exhibiting superior performance at energies greater than 0.662 MeV. The RSE of our triple layered sample was 100 % for energies less than 0.06 MeV and 97.5 % at 0.662 MeV, and the RSE of our double layered sample with a thickness of 18 cm was 93.5 % and 92.3 % for energies of 1.173 and 1.33 MeV, respectively.

Study on electromagnetic interference and shielding efficiency of power grid on-line elimination equipment

The robot-based automatic power grid defect elimination device represents the future direction of power grid inspection and defect elimination devices. However, the presence of strong electromagnetic interference in the vicinity of power grids poses potential risks to the application of automatic defect elimination devices. This study initially conducts theoretical analysis and calculations to analyse the spatial distribution of electromagnetic fields around 220kV 100MW high-voltage lines in a power grid. The results indicate that electric field intensity can exceed 70kV/m in areas near these high-voltage lines. Subsequently, electromagnetic fields within the operational range of the elimination device are simulated and analysed, leading to selection and optimization of shielding materials and structures. When non-metallic insulating materials are used, equipment is fully exposed to the power grid’s electromagnetic field, making internal devices susceptible to interference; however, employing metal aluminum materials achieves better shielding effects. A continuous metal shielding layer effectively shields against electric fields, while openings or gaps in the shell lead to deteriorated shielding performance. These findings demonstrate that appropriate selection of shielding materials and suitable structural design are crucial factors for achieving excellent shielding effects. To ensure both safety and efficient electromagnetic shielding, a multi-layer composite shielding structure is necessary for power grid elimination devices. Overall, these analysis results provide valuable guidance for designing, operating, and maintaining such devices.

Multilayer Shielding Design and Analysis of Optimal Thickness for the Storage of Highly Radioactive Sources Concerning Environmental Safety

Multilayer Shielding Design and Analysis of Optimal Thickness for the Storage of Highly Radioactive Sources Concerning Environmental Safety

High-efficiency radiation attenuation shields of polymer composites for the low earth orbit space environment – multilayer shielding simulation system-based investigations

The polymer/metal hybrids have been used as a solution for the mitigation of ionizing radiation in space for sensitive electronics components, particularly for a proton-rich Low Earth Orbit (LEO) environment. Consequently, radiation attenuation analysis of polymer/metal hybrid composites has been investigated. Radiation attenuation analysis has been performed using online GEANT4 (simulation toolkit) and the Multilayer Shielding Simulation System (MULASSIS) for the LEO space environment. The shielding potential of polymers, such as poly(dimethyl siloxane), poly(methyl methacrylate), polyurethane and ultra-high molecular weight polyethylene, were analyzed with optimized compositions. It was observed that the pristine PDMS attenuated relatively more radiations than other polymer matrices. For modelling of hybrid radiation material composition, PDMS and carbon fibre fabric-derived composite laminates along with metal sheets (Aluminum Al, Tantalum Ta or Tungsten W) were used to analyze hybrid compositions. Here, hybrid composition performance was analyzed as a function of various areal densities. Analyzed polymer laminate/metal hybrid compositions performed better to attenuate LEO radiations up to 42.29%, compared to conventional Al (areal densities of 0.2–1.0 g/cm2). The maximum magnitude of attenuation was found at an areal density of 1.0 g/cm2 for Ta and W metal composition (39.44% and 42.29%, respectively), and so performed better than Al metal. Improved attenuation ratios of the hybrid compositions revealed that the hybrid laminate/metal shields can replace conventional Al shields towards LEO space radiations.

Simulation of radiation environment and design of multilayer radiation shield for orbital exploration of Jupiter

The harsh radiation environment of Jupiter imposes significant constraints on the shield design of spacecraft. Due to these constraints, traditional aluminum shields cannot meet the radiation shielding requirements needed for the exploration of Jupiter. In this paper, the design for a highly efficient radiation shield structure is proposed that utilizes a combination of high-Z/low-Z elements. A typical exploration orbit of Jupiter is selected, and the energetic particle radiation environment is calculated using the D&G83 model. The Geant4 toolkit is used to evaluate the shielding performance of materials, and quantitative simulations are performed to analyze the shielding efficiency of bilayer and trilayer shield structures under an areal density constraint of 4.5 g/cm2. Based on the simulations, an optimal shield structure is determined. The simulation results show that the integral electron flux with energy greater than 3 MeV is approximately three orders of magnitude greater than that of geostationary orbit with an orbit of 4000 km at the perijove and 5420000 km at the apojove, resulting in an enormous total dose effect. The optimal shield structure is a bilayer structure that comprises of a tantalum outer layer with a density of 3.5 g/cm2 and a polyethylene inner layer with a density of 1.0 g/cm2. This shield has the ability to reduce the total radiation dose to 1559 Gy per year, which is 32 % lower than that of traditional aluminum shields. Findings in this research are critical for design of radiation shields, and can be used for performing reliability analyses and predicting the lifespan of spacecraft during the development process.

