• 한국진공학회:학술대회논문집
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• 한국진공학회 1999년도 제17회 학술발표회 논문개요집
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• pp.191-191
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• 1999

Extended X-ray Absorption Fine Structure (EXAFS)는 일반적으로 널리 사용하는 X선 회절분광기로 분석하기 힘든 chemical 또는 biological system의 structural analyses에 매우 유용한 분석방법이다. 특히 세라믹이나 유전체 비정질 재료의 미세 원자 구조에 관한 정보를 얻는데는 가장 강력한 분석방법중의 하나로 알려져 있다. 현재까지 대부분의 EXAFS 실험은 방사광 가속기를 이용하여 수행하였다. 그런데 신제품 개발의 순환주기가 급속하게 단축되는 현실적인 문제에 부응하기 위하여 실험실에서 EXAFS 실험을 수행할 수 있는 system을 개발하게 되었다. 개발한 XIEES 장비는 rotating anode 형의 18kW X-ray source, Optical system, Detection system, Stepping motor control system, vacuum system, Utility 등으로 구성하였다. Optical system에서의 6개의 Johanson type monochromator를 사용하여 분석가능한 x-ray energy range를 480eV에서 41keV까지 구현하였다. 이는 산소에서 우라늄까지 분석이 가능함을 의미하는 것으로, 산화물 연구에 많이 활용할 것으로 기대한다. XIEES는 투과 및 형광 X-ray를 검출할 수 있는 기능과 X-ray에 의해 여기 되는 모든(광전자, Aiger 전자, 이차전자)들을 검출할 수 있는 기능을 갖추고 있는데 이를 Total Electron Yield 측정이라고 한다. Total Electron Yield 측정은 박막 시료와 같이 투과가 되지 않는 시료를 분석할 뿐만 아니라, 경원소 분석, 낮은 에너지에서 흡수 edge가 나타나는 L-edge 측정을 통한 전자 구조 분석 등에 유용한다. 실험실용 XIEES 장비는 방사광가속기에 비해 x-ray flux가 크게 뒤지는 문제와 Total Electron Yield를 측정하는 데 있어서 source에서 나오는 x-ray beam이 진공용기 안에서 산란되어 이차전자를 여기하고 이 이차전자들이 전자검출기에 유입되어 측정에 영향을 미치는 background 문제 등이 있다. 이 두 가지 문제를 해결하기 위하여 Capillary tube를 사용하였다. 본 연구에서는 실험실용 XIEES 장비를 소개하고 이를 이용하여 Cu standard 시료에서 측정한 EXAFS 결과와 Capillary tube를 사용하여 얻은 x-ray flux 증진 및 background 제거 효과에 대해서 발표한다.

• Journal of Astronomy and Space Sciences
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• 제30권2호
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• pp.83-85
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• 2013

Anomalous X-ray pulsars (AXPs) are thought to be magnetars which are young isolated neutron stars with extremely strong magnetic fields of > $10^{14}$ Gauss. Their tremendous magnetic fields inferred from the spin parameters provide a huge energy reservoir to power the observed X-ray emission. High-energy emission above 0.3 MeV has never been detected despite intensive search. Here, we present the possible Fermi Large Area Telescope (LAT) detection of ${\gamma}$-ray pulsations above 200 MeV from the AXP, 1E 2259+586, which puts the current theoretical models of ${\gamma}$-ray emission mechanisms of magnetars into challenge. We speculate that the high-energy ${\gamma}$-rays originate from the outer magnetosphere of the magnetar.

• 전력전자학회논문지
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• 제8권2호
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• pp.192-198
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• 2003

본 논문에서는 의료 진단용 40kw(125kV, 80mA)급 X-선 전원 장치에 대하여 연구하였다. 의료 X-선용 고전압 발생 장치의 구성과 X-선 관전압과 관전류 그리고 피폭량 제어에 대하여 기존 제어 방식과 비교 설명하였고 제어기 설계시 고려할 사항에 대하여 언급하였다. 또한, 본 시스템의 핵심이라 할 수 있는 고주파 고전압 변압기의 등가회로를 통한 기생 성분에 대하여 기술하였으며 본 연구에서 제작된 의료 X-선용 HFG 시스템의 출력특성의 우수성을 X-전관 부하 변동에 따른 X-선 관전류와 관전압 파형을 통하여 입증하였다.

