• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.1307_1308
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• 2009

고온초전도체 REBCO(RE=rare earth) 선재는 높은 전류전송밀도를 가지고 있기 때문에 고용량의 전류가 요구되는 응용분야에 사용되어 전력기기 등의 성능을 높일 수 있을 것으로 기대되고 있다. 이전까지 대부분의 REBCO 선재 연구들은 GdBCO, NdBCO, YBCO 등 비교적 Tc값이 높은 고온초전도체에 집중되어 왔다. 반면에 TmBCO는 대부분의 REBCO 보다 Tc값이 낮기 때문에 선재 연구 분야에서 거의 주목받지 않았다. 하지만 본 연구 결과에 따르면 TmBCO 선재는 비교적 낮은 Tc(88K) 값에도 불구하고 우수한 전류전송밀도(Jc=2.3MA/$cm^2$) 특성을 나타내기 때문에 고온초전도 선재로서 활용이 가능하다. 또한 NdBCO 선재에 비해 낮은 기판온도에서 제조가 가능함으로써 공정상의 이점을 가질 수 있음을 확인하였다.

• Progress in Superconductivity
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• v.7 no.2
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• pp.152-157
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• 2006

New precursor solution with dichloroacetic acid (DCA) was developed for fabricating high $J_c$ REBCO film. DCA based-precursor solution was coated on $LaAlO_3$(001) substrate by dip coating method. Processing parameters such as oxygen partial pressure, water vapor, ramping rate and pyrolysis temperature were controlled in order to obtain a good epitaxial film. The film with thickness of 0.5 micrometer was obtained by single coating and no crack was observed at calcined films. Oxygen partial pressure was controlled in the range of $100{\sim}1,000$ ppm and conversion heat treatment was carried out at the temperature range of $705-765^{\circ}C$. A critical transition temperature ($T_c$) of 90 K and a critical transport current density ($J_c$) of $>0.5\;MA/cm^2$ (77 K and self-field) were obtained for the GdBCO film. It is thought that fluorine-free MOD solution using DCA is promising precursor solution for fabricating high quality REBCO films.

• Nuclear Engineering and Technology
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• v.56 no.6
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• pp.2388-2394
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• 2024

In our previous works, two different spherical burnable poison particles (BPPs) as B₄C and Gd₂O₃ in pin-in block type HTGR core had utilized to suppress the excess reactivity and to control long-term reactivity during the burnup period. In the present work, we performed the neutronic analysis of a prismatic HTGR operating at 850 ℃ with thermal power of 100 MW containing spherical and cylindrical BPPs and then studied the self-shielding effect of BPPs and shape effect. The calculations were performed when the surface area (1) or volume (2) of cylindrical BPPs equals to that of the spherical BPPs. The calculations showed that the neutronic parameters were slightly better for the second case than the first one, such as the excess reactivity of the reactor core at the beginning of the cycle were more suppressed, the core lifetime were more extended, and the fuel-burning were more efficiently. The neutron spectrum in each region of the cylindrical BBPs slightly differs than that of the spherical BPPs. Therefore, the self-shielding effect of BPPs on reactor core performance depends on the particle's geometrical shape.

• Journal of Radiation Protection and Research
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• v.47 no.4
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• pp.214-225
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• 2022

