• Journal of Radiation Protection and Research
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• 제42권3호
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• pp.141-145
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• 2017

Background: The concrete walls inside the vaults of cyclotron facilities are activated by neutrons emitted by the targets during radioisotope production. Reducing the amount of radioactive waste created in such facilities is very important in case they are decommissioned. Thus, we proposed a strategy of reducing the neutron activation of the concrete walls in cyclotrons during operation. Materials and Methods: A polyethylene plate and B-doped Al sheet (30 wt% of B and 2.5 mm in thickness) were placed in front of the wall in the cyclotron room of a radioisotope production facility for pharmaceutical use. The target was Xe gas, and a Cu block was utilized for proton dumping. The irradiation time, proton energy, and beam current were 8 hours, 30 MeV, and $125{\mu}A$, respectively. To determine a suitable thickness for the polyethylene plate set in front of the B-doped Al sheet, the neutron-reducing effects achieved by inserting such sheets at several depths within polyethylene plate stacks were evaluated. The neutron fluence was monitored using an activation detector and 20-g on de Au foil samples with and without 0.5-mm-thick Cd foil. Each Au foil sample was pasted onto the center of a polyethylene plate and B-doped Al sheet, and the absolute activity of one Au foil sample was measured as a standard using a Ge detector. The resulting relative activities were obtained by calculating the ratio of the photostimulated luminescence of each foil sample to that of the standard Au foil. Results and Discussion: When the combination of a 4-cm-thick polyethylene plate and B-doped Al sheet was employed, the thermal neutron rate was reduced by 78%. Conclusion: The combination of a 4-cm-thick polyethylene plate and B-doped Al sheet effectively reduced the neutron activation of the investigated concrete wall.

• Journal of the Korean Physical Society
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• 제80권
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• pp.640-646
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• 2022

Hybrid PET/MRI is a useful imaging system that can improve diagnostic accuracy by providing both functional and anatomical information. However, the combination of PET and MRI can lead to mutual interference, which can degrade the performances of both imaging systems. One of the methods that is capable of preserving the performance of both modalities is to apply RF shielding to PET detectors and electronics. The purpose of this study was to propose a new RF shielding method using Au-plated conductive fabric (PCF) tape that could not only minimize RF interference and eddy current, but that could also be applied to complex PET gantry and detector module structures more easily than thin Cu foils, which have been widely used as a shielding material for hybrid PET/MRI systems. To evaluate the performance of the proposed new RF shielding method, the effects of the two RF shield materials (Cu and Au) on the B1 + field generated by the RF head coil were estimated using a computer simulation method. The effects of the Au PCF tape and Cu foil on the homogeneity and SNR of the MR image were also experimentally evaluated using a commercial 3-T MRI. The uniformity of the B1 + field map was slightly decreased by the use of Cu and Au RF shields. The deterioration in the MR image quality caused by the Au PCF tape was less than that caused by Cu foil. The simulation and experimental results indicate that Au PCF tape can serve as an alternative shielding material that reduces RF interference and eddy current for hybrid PET/MRI systems.

• Progress in Superconductivity
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• 제12권1호
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• pp.41-45
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• 2010

Low temperature micro-calorimeters have been employed in the field of high resolution alpha spectrometers. These alpha detectors typically consist of a superconducting or metal absorber and a temperature sensor. The temperature sensor can be a transition edge sensor (TES), a metallic magnetic calorimeter (MMC) or other low temperature detectors for an accurate measurement of temperature change due to an alpha particle absorption. We report a recent study of the heat flow between a replaceable absorber and a temperature sensor. A piece of gold foil in $2.4{\times}2.7{\times}0.03\;mm^3$ is used as an absorber. A $40\;{\mu}m$ diameter Au:Er paramagnetic sensor is attached to another small piece of gold foil in $400{\times}200{\times}30\;{\mu}m^3$ to serve as the temperature sensor. This sensor assembly, Au:Er and gold foil, is placed on a miniature SQUID susceptometer in a gradiometric configuration. The thermal connection between the absorber and the sensor was made with three gold bonding wires. The measured thermal conductance shows a linear dependence to the temperature. The values are in a good agreement with Wiedemann-Franz type thermal conductance of the gold wires.

• Nuclear Engineering and Technology
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• 제36권3호
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• pp.203-209
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• 2004

In-phantom neutron flux distribution is measured at the HANARO BNCT irradiation facility. The measurements are performed with Au foil and wires. The thermal neutron flux and Cd ratio obtained at the HANARO BNCT facility are $1.19{\times}10^9\;n/cm^{2}s$ and 152, respectively, at 24 MW reactor power. The measured in-phantom neutron flux has a maximum value at a depth of 3 mm in the phantom and then decreases rapidly. The maximum flux is about $25\%$ larger than that of the phantom surface, and the measured value at a depth of 22 mm in the phantom is about a half of the maximum value. In addition, the neutron beam is limited well within the aperture of the neutron collimator. The two-dimensional in-phantom neutron flux distribution is determined. Significant neutron irradiation is observed within 20 mm from the phantom surface. The measured neutron flux distribution can be utilized in irradiation planning for a patient.

