• Nuclear Engineering and Technology
• /
• 제29권6호
• /
• pp.459-467
• /
• 1997

The steady-state behavior of recycling neutral atoms in a tokamak edge region has been analyzed through a two-dimensional Monte Carlo simulation. A particle tracking algorithm used in earlier research on the neutral particle transport is applied to this Monte Carlo simulation in order to perform more accurate calculations with the EDGETRAN code which was previously developed for a two-dimensional edge plasma transport in the authors' laboratory. The physical model of neutral recycling includes charge-exchange and ionization interactions between plasmas and neutral atoms. The reflection processes of incident particles on the device wall are described by empirical formulas. Calculations for density, energy, and velocity distributions of neutral deuterium-tritium atoms have been carried out for a medium-sized tokamak with a double-null configuration based on the KT-2 conceptual design. The input plasma parameters such as plasma density, ion and electron temperatures, and ion fluid velocity are provided from the EDGETRAN calculations. As a result of the present numerical analysis, it is noticed that a significant drop of the neutral atom density appears in the region of high plasma density and that the similar distribution of neutral energy to that of plasma ions is present as frequently reported in other studies. Relations between edge plasma conditions and the neutral recycling behavior are discussed from the numerical results obtained herein.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1994년도 하계학술대회 논문집 C
• /
• pp.1589-1592
• /
• 1994

We developed the ion plating system, consisted of the Facing Target Magnetron Sputtering System and the r.f, electrode of the coil type, which was available to control the reactive and the adhesion between thin film and substrate, and studied about the discharge characteristics and the optimum condition in order to form the high quality thin film. The characteristics of discharge and plasma was measured as Double Probe and Electrostatic Retarding Grid Analyzer. The incident ion energy on the substrate was increased as the increasing r.f power, bias voltage. By the r.f electrode, the ionization rate of the sputtered particles was about 75%, and the mean incident ion energy depend on the value which was difference between the plasma potential and biased substrate potential.

• 대한화학회지
• /
• 제40권4호
• /
• pp.235-242
• /
• 1996

기체 크로마토그래피와 쉽게 연결할 수 있는 Surfatron형의 MIP(Microwave Induced Plasma)용 cavity를 제작하고 헬륨, 아르곤, 질소 등을 플라스마 가스로 사용하여 플라스마를 생성시키고 스펙트럼을 비교하였다. 또한 헬륨과 아르곤, 질소에 미량의 CO2를 혼합하여 각 기체의 스펙트럼을 비교 분석하였으며, 제작한 MIP cavity가 질량분석기와 연결되었을 때 분자이온을 생성시킬 수 있는 이온원으로서의 가능성을 연구하였다. 헬륨과 아르곤 MIP는 높은 준안정 준위의 에너지를 가지기 때문에 분자들이 거의 다 깨어지므로 분자상태로 시료기체의 검출은 거의 불가능하였다. 그러나 질소는 다른 비활성기체에 비하여 낮은 준안정 준위의 어네지를 가지므로 검출하려는 기체성분이 상당부분 분자상태로 존재함을 알 수 있었다.

• 한국의학물리학회지:의학물리
• /
• 제32권4호
• /
• pp.122-129
• /
• 2021

Purpose: This study aimed to design a multipurpose dose verification phantom for external audits to secure safe and optimal radiation therapy. Methods: In this study, we used International Atomic Energy Agency (IAEA) LiF powder thermoluminescence dosimeter (TLD), which is generally used in the therapeutic radiation dose assurance project. The newly designed multipurpose phantom (MPP) consists of a container filled with water, a TLD holder, and two water-pressing covers. The size of the phantom was designed to be sufficient (30×30×30 cm³). The water container was filled with water and pressed with the cover for normal incidence to be fixed. The surface of the MPP was devised to maintain the same distance from the source at all times, even in the case of oblique incidence regardless of the water level. The MPP was irradiated with 6, 10, and 15 MV photon beams from Varian Linear Accelerator and measured by a 1.25 cm³ ionization chamber to get the correction factors. Monte Carlo (MC) simulation was also used to compare the measurements. Results: The result obtained by MC had a relatively high uncertainty of 1% at the dosimetry point, but it showed a correction factor value of 1.3% at the 5 cm point. The energy dependence was large at 6 MV and small at 15 MV. Various dosimetric parameters for external audits can be performed within an hour. Conclusions: The results allow an objective comparison of the quality assurance (QA) of individual hospitals. Therefore, this can be employed for external audits or QA systems in radiation therapy institutions.

