• Proceedings of the IEEK Conference
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• 2000.06b
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• pp.290-293
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• 2000

Low frequency(<100Hz) weak magnetic field(<20gauss) is applied axially to an inductively coupled oxygen plasma(ICP), and its plasma characteristics are monitored by OES(Optical Emission Spectroscopy) and Langmuir probe. It is found that periodic magnetic field enhances ashing rate by 25％ and improves its uniformity upto 4.5％ over 8" wafer. From electron energy distribution function, both low and high energy electrons are identified and relative abundancy is found to be controlled by the applied frequency. Moreover, it is observed that ionization and dissociation species are varied with applied frequency. We insert an aluminium baffle in the chamber to get better uniformity and less plasma damage.

• Transactions of the Korean hydrogen and new energy society
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• v.8 no.4
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• pp.155-160
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• 1997

Generation of hydrogen and oxygen gas from water is mostly accomplished by electrolysis. In this report, a scheme is presented regarding the gas generation based on plasmolysis. Unlike electrolysis water dissociation by electrical discharge (plasmolysis) requires a high voltage to cause either electron emission or electron capture, and subsequent ionization of involved molecular species. When electrical discharge is initiated between electrodes separated by water-vapor interface, a very large electric field(~100kV/cm) is developed at the tip of the electrode placed in the vapor phase. It is found that the efficiency of plasmolysis depends on the polarity of the electrode placed in the vapor phase. Also presented is the scheme of hydrogen and oxygen generation by such electrical discharge.

• Journal of Radiation Protection and Research
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• v.1 no.1
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• pp.22-30
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• 1976

The perturbation of dose distribution adjacent to cavities in high energy electron has shown that the percentage of dose increase varies markedly as a function of the build-up layer, the length and thickness of the cavities, and the electron energy. The dose distribution showed that cavities similar in size to those encountered in the head and neck measured by industrial film dosimetry and corrected by ionization chambers. The most increased doses by measuring are resulted in a localized dose of up to 130% of that measured at the depth of maximum dose within a homogeneous tissue equivalent phantom. The measured values and correction factors of dose perturbation due to air cavities showed in diagrams and would be summarized as follows. 1. In $8{\sim}12MeV$ electron beams, the most marked dose is observed when the build-up layer thickness is 0.5cm and cavity volume is $2{\times}2{\times}2cm^3$. 2. The highest dose point is located under cavity when the energy is increased and cavity length is longer. 3. The cavity length at which the maximum percentage dose occurs decreases with increasing energy. 4. The highest percentage cavity doses are obtained when the energy is high, the build-up layer is thin, the thickness of the cavity is large, and the length of the cavity is approximately 1 to 3cm. 5. The doses of upper portion of cavity are less than the standard dose distribution as 5 to 10%. 6. The maximum range of electron beam are extended as much as thickness of cavity. 7. A cavity having a length of 5cm closely approximates a cavity of infinite length.

• Journal of the Korean Chemical Society
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• v.41 no.3
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• pp.117-122
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• 1997

On the basis of our previous paper[Bull. Korean Chem. Soc. 1995, 16, 1015], the relative stability, ionization potential, and chemical reaction of the neutral and multiply charged $C_{60}$n ions(n=3+ to 6-) have been investigated by the semi-empirical MNDO method. $C_{60}^{1-}$ has the highest stability. The ionization potential values of the $C_{60}$ ions range from 15.31 eV of $C_{60}^{2+}$ to -13.01 eV of $C_{60}^{6-}$. These values show a linear relationship according to charges. The average IP per charge is 3.15 eV from our calculations and 3.22 eV from the linear function of IP. A charge- or electron-transfer reaction of $C_{60}^{n+}$ will only occur if the ionization potential of any guest molecule is lower than the electron affinity of the host $C_{60}^{n+}$. If the energy gap between ionization potential and electron affinity, ${\Delta}_{IP-EA}$, is high, charge-transfer reactions arise by the charge-controlled effect. However, if ${\Delta}_{IP-EA}$ is low, electron-transfer reactions arise by the frontier-controlled effect.

• Progress in Medical Physics
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• v.31 no.4
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• pp.145-152
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• 2020

Purpose: In ionization-chamber dosimetry for high-dose-rate electron beams-above 20 mGy/pulse-the ion-recombination correction methods recommended by the International Atomic Energy Agency (IAEA) and the American Association of Physicists in Medicine (AAPM) are not appropriate, because they overestimate the correction factor. In this study, we suggest a practical ion-recombination correction method, based on Boag's improved model, and apply it to reference dosimetry for electron beams of about 100 mGy/pulse generated from an electron linear accelerator (LINAC). Methods: This study employed a theoretical model of the ion-collection efficiency developed by Boag and physical parameters used by Laitano et al. We recalculated the ion-recombination correction factors using two-voltage analysis and obtained an empirical fitting formula to represent the results. Next, we compared the calculated correction factors with published results for the same calculation conditions. Additionally, we performed dosimetry for electron beams from a 6 MeV electron LINAC using an Advanced Markus^® ionization chamber to determine the reference dose in water at the source-to-surface distance (SSD)=100 cm, using the correction factors obtained in this study. Results: The values of the correction factors obtained in this work are in good agreement with the published data. The measured dose-per-pulse for electron beams at the depth of maximum dose for SSD=100 cm was 115 mGy/pulse, with a standard uncertainty of 2.4%. In contrast, the k_s values determined using the IAEA and AAPM methods are, respectively, 8.9% and 8.2% higher than our results. Conclusions: The new method based on Boag's improved model provides a practical method of determining the ion-recombination correction factors for high dose-per-pulse radiation beams up to about 120 mGy/pulse. This method can be applied to electron beams with even higher dose-per-pulse, subject to independent verification.