Background: The conventional cerium-doped Gd₂Al₂Ga₃O₁₂ (GAGG(Ce)) scintillator-based gamma-ray imager has a bulky detector, which can lead to incorrect positioning of the gammaray source if the shielding against background radiation is not appropriately designed. In addition, portability is important in complex environments such as inside nuclear power plants, yet existing gamma-ray imager based on a tungsten mask tends to be weighty and therefore difficult to handle. Motivated by the need to develop a system that is not sensitive to background radiation and is portable, we changed the material of the scintillator and the coded aperture. Materials and Methods: The existing GAGG(Ce) was replaced with Bi₄Ge₃O₁₂ (BGO), a scintillator with high gamma-ray detection efficiency but low energy resolution, and replaced the tungsten (W) used in the existing coded aperture with lead (Pb). Each BGO scintillator is pixelated with 144 elements (12 × 12), and each pixel has an area of 4 mm × 4 mm and the scintillator thickness ranges from 5 to 20 mm (5, 10, and 20 mm). A coded aperture consisting of Pb with a thickness of 20 mm was applied to the BGO scintillators of all thicknesses. Results and Discussion: Spectroscopic characterization, imaging performance, and image quality evaluation revealed the 10 mm-thick BGO scintillators enabled the portable gamma-ray imager to deliver optimal performance. Although its performance is slightly inferior to that of existing GAGG(Ce)-based gamma-ray imager, the results confirmed that the manufacturing cost and the system's overall weight can be reduced. Conclusion: Despite the spectral characteristics, imaging system performance, and image quality is slightly lower than that of GAGG(Ce), the results show that BGO scintillators are preferable for gamma-ray imaging systems in terms of cost and ease of deployment, and the proposed design is well worth applying to systems intended for use in areas that do not require high precision.

• Nuclear Engineering and Technology
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• v.56 no.9
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• pp.3545-3552
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• 2024

Polymers have become widely used substrate materials for shielding neutron rays because of their high hydrogen content and easy processing procedures. Rare-earth materials are also being gradually adopted as neutron absorbers because of their considerable thermal neutron absorption cross-sections. This paper utilizes the FLUKA Monte Carlo simulation program to compare the shielding effects of various polymers and rare-earth oxides on neutron rays across different energy ranges. The study investigates the superior shielding materials for neutron radiation in each energy range. Subsequently, a series of materials are simulated by combining the preferred shielding materials for neutron rays in each energy range, exploring the influence of material composition and composite structure on the effectiveness of neutron ray shielding. It is revealed that the preferred material for shielding neutron rays changes for different energy ranges. For low-energy neutron rays, rare-earth oxides such as Sm₂O₃ and Gd₂O₃ demonstrate the most effective shielding, whereas for high-energy neutron rays, polyethylene (PE) provides the best shielding performance. Materials with different compositions show varying preferred structures when dealing with a ²⁵²Cf neutron source. However, in mitigating the secondary gamma rays generated during the neutron shielding process, stacked-type materials exhibit the most effective shielding performance.

• Journal of Radiation Protection and Research
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• v.39 no.4
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• pp.199-205
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• 2014

In the field of neutron detections, $^3He$ gas, the so-called "the gold standard," is the most widely used material for neutron detections because of its high efficiency in neutron capturing. However, from variable causes since early 2009, $^3He$ is being depleted, which has maintained an upward pressure on its cost. For this reason, the demands for $^3He$ replacements are rising sharply. Research into neutron converting materials, which has not been used well due to a neutron detection efficiency lower than the efficiency of $^3He$, although it can be chosen for use in a neutron detector, has been highlighted again. $^{10}B$, which is one of the $^3He$ replacements, such as $BF_3$, $^6Li$, $^{10}B$, $Gd_2O_2S$, is being researched by various detector development groups owing to a number of advantages such as easy gamma-ray discrimination, non-toxicity, low cost, etc. One of the possible techniques for the detection is an indirect neutron detection method measuring secondary radiation generated by interactions between neutrons and $^{10}B$. Because of the mean free path of alpha particle from interactions that are very short in a solid material, the thickness of $^{10}B$ should be thin. Therefore, to increase the neutron detection efficiency, it is important to make a $^{10}B$ thin film. In this study, we fabricated a $^{10}B$ thin film that is about 60 um in thickness for neutron detection using well-known technology for the manufacturing of a thin electrode for use in lithium ion batteries. In addition, by performing simple physical tests on the conductivity, dispersion, adhesion, and flexibility, we confirmed that the physical characteristics of the fabricated $^{10}B$ thin film are good. Using the fabricated $^{10}B$ thin film, we made a proportional counter for neutron monitoring and measured the neutron pulse height spectrum at a neutron facility at KAERI. Furthermore, we calculated using the Monte Carlo simulation the change of neutron detection efficiency according to the number of thin film layers. In conclusion, we suggest a fabrication method of a $^{10}B$ thin film using the technology used in making a thin electrode of lithium ion batteries and made the $^{10}B$ thin film for neutron detection using suggested method.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.202.1-202.1
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• 2015

