Additional Shielding Research Articles

Relative nuclear abundance from C to Fe and integrated flux inside the Russian part of the ISS with the Sileye-3/Alteino experiment

In this work we present data from the Sileye-3/Alteino detector on board the International Space Station (ISS), which was gathered following a recalibration after several years in orbit. We also measure the relative nuclei abundance and integrated flux, which were normalized to the solar modulation values of August 2007. The measurements were made at different locations of the Russian part of the ISS. The relative nuclear abundances of C to Fe in relation to C, in an energy range above ≃ 60 MeV/n, shows high levels of odd Z particles inside the ISS and an under-abundance of C and O compared with the galactic spectrum, as presented by Simpson in 1983. In addition, the values of the integrated flux varies primarily according to location and detector orientation. An additional polyethylene shield also reduces the flux, although in a lower amount than changes in the orientation of the telescope. Data were taken as part of the ESA ALTCRISS project from late 2005 through to 2007.

The ocular surface epithelial barrier and other mechanisms of mucosal protection

Studies completed in the last decade provide new insights into the role of the epithelial glycocalyx in maintaining ocular surface barrier function. This review summarizes these findings, their relevance to allergic and infectious disease, and highlights the potential benefits of exploiting the modulation of barrier integrity for therapeutic gain. The molecular components sealing the space between adjacent ocular surface epithelial cells, such as tight junctions, have been extensively characterized, and their contribution to the paracellular barrier established. A second layer of protection - the transcellular barrier - is provided by transmembrane mucins and their O-glycans on the glycocalyx. Cell surface glycans bind carbohydrate-binding proteins to promote formation of complexes that are no longer thought to be a static structure, but, instead, a dynamic system that responds to extrinsic signals and modulates pathogenic responses. Although functioning as a protective mechanism to maintain homeostasis, the glycocalyx also restricts drug targeting of epithelial cells. The traditional model of intercellular junctions protecting the ocular surface epithelia has recently been expanded to include an additional glycan shield that lines apical membranes on the ocular surface. A better understanding of this apical barrier may lead to better management of ocular surface disease.

Simple improvement of the sensitivity of a heat flux reaction calorimeter to monitor bioprocesses with weak heat production

Many studies demonstrate the suitability of the heat production rate for analysing and controlling aerobic growth and production processes ranging from the μL to the m3 range. Recently anaerobic bioprocesses leading to biofuels (e.g. ethanol, n-butanol), biogas, solvents (e.g. acetone, 1,2 butandiol) and small organic acids (e.g. acetate, butyrate) have attracted industrial attention. However, calorimetric monitoring of such processes challenges particularly the sensitivity of the applied sensors. A simple and cost-efficient solution for large scale reaction calorimeters is needed. We show that the sensitivity of a standard heat flux reaction calorimeter (here tested for RC1e) can be improved by the factor of 10 to (1.886±0.012)KW−1 by simply adding an additional internal thermal shield. Signals of about 5mWL−1 can be detected this way and the steady-state response time is about 10min. Both criteria of relevance (sensitivity and steady-state response times) are sufficient for anaerobic growth processes. This was successfully demonstrated at the example of the acetone–butanol–ethanol (ABE) fermentation using Clostridium acetobutylicum. Here the calorimetric signal matches perfectly other simultaneously measured on-line signals and parallel measurements with a high-sensitive microcalorimeter.

