• Korean Journal of Food Science and Technology
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• v.2 no.1
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• pp.113-120
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• 1970

For the purpose of disinfection and efficient storage, Korean Paldal variety rice was hulled into the unpolished and polished ones and packed in the kraft paper bags, irradiated with relatively high doses, 500, 800, and 1,000 krad from the $CO^{60}$ source and stored at room temperature, a variety of changes were observed as follows. 1) With 1,000 krad irradiation, mold was almost sterilized. 2) Fat acidity increased during storage and continued to increase more with increased doses. 3) The content of riboflavin eras severely reduced with higher doses. 4) The results of organoleptic test were featured by a yellow color and a keen irradiation odor appearing in the boiled rice. 5) In the irradiated rice starch with 3,000 krad, hydrolysis with ${\alpha}$-amylase was not effective while accelerated with diastase.

• Journal of the Korean institute of surface engineering
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• v.38 no.5
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• pp.202-206
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• 2005

Nitriding treatments were conducted on tool steel (SKD 61) at a temperature of $500^{\circ}C$ for 5 hr using high vacuum direct current (DC) plasma, with ammonia and argon as source gases. The structural and compositional changes produced in the nitrided layers by applying different ratios of Ar to $NH_{3}\;(n_{Ar}/n_{NH3}) were investigated using glancing x-ray diffraction (GXRD), optical microscopy, atomic force microscopy (AFM), micro-Vickers hardness testing, and pin-on-disc type tribometer. Nitriding case depths of around of $50{\mu}m$ were produced, varying slightly with different ratios of $n_{Ar}/n_{NH3}. It was found that the specimen surface hardness was 1150 Hv with $n_{Ar}/n_{NH3}=1, increasing to a maximum value of 1500 Hv with $n_{Ar}/n_{NH3}=5. With a further increase in ratio to $n_{Ar}/n_{NH3}=10, the surface hardness of the specimen reduced slightly to a value of 1370 Hv. These phenomena were caused by changes of the crystallographic structure of the nitride layers, i.e the $\gamma'-Fe_{4}N$ phase only was observed in the sample treated with $n_{Ar}/n_{NH3}$=1, and the intensity of the $\gamma'-Fe_{4}N$ phase were reduced but new phase of $\varepsilon'-Fe_{3}N$, which was known as a high hardness, with increasing $n_{Ar}/n_{NH3}. Also, the relative weight loss of counterface of the pin-on-disc with unnitrided steel was 0.2. And that of nitrided steel at a gas mixture ($n_{Ar}/n_{NH3}) of 1, 5, 7, and 10 was 0.4, 0.7, 0.6, and 0.5 mg, respectively. This means that the wear resistance of the nitrided samples could be increased by a factor of 2 at least than that of unnitrided steel.

• Korean Journal of Food Science and Technology
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• v.30 no.3
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• pp.498-501
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• 1998

It was determined whether photostimulated luminescence (PSL) is applicable to the detection of post-irradiation of foods by measuring PSL photon counts for unirradiated and irradiated pepper powder, dried herbs, fresh shrimp, potato, soybean, dried fig, chestnut, dried squid, and dried cod. The samples were irradiated with $^{60}Co\;{\gamma}-ray$ source and PSL photon counts were measured for them. The photon counts of unirradiated samples were lower than 2,000 for potatoes and less than 1,000 for the others. The photon counts of the irradiated samples except dried figs (0.5 kGy), chestnuts (0.2 kGy), and dried squid (0.5 kGy) were higher than 1,000, and the photon counts increased with dose. Thus, PSL might be applied to the primary detection of irradiated foods.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2001.11a
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• pp.35-35
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• 2001