• Nuclear Engineering and Technology
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• v.52 no.7
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• pp.1511-1516
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• 2020

The Korea Research Institute of Standards and Science (KRISS) established a new standard of the absorbed dose to water in LINAC X-ray beams. To confirm the equivalence of the new standard with other national metrology institutes (NMIs), a bilateral comparison study of the absorbed dose to water in high energy X-ray beams was performed between the KRISS and the National Metrology Institute of Japan (NMIJ). The comparison was made in-directly. Three transfer chambers were calibrated in the high energy X-ray beams by both laboratories and the calibration coefficients were compared. The average ratios of the calibration coefficients of the three transfer chambers obtained by the KRISS to those obtained by the NMIJ were 1.004, 1.006, 1.006, 1.007 for 6, 10, 15 and 18 MV X-ray beams, respectively. The calibration coefficients obtained at the KRISS were higher than those at the NMIJ but they were in good agreement within the expanded uncertainty of 1.0% (k = 2). The results of this study will be used as the evidence for the KRISS standard being comparable with those of other NMIs, temporarily, in the interim period up to finalizing a key comparison study, BIPM.RI(I)-K6 managed by the Consultative Committee for Ionizing Radiation.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08b
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• pp.1380-1383
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• 2007

The secondary electron emission coefficient (${\gamma}$) of the cathode is an important factor for improving the discharge characteristics of AC-PDP, because of its close relationship to discharge voltage. In this experiment, we have investigated the electronic structure of the energy band in the MgO layer responsible for the high ${\gamma}$. We used three kinds of MgO pellet that have another component, and each MgO layers have been deposited by electron beam evaporation method. The work-functions of MgO layer have been investigated from their ion-induced secondary electron emission coefficient (${\gamma}$), respectively, using various ions with different ionization energies in a ${\gamma}-FIB$ (Focused Ion Beam) system. We have compared work-function with ${\gamma}-FIB$ system current signal for measurement defect energy level in MgO layer. MgO-A in the three types has lowest work-function value (4.12eV) and there are two defect energy levels.

• Mass Spectrometry Letters
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• v.2 no.2
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• pp.57-60
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• 2011

As background significantly affects measurement accuracy and a detection limit in determination of the trace amounts of uranium, it is necessary to determine the impurities in the Lexan detector film for single particle measurements by thermal ionization mass spectrometry coupled with fission track technique (FT-TIMS). We have prepared various micro sizes of the blank Lexan detector film using a micromanipulation technique for uranium measurements by TIMS. Few tens of fg of uranium background with no remarkable dependency on the film sizes were observed in the blank Lexan films with the sizes from $50{\times}50\;{\mu}m^2$ to $300{\times}300\;{\mu}m^2$. Based on the determination of the uranium background in the Lexan film, any background correction is necessary in the isotopic analysis of a uranium single particle with micron sizes when the particle bearing Lexan film is dissected with less than $300{\times}300\;{\mu}m^2$ size. The isotopic analysis of a uranium particle in U030 standard material using TIMS was carried out to verify the applicability of the Lexan film to the single particle analysis with high accuracy and precision.

• Proceedings of the Materials Research Society of Korea Conference
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• 1992.05a
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• pp.6-6
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• 1992

Ionized cluster beam deposition (ICBD) technique has been employed to fabricate high-purity crystalline polyimide (PI) film. The pyromellitic dianhydride (PMDA) and oxydianiline (ODA) were deposited using dual ICB sources, Fourier trans forminfraredspectroscopy (FT-IR), X-ray photoemission spectroscopy (XPS), and Transmission electron microscopy (TEM)study show that the bulk and surface chemical properties and the crystalline structure are very sensitive to the ICBD conditions such as cluster ion acceleration voltage and ionization voltage, At optimum ICBD conditions, the PI films have a maximum imidization, negligible impurities(∼1% isoimide), and a good crystalline structure probably due to the high surface migration energy and surface cleaning effect. These characteristics are superior to those of films deposited by other techniques such as colvent cast, vapowr deposition, or sputtering techniques.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.88-88
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• 2010

The liquid metal ion sources(LMIS) in FIB system have many advantages of high current density, high brightness, and low ion energy spread. Most FIB systems use LMIS because the beam spot size of LMIS is smaller than of gas field ionization sources(GFIS). LMIS basically consists of a emitter(needle, anode), a reservoir(gallium) and a extractor(cathode). But several LMIS have new electrode called the suppressor. We investigated characteristics of LMIS with a suppressor. The characteristics of the threshold voltage and current-voltage (I-V) were observed under the varying extracting voltage with floated suppressor voltage, and under the varying suppressor voltages with fixed extractor voltage. We also simulated LMIS with the suppressor through CST(Computer Simulation Technology). We can explain characteristics of LMIS with a suppressor using the electric field.