• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.265-266
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• 2012

의료용 X-ray의 발전에 따라, 영상의 Digital화가 필요하게 되었다. Digital 영상 구현을 위해 다양한 형태의 영상 검출기가 개발되었다. 진단 영상의 조건으로는 구현 시간이 빠르고 해상도가 높아야 한다. 조건에 부합하는 Flat panel 형태의 직접방식과 간접방식 검출기의 개발이 주로 이루어졌으며, X-ray 검출 효율이 높고 공간 분해능이 높은 직접 방식의 검출기에 대한 연구가 활발히 진행되고 있다. 기존 직접방식의 X-ray 검출물질로는 A-Se이 이용되었다. 하지만 A-Se의 경우 낮은 원자번호로 인해 X-ray에 대한효율이 낮으며, 제조 공정과 수율의 문제로 인해 대체 물질의 개발과 공정의 개선이 필요하다. 선행 연구를 통해 X-ray 검출물질의 전기적 특성을 파악을 통해 대체 물질로서 가능성을 알아보았다. 본 연구에서는 기존에 제작된 X-ray 검출물질의 상부전극 증착 물질과 증착법 선정에 대한 연구이다. 선행 연구를 통해 선정된 X-ray 검출물질은 HgI2이다. 상, 하부 전극 선택에 있어 HgI2의 일함수 값(4.15eV)을 고려하여 그와 비슷한 일함수 값을 가진 물질로 전기적 장벽을 제거하여야 한다. 따라서, ITO (일함수 4.45eV)와 Au (일함수 5.1eV)을 선택하였다. ITO의 증착으로 이용된 방법으로는 on-axis 형태의 magnetron plasma sputtering을 이용하였으며, Au의 증착으로 이용된 방법은 Thermal evaporation deposition을 이용하였다. plasma sputtering에 이용된 타겟은 In2O3;SnO2 (조성비:90:10wt%)를 사용하였으며, Chamber의 크기는 넓이 456 ${\phi}cm^2$ 높이 25 cm이며, 로 target과 기판과의 거리는 15cm이다. plasma발생에 필요한 가스로는 Ar과 O2를 이용하였다. 고 진공 환경 조성에 이용된 장비로는 Rotary pump와 Turbo molecular pump이다. plasma 발생 전 진공도는 $3.2{\times}10^{-5}$ Torr, 발생 후 진공도는 $5.1{\times}10^{-5}$ Torr이다. plasma 환경이 조성된 후 증착 시간은 1분 30초이다. Au는 순도 99.999%를 이용하였으며, 이용된 금은 1회 증착에 0.3 g을 이용하였다. Chamber의 넓이 1,444 ${\phi}cm^2$이며, 높이 40 cm, boat와 기판과의 거리는 25 cm이다. 고 진공 환경 조성에 이용된 장비로는 Rotary pump와 diffusion pump를 이용하였다. Au의 승화 전 진공도는 $2.4{\times}10^{-5}$ Torr 증착 시 진공도는 $4.2{\times}10^{-5}$ Torr이며, Boat에 가해준 전압, 전류는 0.97 V, 47 A이며, 증착 시간은 1분 30초이다. 광도전체 층에 각각 증착된 전극의 저항을 통해 증착상태를 판단하였다. DMM (Digital Multimeter)로 1 cm 간격으로 측정된 표면의 저항은 ITO 약 $8{\Omega}$, Au 약 $3{\Omega}$으로 전극으로서 이용이 가능한 상태이다. Au와 ITO가 증착된 HgI2 시편의 전기적 특성은 기존에 이용된 X-ray 변환물질의 성능보다 우수하였다. 하지만 Au와 ITO가 각각 증착된 시편의 전기적 특성은 큰 차이를 보이지 않았다. ITO의 경우 진공 상태에서 이용되는 Gas가 이용되며, Plasma 환경 조성 유지가 어려운 점이 있다. Au전극은 증착 환경 조성이 쉽지만, 전극 물질 이용효율이 떨어지는 단점이 있다. 본 연구를 통해 X-ray 변환물질인 HgI2의 전극물질로 Au와 ITO의 이용가능성을 알아보았다. 두 전극으로 제작된 검출기의 성능은 큰 차이 없이 우수하였고, 전기적 장벽 상태가 낮아 높은 검출 효율을 보였다. 상대적으로 Au 전극의 공정이 간단하고 수율이 높다. 하지만 Au Source의 이용 효율이 떨어지는 단점이 있다. 본 연구의 결과를 통해 공정상의 유리함과 Source의 이용효율을 고려한 분석에 대한 연구가 필요할 것으로 사료된다.