• Journal of the Optical Society of Korea
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• 제12권2호
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• pp.112-117
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• 2008

Single-mode propagation conditions of X-ray waveguides are investigated by numerical calculations in order to understand the importance of waveguide design parameters, such as core thickness and the optical constants of waveguide materials, on the transmission and coherence properties of the waveguide. The simulation code for mode analyzing is developed based on a numerical solution of the parabolic wave equation. The initial boundary value problem is solved numerically using a finite-difference scheme based on the Crank-Nicolson scheme. The E-field intensities in a core layer are calculated at an X-ray energy of 8.0 keV for air and beryllium(Be) core waveguides with different cladding layers such as Pt, Au, W, Ni and Si to determine the dependence on waveguide materials. The highest E-field intensity radiated at the exit of the waveguide is obtained from the Pt cladded beryllium core with a thickness of 20 nm. However, the intensity from the air core waveguide with Pt cladding reaches 64% of the Be-Pt waveguide. The dependence on the core thickness, which is the major parameter used to generate a single mode in the waveguide, is investigated for the air-Pt, and Be-Pt waveguides at an X-ray energy of 8.0 keV. The mode profiles at the exit are shown for the single mode at a thickness of up to 20 nm for the air-Pt and the Be-Pt waveguides.

• Journal of the Optical Society of Korea
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• 제11권2호
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• pp.76-81
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• 2007

The compound refractive X-ray lens (CRL) for focusing hard X-rays is investigated to determine the parameters such as the focal length, the focal spot size, and spatial distribution at the focal spot using a simple theoretical calculations and CRLs fabricated by the self-assembly method. The number of individual compound lenses are defined for the given focal length of 1 m. The X-ray energy of 1 to 40 keV is used in the calculations. The CRL for focusing hard X-rays which generated from the X-ray tube is fabricated by nanoparticle-polymer composite in the form of circular concaves. The self-assembly method is applied to form the nanoaluminum-poly (methly meth-acrylate) composite and carbon-polymer composite CRL lenses. Aluminum nanoparticles of 100 nm and carbon microparticles are diffused in the polymer solution then the high gravity up to 6000G is applied in it to form the concave lens shape. X-ray energy at 8 keV is used for characterization of the composite CRLs. The FWHM of intensity for the fabricated nanoaluminium composite CRL system, N=10 is measured as 1.8 mm, which would give about $70{\mu}m$ in FWHM at 1 m of the focal length.

• 천문학회보
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• 제45권1호
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• pp.37.1-37.1
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• 2020

Cosmic-ray protons (CRp) are efficiently produced at starburst galaxies (SBGs), where the star formation rate (SFR) rate is high. In this talk, we present estimates of gamma-ray and neutrino emissions from nearby SBGs, M82, NGC253, and Arp220. Inside the starburst nucleus (SBN), CRp are accelerated at supernova remnant (SNR) shocks as well as at stellar wind (SW) termination shocks, and their transport is governed by the advection due to starburst-driven wind and diffusion mediated by turbulence. We here model the momentum distributions of SNR and SW-produced CRp with single or a double power-law forms. We also employ two different diffusion models, where CRp are resonantly scattered off large-scale turbulence in SBN or self-excited waves driven by CR streaming instability. We then calculate gamma-ray/neutrino fluxes. The observed gamma-ray fluxes by Fermi-LAT, Veritas, and H.E.S.S are well reproduced with double power-law distribution for SNR-produced CRp and the CRp diffusion by self-excited turbulence. The estimated neutrino fluxes are <~10-3 of the atmospheric neutrino flux in the energy range of Eneutrino <~100 GeV and <~10-1 of the IceCube point source sensitivity in the energy range of Eneutrino >~60 TeV.

• Nuclear Engineering and Technology
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• 제56권4호
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• pp.1544-1551
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• 2024

A unique brick series based on Vietnamese clay was manufactured at 114.22 MPa pressure rate for γ-ray attenuation purposes, consisting of (x) metallic waste & (90%-x) red clay mineral & 10% (hardener mixed with epoxy resin), where (x) is equal to the values 0%, 20%, 40%, 50%, and 70%. The impacts of industrial metal waste ratio in the structure and radiation protective characteristics were evaluated experimentally. The increase in metallic waste doping concentrations from 0% to 70% was associated with an increase in the manufactured brick's density (ρ) from 2.103 to 2.256 g/cm³ while the fabricated samples' porosity (Φ) decreased from 11.7 to 1.0%, respectively. Together with a rise in fabricated brick's density and a decrease in their porosities, the manufactured bricks' γ-ray attenuation capacities improved. The measured linear attenuation coefficient (μ, cm^-1) was improved by 30.8%, 22.1%, 21.6%, and 19.7%, at E_γ equal to the values respectively 0.662, 1.173, 1.252, and 1.332 MeV, when the metallic waste concentration increased from 0% to 70%, respectively. The study demonstrates that manufactured bricks exhibit superior radiation shielding properties, with radiation protection efficiencies of 88.4%, 90.0%, 91.7%, 92.1%, and 92.4% for bricks with industrial metal waste contents of 0%, 20%, 40%, 50%, and 70%, respectively, at γ-ray energy (E_γ) of 1.332 MeV.