• Journal of Radiation Protection and Research
• /
• 제48권3호
• /
• pp.124-130
• /
• 2023

Background: When bipolar junction transistors (BJTs) are used as switches, their switching characteristics can be deteriorated because the recombination time of the minority carriers is long during turn-off transient. When BJTs operate as low frequency switches, the power dissipation in the on-state is large. However, when BJTs operate as high frequency switches, the power dissipation during switching transients increases rapidly. Materials and Methods: When silicon (Si) BJTs are irradiated by fast neutrons, defects occur in the Si bulk, shortening the lifetime of the minority carriers. Fast neutron irradiation mainly creates displacement damage in the Si bulk rather than a total ionization dose effect. Defects caused by fast neutron irradiation shorten the lifetime of minority carriers of BJTs. Furthermore, these defects change the switching characteristics of BJTs. Results and Discussion: In this study, experimental results on the switching characteristics of a pnp Si BJT before and after fast neutron irradiation are presented. The results show that the switching characteristics are improved by fast neutron irradiation, but power dissipation in the on-state is large when the fast neutrons are irradiated excessively. Conclusion: The switching characteristics of a pnp Si BJT were improved by fast neutron irradiation.

• Bulletin of the Korean Chemical Society
• /
• 제28권9호
• /
• pp.1499-1509
• /
• 2007

Proteomic analyses of synaptic vesicle fraction from rat brain have been performed for the better understanding of vesicle regulation and signal transmission. Two different approaches were applied to identify proteins in synaptic vesicle fraction. First, the isolated synaptic vesicle proteins were treated with trypsin, and the resulting peptides were analyzed using a high-pressure capillary reversed phase liquid chromatography/tandem mass spectrometry (cRPLC/MS/MS). Alternatively, proteins were separated by two-dimensional gel electrophoresis (2DE) and identified by matrix-assisted laser desorption ionization mass spectrometry (MALDI-TOF/MS). Total 18 and 52 proteins were identified from cRPLC/MS-MS and 2DE-MALDI-TOF-MS analysis, respectively. Among them only 2 proteins were identified by both methods. Of the proteins identified, 70% were soluble proteins and 30% were membrane proteins. They were categorized by their functions in vesicle trafficking and biogenesis, energy metabolism, signal transduction, transport and unknown functions. Among them, 27 proteins were not previously reported as synaptic proteins. The cellular functions of unknown proteins were estimated from the analysis of domain structure, expression profile and predicted interaction partners.

• Journal of the Optical Society of Korea
• /
• 제7권3호
• /
• pp.145-149
• /
• 2003

The anisotropy of electron energy distribution in oxygen plasmas produced by a high intensity laser was investigated by using polarization spectroscopy. An ultra-short pulsed laser with a pulse duration of 66.5 fs and a power density of $1 {\times} 10^17/ W/$\textrm{cm}^2$$ was used. At this power density and pulse duration, the plasma was generated predominantly by optical field ionization. The degree of polarization of OVI 1s$^2$2p$^2$p2- 1s$^2$4d$^2$D$^{0}$ (J = 1/2-3/2 and 3/2-5/2) transition line at 129.92 $\AA$ was measured. O VI 1s$^2$2p$^2$P$^2$ -1s$^2$4s$^2$S$^2$ (J = 1/2-1/2 and 3/2-1/2) transition line at 132.26 $\AA$ was used to calibrate the sensitivity of the optical system. The dependencies of the degree of polarization on the initial gas density and on the laser polarization were investigated. When the laser polarization was changed from a linear to a circular polarization, the degree of polarization was decreased. When the initial gas density was increased, the degree of polarization was decreased.