• Journal of The Korean Astronomical Society
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• v.52 no.1
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• pp.1-9
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• 2019

We present the results of the spectral and temporal analysis of eight X-ray point sources in five nearby (distance < 20 Mpc) galaxies observed with Chandra. For spectral analysis, an absorbed powerlaw and an absorbed diskblackbody were used as empirical models. Six sources were found to be equally fitted by both the models while two sources were better fitted by the powerlaw model. Based on model parameters, we estimate the X-ray luminosity of these sources in the energy range 0.3 - 10.0 keV, to be of the order of ${\sim}10^{39}ergs\;s^{-1}$ except for one source (X-8) with $L_X>10^{40}ergs\;s^{-1}$. Five of these maybe classified as Ultraluminous X-ray sources (ULXs) with powerlaw photon index within the range, ${\Gamma}{\sim}1.63-2.63$ while the inner disk temperature, kT ~ 0.68 - 1.93 keV, when fitted with the disk blackbody model. The black hole masses harboured by the X-ray point sources were estimated using the disk blackbody model to be in the stellar mass range, however, the black hole mass of one source (X-6) lies within the range $68.37M_{\odot}{\leq}M_{BH}{\leq}176.32M_{\odot}$, which at the upper limit comes under the Intermediate mass black hole range. But if the emission is considered to be beamed by a factor ~ 5, the black hole mass reduces to ${\sim}75M_{\odot}$. The timing analysis of these sources does not show the presence of any short term variations in the kiloseconds timescales.

• Journal of Information Processing Systems
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• v.12 no.1
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• pp.35-45
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• 2016

To resolve the problems of Poisson/impulse noise, blurriness, and sharpness in degraded X-ray images, a novel and efficient enhancement algorithm based on X-ray image fusion using a discrete wavelet transform is proposed in this paper. The proposed algorithm consists of two basics. First, it applies the techniques of boundary division to detect Poisson and impulse noise corrupted pixels and then uses the Wiener filter approach to restore those corrupted pixels. Second, it applies the sharpening technique to the same degraded X-ray image. Thus, it has two source X-ray images, which individually preserve the enhancement effects. The details and approximations of these sources X-ray images are fused via different fusion rules in the wavelet domain. The results of the experiment show that the proposed algorithm successfully combines the merits of the Wiener filter and sharpening and achieves a significant proficiency in the enhancement of degraded X-ray images exhibiting Poisson noise, blurriness, and edge details.

• Journal of Biomedical Engineering Research
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• v.29 no.2
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• pp.107-113
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• 2008

We introduce a rotating-gantry-based x-ray micro-tomography system to be used for small animal imaging studies. It has the zoom-in imaging capability for high resolution imaging of a local region inside the animal subject without any contrast anomalies arising from truncation of the projection data. With the sliding mechanism mounted on the rotating gantry holding the x-ray source and the x-ray detector, we can control the magnification ratio of the x-ray projection data. By combining the projection data from the large field of view (FOV) scan of the whole animal subject and the projection data from the small FOV scan of the region of interest, we can obtain artifact-free zoomed-in images of the region of interest. For the acquisition of x-ray projection data, we use a $1248{\times}1248$ flat-panel x-ray detector with the pixel pitch of 100 mm. It has been experimentally found that the developed system has the spatial resolution of up to 121p/mm when the highest magnification ratio of 5:1 is applied to the zoom-in imaging. We present some in vivo rat femur images to demonstrate utility of the developed system for small animal imaging.

• Proceedings of the KIPE Conference
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• 1999.07a
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• pp.234-238
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• 1999

In order to radiate X-ray, the low ripple stabilized high voltage DC over the range of 40KV to 150KV is directly inflicted to X-ray tube. The energy characteristics of the radiated X-ray depend on the pulsating waveforms of the DC voltage supplied X-ray tube. In general, the low ripple voltage waveforms with fast rising times are required to increase with the dosage per unit time lest the exposure time should be longer in orde that the motion artifacts of an object may be eliminated in actual. The conventional types of X-ray generators were bulky in physical size and heavy in weight, and the control accuracies of the output voltages were not always satisfactory. The high frequency switching inverter and converter technology on power conversion and control systems have been greatly closed up introducing new power semiconductor devices. To decreasing the volume and the weight of high voltage transformer, and to stabilize ripple, a high frequency PWM inverter is connected between DC source and high voltage transformer. This paper describes the output characteristics according to stabilize ripple of X-ray tube voltage and compared the reproducibility, direcibility and doesage.