agnesium Oxide (MgO) with a NaCI structure is well known to exhibit high secondary electron emission, excellent high temperature chemical stability, high thermal conductance and electrical insulating properties. For these reason MgO films have been widely used for a buffer layer of high $T_c$ superconducting and a protective layer for AC-plasma display panels to improve discharge characteristics and panel lifetime. Up to now MgO films have been synthesized by lE-beam evaporation, Molecular Beam Epitaxy (MBE) and Metalorganic Chemical Vapor Deposition (MOCVD), however there have been some limitations such as low film density and micro-cracks in films. Therefore magnetron sputtering process were emerged as predominant method to synthesis high density MgO films. In previous works, we designed and manufactured unbalanced magnetron source with high power density for the deposition of high quality MgO films. The magnetron discharges were sustained at the pressure of O.lmtorr with power density of $110W/\textrm{cm}^2$ and the maximum deposition rate was measured at $2.8\mu\textrm{m}/min$ for Cu films. In this study, the syntheses of MgO films were carried out by unbalanced magnetron sputtering with various $O_2$ partial pressure and specially target power densities, duty cycles and frequency using pulsed DC power supply. And also we investigated the plasma states with various $O_2$ partial pressure and pulsed DC conditions by Optical Emission Spectroscopy (OES). In order to confirm the relationships between plasma states and film properties such as microstructure and secondary electron emission coefficient were analyzed by X-Ray Diffraction(XRD), Transmission Electron Microscopy(TEM) and ${\gamma}-Focused$ Ion Beam (${\gamma}-FIB$).

• Analytical Science and Technology
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• v.21 no.6
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• pp.474-479
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• 2008

Radioactivity of naturally occurring radioactive nuclides (NORN) such as $^{226}Ra$, $^{228}Ac$ and $^{40}K$ were investigated for surface sediments collected from Ordos, Alashan, Taklimakan deserts and Loess plateau regions in China. By a Gamma-ray spectrometry, specific activity (SA) and SA ratio (SAR) of the NORN were determined for each source region of Asian dust. Characterization of the source regions of Asian dust was performed with the SA and SAR values. SA of $^{226}Ra$ in the three desert regions have almost same values in the range of mean value 17.9~21.9 Bq/kg, however, the SA in Loess Plateau has much higher values in the mean value of 35 Bq/Kg. SA of $^{228}Ac$ in the Ordos and Alashan desert regions have almost same values in the range of mean value 27.1~27.2 Bq/kg, and those in Taklimakan desert and Loess Plateau were 31.7 and 49.0 Bq/kg, respectively. In case of 40K, the SA in all regions have similar values in the range of 636~943 Bq/kg. The mean SAR value of $^{226}Ra/^{228}Ac$ in four source regions was almost same in the range of 0.708-0.721. It is shown that relationship between $^{226}Ra$ and $^{228}Ac$ is clearly presented in the source regions. The mean SAR values of $^{226}Ra/^{40}K$, $^{228}Ac/^{40}K$ are 0.0209-0.056, 0.0287-0.0773, respectively.

• Advances in materials Research
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• v.2 no.1
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• pp.15-36
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• 2013

Incorporation of polar functional moieties into polyethylene (PE) film has been achieved by graft copolymerization of polar monomers such as methacrylic acid (MAAc) and acrylamide (AAm) on to PE film, preirradiated with ${\gamma}$-rays from $^{60}Co$ source, using benzoyl peroxide (BPO) as initiator in aqueous medium. Percentage of grafting of MAAc and AAm was determined as a function of irradiation dose, monomer and initiator concentration, temperature, reaction time and amount of water. Maximum percentage of grafting of MAAc (1453%) and AAm (21.28%) was obtained at [MAAc] = $235.3{\times}10^{-2}$ mol/L, [AAm] = $23.4{\times}10^{-2}$ mol/L, [BPO] = $5.5{\times}10^{-2}$ mol/L and $16.5{\times}10^{-2}$ mol/L at $80^{\circ}C$, $90^{\circ}C$ in 180 min and 90 min respectively. The grafted PE films were characterized by FTIR, Thermogravimetric analysis (TGA) Scanning Electron Micrography (SEM) and X-ray diffraction methods. Some selective properties of grafted films such as swelling behavior, ion and metal uptake have been carried out. The biodegradation studies of the grafted PE films have also been investigated. The grafted films developed superior swelling behavior with maximum swelling (480%) in water as compared to pristine PE (13.55%), better thermal stability and ion and metal uptake studies showed promising results that can be effectively used for desalination of brackish water and separation of metals from the industrial effluents.

