• 한국방사선학회논문지
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• 제13권4호
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• pp.661-666
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• 2019

확산형 콜리메이터는 촬영 대상을 축소 촬영하거나 넓은 관심영역을 작은 감마카메라를 사용하여 검출하기 위해서 사용한다. 확산형 콜리메이터와 블록형 섬광체 및 픽셀형 섬광체 배열을 사용하는 감마카메라에서 방사선원이 관심영역 주변에 위치할 때 섬광체 표면에 감마선이 대각선으로 입사하게 되면, 섬광체 깊이 방향으로 대각선으로 검출되기 때문에 공간 분해능이 저하된다. 본 연구에서는 이러한 관심영역 외곽에서의 공간 분해능을 향상하기 위한 새로운 시스템을 설계하였다. 사다리꼴 픽셀형 섬광체를 사용하여 각 섬광 픽셀을 콜리메이터 구멍의 각도와 크기에 맞게 일치하도록 구성하면, 감마선이 섬광체의 여러 깊이에서 반응하더라도, 하나의 섬광 픽셀 위치로 영상화 할 수 있다. 즉, 대각선 방향의 여러 지점에서 검출되더라도, 감마선은 하나의 섬광 픽셀과 상호 작용하기 때문에 공간 분해능의 저하가 발생하지 않는다. Geant4 Application for Tomographic Emission (GATE) 시뮬레이션을 통해 블록형 섬광체를 사용한 감마카메라와 사다리꼴 픽셀형 섬광체를 사용한 감마카메라를 설계하여 공간 분해능을 비교 평가하였다. 관심영역 외곽에서 발생한 감마선을 통해 획득한 영상에서 공간 분해능은 블록형 섬광체를 사용한 감마카메라에서는 4.05 mm였고, 사다리꼴 픽셀형 섬광체를 사용한 감마카메라에서는 2.97 mm의 공간 분해능을 보였다. 사다리꼴 셀형 섬광체를 사용한 시스템에서 26.67% 공간 분해능이 향상됨을 확인할 수 있었다.

• Current Optics and Photonics
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• 제5권3호
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• pp.250-260
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• 2021

A tapered As₂S₃ photonic crystal fiber (PCF) with four layers of air holes in a hexagonal array around the core is designed in this paper. Numerical simulation shows that the dispersion D decreases and the nonlinearity coefficient γ increases from the thick to the thin end along the tapered PCF. We simulate the midinfrared pulse compression in the tapered As₂S₃ PCF using the adaptive split-step Fourier method. Initial Gaussian pulses of 4.4 ps and a central wavelength of 2.5 ㎛ propagating in the tapered PCF are located in the anomalous dispersion region. With an average power of assumed input pulses at 3 mW and a repetition frequency of 81.0 MHz, we theoretically obtain a pulse duration of 56 fs and a compression factor of 78 when the pulse propagates from the thick end to the thin end of the tapered PCF. When confinement loss in the tapered PCF is included in the simulation, the minimum pulse duration reaches 72 fs; correspondingly, the maximum compression factor reaches 61. The results show that in the anomalous-dispersion region, midinfrared pulses can be efficiently compressed in a dispersion-decreasing and nonlinearity-increasing tapered As₂S₃ PCF. Due to confinement loss in the tapered fiber, the efficiency of pulse compression is suppressed.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2001년도 추계학술발표회 초록집
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• pp.67-67
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• 2001

The structure zone model has been used to provide an overview of the relationship between the microstructure of the films deposited by PVD and the most prominent deposition condition.s. B.AMovchan and AV.Demchishin have proposed it firstls such model. They concluded that the general features of the resulting structures could be correlated into three zones depending on $T/T_m$. Here T m is the melting point of the coating material and T is the substrate temperature in kelvines. Zone 1 ($T/Tm_) is dominated by tapered macrograins with domed tops, zone 2 ($O.3) by columnar grains with denser boundaries and zone 3 ($T/T_m>O.5$) by equiaxed grains formed by recrystallization. J.AThomton has extended this model to include the effect of the sputtering gas pressure and found a fourth zone termed zone T(transition zone) consisting of a dense array of poorly defined fibrous grains. R.Messier found that the zone I-T boundary (fourth zone of Thorton) varies in a fashion similar to the film bias potential as a function of gas pressure. However, there has not nearly enough model for explaining the change in morphology with crystal orientation of the films. The structure zone model only provide an information about the morphology of the deposited film. In general, the nucleation and growth mechanism for granular and fine structure of the deposited films are very complex in an PVD technique because the morphology and orientation depend not only on the substrate temperature but also on the energy of deposition of the atoms or ions, the kinetic mechanism between metal atoms and argon or nitrogen gas, and even on the presence of impurities. In order to clarify these relationship, AI and Mg thin films were prepared on SPCC steel substrates by PVD techniques. The influence of gas pressures and bias voltages on their crystal orientation and morphology of the prepared films were investigated by SEM and XRD, respectively. And the effect of crystal orientation and morphology of the prepared films on corrosion resistance was estimated by measuring polarization curves in 3% NaCI solution.