탄소의 $sp^2$ 혼성으로 이루어진 2차원 단일시트(two-dimensional single sheet)인 그래핀은 기계적, 열역학적, 전기적 특성이 매우 우수하며 특히 고유연성과 투명성을 가진다는 장점 때문에 오랜 기간 주목 받으며 다양한 분야에서 연구되어 왔다. 이러한 그래핀을 만드는 방법에는 화학적 증기 증착법 및 흑연으로부터의 물리적, 화학적 박리 방법이 있다. 양질의 그래핀을 대면적에서 획득 할 수 있는 화학적 증기 증착법의 경우 높은 공정 비용과 함께 수반되어야 하는 전사과정의 어려움으로 인하여 실제 상용화에 어려움이 있다. 이러한 단점의 극복을 위해 대량의 그래핀을 저렴하게 확보 할 수 있는 화학적 박리 방법이 주목을 받고 있다. 화학적 박리 방법의 경우 박리 과정에서 수반되는 산화 그래핀의 환원과정이 필요하였으며, 이를 위해 강력한 환원제를 이용한 화학적 환원 방법, 고온에서의 열처리를 이용한 열역학적 환원 방법, 및 빛을 노광시켜 산화 그래핀을 환원시키는 광학적 방법이 시도되었다. 화학적 및 열역학적 환원방법의 경우 고품질의 환원된 산화 그래핀을 획득 할 수 있으나, 강한 환원제 및 높은 열처리 온도로 인하여 유연 기판의 사용이 제한되는 단점이 있다. 이러한 단점을 극복하기 위해 빛을 이용한 광학적 방법이 제시되었으나, 환원과정에 사용되는 단파장의 자외선 광원의 높은 가격으로 인하여 경제성의 확보가 제한된다. 본 논문에서는 우수한 광학적 특성을 보이는 란타넘족 이온을 사용하여 선택적 파장 대에서 높은 광흡수도를 가지는 산화 그래핀-란타넘 이온 혼합용액을 만들었으며, 가시광선대역의 파장을 가지는 레이저를 사용하여 우수한 품질을 가지는 환원된 산화 그래핀을 제작하였다. 구체적으로 산화 그래핀은 modified hummer's method를 이용하여 만들어졌으며, 자외선 대역을 흡수하는 $Gd_{3+}$, 녹색 레이저를 흡수하는 $Tb_{3+}$, 적색 레이저를 흡수하는 $Eu^{3+}$를 1 mM 섞어주었다. 그 후, 300~800 nm의 파장을 가지는 레이저를 $1mW/cm^2$를 노광시켜 산화 그래핀을 환원시켰다. 환원된 산화 그래핀의 특성은 FT-IR, UV-Vis, 저온 PL, SEM, XPS 및 전기측정을 이용해 측정하여 재현성 및 반복성을 확인하였다.

• Progress in Medical Physics
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• v.15 no.1
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• pp.1-8
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• 2004

Patient dose verification is one of the most Important responsibilities of the physician in the treatment delivery of radiation therapy. For the task, it is necessary to use an accurate dosimeter that can verify the patient dose profile, and it is also necessary to determine the physical characteristics of beams used in intensity modulated radiation therapy (IMRT) The Beam Intensity Scanner (BInS) System is presented for the dosimetric verification of the two dimensional photon beam. The BInS has a scintillator, made of phosphor Terbium-doped Gadolinium Oxysulphide (Gd$_2$O$_2$S:Tb), to produce fluorescence from the irradiation of photon and electron beams. These fluoroscopic signals are collected and digitized by a digital video camera (DVC) and then processed by custom made software to express the relative dose profile in a 3 dimensional (3D) plot. As an application of the BInS, measurements related to IWRT are made and presented in this work. Using a static multileaf collimator (SMLC) technique, the intensity modulated beam (IMB) is delivered via a sequence of static portals made by controlled leaves. Thus, when static subfields are generated by a sequence of abutting portals, the penumbras and scattered photons of the delivered beams overlap in abutting field regions and this results in the creation of “hot spots”. Using the BInS, inter-step “hot spots” inherent in SMLC are measured and an empirical method to remove them is proposed. Another major MLC technique in IMRT, the dynamic multileaf collimator (DMLC) technique, has different characteristics from SMLC due to a different leaf operation mechanism during the irradiation of photon and electron beams. By using the BInS, the actual delivered doses by SMLC and DMLC techniques are measured and compared. Even if the planned dose to a target volume is equal in our experimental setting, the actual delivered dose by DMLC technique is measured to be larger by 14.8% than that by SMLC, and this is due to scattered photons and contaminant electrons at d$_{max}$.

