• 대한방사선기술학회지:방사선기술과학
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• 제44권6호
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• pp.629-633
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• 2021

This article is designed to look into the radiation exposure dose to each body part and the shielding effect for workers using an additional shielding to reduce their radiation exposured by scattering radiation which is generated in a space between the operating table and lead curtain during interventional radiology(IR) procedures. After placing a human phantom on the table of SIEMENS' angiography machine, the following measurements were taken, depending on the presence of an additional shield of lead equivalent of 0.25 mmPb, manufactured for this purpose: dose to gonad, dose to an area where the personal dosimeter is placed, and dose to an area of eye lens is located. An ion chamber(chamber volume 1,800 cc) was utilized to measure scattering radiation. The two imaging tests were carried out as follows: fluoroscopy of the abdomen (66 kV, 100 mA, 60 seconds) and of the head (70 kV, 65 mA, 60 seconds); and digital subtraction angiography(DSA) of the abdomen (67 kV, 264 mA, 20 seconds) and of the head (79 kV, 300 mA, 20 seconds). In all the experiments, the shielding efficiency of the gonad position was the largest at 59.8%. In case an additional shielding was used as protection against scattering radiation that came through the operating table and the lead curtain during an IR, the radiation shielding efficiency was estimated to be up to 59.8%, leading to a conclusion that its presence may effectively reduce the radiation exposure dose of medical staffs.

• 전기학회논문지
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• 제60권4호
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• pp.694-699
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• 2011

This paper compares the performance of lightning shielding analysis methods using the seven striking distance formulae in substation. For comparison, we evaluate the number of expected strikes and exposed area using WinIGS Software. Seven striking distance formulae are compared using the electrogeometric model analysis and the rolling sphere method. Based on the electrogeometric model analysis, the risk of shielding failure in either the whole substation or parts of it is determined. According to the simulation results, one can justify whether the substation satisfies the criterion of shielding design. In particular, according to the rolling sphere method, the exposed areas in substation determine the location of the additional shielding poles or shield wires. Therefore, the installation of the additional shielding poles and shield wires in substation was accepted by shield design at the phase conductors exposed in the larger area.

• 한국전자파학회논문지
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• 제28권12호
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• pp.1011-1014
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• 2017

EMP(Electromagnetic Pulse) 공격에 대한 피해를 방호하기 위해 정화조에 사용되는 배수관에는 별도의 금속 차폐 구조물의 추가 설치가 고려된다. 이러한 차폐 구조물은 EMP 공격을 막아주지만, 물에 함께 섞여 흘러오는 불순물이 차폐 구조물을 통과하지 못해 배수관 본연의 역할을 잃게 하며, 이를 관리하기 위해 추가적인 유지보수 인력을 필요로 한다. 위의 문제점들을 해결하기 위해 본 논문에서는 차폐 구조물 없이 물의 감쇠 특성을 고려한 배수관 구조를 제안하였다. 배수관 직경을 100 mm로 고정한 채로 물에 잠기는 깊이를 400 mm부터 800 mm까지 변화시켰을 때, 각각의 차폐 효과는 2 GHz 주변에서 70 dB부터 100 dB까지 증가됨을 확인하였다. 검증 과정을 통해 추가적인 차폐 구조물 없이 배수관 본연의 기능을 유지하고, EMP 공격을 차폐할 수 있는 효율적인 설계의 가이드라인을 제안하였다.

• Wind and Structures
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• 제36권1호
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• pp.1-14
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• 2023

To evaluate the wind shielding effect of bridge towers with multiple limbs on high-speed trains, a wind tunnel test was conducted to investigate the aerodynamic characteristics of vehicles traversing multi-limb towers, which represented a combination of the steady aerodynamic coefficient of the vehicle-bridge system and wind environment around the tower. Subsequently, the analysis model of wind-vehicle-bridge (WVB) system considering the additional moments caused by lift and drag forces under nonuniform wind was proposed, and the reliability and accuracy of the proposed model of WVB system were verified using another model. Finally, the factors influencing the wind shielding effect of multi-limb towers were analyzed. The results indicate that the wind speed distributions along the span exhibit two sudden changes, and the wind speed generally decreases with increasing wind direction angle. The pitching and yawing accelerations of vehicles under nonuniform wind loads significantly increase due to the additional pitching and yawing moments. The sudden change values of the lateral and yawing accelerations caused by the wind shielding effect of multi-limb tower are 0.43 m/s² and 0.11 rad/s² within 0.4 s, respectively. The results indicate that the wind shielding effect of a multi-limb tower is the controlling factor in WVB systems.

• 대한방사선기술학회지:방사선기술과학
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• 제42권6호
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• pp.429-434
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• 2019

The gonads are directly affected by radiation exposure during radiography of the pelvis, abdomen, and spine. Exposure of the gonads to radiation can cause genetic mutations and can result in the occurrence of malignant tumors. In this study, we created three types of shielding material shapes for shielding of the ovaries, which are the gonads of female during radiography of the pelvis, and comparative evaluations using shadow shielding methods. The source surface distance(SSD) was 100 cm and the field size was 42 cm × 43 cm. The three types of shielding material shapes(type 1, 2 and 3) were assessed and the entrance surface dose in the ovaries were measured. The thickness of the shielding material was expanded from 0.3 mm to 2.4 mm and after five repetitions, radiation values were measured and mean values were calculated. The mean dose were 3.09 mGy for type 1, 3.54 mGy for type 2, and 3.19 mGy for type 3, indicating that the measurements were the lowest for type 1. When an additional filter of 0.2 Cu + 1 Al was used, the dose were 3.72 mGy for type 1, 5.43 mGy for type 2, and 4.05 mGy for type 3, indicating that the measurements were the lowest for type 1. The results show that, even if the shielding material is not thick, in other words, even with a thickness of 2.94 mGy for the SN 3(0.9 mm) of type 1, shielding can be achieved, with a patient dose lower than the diagnostic reference level(3.42 mGy). Additionally, among the three types of shielding material, the type 1 appeared to be the most appropriate shielding material. It is thought that the use of shielding material could reduce the risk factors for stochastic effects or critical effects of ionizing radiation during pelvic or lumbar radiography.