TH-A-134-01: Breast Imaging QA

Implementation of a New Breast Tomosynthesis Program: A Clinical Medical Physicist's Experience-W Geiser Digital breast tomosynthesis (DBT) was approved by the FDA as a screening tool for breast cancer in February 2011. Many systems were preinstalled as 2D systems and are now being upgraded for DBT and there is evidence that DBT is helping reduce recall rates while increasing cancer detection rates. As of February 2013 there were approximately 500 systems certified by the FDA for DBT and it is expected that there will be more than 700 certified systems by the third quarter of 2013. Facilities implementing a breast tomosynthesis program need to be aware that there are many hurdles to be overcome before tomosynthesis studies can be performed. The purpose of this lecture is to provide medical physicists assisting facilities that are upgrading 2D systems or installing new DBT systems, the knowledge to assist with facility design, image storage requirements, choice of PACS, and optimization of diagnostic review. New educational requirements for medical physicists to qualify to perform acceptance testing and continued annual testing of DBT systems will also be reviewed. Learning Objectives: 1. Be able to assist with implementation of breast tomosynthesis at their facility. 2. Know the process for accreditation and certification of DBT systems. 3. Understand additional shielding requirements and facility design for a facility installing digital breast tomosynthesis. Breast MR Imaging and Quality Control — D Reeve MR imaging of the breast is an important adjunct to mammography and ultrasound for the detection of breast cancer and for breast biopsy guidance. Diagnostic breast MRI protocols typically include T2-weighted fat saturated images and 3D T1-weighted dynamic contrast enhanced (DCE) multiphase images using a Gadolinium-based contrast agent. The DCE images are used to determine the kinetic signature of enhancing tissues in order to differentiate between benign and malignant lesions. MR spectroscopy and diffusion weighted images (DWI) may also be acquired in order to provide additional diagnostic information. The diagnostic value of breast MRI scans can be improved by choosing acquisition parameters that optimize image quality parameters such as SNR, contrast and spatial resolution. As with any MRI protocol, achieving the desired image quality must balance the need for acceptable scan times. The timing and temporal resolution of the DCE series are important considerations. Breast radiofrequency (RF) coils are phased array coils capable of simultaneous bilateral imaging. A comprehensive breast MRI quality control program is important to assess the performance of the MRI system as well as the breast RF coils. Learning Objectives: 1. Provide an overview of breast MR imaging and MR-guided biopsy procedures. 2. Describe breast MR image quality criteria and protocol optimization. 3. Discuss the components of a breast MRI quality control program.

Effective dose to patients and staff when using a mobile PET/SPECT system

The purpose of this study was to determine the number of weekly acquisitions permissible using a mobile PET/SPECT scanner for myocardial perfusion/viability imaging in an intensive care unit (ICU) based on the effective dose to patients and staff. The effective dose to other patients and staff in an ICU was calculated following recommendations from the American Association of Physicists in Medicine Task Group 108 report (AAPM TG‐108). The number of weekly acquisitions using 555 MBq (15 mCi) Tc‐99m for myocardial perfusion or F‐18 for myocardial viability was determined using the regulatory limits described in the Code of Federal Regulations 10 CFR 20. To increase the number of weekly acquisitions allowed, a reduction in administered dose and portable shielding was considered. A single myocardial perfusion image can be acquired with Tc‐99m each week with a dose reduction to 455 MBq (12.3 mCi) without additional shielding. To acquire a myocardial viability image with F‐18, an activity reduction to 220 MBq (5.9 mCi) is required to meet the regulatory effective dose limit without additional shielding. More than one weekly acquisition can be performed if additional shielding or activity reduction is utilized. A method for calculating dose to patients and staff in an ICU has been developed using conservative assumptions and following AAPM TG‐108. This calculation must be repeated for each individual clinic before any acquisition is performed.PACS number: 87.57.uq

An Exploration to Develop Concrete Walls Using Mn<sub>x</sub>Zn<sub>1-x</sub>Fe<sub>2</sub>O<sub>4</sub> Ferrite as Absorbing Material to Provide Defense against Electromagnetic Pollution

Concern regarding the shielding effectiveness (SE) of building materials is gaining more response nowadays due to the awareness on the electromagnetic pollution (EMP) that is believed to results in disastrous consequence. A pure concrete inherently providing certain level of SE but it is not enough. Hence additional shielding and absorbing additives are added into the concrete. In this work MnxZn1-xFe2O4will be added into the pure concrete to enhance its SE performance. The effect of microstructure, compositions, grain sizes, homogeneity, mixture volume of the MnxZn1-xFe2O4will be considered for the optimization in this mixture. The key component to determine the SE of concrete is their electrical characteristic (relative permittivity and relative permeability). The parallel plate which is proposed previously will be used to determine the electrical characteristic of material and it will also be used for SE measurement.