• The Korean Journal of Pharmacology
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• v.32 no.1
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• pp.75-82
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• 1996

The hypothesis that calcium provoke $O_2^-$ formation by Kupffer cells and may contribute to carbon tetrachloride $(CCl_4)$ induced liver injury was studied in SD rats. In $CCl_4-treated$ animals, hepatic malonaldehyde (nmole/gm liver) and plasma ALT (IU/ml) levels elevated significantly from $119.63{\pm}13.00$ to $268.97{\pm}14.82$ and from $17.3{\pm}0.18$ to $806.08{\pm}37.63$, respectively, compared to those in controls. Activation of Kupffer cells with high dose of retinol (250,000 IU/kg/day, po, for 7 day) significantly enhanced ALT levels, while inactivation of Kupffer cells with gadolinium chloride (7.5 mg/kg/day, ip, for 2 day) attenuated the increase of serum ALT level following $CCl_4$ treatment. Diltiazem (10 mg/kg/day, ip for 2 day) given in combination with retinol led to a marked decrease in ALT levels compare to the level in rats treated only with retinol against $CCl_4$ treatment. In order to determine any alterations in cytochrome P450 activities, the P450 content and the CYP2E1 activity were measured and all $CCl_4-treated$ rats showed significantly lower levels compared to those in controls and vehicle-treated animals. There were significant increases in glutathione peroxidase in all $CCl_4-treated$ rats except diltiazem treated groups. No difference was found among untreated and vehicle-treated rats. It is concluded that Kupffer cells contribute to $CCl_4-induced$ liver injury and that calcium antagonist attenuated the increased $CCl_4-induced$ liver injury due to activation of Kupffer cells.

• Nuclear Medicine and Molecular Imaging
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• v.42 no.6
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• pp.469-477
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• 2008

Purpose: The goal of this paper is to present the design and performance of a position encoding circuit for $16{\times}16$ array of position sensitive multi-anode photomultiplier tube for small animal PET scanners. This circuit which reduces the number of readout channels from 256 to 4 channels is based on a charge division method utilizing a resistor array. Materials and Methods: The position encoding circuit was simulated with PSpice before fabrication. The position encoding circuit reads out the signals from H9500 flat panel PMTs (Hamamatsu Photonics K.K., Japan) on which $1.5{\times}1.5{\times}7.0\;mm^3$ $L_{0.9}GSO$ ($Lu_{1.8}Gd_{0.2}SiO_{5}:Ce$) crystals were mounted. For coincidence detection, two different PET modules were used. One PET module consisted of a $29{\times}29\;L_{0.9}GSO$ crystal layer, and the other PET module two $28{\times}28$ and $29{\times}29\;L_{0.9}GSO$ crystal layers which have relative offsets by half a crystal pitch in x- and y-directions. The crystal mapping algorithm was also developed to identify crystals. Results: Each crystal was clearly visible in flood images. The crystal identification capability was enhanced further by changing the values of resistors near the edge of the resistor array. Energy resolutions of individual crystal were about 11.6%(SD 1.6). The flood images were segmented well with the proposed crystal mapping algorithm. Conclusion: The position encoding circuit resulted in a clear separation of crystals and sufficient energy resolutions with H9500 flat-panel PMT and $L_{0.9}GSO$ crystals. This circuit is good enough for use in small animal PET scanners.