• Nuclear Engineering and Technology
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• 제11권1호
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• pp.21-27
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• 1979

TRIGA Mark II 원자로심에서 반응율을 측정하여 중성자 spectrum parameter인 상대적인 증성자 온도 T$^{n}$ 과 열외중성자 지수 (equation omitted)를 얻기 위해 해석하였다. 측정은 경수 환경하에 있는 central thimble과 F2위치에서 수행되었다. 상대적인 중성자 온도는 Lu과 Mn의 방사화율로 표시되며 열외중성자 지수는 Au와 Mn의 반응율에 의go서 측정된다. 이들 검출박의 상대적인 ${\gamma}$-에너지는 multichannel analyzer에 의해서 분석되었다. 실험 결과는 이론적인 계산치와 비교 평가되었다.

• 보존과학연구
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• 통권14호
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• pp.45-76
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• 1993

Au-Cu alloyed coating layer were found by Hg-amalgam process and it seemed to be used Cu-amalgam process similar to Au-amalgam. Coated layer is dense and unique, Thickness of layer was 1.5 to $18.0\mum$ which had 95.3 to 99.8% purity of gold Matrix metal mostly cosists of forged copper alloy which had high purity and ferrite ($\alpha$) strusture. It showed excellent refining technical level at that time. Aowever, the nail, ferrous matrix used for strength needed, composed of silver foil packed and gold layer for adherence between ferrous matrix and gold layer

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.618-618
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• 2013

Graphene is only one atom thick planar sheet of sp2-bonded carbon atoms arranged in a honeycomb crystal lattice, which has flexible and transparent characteristics with extremely high mobility. These noteworthy properties of graphene have given various applicable opportunities as electrode and/or channel for various flexible devices via suitable physical and chemical modifications. In this work, for the development of all-graphene devices, we performed to synthesize alternately patterned structure of mono- and multi-layer graphene by using the patterned Ni film on Cu foil, having much different carbon solid solubilities. Depending on the process temperature, Ni film thickness, introducing occasion of methane and gas ratio of CH4/H2, the thickness and width of the multi-layer graphene were considerably changed, while the formation of monolayer graphene on just Cu foil was not seriously influenced. Based on the alternately patterned structure of mono- and multi-layer graphene as a channel and electrode, respectively, the flexible TFT (thin film transistor) on SiO2/Si substrate was fabricated by simple transfer and O2 plasma etching process, and the I-V characteristics were measured. As comparing the change of resistance for bending radius and the stability for a various number of repeated bending, we could confirm that multi-layer graphene electrode is better than Au/Ti electrode for flexible applications.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.430-430
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• 2013

Field effect transistor based on semiconductor nanowires has been attracting lots of concerns and studies of scientists because of its different characteristic comparing with other morphology like thin film. Nowadays, graphene is introducing a great promise as an active layer in field effect transistor due to its unique electronic and optoelectronic properties. Thus, a mix structure between etched graphene and semiconductor nanowires is believed to expose novel electrical characteristics. In this study, CuO nanowires (20~80 nm in diameter and $1{\sim}10{\mu}m$ length) were grown during oxidizing Cu foil at $450^{\circ}C$ for 24 h. Besides, 3-layersetched graphene was deposited on Cu foil at $1,000^{\circ}C$ using a feedstock of $CH_4$/$H_2$ mixed gas in CVD system. A structure of Ni/Au electrode + CuO nanowires + etched graphene was fabricated, afterward. Finally, field effect properties of the device was revealed and compared with individual devices of just nanowires and just graphene.

• Progress in Superconductivity
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• 제14권2호
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• pp.102-105
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• 2012

We are developing meander-shaped metallic magnetic calorimeters using micro-fabrication methods. A planar Nb coil in a meander shape was fabricated on a Si substrate. The coil was designed to have a persistent current using a metal heater evaporated on a part of the coil. A paramagnetic sensor, $5{\mu}m$ thick Au:Er foil, was glued on top of the meander structure with epoxy. The magnetization and heat capacity were measured at different temperatures, and applied field currents matched well with expected values. The detector showed an energy resolution of 4 keV FWHM for the 5.5 MeV alpha particles.

• 박물관보존과학
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• 제30권
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• pp.47-70
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• 2023

2019년 석조불좌상의 원위치와 사역 구조를 파악하기 위해 경주 남산 약수곡 제4사지의 첫 발굴 조사가 실시되었다. 발굴 조사를 통해 출토된 석재 불두는 인근에 방치되어 있던 머리가 없는 석조불좌상과의 비교 분석을 통해 암석학적 및 광물학적으로 동질한 것으로 확인되었다. 땅에 묻혀 있던 불두의 오른쪽 얼굴 일부분에서 금박과 검은색 접착제의 흔적이 발견되었는데 대형 석조 불상에 바탕층 없이 옻칠 도금 기법을 적용하는 것이 매우 드물기 때문에 사용된 재료의 특성을 분석하여 당시의 도금 기법을 조사하고자 하였다. 분석 현미경과 주사전자현미경-에너지 분산형 분광기를 통해 금박의 구조를 관찰하고 금(Au) 성분을 분석하였다. 열분해-기체 크로마토그래프/질량분석기를 이용하여 검은색 접착제를 분석한 결과 탄화수소, 지방산, 카테콜 그리고 카테콜 산화물 등의 열분해 화합물이 검출되었다. 이는 우루시올을 주성분으로 하는 옻나무 수종에서 채취한 옻칠을 분석하였을 때 나타나는 특징과 일치하였다. 따라서 약수곡 제4사지에서 출토된 석재 불두가 인근의 석조불좌상에서 분리된 것이며 금박을 부착하기 위해 한국, 중국, 일본 등지에서 자생하는 옻 나무에서 채취한 옻 수액을 사용한 것을 확인하였다.