Prescribing Greater Protection for Rights: Administrative Law and Section 1 of the Canadian Charter of Rights and Freedoms

In interpreting the “prescribed by law” requirement contained in section 1 of the Charter of Rights and Freedoms, Canadian courts have struggled with an abundance of difficult distinctions: between law and discretion, general norms and individualized decisions, and administrative law and constitutional law.A purposive approach assists in identifying the key functions of the “prescribed by law” requirement. First, it has both formal and substantive senses which are intimately related to the rule of law. Second, it performs an accountability function by forcing government to take responsibility for general norms that infringe Charter rights. Third, consistent with the intention of the drafters of the Charter, it provides additional protection for the individual from rights-infringing conduct by state actors.These functions are frustrated somewhat by the analytical framework set out by the Supreme Court of Canada in Slaight Communications v. Davidson (1989). Unfortunately, in its recent decision in Dore v. Barreau du Quebec (2012), the Court has only worsened the situation. It did away with the application of the proportionality test where Charter infringements can be attributed to individualized decisions of state officials, substituting instead the more deferential reasonableness test applied in judicial review of administrative action. Accordingly, a return to the pre-Dore situation, as outlined in the majority reasons of Justice Charron in Multani v. Commission scolaire Marguerite-Bourgeoys (2006), would be appropriate.Moreover, improvements to the analytical framework within which the “prescribed by law” requirement is applied can be effected by using the tools of administrative law. Justification, transparency and intelligibility are the touchstones of reasonableness in administrative decision-making, as the Court itself has acknowledged. Accordingly, administrative decision-makers who fail to confine, structure and check their discretion by adopting “soft law” instruments, such as publicly available guidelines, risk seeing their decisions struck down as unreasonable by reviewing courts. And if decisions are unreasonable, they cannot be “prescribed by law” within the meaning of section 1 of the Charter.Requiring the adoption of “soft law” instruments gives effect to the formal and substantive senses of the phrase “prescribed by law” by improving the accessibility and precision of administrative discretion; enhances its accountability function by allowing individuals to identify the source of rights-infringing official action and providing a focal point for debate; and hands an additional shield to the individual with which to fend off infringements of the Charter.

Total Body Irradiation Using a Modified Standing Technique: In Vivo Dosimetry with Semiconductor Diodes

The aim of this study was to establish a fast and simple online dosimetric verification method for total body irradiation (TBI) using semiconductor diodes. Twenty one patients were treated with fractionated TBI (12 Gy, 2 Gy BID) using a modified standing technique between February 2010 and March 2012. The prescribed dose was administered to the patient’s mid-plane at the level of the umbilicus. The lungs were shielded to allow only the absorption of an 8 Gy dose. To verify the dose administered during TBI, 12 semiconductor diodes were attached to the patient’s skin to measure the entrance and exit doses at six anatomical reference points (umbilicus, lungs, neck, forehead, hand, and knee). An adapted version of the arithmetic method which uses a correction factor was used to calculate the mid-plane doses from the entrance and exit dose measurements. The mid-plane doses were then compared with the expected doses. The results of in vivo dosimetry showed that the mid-plane dose calculations conducted using the adapted arithmetic method were consistent with the expectations of the treatment plan. The average percentage dose differences and standard deviations were -0.5 ± 5.3 % for the neck, -2.1 ± 3.7 % for the umbilicus, 2.8 ± 5.2 % for the forehead, and -5.9 ± 11.1 % for the lungs. The extremity doses (hand and knee) were not calculated in the treatment planning program; however they were measured for documentary purposes. In vivo dose verification under TBI conditions was efficiently conducted through the use of semiconductor diodes. The measurement results were consistent with treatment plan dose calculations. The modified standing technique provides a practical method for TBI treatments. The observed heterogeneity is acceptable, the technique does not require additional shields or bolus material, the dosimetric verification is simple and fast, the set-up of the patient is easily reproducible, and the treatment time is within the acceptable limits for a non-dedicated treatment machine.