Influence of Tic on Density and Microstructure of Al2O3 Ceramics Doped with Nb2O5 and Lif

Ceramic matrix composites are widely studied in the ballistic sector due to their high hardness, fracture toughness, and improved ballistic performance in multilayer shielding systems. However, the presence of dopants in ceramics can pose challenges during processing and potentially compromise the final properties of the sintered material. This study focused on the ceramic processing of Al2O3-based ceramic matrix composites by adding 4 wt.% Nb2O5 (niobium oxide), 0.5 wt.% LiF (lithium fluoride), and 38.5 wt.% TiC (titanium carbide). The composites were produced using cold uniaxial pressing and conventional sintering at 1400 °C for 3 h. The composites were characterized using Archimedes’ principle and scanning electron microscopy (SEM). The results revealed that the samples to which TiC was added exhibited low initial densities, indicating that the applied pressure of 50 MPa during cold pressing was insufficient to adequately densify the green bodies. Moreover, the presence of TiC led to a significant reduction in densification, making it challenging to apply a conductive coating for SEM analysis. Adjustments to the intensity of the electron beam were necessary to conduct the analysis successfully. Conversely, the samples to which TiC was not added exhibited high density values in the green state and yielded consistent results after sintering in line with previous research, indicating a satisfactory degree of sintering in the absence of TiC. These findings highlight the importance of carefully considering the addition of TiC in ceramic matrix composites during processing, which can have a significant impact on densification and subsequent material properties. The results contribute to the understanding of processing parameters with regard to the production of ceramic composites with desirable characteristics for ballistic applications.

Multilayer radiation shielding system with advanced composites containing heavy metal oxide nanoparticles: a free-lead solution

With the use of multilayer materials such as concrete, mortar and ceramics that were fortified with PbO, WO3 and Bi2O3 nanoparticles, our study's objective was to produce a an effective photon shielding system. Experimental evaluation of the radiation shielding efficiency of two sets of samples with various thicknesses was conducted. The elemental content and morphology of the samples were corroborated by SEM and EDX studies, with ceramic samples exhibiting superior particle distribution and fewer voids than concrete and mortar specimens. The linear attenuation coefficient (LAC) was studied both experimentally and numerically using the Phy-X program, and it was found that the two sets of values were in satisfactory agreement. The values of LAC were consistently greater for samples with 30% of the selected heavy metal oxides than for those with 10%. The LAC for Cer-1 was 5.003 cm−1 at 0.059 MeV, whereas the corresponding LAC for Cer-2 was 2.123 cm−1. The LAC values were as follows: ceramics (5.003 cm−1), mortar (2.999 cm−1), concrete (2.733 cm−1), and the transmission factor (TF) examination of the multiple-layer specimens showed that the TF of the 3 cm thick multilayer sample was lower than that of the 2 cm thick sample and that both multilayer samples displayed better attenuation efficiency in comparison to single-layer specimens. The results show the possibility for employing multilayer structures with different densities, thicknesses, and sizes in suitable radiation shielding applications.

Total ionising dose multilayer shielding optimisation for nanosatellites on geostationary transfer orbit

The rising number of proposed nanosatellite missions with Commercial Off-The-Shelf electronics to higher orbits necessitates innovative, compact, and lightweight radiation shielding. In this study, several thousand multilayer radiation shielding configurations were simulated against trapped particle spectra predicted for a geostationary transfer orbit to demonstrate how material combinations and layer structures can be selected to minimise the total ionising dose inside nanosatellites with constrained mass budgets. The Geant4 Radiation Analysis for Space (GRAS) application was used to calculate ionising dose deposition behind multilayer shielding. Thousands of planar shielding stacks were procedurally generated and simulated on top of silicon plates representing sensitive semiconductor devices. To allow for comparison between configurations, all shielding stacks had a total mass of 1.5 g/cm2, and shielding performance was evaluated based on the total ionising dose absorbed by the silicon plates. The simulations consistently show that configurations with low-atomic-number (low-Z) materials on top of high-Z materials yield the lowest doses. The two- and three-layer mass allocation optimisations demonstrate the non-linear dependence of ionising dose on mass allocation between materials. Optimised polyethylene-lead shields achieved up to 30% lower ionising doses compared to an equal mass of either of the two materials or up to 50% lower than the same mass of aluminium. Contrary to previous claims about Z-graded shielding, no significant improvements were observed for using more than two different materials, and optimisation of multilayer shields tends to reduce them to two-layer structures. Optimal multilayer radiation shielding depends on various factors and must be tailored to specific radiation environments and mission requirements. The primary contributions of this article are the methods presented for achieving this tailoring using open-source software and parallel computing. The multilayer simulations performed for this work resulted in an extensive dataset for multilayer shielding performance that enabled novel visualisations of the ionising dose dependence on shielding composition based on quantitative results.

