• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.243.1-243.1
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• 2014

For two-dimensional grid electrodes immersed in plasmas, sheath expansion due to negative high-voltage pulse applied to the electrode generates high-energy pseudowave. The high-energy pseudowave can be used as ion beam for ion implantation. To estimate ion dose due to high-energy pseudowave, investigation on sheath expansion of grid electroes is necessary. To investigate sheath expansion, an analytic model was developed by Vlasov equation and applying the 1-D sheath expansion model to 2-D. Because of lack of generalized 2-D Child-Langmuir current, model cannot give solvable equation. Instead, for a given grid electrode geometry, the model found the relations between ion distribution functions, Child-Langmuir currents, and sheath expansions. With these relations and particle-in-cell (PIC) simulations, for given grid electrode geometry, computation time was greatly reduced for various conditions such as electrode voltages, plasma densities, and ion species. The model was examined by PIC simulations and experiments, and they well agreed.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2019년도 전력전자학술대회
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• pp.248-250
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• 2019

입자가속기는 물질의 미세 구조를 밝히기 위해 기본 입자를 가속, 충돌시키는 장치로 최근 암치료 등 의학적 용도로도 이용되고 있다. 그러나 고속으로 고압을 인가시켜야 하는 장치인 만큼 기존에 명확히 설립된 회로가 없다. 이에 본 논문에서는 Ion gate를 등가회로로 구성하여 Fast Switch 장치의 기본 회로를 제안 및 분석, 실험하였다. 또한 기본 회로에서 발생하는 문제들을 개선하고자 RC Input filter와 기타 파라미터들의 설계와 Fast switch와 Ion gate를 잇는 wire 내의 기생성분을 고찰하였고 Ion gate 구동을 위해 기준이 되는 명확한 Fast switch 회로를 제안한다.

• Journal of Korean Vacuum Science & Technology
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• 제6권3호
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• pp.116-119
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• 2002

A performance of a new positron polarimeter is investigated by simulation using a charged-particle trajectory program. The results of the ray tracing are presented along with the details of the design parameters and projected system performance. A ray tracing analysis indicates that this design is capable of effectively transmitting positrons at beam energies varying from 0.1 to 30 keV within the beam diameter of 2-6mm. However, the observed reflection of the positrons(lower than 2 keV) at 12 kGauss indicated that further refinement of beam design is needed to produce a better positron polarimeter.

• 한국분말재료학회지
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• 제19권2호
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• pp.140-145
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• 2012

This paper describes the manufacturing process of tilting pad gas bearing with a diameter of 5 mm and a length of 0.5-1 mm for power MEMS (Micro Electomechanical Systems) applications. The bearing compacts with nanopowder feedstock were prepared by Ni-metal mold with 2-mold system using LIGA process. The effect of the manufacturing conditions on sintering properties of nanopowder gas bearing was investigated. In this work, Fe-45 wt%Ni nanopowder with an average diameter of 30-50 nm size was used as starting material. After mixing the nanopowder and the wax-based binders, the amount of powder was controlled to obtain the certain mixing ratio. The nanopowder bearing compacts were sintered with 1-2 hr holding time under hydrogen atmospheres and under temperatures of $600^{\circ}C$ to $1,000^{\circ}C$. Finally, the critical batch of mixed powder system was found to be 70% particle fraction in total volume. The maximum density of the sintered bearing specimen was about 94% of theoretical density.

• Nuclear Engineering and Technology
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• 제53권4호
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• pp.1289-1296
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• 2021

In this study, an electron-scattering device was fabricated to practically use the ultra-high dose rate electron beams for the FLASH preclinical research in Dongnam Institute of Radiological and Medical Sciences. The Dongnam Institute of Radiological and Medical Sciences has been involved in the investigation of linear accelerators for preclinical research and has recently implemented FLASH electron beams. To determine the geometry of the scattering device for the FLASH preclinical research with a 6-MeV linear accelerator, the Monte Carlo N-particle transport code was exploited. By employing the fabricated scattering device, the off-axis and depth dose distributions were measured with radiochromic films. The generated mean energy of electron beams via the scattering device was 4.3 MeV, and the symmetry and flatness of the off-axis dose distribution were 0.11% and 2.33%, respectively. Finally, the doses per pulse were obtained as a function of the source to surface distance (SSD); the measured dose per pulse varied from 4.0 to 0.2 Gy/pulse at an SSD range of 20-90 cm. At an SSD of 30 cm with a 100-Hz repetition rate, the dose rate was 180 Gy/s, which is sufficient for the preclinical FLASH studies.