Protection of W7-X diagnostics from radiation heat loads

Wendelstein 7-X (W7-X), a modular advanced stellarator, is presently under construction at the Max Planck Institute for Plasma Physics in Greifswald. Part of the inner plasma vessel (PV) surface is covered by graphite tiles which are bolted onto water-cooled CuCrZr heat sink plates. This so-called heat shield is an in-vessel component and shall protect the PV wall and diagnostic components from plasma-edge-radiation and convective heat loads. Numerous diagnostics (e.g. diamagnetic loops, Rogowski coils, etc.) are located in between the heat shield and plasma vessel wall. They are loaded by thermal radiation from the hot heat shield backside, stray radiation from the electron cyclotron resonance heating (ECRH), and plasma radiation through remaining gaps between the tiles. In order to keep the temperatures of the diagnostics within their specified limits, additional shielding is required. The paper presents the design of such a shielding for the diamagnetic loops. Several options of copper shields and loosely attached Sigraflex®-layers, and combinations thereof, are compared with respect to their abilities to reduce the temperatures of the sensitive parts of the diagnostics. To increase the confidence in the results, a sensitivity study with widely varying radiative material properties has been carried out. The advantages and disadvantages of the potential solutions are discussed. As a result two copper shield variants which also reduce the load onto the plasma vessel are presented.

Minimizing Nuclear Medicine Technologist Radiation Exposure during 131I-MIBG Therapy

131I-metaiodobenzylguanidine is a norepinephrine analog that concentrates in adrenergic tissue and has been shown to be an effective radiotherapeutic agent used to treat tumors of neural crest origin, particularly neuroblastoma, a sympathetic nervous system malignancy of children. The purpose of this study was to determine the radiation dose received by nuclear medicine technologists while preparing and administering 131I-metaiodobenzylguanidine therapy dosages, and if any changes could be implemented that would reduce a technologist's dose. The study involves the collection of total whole body doses received by technologists during the treatment of six patients. Patient dosages ranged from 9.25 to 31.1 GBq, with radiation exposures to the nuclear medicine technologists averaging 0.024 μSv per MBq administered to the patient. Subsequently, the doses received by the technologists were analyzed with respect to specific process steps performed during 131I-metaiodobenzylguanidine therapy including package receipt, dosage preparation, and dosage administration. Results show that the largest contribution to the technologist's whole body radiation dose (>83%) is received during the dosage administration process step. After additional shielding was installed for use during the dosage administration process step, technologists' doses decreased 80%.

Characterization of a SPECT pinhole collimator for optimal detector usage (the lofthole)

In single-photon emission computed tomography (SPECT), multi-pinhole collimation is often employed nowadays. Most multi-pinhole collimators avoid overlap (multiplexing) of the projections on the detector. This can be done by using additional shielding or by spacing the pinholes far enough apart. Using additional shielding has the drawback that it increases weight, design complexity and cost. Spacing the pinholes far enough apart results in sub-optimal detector usage, the valuable detector area is not entirely used. This is due to the circular projections of pinholes on the detector; these ellipses can not be tiled with high detector coverage. To overcome this we designed a new pinhole geometry, the lofthole, that has a rectangular projection on the detector. The lofthole has a circular aperture and a rectangular entrance/exit opening. Sensitivity formulae have been derived for pinholes and loftholes. These formulae take the penumbra effect into account; the proposed formulae do not take penetration into account. The derived formulae are valid for geometries where the field-of-view and the sensitivity of the aperture are solely limited by the exit window. A flood map measurement was performed to compare the rectangular projection of a lofthole with the circular projection of a pinhole. Finally, measurements were done to compare the amount of penetration of pinholes with the amount of penetration of a lofthole. A square lofthole collimator has less penetration than a knife-edge pinhole collimator that irradiates the same rectangular detector area with full coverage. A multi-lofthole collimator allows high detector coverage without using additional shielding. An additional advantage is the lower amount of penetration.