• 한국초전도ㆍ저온공학회논문지
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• 제17권1호
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• pp.40-43
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• 2015

Wireless power transfer technology is using the magnetic resonance recently drawing increased attention. It uses the resonance between transmitter and receiver coils to transfer power. Thus, it can improve the transfer distance and efficiency compared with the existing magnetic induction technique. The authors found from the previous study that the application of the superconductor coil to the magnetic resonance wireless power transfer system improved its efficiency. Its application to real life, however, requires the additional study on the effects of adjacent materials. In this study, the two resonance coils made by superconductor coils were used to aluminum and plastic shielding materials was placed between the coils. S-parameters were analyzed according to the position of the shielding material between the transmitter and receiver coils. As a result, the plastic of shielding material had no effect, but the aluminum of shielding material affected the wireless power transfer due to the shielding effectiveness.

• 한국의학물리학회지:의학물리
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• 제15권4호
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• pp.247-254
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• 2004

신체 심부의 악성종양치료를 위한 6～15 MV의 강력한 에너지의 방사선과 종양만을 조사하기 위한 입체조형치료, 세기 조절방사선치료, 입체적 치료방법 등이 개발됨으로써 방사선의 사출구가 전체 공간으로 확대되고 출력선량도 환자당 5～10 Gy의 과다 선량을 방출하기 때문에 고밀도의 차폐벽이 요구된다. 저자들은 세기조절방사선치료(IMRT)용 고 에너지 선형가속기를 기존건물에 설치하기 위하여 일반 콘크리트와 철, 티타늄등 중금속을 혼합한 고 밀도 차폐벽돌을 제작하여 방어벽을 설계하고 건축된 차폐벽으로부터 투과 산란된 선량을 측정하여 상호 비교하였다. 고 밀도 차폐벽돌을 사용함으로서 기존의 콘크리트(3.5 g/cc)에 비하여 고 에너지의 차폐율 즉 반가층 두께를 약 1/2로 줄일 수 있었다.

• Nuclear Engineering and Technology
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• 제54권9호
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• pp.3470-3477
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• 2022

Soils are porous materials with high shielding capability to attenuate gamma and X-rays. The disposal of radionuclides throughout the soil profile can expose the living organisms to ionizing radiation. Thus, studies aiming to analyze the shielding properties of the soils are of particular interest for radiation shielding. Investigations on evaluating the shielding capabilities of highly weathered soils are still scarce, meaning that additional research is necessary to check their efficiency to attenuate radiation. In this study, the radiation shielding properties of contrasting soils were evaluated. The radiation interaction parameters assessed were attenuation coefficients, mean free path, and half- and tenth-value layers. At low photon energies, the photoelectric absorption contribution to the attenuation coefficient predominated, while at intermediate and high photon energies, the incoherent scattering and pair production were the dominant effects. Soils with the highest densities presented the best shielding properties, regardless of their chemical compositions. Increases in the attenuation coefficient and decreases in shielding parameters of the soils were associated with increases in clay, Fe₂O₃, Al₂O₃, and TiO₂ amounts. In addition, this paper provides a comprehensive description of the shielding properties of weathered soils showing the importance of their granulometric fractions and oxides to the attenuation of the radiation.

• 전기전자학회논문지
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• 제11권4호
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• pp.247-251
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• 2007

The recessed gate IGBT has a lower on-state voltage drop compared with the DMOS IGBT, because there is no JFET resistance. But because of the electric field concentration in the corner of the gate edge, the breakdown voltage decreases. This paper is about the new structure to effectively improve the Vce(sat) voltage without breakdown voltage drop in 1700V NPT type recessed gate IGBT with p floating shielding layer. For the fabrication of the recessed gate IGBT with p floating shielding layer, it is necessary to perform the only one implant step for the shielding layer. Analysis on the Breakdown voltage shows the improved values compared to the conventional recessed gate IGBT structures. The result shows the improvement on Breakdown voltage without worsening other characteristics of the device. The electrical characteristics were studied by MEDICI simulation results.

• Nuclear Engineering and Technology
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• 제49권6호
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• pp.1240-1249
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• 2017

An essential component of the neutron transport solver is the resonance self-shielding calculation used to determine equivalence cross sections. The neutron transport code, MPACT, is currently using the subgroup self-shielding method, in which the method of characteristics (MOC) is used to solve purely absorbing fixed-source problems. Recent efforts incorporating multigroup kernels to the MOC solvers in MPACT have reduced runtime by roughly $2{\times}$. Applying the same concepts for self-shielding and developing a novel lumped parameter approach to MOC, substantial improvements have also been made to the self-shielding computational efficiency without sacrificing any accuracy. These new multigroup and lumped parameter capabilities have been demonstrated on two test cases: (1) a single lattice with quarter symmetry known as VERA (Virtual Environment for Reactor Applications) Progression Problem 2a and (2) a two-dimensional quarter-core slice known as Problem 5a-2D. From these cases, self-shielding computational time was reduced by roughly $3-4{\times}$, with a corresponding 15-20% increase in overall memory burden. An azimuthal angle sensitivity study also shows that only half as many angles are needed, yielding an additional speedup of $2{\times}$. In total, the improvements yield roughly a $7-8{\times}$ speedup. Given these performance benefits, these approaches have been adopted as the default in MPACT.