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Analytic Model of Energy-Absorption Response Functions in Compound X-ray Detector Materials
Seungman Yun,Ho Kyung Kim,Hanbean Youn,Tanguay, Jesse,Cunningham, Ian A. IEEE 2013 IEEE transactions on medical imaging Vol.32 No.10
<P>The absorbed energy distribution (AED) in X-ray imaging detectors is an important factor that affects both energy resolution and image quality through the Swank factor and detective quantum efficiency. In the diagnostic energy range (20-140 keV), escape of characteristic photons following photoelectric absorption and Compton scatter photons are primary sources of absorbed-energy dispersion in X-ray detectors. In this paper, we describe the development of an analytic model of the AED in compound X-ray detector materials, based on the cascaded-systems approach, that includes the effects of escape and reabsorption of characteristic and Compton-scatter photons. We derive analytic expressions for both semi-infinite slab and pixel geometries and validate our approach by Monte Carlo simulations. The analytic model provides the energy-dependent X-ray response function of arbitrary compound materials without time-consuming Monte Carlo simulations. We believe this model will be useful for correcting spectral distortion artifacts commonly observed in photon-counting applications and optimal design and development of novel X-ray detectors.</P>
Seungman Yun,Ho Kyung Kim,Chang Hwy Lim,Min Kook Cho,Achterkirchen, T.,Cunningham, I. IEEE 2009 IEEE transactions on nuclear science Vol.56 No.3
<P>We report the measurement results of signal and noise characteristics induced by the direct x-rays in an indirect-conversion CMOS photodiode array detector. In order to isolate the signal and noise due to the direct x-rays from those due to the optical photons, we inserted a light-absorbing blackout material between a phosphor screen and the photodiode array. From the images irradiated with and without the blackout paper, the signal and noise characteristics due to the optical photons emitted from a phosphor screen were estimated. For the analysis of the measurements, we have developed a model describing the signal and noise transfers based on the cascaded linear-systems approach. The measured results show the direct x-ray is very harmful to the detector performances, such noise power spectrum (NPS) and signal-to-noise ratio (SNR). However, from the theoretical estimation, the degradation of NPS and SNR would not be due to the directly absorbed x-ray photons, but we believe that other sources, such as Compton and photoelectric scattered rays from a scintillator, a photodiode passivation layer or bulk substrate, are main causes.</P>
Human-Environmental Ecological City
Seungman Baek 대한건축학회 2009 Architectural research Vol.11 No.1
While the ideal universality of the modern period has achieved outstanding results in terms of establishing sanitary cities in contemporary urban environments, it has caused the decline of the genius loci. This study raises the question of the lost sense of place and proposes a solution, ‘The Human-Environmental Ecological City’. The Human-Environmental Ecological City, called ‘Ecoumenal City’, does not provide a fake idealism with the conclusion of modernity of non-place or sense of place without modernity. It is both cosmological and geogenic, and the technology of the time is projected onto it human-environmentally. It does not pursue any more a urban planning as the overall work of an individual, but it aims at a balance rediscovered through the individual spontaneousness.
확산화염의 PAH LIF 신호 측정에 대한 LII 간섭
배승만(Seungman Bae),이상구(Sanggu Lee),안태국(Taekook Ahn),이원남(Wonnam Lee) 한국연소학회 2011 KOSCOSYMPOSIUM논문집 Vol.- No.42
The LII interference on the measurement of PAH LIF signal from a diffusion flame with 488 ㎚ wavelength Argon-ion laser excitation has been experimentally investigated. The signals measured in the region, where soot particles do not exist, can be interpreted as PAH LIF signals. However, in the region, where soot particles exist, the measured signals should be mostly considered as Mie scattering signals and/or LII signals depending on the measurement condition. In the region, where soot particles and PAH’s co-exist, the detection of PAH LIF signals would be difficult if not impossible with current measurement techniques.