Dosimetry and Radiobiological Studies of Automated Alpha-Particle Irradiator

Understanding the effect of alpha radiation on biological systems is an important component of radiation risk assessment and associated health consequences. However, due to the short path length of alpha radiation in the atmosphere, in vitro radiobiological experiments cannot be performed with accuracy in terms of dose and specified exposure time. The present paper describes the design and dosimetry of an automated alpha-particle irradiator named 'BARC BioAlpha', which is suitable for in vitro radiobiological studies. Compared to alpha irradiators developed in other laboratories, BARC BioAlpha has integrated computer-controlled movement of the alpha-particle source, collimator, and electronic shutter. The diaphragm blades of the electronic shutter can control the area (diameter) of irradiation without any additional shielding, which is suitable for radiobiological bystander studies. To avoid irradiation with incorrect parameters, a software interlock is provided to prevent shutter opening, unless the user-specified speed of the source and collimator are achieved. The dosimetry of the alpha irradiator using CR-39 and silicon surface barrier detectors showed that ~4 MeV energy of the alpha particle reached the cells on the irradiation dish. The alpha irradiation was also demonstrated by the evaluation of DNA double-strand breaks in human cells. In conclusion, 'BARC BioAlpha' provides a user-friendly alpha irradiation system for radiobiological experiments with a novel automation mechanism for better accuracy of dose and exposure time.

Polymer-Composite Materials for Radiation Protection

Unwanted exposures to high-energy or ionizing radiation can be hazardous to health. Prolonged or accumulated radiation dosage from either particle-emissions such as alpha/beta, proton, electron, neutron emissions, or high-energy electromagnetic waves such as X-rays/γ rays, may result in carcinogenesis, cell mutations, organ failure, etc. To avoid occupational hazards from these kinds of exposures, researchers have traditionally used heavy metals or their composites to attenuate the radiation. However, protective gear made of heavy metals are not only cumbersome but also are capable of producing more penetrative secondary radiations which requires additional shielding, increasing the cost and the weight factor. Consequently, significant research efforts have been focused toward designing efficient, lightweight, cost-effective, and flexible shielding materials for protection against radiation encountered in various industries (aerospace, hospitals, and nuclear reactors). In this regard, polymer composites have become attractive candidates for developing materials that can be designed to effectively attenuate photon or particle radiation. In this paper, we review the state-of-the-art of polymer composites reinforced with micro/nanomaterials, for their use as radiation shields.

The design, construction, and initial characterization of an ultra-low-background gas-proportional counting system

Over the past several years, the Pacific Northwest National Laboratory (PNNL) has developed an ultra-low-background proportional counter (ULBPC) technology. The resulting detector is the product of an effort to produce a low-background, physically robust gas proportional counter for applications like radon emanation measurements, groundwater tritium, and 37Ar. In order to fully take advantage of the inherent low-background properties designed into the ULBPC, a comparably low-background dedicated counting system is required. An ultra-low-background counting system (ULBCS) was recently built in the new shallow underground laboratory at PNNL. With a design depth of 30 m water-equivalent, the shallow underground laboratory provides approximately 100× fewer fast neutrons and 6× fewer muons than a surface location. The ULBCS itself provides additional shielding in the form of active anti-cosmic veto (via 2-in-thick plastic scintillator paddles) and passive borated poly (1 in.), lead (6 in.), and copper (~3 in.) shielding. This work will provide details on PNNL’s new shallow underground laboratory, examine the motivation for the design of the counting system, and provide results from the characterization of the ULBCS, including initial detector background.

Sidebar: Economics, Physical Activity, and Community Design

**1202** ### **Objectives** Yttrium-90 microspheres are used for the treatment of unresectable liver tumors. Yttrium-90 results in pair production ( e+e- ) in 32 out of 1 million decays. This characteristic allows us to acquire PET images in patients treated with Y-90 microspheres. The aim of this study was to analyze the utility of Y-90 PET to localize the distribution of microspheres in relation to the hepatic tumor foci and also detect sites of non-targeted delivery. ### **Methods** Y-90 PET/CT was performed on 49 patients (30 males and 19 females, age range 34 -83 years) 2-12 hrs after Y-90 microsphere radioembolization. PET imaging of abdomen was performed using time of flight (TOF) reconstruction and without use of additional shielding. Thirty patients had hepatocellular cancer and 19 had hepatic metastasis ( colorectal 9, carcinoid 3, melanoma 3, esophageal 2 , breast 1, lung 1). ### **Results** In 41 of 49 cases Y- 90 distribution matched the tumor foci in the liver with high target to background ratio. In 14 of the 49 patients (29%) management was modified based on the distribution of Y-90 microspheres on PET scan. Eight patients had incomplete coverage of the tumor foci needing further intervention. Complications from non targeted delivery of Y-90 were able to be predicted in 6 cases (gallbladder related 3 cases, bowel 2 and omentum one case). ### **Conclusions** Y-90 PET/CT is a useful noninvasive tool to map out the distribution of Y-90 microspheres delivered to the liver via radioembolization procedure. Localization of Y-90 microsphere distribution by Y-90 PET, impacts management and helps in predicting potential complications

SU‐C‐217A‐01: Digital Breast Tomosynthesis: Is the Room Shielding a Need?