An investigation on gamma-ray and neutron attenuation properties of multi-layered Al/B4C composite

Nowadays, the concept of multi-layered composite materials is attracting the researchers in terms of enhancing the capabilities of shielding materials as well as extending the scope of utilization towards space sciences and cosmic radiation application. In this study, we report the manufacturing, design, and experimental investigation on newly developed multi-layered Al/B4C shielding composites. Al powder material with a purity of 99% and an average size of 15 µm is used as matrix material. Next, B4C powders with an average size of 9 µm are incorporated into the matrix as reinforcement material. Accordingly, we manufactured several different multilayer Al-B4C shield samples of 3 cm diameter and 1 cm height through powder metallurgy method. Gamma-ray transmission properties are determined using 3 × 3 NaI(Tl) scintillation detector through 60Co and 137Cs point isotropic radioisotopes. Moreover, MCNPX (version 2.7.0) is utilized for deposited energy amount and transmission factor calculations for gamma and neutron radiation. Our results showed that geometric configuration plays a crucial role in shielding efficiency of multi-layered materials. Among the manufactured samples, B4C-Al-B4C sample is reported with promising shielding properties against gamma-ray and neutron radiation. A direct relationship between the overall transmission factor values and deposited energy amount (MeV/g) in each sample is also explored for multi-layered composite shields.It was also seen that combination of layers made significantly improvement of radiation shielding properties of materials.

Additively manufactured high permeability Fe-Ni alloys and novel bi-metallic magnetic shields

The sensitivity and sophistication of spacecraft for Earth Science and Planetary Science missions are increasing with each successive mission. Advances in instrumentation, robotics, remote sensing, avionics and controls are allowing un-crewed missions to be incredibly sophisticated. Effective electromagnetic shielding is critical for high fidelity functioning of the spacecraft and onboard instrumentation. Moreover, the geometrical complexity of the shielding arrangement and the constraints of size and shape, make additive manufacturing (AM) a critical, enabling technology for current and future missions. Two AM approaches - directed energy deposition (DED) and laser powder bed fusion (LPBF) - were used to produce Fe-80Ni-5Mo alloy rings and shields. The microstructure and magnetic properties of the materials produced through these processes are reported in this paper. A mechanism relating the microstructure to the soft magnetic performance of the material is proposed. The AM material produced in this work demonstrated the highest reported magnetic permeability and lowest reported coercivity of any additively manufactured soft magnetic material. Two different combinations of bi-metallic shields, Fe-80Ni-5Mo/FeCo-2V and Fe-80Ni-5Mo/Fe-49Ni, were fabricated using the DED process. The creation of these shields as monoliths in general, and for space-related applications in particular, is a novel aspect of this work. These multi-alloy, multi-layer shields showed a nearly 10 dB increase in shielding performance over Fe-80Ni-5Mo single alloy shielding, a significant improvement. For the DED builds, the coercivity decreases and permeability increases (better soft magnetic performance) with increasing build power. With increasing build power in the DED process, the grain size in the printed part increases. The corresponding reduction in the grain boundary area results in fewer obstacles to the movement of magnetic domain walls.

Shielding Analysis of a Preclinical Bremsstrahlung X-ray FLASH Radiotherapy System within a Clinical Radiation Therapy Vault.

A preclinical radiotherapy system producing FLASH dose rates with 12 MV bremsstrahlung x rays is being developed at Stanford University and SLAC National Accelerator Laboratory. Because of the high expected workload of 6,800 Gy w -1 at the isocenter, an efficient shielding methodology is needed to protect operators and the public while the preclinical system is operated in a radiation therapy vault designed for 6 MV x rays. In this study, an analysis is performed to assess the shielding of the local treatment head and radiation vault using the Monte Carlo code FLUKA and the empirical methodology given in the National Council on Radiation Protection and Measurements Report 151. Two different treatment head shielding designs were created to compare single-layer and multilayer shielding methodologies using high-Z and low-Z materials. The multilayered shielding methodology produced designs with a 17% reduction in neutron fluence leaking from the treatment head compared to the single layered design of the same size, resulting in a decreased effective dose to operators and the public. The conservative assumptions used in the empirical methods can lead to over-shielding when treatment heads use polyethylene or multilayered shielding. High-Z/Low-Z multilayered shielding optimized via Monte Carlo is shown to be effective in the case of treatment head shielding and provide more effective shielding design for external beam radiotherapy systems that use 12 MV bremsstrahlung photons. Modifications to empirical methods used in the assessment of MV radiotherapy systems may be warranted to capture the effects of polyethylene in treatment head shielding.