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- 검색키워드
- 저자 : Hyoungtaek Kim (검색결과 17 건)
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Kim, Min Chae,Kim, Hyoungtaek,Han, Haegin,Lee, Jungil,Lee, Seung Kyu,Chang, Insu,Kim, Jang-Lyul,Kim, Chan Hyeong Elsevier 2019 Radiation measurements Vol.126 No.-
<P><B>Abstract</B></P> <P>In case of a radiation emergency, thermoluminescence (TL) and optically stimulated luminescence (OSL) measurements from materials in a mobile phone have been developed to enable classification of exposed individuals within a short period of time. A reconstructed dose from a mobile phone does not, however, correspond directly to a human body dose. Therefore, several studies were tried to convert a phone dose to a human body dose. Because of the difficulty in obtaining conversion factors experimentally, Monte Carlo simulations have been carried out using human phantoms for various accident situations. In recent years phantoms made of mesh have been developed to solve some problems in traditional voxel phantoms such as limited posture. In the present study, simulations using the GEANT4 computer code were performed to obtain conversion factors using mesh phantoms. The geometry of a mobile phone was designed, reflecting latest structures, and a display glass was selected as a dosimetric material due to its wide detection area with a high radiation sensitivity. Four different positions (chest, hip, thigh, and hand) of a mobile phone on the phantom were considered. In addition, six exposure conditions of anterior-posterior (AP), posterior-anterior (PA), left-lateral (LLAT), right-lateral (RLAT), isotropic (ISO), and rotational (ROT) exposure geometries and three different postures of standing, kneeling, and squatting were selected to reflect actual working situations. Three commonly used radiation sources (Iridium-192, Cesium-137, and Cobalt-60) were applied.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Simulation was conducted to convert a phone dose to human body dose using the mesh phantoms for various postures. </LI> <LI> The evaluated doses of a mobile phone were differently affected by body shielding effects. </LI> <LI> Four different positions (chest, hip, thigh, and hand) of a mobile phone on the phantom were considered. </LI> </UL> </P>
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Kim, Hyoungtaek,Kim, Min Chae,Lee, Jungil,Chang, Insu,Lee, Seung Kyu,Kim, Jang-Lyul Elsevier 2018 Radiation measurements Vol.118 No.-
<P><B>Abstract</B></P> <P>Phototransferred thermoluminescence (PTTL) characteristics of LiF:Mg,Cu,Si, developed by the Korea Atomic Energy Research Institute, are presented as part of a simple and reliable method for dose re-evaluation that is compatible with routine personal dosimetry services. A 4.5 mm diameter 0.8 mm thick pellet-type thermoluminescence dosimeter (TLD) was used after dual-step thermal annealing at 300 °C for 10 min, and then at 260 °C for 10 min, in order to obtain thermal stability. For optimal UV illumination, samples were placed under a 254 nm ultraviolet (UV) lamp for 90 min. The PTTL signal was only lower than 2% that of the TL because of low residual signals in high-temperature deep traps. The difference of the PTTL signals between samples appeared up to two times, indicating high variation in the charge density of the deep traps between samples. Various thermal treatments were performed after each PTTL measurement to remove the residual PTTL signal. UV exposure at 250 °C for 20 min fully reset the residual PTTL signals to the same level as that after dual-step annealing. No degradation of the TL peak from repeated thermal treatments was observed until after the eighth treatment when a decrease was noticeable. The measured dose response of PTTL in the range of 1.14–51.3 mGy showed good linearity. The zero dose and minimal detectable dose of the PTTL were 1.36 ± 0.51 mGy and 1.53 mGy, respectively. The attenuation of the PTTL signal resulting from successive TL measurements was recorded to provide a correction factor for quarterly recorded TL measurements applicable to the dose re-evaluation of TLDs in routine personal dosimetry services.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Dose re-evaluation using LiF:Mg,Cu,Si TLD is possible. </LI> <LI> Phototransferred thermoluminescence of LiF:Mg,Cu,Si was characterized. </LI> <LI> Heat treatment is required to remove residual phototransferred thermoluminescence. </LI> </UL> </P>
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Characterization of silicon photomultipliers at National Nano-Fab Center for PET-MR
Kim, Hyoungtaek,Sul, Woo Suk,Cho, Gyuseong American Institute of Physics 2014 Review of scientific instruments Vol.85 No.10
<P>The silicon photomultipliers (SiPMs) were fabricated for magnetic resonance compatible positron emission tomography (PET) applications using customized CMOS processes at National NanoFab Center. Each micro-cell consists of a shallow n+/p well junction on a p-type epitaxial wafer and passive quenching circuit was applied. The size of the SiPM is 3 3 mm(2) and the pitch of each micro-cell is 65 μm. In this work, several thousands of SiPMs were packaged and tested to build a PET ring detector which has a 60 mm axial and 390 mm radial field of view. I-V characteristics of the SiPMs are shown good uniformity and breakdown voltage is around 20 V. The photon detection efficiency was measured via photon counting method and the maximum value was recorded as 16% at 470 nm. The gamma ray spectrum of a Ge-68 isotope showed nearly 10% energy resolution at 511 keV with a 3 3 20 mm(3) LYSO crystal.</P>
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Lim, Kyung Taek,Kim, Hyoungtaek,Kim, Myungsoo,Kim, Yewon,Lee, Chang-yeop,Cho, Gyuseong Pergamon 2019 Radiation physics and chemistry Vol.155 No.-