Purpose: With FDA approval of Digital Breast Tomosynthesis (DBT), a question on its room shielding is raised. According to NCRP147, standard gypsum wallboard construction is adequate to shield the walls of a conventional mammographic unit. This recommendation may not be valid for DBT which acquires data from multiple angles therefore potentially leads to larger scattered radiation. The DBT room shielding may be reconsidered. This study is to investigate if additional room shielding is necessary for DBT. Methods: Room shielding was first calculated following NCRP147 by adjusting recommended air kerma with the ratio of acquisition numbers. We assumed that comparable techniques were used for data acquisition of DBT and conventional mammography. Scattered radiations at locations inside and outside of the door were then measured with Ludlum 9DP survey meter for comparison with shielding design goal, e.g. 0.02 mGy/week. CIRS breast biopsy training phantom was used for the measurements. Two phantoms were overlapped (approximately 6 cm) to simulate a relatively large breast thickness. 150 patients/week was assumed for calculations. Results: Based on both calculation and measurements, the current room without any special shielding is adequate for conventional mammography with 4 images/patient. DBT with 30 to 34 (per patient, tomosythesis vs. combo) radiographic acquisitions requires approximately 20 mm of gypsum wallboard. Standard gypsum wallboard construction may still meet this requirement. However, DBT requires the thickness of solid wood door of approximately 170 mm according to the calculation and approximately 60mm based on the measurements, respectively, with a full occupancy factor. Most current solid wood door cannot meet this requirement. The measurement outside the door also shows high scattered radiation, approximately 0.09mGy/week, which is only acceptable for less occupied areas. Conclusions: With the increasing data acquisitions of DBT, the room shielding needs reconsideration, although both calculation and measurements are very conservative.

Cosmic Radiation Exposure of Biological Test Systems During the EXPOSE-E Mission

In the frame of the EXPOSE-E mission on the Columbus external payload facility EuTEF on board the International Space Station, passive thermoluminescence dosimeters were applied to measure the radiation exposure of biological samples. The detectors were located either as stacks next to biological specimens to determine the depth dose distribution or beneath the sample carriers to determine the dose levels for maximum shielding. The maximum mission dose measured in the upper layer of the depth dose part of the experiment amounted to 238±10 mGy, which relates to an average dose rate of 408±16 μGy/d. In these stacks of about 8 mm height, the dose decreased by 5-12% with depth. The maximum dose measured beneath the sample carriers was 215±16 mGy, which amounts to an average dose rate of 368±27 μGy/d. These values are close to those assessed for the interior of the Columbus module and demonstrate the high shielding of the biological experiments within the EXPOSE-E facility. Besides the shielding by the EXPOSE-E hardware itself, additional shielding was experienced by the external structures adjacent to EXPOSE-E, such as EuTEF and Columbus. This led to a dose gradient over the entire exposure area, from 215±16 mGy for the lowest to 121±6 mGy for maximum shielding. Hence, the doses perceived by the biological samples inside EXPOSE-E varied by 70% (from lowest to highest dose). As a consequence of the high shielding, the biological samples were predominantly exposed to galactic cosmic heavy ions, while electrons and a significant fraction of protons of the radiation belts and solar wind did not reach the samples.