• 한국방사선학회논문지
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• 제10권8호
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• pp.565-569
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• 2016

최근 다엽콜리메이터를 부착한 선형가속기를 이용한 방사선수술의 빈도가 점차 높아지고 있다. 이러한 정교한 방사선 수술은 소조사면 내에 고선량의 방사선이 집중적으로 조사되기 때문에 체계적이고 정확한 정도관리가 필수적이다. 본 연구는 PIB(Particle in Binder) 방식 중 침전법을 이용하여 $400{\mu}m$ 두께의 요오드화납($PbI_2$)과 요오드화수은($HgI_2$) 광도전체 센서 시편를 제작하였다. 제작된 시편의 전기적 특성은 암전류, 출력전류, 응답특성 및 선형성을 평가하였다. 평가 결과, $HgI_2$ 가 우수한 신호발생량과 선형성을 보였다. 끝으로, 두께에 따른 $HgI_2$ 센서의 신호반응 특성 결과, $400{\mu}m$ 두께에서 신호발생효율이 가장 높았고, ${\pm}2.5%$ 이내의 우수한 재현성을 보였다.

• 콘크리트학회논문집
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• 제22권5호
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• pp.633-640
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• 2010

이 연구에서는 숏크리트에 적용하기 위한 고분말도 시멘트의 기본 특성을 검토하고자 하였다. 고분말 시멘트의 주요특성을 연구하기 위하여 입도분포, 응결시간, 압축강도를 측정하였으며, SEM 관찰, DSC 열분석, X선 회절분석을 실시하였다. 고분말도 시멘트는 일반 포틀랜드 시멘트와 비교하여 응결시간이 크게 단축되었으며 압축강도가 개선되었다. 기기분석 결과 고분말도 시멘트는 초기수화물이 보다 미세하고 광범위하게 분포하는 것으로 확인되었으며, 이러한 결과는 시멘트의 분말도가 상승함에 따라 시멘트 입자와 물과의 접촉면이 증가하기 때문이다. SEM 관찰, DSC 열분석, X선 회절분석 결과 알루미네이트계 급결제는 칼슘알루미늄 수화물의 생성을 촉진하고, 알칼리프리계 급결제는 에트린자이트와 모노설페이트의 생성을 증진하는 것으로 나타났다. 페이스트 응결시간 측정으로부터 알루미네이트계 급결제와 알칼리프리계 급결제가 응결시간을 단축시키는 것으로 확인되었으며, 고분말도 시멘트는 압축강도가 크게 향상 되는 것으로 나타났다. 특히 알루미네이트계 급결제는 응결시간 단축에 효과적이며, 알칼리프리계 급결제는 7일 이후의 강도증진에 효과적인 것으로 확인되었다.

• Journal of Radiation Protection and Research
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• 제45권3호
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• pp.130-141
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• 2020