• Journal of The Korean Astronomical Society
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• v.48 no.4
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• pp.207-212
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• 2015

We introduce the Lee Sang Gak Telescope (LSGT), a remotely operated, robotic 0.43-meter telescope. The telescope was installed at the Siding Spring Observatory, Australia, in 2014 October, to secure regular and exclusive access to the dark sky and excellent atmospheric conditions in the southern hemisphere from the Seoul National University (SNU) campus. Here, we describe the LSGT system and its performance, present example images from early observations, and discuss a future plan to upgrade the system. The use of the telescope includes (i) long-term monitoring observations of nearby galaxies, active galactic nuclei, and supernovae; (ii) rapid follow-up observations of transients such as gamma-ray bursts and gravitational wave sources; and (iii) observations for educational activities at SNU. Based on observations performed so far, we find that the telescope is capable of providing images to a depth of R = 21:5 mag (point source detection) at 5-σ with 15 min total integration time under good observing conditions.

• Nuclear Engineering and Technology
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• v.10 no.4
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• pp.195-201
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• 1978

The radiation-induced graft polymerization of methacrlic acid and methyl methacrylate onto a polyester fabric was investigated with ${\gamma}$-ray as the radiation source, and the rate of grafting was examined. When acrylic acid, methacrylic acid, and methyl methacrylate were grafted onto a polyester fabric, grafting efficiency was depened upon the dielectric constant of the solvent in the monomer mixture. The yield of the graft polymerization was related to the total dose, the concentration of the monomer, and the concentration of the swelling agent. The melting point and the glass transition temperature of MA and MMA grafted copolymers were analysed by means of DTA. Physical properties, such as the moisture regain, the antistatic property, and the wicking time were measured.

• Journal of Electrical Engineering and Technology
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• v.12 no.4
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• pp.1619-1626
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• 2017

Electronic components that are used in high-level radiation environment require a semiconductor device having a radiation-hardened characteristic. In this paper, we proposed a radiation-hardened I-gate n-MOSFET (n-type Metal Oxide Semiconductors Field Effect Transistors) using a layout modification technique only. The proposed I-gate n-MOSFET structure is modified as an I-shaped gate poly in order to mitigate a radiation-induced leakage current in the standard n-MOSFET structure. For verification of its radiation-hardened characteristic, the M&S (Modeling and Simulation) of the 3D (3-Dimension) structure is performed by TCAD (Technology Computer Aided Design) tool. In addition, we carried out an evaluation test using a $Co^{60}$ gamma-ray source of 10kGy(Si)/h. As a result, we have confirmed the radiation-hardened level up to a total ionizing dose of 20kGy(Si).

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.324-327
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• 2002

For a next generation PET that realizes high sensitivity and high resolution, we proposed a design of a depth of interaction detector. A unit of the detector is constructed of four stages rectangular blocks of 2 by 2 Gd$_2$SiO$\sub$5/: Ce (GSO) crystal array optically coupled to position sensitive photomultiplier tube (PS-PMT). The 256ch flat panel PS-PMT is under development by Hamamatsu Photonics K.K., JAPAN. It has large cathode area, 51.7 by 51.7 mm$^2$, and the ratio of the effective area to external size is about 90%. The feature will contribute high packing fraction, accordingly high sensitivity. The 256 anodes are arranged in 16 by 16 at intervals of 3.0 mm. So as to evaluate the detector capability for identifying crystal of interaction, we got positioning image histograms with coupling a 16 by 5 array of GSO crystals, 2.9 by 2.9 by 7.5 mm$^3$, to the PS-PMT by irradiating a gamma ray uniformly from a point source. Flat panel PS-PMT is a new promising device for PET. We need to evaluate it if its performance is sufficiency. The performance was compared to the one with a 16ch PS-PMT.