Assessment of the Operational Dose Rate in Polymer Insulators in the Test Cell of the IFMIF Neutron Source

Insulators for electrical connections of the test modules in the test cell of the International Fusion Materials Irradiation Facility (IFMIF) neutron source will be exposed to intense ionizing radiation even if they are located away from the neutron source. The aim of this work was to check whether radiation-hard polymers, for example polyimide, would be sufficiently long-lasting in such an environment. The calculations presented here were survey calculations to aid with the decisions on possible insulator candidates. The calculations have been done with the McDeLicious code and a detailed 3-D neutronics model of the IFMIF test cell. Mesh tallies were utilized to calculate dose rate maps 10 cm below the ceiling of the test cell where the connectors would be located. The calculated dose deposited within one full power year would be higher than 200 MGy nearly everywhere in the test cell. This value excludes most polymers as candidates for insulators, but even polyimide would reach its limits. It was found that the calculated dose contribution from gamma rays was considerably dependent on the nuclear data library used for describing the lithium in the lithium loop. We have also checked the effect of an additional lead shield of 10 cm thickness which reduced the deposited dose by a factor of 2-5. A new neutronics model has become available recently which was derived from the latest IFMIF test cell design. We have performed preliminary calculations for dose rates in anticipated locations of connector insulators. The results confirm the high dose rate values calculated with the previous neutronics model.

다층 지하 구조물로의 고고도 전자기파(HEMP) 커플링 현상에 대한 전자기적 모델링

본 논문에서는 다층 지하 구조물로의 고고도 전자기파(high altitude electromagnetic pulse: HEMP)의 커플링 현상을 분석하였다. 이를 위하여, 고고도 전자기파에 대한 모델링을 통하여, 고고도 전자기파의 스펙트럼이 100 MHz 이상의 대역에서 -30 dB 이하로 급격히 감소함을 확인하였다. 또한, 고고도 전자기파의 커플링 영역인 다층 지하 구조물은 지구의 표면과 내부를 구성하는 5층 구조물로 가정하여, 본 구조물을 구성하는 물질의 전파 상수(propagation constant)를 바탕으로 투과 현상을 분석하였다. 그 결과, 50 kV/m의 평면파를 입사시켰을 때, 지상에서 100 m 깊이에 위치한 지하 터널에서 0.1 MHz와 1 MHz의 평면파에 대하여 각각 약 10 kV/m와 5 kV/m의 투과 현상이 발생함을 확인하였다. 투과된 전기장의 효과적인 차폐 효과 확보를 위하여 토양층의 감쇠 상수(attenuation constant)를 이용한 자연 차폐 방법과 금속 격자 구조물의 필터링(filtering) 현상을 이용한 차폐 방법을 통하여 각각 최대 20 dB와 90 dB의 차폐 효과를 얻을 수 있음을 분석하였다. This paper gives a electromagnetic coupling mechanism of the high altitude electromagnetic pulse (HEMP) into large- scale underground multilayer structures using analytic and numerical methods. The modeling methods are firstly addressed to the HEMP source which can be generated by intentional nuclear explosion. The instantaneous and intense electromagnetic pulse of the HEMP source is concerned from DC to 100 MHz band, because the power spectrum of the HEMP is rapidly decreased under -30 dB over the 100 MHz band. Through this range, a penetrated electric field distribution is computed within the large-scale underground multilayer structures. As a result, the penetrated electric field intensities at 0.1 and 1 MHz are about 10 and 5 kV/m, respectively. Therefore, additional shielding techniques are introduced to protect buried structures within the large-scale underground structures such as high-lossy material and filtering structures (wire screen).

Computer Models of Meander Slow-wave System with Additional Shields

In microwave devices various types of slow-wave systems are used. Meander slow-wave systems are widely used as delay lines and deflection systems because pass-band of such systems starts at low frequencies. Wideband signals which propagate through the meander slow-wave system are distorted because of the phase delay time dispersion. In this paper possibilities of reducing a phase delay time dispersion and widening the pass-band of meander slow wave system are analyzed. Three new models of a meander slow-wave system with additional shields are presented. Models are designed and analyzed using Sonnet ® software. For comparison of the models phase delay time dependence on frequency is calculated from S 21 parameters. The impact on dispersion properties of meander slow-wave system of grounding point of additional shield is investigated. Ill. 6, bibl. 16 (in English; abstracts in English and Lithuanian). DOI: http://dx.doi.org/10.5755/j01.eee.119.3.1365