• Proceedings of the Korean Society of Medical Physics Conference
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• 1999.11a
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• pp.264-265
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• 1999

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.86-86
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• 2016

최근 포항가속기연구소 10A 빔라인에 Scanning Transmission X-ray Microscopy (STXM)가 완성되어 운영 중이다. Soft x-ray imaging 장치로서 기술적으로 Sample scanning 기법이 활용된다. 이는 Zone plate를 통해 집속된 빔이 샘플에 조사되고 검출되는 방식이다. 이러한 Scanning 기법을 활용하고 있는 10A STXM은 기본적으로 흡수분광기법 (x-ray absorption spectroscopy)을 이용하고 있다. 특히, 10A 빔라인 STXM은 최고 20 nm까지 공간분해능이 가능하다는 장점이 있다. 따라서 수십에서 수백 나노미터 크기의 시료들 또는 나노구조에 대한 물리화학적 상태 분석이 쉽게 이루어지고 있다. 주로 시료를 투과하면서 흡수되는 X-선 세기 대비를 맵핑하는 형식의 이미지 데이터와 더불어 X-선의 에너지를 조정함으로써 각 에너지에 해당하는 이미지스택을 결과로 얻게 된다. 이러한 이미지 결과로부터 시료의 나노크기에서 오는 물리화학적 상태를 분석하고 물리에서 바이오까지 다양한 분야의 실험 활용이 가능한 상태다.

• Nuclear Engineering and Technology
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• v.42 no.4
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• pp.426-433
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• 2010

The characteristic X-rays emitted from materials after gamma ray exposure was simulated and measured. A CdTe semiconductor detector and a $^{57}Co$ radiation source were used for energy spectroscopy. The types of materials could be identified by comparing the measured energy spectrum with the theoretical X-ray transition energy of the material. The sample composition was represented by the $K_{\alpha1}$-line (Siegbahn notations), which has the highest intensity among the characteristic X-rays of each atom. The difference between the theoretic prediction and the experimental result of K-line measurement was < 0.61% even if the characteristic X-rays from several materials were measured simultaneously. 2D images of the mixed materials were acquired with very high selectivity.

• Journal of radiological science and technology
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• v.33 no.3
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• pp.179-184
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• 2010

A hard X-ray microscope system for obtaining images of nano-spatial resolution has been widely studied and requires monochromatic X-ray. A multilayer mirror of 84% reflectivity was designed to acquire tungsten characteristic X-ray of 8.4 keV from the white beam generated from an X-ray tube, and the C/W multilayer mirror of $50{\times}50\;mm$ size and 5.65 nm d-spacing was fabricated by the ion-beam sputtering system. The C/W multilayer had a uniformity of 99.5%, and the structure of the multilayer mirror was verified by a TEM image. The obtainable x-ray reflectivity for the C/W multilayer mirror at 8.4 keV was estimated from measuring the X-ray reflectivity using the copper characteristic X-ray of 8.05 keV. Monochromatic X-ray of 8.4 keV was generated by combining a X-ray tube, and the reflectivity and monochromaticity were 77.1% and 0.21 keV, respectively. Monochromatic X-ray generated from the combination of an X-ray tube and an C/W multilayer mirror has enough potential to use X-ray source for hard X-ray microscope system of laboratory size. If the C/W multilayer mirror of d-spacing of a few nanometers can be fabricated, monochromatic X-ray corresponded to 17.5 keV, molybdenum characteristic X-ray, can be obtained and applied to mammography in the medical application.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.147.2-147.2
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• 2011

We have initiated a long-term identification campaign of supernova remnant candidates in X-ray regime. In the short-listed unidentified sources from the ROSAT All Sky Survey, we have chosen the brightest candidate, G308.3-1.4, as our pilot target for a dedicated investigation with Chandra X-ray Observatory. Our observation has revealed an incomplete shell-like X-ray structure which well-correlated with the radio feature. Together with the spectral properties of a shocked heated plasma, we confirm that G308.3-1.4 is indeed a supernova remnant. A bright X-ray point source which locates close to the remnant center is also uncovered in this observation. Its spectral behavior conform with those observed in a rare class of neutron stars. The properties of its optical/infrared counterpart suggests the evidence for a late-type companion star. Interestingly, possible excesses in B-band and H-alpha have been found which indicate this can be an accretion-powered system. With the further support from the putative periodicity of ~1.4 hrs, this source can possibly provide the direct evidence of a binary system survived in a supernova explosion for the first time.