<P><B>Abstract</B></P> <P>In this paper, we investigate how the SiPM characteristics might vary in different electric field conditions in terms of parameters such as dark count rate and photon detection efficiency and present their relationships via SiPM photon–number–resolution (R<SUB>SiPM</SUB>). The device samples were fabricated on 200 mm epitaxial wafers with a sensor area of 2.95 × 2.95 mm<SUP>2</SUP> and a micro-cell size of 65 µm. Keeping all other fabrication conditions identical, four different p-well implantation conditions were selected to produce four different electric field profiles: 5.0 × 10<SUP>12</SUP>, 4.0 × 10<SUP>12</SUP>, 3.0 × 10<SUP>12</SUP>, and 2.5 × 10<SUP>12</SUP> atoms/cm<SUP>2</SUP>. From the fabricated samples, measurements on the breakdown voltage, dark count rate, and photon detection efficiency were obtained accordingly. Based on the measured device parameters, R<SUB>SiPM</SUB> of each sample was calculated to demonstrate how the electric field in the depletion region could influence the device performance. The intention of this study is to provide a guideline for obtaining the optimal SiPM parameters for target applications under a given fabrication condition.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The degree to which electric field could influence SiPM behavior is examined. </LI> <LI> SiPM photon–number–resolution as a design indicator for a target application. </LI> <LI> Reduced electric field as a reasonable approach for low photon flux detection. </LI> </UL> </P>
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Lee, Seung Kyu,Chang, Insu,Kim, Sang In,Lee, Jungil,Kim, Hyoungtaek,Kim, Jang-Lyul,Kim, Min Chae The Korean Association for Radiation Protection 2019 방사선방어학회지 Vol.44 No.2
Background: In the calibration and testing laboratory of Korea Atomic Energy Research Institute, the old X-ray generator used for the production of reference X-ray fields was replaced with a new one. For this newly installed X-ray irradiation system, beam alignment as well as the verification of beam qualities was conducted. Materials and Methods: The existing X-ray generator, Phillips MG325, was replaced with YXLON Y.TU 320-D03 in order to generate reference X-ray fields. Theoretical calculations and Monte Carlo simulations were used to determine initial filter thickness. Beam alignment was performed in three steps to deliver a homogeneous radiation dosage to the target at different distances. Finally, the half-value layers were measured for different X-ray fields to verify beam qualities by using an ion chamber. Results and Discussion: Beam alignment was performed in three steps, and collimators and other components were arranged to maintain the uniformity of the mean air kerma rate within ${\pm}2.5%$ at the effective beam diameter of 28 cm. The beam quality was verified by using half-value layer measurement methods specified by American National Standard Institute (ANSI) N13.11-2009 and International Organization for Standardization (ISO)-4037. For each of the nine beams than can be generated by the new X-ray irradiation system, air kerma rates for X-ray fields of different beam qualifies were measured. The results showed that each air kerma rate and homogeneity coefficient of the first and second half-value layers were within ${\pm}5%$ of the recommended values in the standard documents. Conclusion: The results showed that the new X-ray irradiation system provides beam qualities that are as high as moderate beam qualities offered by National Institute of Standards and Technology in ANSI N13.11-2009 and those for narrow-spectrum series of ISO-4037.
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Effect of F− Implantation on the Optical and the Electrical Properties of GaInZnO Thin Films
HyeRyong Kim,PilSeong Jeong,HyoungTaek Oh,Suk-Ho Choi 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.2
GaInZnO (GIZO) thin films have been deposited on 100 nm SiO2/(100) Si wafers by RF magnetron sputtering and were subsequently implanted with F− ions at various fluences and energies. Broad photoluminescence (PL) spectra, peaked at about 715 nm, are observed in as-deposited GIZO films, and are attributed to oxygen-deficient defects. The implantation reduces the PL intensity and enhances the conductivity. The PL enhancement is more effective at higher fluences and energies. The influence of annealing on the PL and the conductivity after implantation is much larger than that of annealing without implantation. These results indicate that the F− ions are substitutionally incorporated in the GIZO films as shallow donors producing free carriers and that they occupy the oxygen vacancies, thereby reducing the defect density. GaInZnO (GIZO) thin films have been deposited on 100 nm SiO2/(100) Si wafers by RF magnetron sputtering and were subsequently implanted with F− ions at various fluences and energies. Broad photoluminescence (PL) spectra, peaked at about 715 nm, are observed in as-deposited GIZO films, and are attributed to oxygen-deficient defects. The implantation reduces the PL intensity and enhances the conductivity. The PL enhancement is more effective at higher fluences and energies. The influence of annealing on the PL and the conductivity after implantation is much larger than that of annealing without implantation. These results indicate that the F− ions are substitutionally incorporated in the GIZO films as shallow donors producing free carriers and that they occupy the oxygen vacancies, thereby reducing the defect density.
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전계에 따른 GM-APD의 다크 카운트와 광 검출효율의 상관관계 연구
유현(Hyun Yoo),김형택(Hyoungtaek Kim),조규성(Gyuseong Cho),설우석(Woo-Suk Sul) 대한전자공학회 2016 대한전자공학회 학술대회 Vol.2016 No.6
In this work, it was comparatively assessed using Silvaco TCAD simulator that the variation of electric filed distribution in GM-APD(Geiger Mode-Avalanche Photodiode) depending on the P-well dose, results in dark count rate(DCR) and photon detection efficiency(PDE). The electric field near the p-n junction interface in GM-APD is mainly affected by P-well dose. According to the dark count extracted from simulation, the increased electric field at the dose over 4.5×10<SUP>12</SUP>(#/㎠) makes DCR generated by band-to-band tunneling(BBT) increase drastically. PDE decreases as the P-well dose level lowers more. In particular, when the dose level is under 4.5×10<SUP>12</SUP>(#/㎠), PDE declines rapidly. Consequently, it will be helpful to reduce the occurrence of dark count by BBT and minimize the deterioration in PDE if the P-well dose of GM-APD is set to 4.5×10<SUP>12</SUP>(#/㎠).
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