Background: Concrete activation in cyclotron vaults is a major concern associated with their decommissioning because a considerable amount of activated concrete is generated by secondary neutrons during the operation of cyclotrons. Reducing the amount of activated concrete is important because of the high cost associated with radioactive waste management. This study aims to investigate the capability of the neutron absorbing materials to reduce concrete activation. Materials and Methods: The Particle and Heavy Ion Transport code System (PHITS) code was used to simulate a cyclotron target and room. The dimensions of the room were 457 cm (length), 470 cm (width), and 320 cm (height). Gd₂O₃, B₄C, polyethylene (PE), and borated (5 wt% ^natB) PE with thicknesses of 5, 10, and 15 cm and their different combinations were selected as neutron absorbing materials. They were placed on the concrete walls to determine their effects on thermal neutrons. Thin B₄C and Gd₂O₃ were placed between the concrete wall and additional PE shield separately to decrease the required thickness of the additional shield, and the thermal neutron flux at certain depths inside the concrete was calculated for each condition. Subsequently, the optimum combination was determined with respect to radioactive waste reduction, price, and availability, and the total reduced radioactive concrete waste was estimated. Results and Discussion: In the specific conditions considered in this study, the front wall with respect to the proton beam contained radioactive waste with a depth of up to 64 cm without any additional shield. A single layer of additional shield was inefficient because a thick shield was required. Two-layer combinations comprising 0.1- or 0.4-cm-thick B₄C or Gd₂O₃ behind 10 cm-thick PE were studied to verify whether the appropriate thickness of the additional shield could be maintained. The number of transmitted thermal neutrons reduced to 30% in case of 0.1 cm-thick Gd₂O₃+10 cm-thick PE or 0.1 cm-thick B₄C+10 cm-thick PE. Thus, the thickness of the radioactive waste in the front wall was reduced from 64 to 48 cm. Conclusion: Based on price and availability, the combination of the 10 cm-thick PE+0.1 cmthick B₄C was reasonable and could effectively reduce the number of thermal neutrons. The amount of radioactive concrete waste was reduced by factor of two when considering whole concrete walls of the PET cyclotron vault.

• 한국분말재료학회지
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• 제12권3호
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• pp.167-173
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• 2005

Production of weakly agglomerated nanopowders with the characteristic size of about 10 nm and a narrow particle size distribution is still a topical problem especially if the matter is an acceptable output (>50 g/hour), a high purity of the final product, and a low (energy consumption. The available experience and literature data show that the most promising approach to production of such powders is the evaporation-condensation method, which has a set of means for heating of the target. From this viewpoint the use of pulsed electron accelerators for production of nanopowders is preferable since they allow a relatively simple adjustment of the energy, the pulse length, and the pulse repetition rate. The use of a pulsed electron accelerator provides the following opportunities: a high-purity product; only the target and the working gas will interact and their purity can be controlled; evaporation products will be removed from the irradiation zone between pulses; as a result, the electron energy will be used more efficiently; adjustment of the particle size distribution and the characteristic size of particles by changing the pulse energy and the irradiated area. Considering the obtained results, we developed a design and made an installation for production of nanopowders, which is based on a hollow-cathode pulsed gas-filled diode. The use of a hollow-cathode gas-filled diode allows producing and utilizing an electron beam in a single chamber. The emission modulation in the hollow cathode will allow forming an electron beam 5 to 100 ms long. This will ensure an exact selection of the beam energy. By now we have completed the design work, manufactured units, equipped the installation, and began putting the installation into operation. A small amount of nanopowders has been produced.

• Journal of Radiation Protection and Research
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• 제41권4호
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• pp.344-349
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• 2016

Background: Carbon ion therapy has achieved satisfactory results. However, patients have a risk to get a secondary cancer. In order to estimate the risk, it is essential to understand particle transportation and nuclear reactions in the patient's body. The particle transport Monte Carlo simulation code is a useful tool to understand them. Since the code validation for heavy ion incident reactions is not enough, the experimental data of the elementary reaction processes are needed. Materials and Methods: We measured neutron production double-differential cross-sections (DDXs) on a carbon bombarded with 430 MeV/nucleon carbon beam at PH2 beam line of HIMAC facility in NIRS. Neutrons produced in the target were measured with NE213 liquid organic scintillators located at six angles of 15, 30, 45, 60, 75, and $90^{\circ}$. Results and Discussion: Neutron production double-differential cross-sections for carbon bombarded with 430 MeV/nucleon carbon ions were measured by the time-of-flight method with NE213 liquid organic scintillators at six angles of 15, 30, 45, 60, 75, and $90^{\circ}$. The cross sections were obtained from 1 MeV to several hundred MeV. The experimental data were compared with calculated results obtained by Monte Carlo simulation codes PHITS, Geant4, and FLUKA. Conclusion: PHITS was able to reproduce neutron production for elementary processes of carbon-carbon reaction precisely the best of three codes.