• 한국의학물리학회지:의학물리
• /
• 제31권4호
• /
• pp.135-144
• /
• 2020

Purpose: Gafchromic films for proton dosimetry are dependent on linear energy transfers (LETs), resulting in dose underestimation for high LETs. Despite efforts to resolve this problem for single-energy beams, there remains a need to do so for multi-energy beams. Here, a bimolecular reaction model was applied to correct the under-response of spread-out Bragg peaks (SOBPs). Methods: For depth-dose measurements, a Gafchromic EBT3 film was positioned in water perpendicular to the ground. The gantry was rotated at 15° to avoid disturbances in the beam path. A set of films was exposed to a uniformly scanned 112-MeV pristine proton beam with six different dose intensities, ranging from 0.373 to 4.865 Gy, at a 2-cm depth. Another set of films was irradiated with SOBPs with maximum energies of 110, 150, and 190 MeV having modulation widths of 5.39, 4.27, and 5.34 cm, respectively. The correction function was obtained using 150.8-MeV SOBP data. The LET of the SOBP was then analytically calculated. Finally, the model was validated for a uniform cubic dose distribution and compared with multilayered ionization chamber data. Results: The dose error in the plateau region was within 4% when normalized with the maximum dose. The discrepancy of the range was <1 mm for all measured energies. The highest errors occurred at 70 MeV owing to the steep gradient with the narrowest Bragg peak. Conclusions: With bimolecular model-based correction, an EBT3 film can be used to accurately verify the depth dose of scanned proton beams and could potentially be used to evaluate the depth-dose distribution for patient plans.

• 대한방사선기술학회지:방사선기술과학
• /
• 제32권2호
• /
• pp.205-212
• /
• 2009

반응보정인자(h)는 고체팬텀에서 전리함의 반응을 물에서의 값으로 변환하기 위한 인자이다. RW3 고체 팬텀의 경우에 고에너지 X-선에 대한 반응보정인자는 선질과 깊이에 의존하는 것으로 알려져 있으나 조사면 크기와 SSD(Source to surface distance), 그리고 전리함 종류에 따른 의존성은 알려진 바가 없다. 본 연구에서는 알려진 의존성을 고찰하고 알려지지 않은 인자들에 대한 의존성을 조사하였다. 본 측정에서는 파머형전리함(FC65G, IBA, Germany)과 소형전리함(CC13, IBA, Germany)이 사용되었으며 대상 선질은 6 MV와 15 MV X-선이었다. 측정 결과 반응보정인자는 6 MV의 경우에 깊이 5 cm와 10 cm에서 각각 h = 1.015, 1.021, 그리고 15 MV의 경우에 깊이 5와 10 cm에서 각각 h = 1.024, 1.029로 나타났다. 결론적으로 반응보정인자는 선질과 깊이에는 의존하였지만 조사면 크기와 SSD에 따른 변화는 적었다. 전리함에 있어서 대상의 두 전리함에 대해서는 차이가 없었으나 다른 종류의 전리함에 대해서 추가적 연구가 필요하다고 생각한다. 본 결과는 RW3에서 전리함을 이용한 측정시 측정값의 분석에 활용될 수 있다.

• 대한의용생체공학회:의공학회지
• /
• 제16권2호
• /
• pp.129-138
• /
• 1995

최근 방사선 치료에서 가속기를 이용한 고에너지, 고선량율 X-선과 전자선을 암환자 치료에 이용하고 있다. 치료시 방사선 조사선량의 5% 증감은 방사선 치료성적의 성패를 직접적으로 간여하고 있다고 국제 방사선 규정협회는 규정하고 있다. 본 논문에서는 방사선 치료에 영향을 미치는 빔 파라메터의 변동여부를 빠르고 간편하게 검출해 낼 수 있는 장치를 범용 실리콘 다이오드를 이용하여 제작한후 그 특성에 관해 고찰해 보았다. 13개 다이오드를 X-축 및 Y-축에 각각 7개씩 배열한 후 조사영역의 빔의 대칭도, 편평도, 안정성 등을 검출하여 보았고 방사선 손상에 대한 고찰, 일정기간 후의 변화량, 에너지 의존성 및 심부량 백분률등을 기존의 측정방법인 기체전리함을 이용한방법, 필름을 이용한 방법, 반도체 소자를 이용한 방법과의 값과 비교 분석하였다.