• Nuclear Engineering and Technology
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• 제56권5호
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• pp.1932-1940
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• 2024

The current work deals with investigation of the gamma ray shielding properties for various natural stones from Vietnam to be applied in the radiation shielding applications. The physical and chemical properties affecting the γ-ray shielding performance were examined. The MH-300A density meter was utilized to measure the density (ρ, g/cm³) of stone samples, as well as the chemical composition of Vietnamese natural stones was measured using the X-ray fluorescence analyzer (Olympus X-5000). The study shows that the increase in Fe + Ca concentrations within the stone samples increases their density (from 2.48 to 2.86 g/cm³) accompanied with a reduction in the porosity (Φ, %) (from 8.23 to 0.15%) and water absorption (K, %) (from 3.42 to 0.05%) factors. Additionally, the increase in Fe + Ca concentrations increases the linear attenuation coefficient (μ, cm^-1) of the studied stones, where the Vietnamese marble stone (M 3.1) with the highest Fe + Ca concentration (65.97 wt%) has the highest linear attenuation coefficient which varied between 3.781 and 0.155 cm^-1 with raising the gamma ray energy between 0.040 and 1.332 MeV.

• 전기전자학회논문지
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• 제19권3호
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• pp.282-287
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• 2015

본 연구에서는 연구에서는 Ce:GAGG 섬광체, 광섬유 그리고 광전자증배관을 이용하여 광섬유 검출기를 제작하였다. 섬광체의 단결정 크기는 MCNPX 코드를 이용하여 섬광체 깊이에 따른 감마선 계수효율을 전산모사하여 $3{\times}3{\times}20mm^3$로 설정하였다. 제작된 검출기는 표준 감마선원인 $^{137}Cs$과 $^{133}Ba$을 이용하여 세기의 따른 선형성 평가와 거리 변화에 따른 계수량 변화 측정을 하였다. 그 결과 추세선식 R-square 값이 0.99741로 매우 좋은 응답선형성을 보였고, 거리에 따른 검출 특성 또한 MCNPX값과 비교하였을 때 2% 이하로 좋은 검출특성을 보였다. 또한 단일선원과 혼합선원에서의 감마선 에너지 분광 결과 $^{137}Cs$은 662keV에서 그리고 $^{133}Ba$은 356keV에서 감마선 에너지 피크를 확인하였다. 광섬유 검출기를 사용한다면 작업자의 작업시간과 피폭을 줄여줄 것으로 보인다.

• 열처리공학회지
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• 제30권5호
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• pp.215-221
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• 2017

The effect of austenitizing temperature on the degree of carbides re-solutionizing, mean graine size, hardness and the volume fraction of retaind austenite ($V_{\gamma}$) etc., has been studied by means of metallography, X-ray diffractometry and hardness measurement in STD 11 tool steel. As austenitizing temperature increases, the amount of alloying elements which is re-dissolved into matrix increases, resulting in increase of $V_{\gamma}$, due to the chemical stabilization of austenite. The Vickers hardness value decreases with increasing austenitizing temperature, which is attributed to grain size as well the volume fractions of $V_{\gamma}$ and carbides. Theoretical diffraction intensity of (200) ${\alpha}^{\prime}$, (211) ${\alpha}^{\prime}$ (200) ${\gamma}$ and (220) ${\gamma}$ peaks obtained by $CuK_{\alpha}$ chracteristics X-ray (${\lambda}=0.15429nm$) was calculated, and quantitative analysis of $V_{\gamma}$ could be carried out by X-ray diffraction method. The resultant value is well coincided with the value obtained by image analysis method. When the quenched specimen is tempered above $200{\sim}400^{\circ}C$ for 30 min, the transition carbides i.e., MC and $M_2C$ in the size of about 20 nm begin to precipitate at $300^{\circ}C$.