http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
An Inner-Crystal Neutron-Scatter Camera: Monte Carlo Simulation
Ajin Jo,Won Ho Lee 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.68 No.9
Neutron energy emitted from special nuclear materials (SNMs) can be measured by using neutronproton scattering; also, the scattering angle can be calculated from the ratio of the scattered energy to the incident energy. By using position and energy information, we can image the original source position by using the backprojection and list-mode maximum-likelihood expectation maximization (MLEM) method. In this paper, we propose an inner-crystal neutron scatter camera system in which the detectors are not separated to obtain interactions at a variety of scatter angles; based on this system, we analyzed the characteristics of the corresponding neutron-scattering camera. The factors that affected the neutron-scatter image were the neutron velocity after scattering, the cut-off level of the time of flight (ToF), and the width of the cones used for image reconstruction. To determine the optimal point for the reconstruction of an image, we estimated the performance of the system by using the figure of merit (FoM). The optimal neutron-velocity (d/ToF) was 0.3 × 107 m/s according to our simulation result, while the optimal cut-off level of the ToF was 4 ns as the latter minimized the noise while maintaining the required efficiency. The widths of the cones (") also affected the full width at half maximum (FWHM) and the noise of the image. In terms of a simple source-geometry, whereby concepts such as “point source” were used, a large " value was suitable to achieve noise reduction; however, regarding the complicated source geometry, a small " value was favorable for precise reconstruction of the original source geometry for both the backprojection and the list-mode MLEM methods.
Jo, Ajin,Lee, Wonho Elsevier 2018 Nuclear Instruments & Methods in Physics Research. Vol.902 No.-
<P><B>Abstract</B></P> <P>We studied the feasibility of a fluorescent X-ray computed tomography (FXCT) system to monitor the uniformity of nuclear fuels; this system could be used for research reactors or power reactors. In general, nuclear fuels contain non-fissile metals for various purposes. To avoid the use of high-enriched uranium (HEU) fuels, U–Mo alloy fuels have been studied to lower the enrichment factor and to enhance the uranium density of fuels to be used in research reactors. (U, Gd)O<SUB>2</SUB> fuel is another uranium-metal alloy in which gadolinium (III) oxide (Gd<SUB>2</SUB>O<SUB>3</SUB>) powder is added to uranium dioxide (UO<SUB>2</SUB>) to adjust the reactivity of the fuel and enhance the performance of UO<SUB>2</SUB>. To guarantee the combustion stability of fuels in reactors, it is important to verify the homogeneity of alloy metals contained in the fuels. The FXCT system, which analyzes materials based on characteristic X-rays emitted from atoms, could be used to verify the homogeneity of the materials contained in nuclear fuels. External radiation sources are not necessary to induce characteristic X-rays from the fuel, as the gamma rays emitted from <SUP>235</SUP>U stimulate the fuel atoms. To verify the feasibility of the system, we measured the energy spectrum of a UO<SUB>2</SUB> pellet, in which small metal pieces of Gd and Mo were attached to the surface. Based on simulation studies, 2D and 3D radiographic images of UO<SUB>2</SUB> fuels with Gd and Mo were reconstructed to verify the effectiveness of the FXCT system.</P>
Monte Carlo Simulation on the 4π Field of a View Compact Compton Camera by Using Scintillators
이원호,Ajin Jo,Taewoong Lee,Dongmyeong Chu,Yong Hyun Chung 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.1
A compact LaCl3(Ce) Compton camera with a 4πfield of view (FOV) was introduced, and the optimized design parameters with the effective choice of the γ-ray interaction order were obtained by using Monte Carlo simulation. The camera consisted of six LaCl3(Ce) planar scintillators with pixelized structure, which could be coupled with position sensitive photomultiplier tubes. Since γ-rays were incident from all direction (4π), all of the scintillators were both scattering and absorbing detectors for Compton image reconstruction, and the interaction sequence was decided based on the deposited energy. According to the simulation results, the reconstructed image showed better angular resolution and smaller variance for all incident radiation energies (300 keV 2 MeV) when the energy of the scattering interaction was assumed to be smaller than that of the absorbing interaction. The optimum thickness of the scintillators to maintain high image resolution and large sensitivity was 1 1.5 cm, and the difference between the center of the camera and the scintillators was set to 7 cm to minimize degradation of image resolution and the loss of detection efficiency. With the optimized conditions, the effect of each parameter causing blurring and variance was estimated. At low energy, the finite energy resolution was the main factor increasing the uncertainties of the reconstructed image. However, at high energy, the pixelization effect and the incorrect choice of interaction sequences also were significant factors in the degraded angular resolution and relative standard deviation of the reconstructed image.
Wonho Lee,Ajin Jo,Changyeon Yoon IEEE 2010 IEEE transactions on nuclear science Vol.57 No.3
<P>Multiple modality γ-ray imaging using mechanical and electronic collimation with different detection methods was proposed and tested by simulation. Although conventional mechanical collimators, which are made from high atomic number and density materials, passively filter the incident radiation, the mechanical collimator reported in this study consisted of LaCl<SUB>3</SUB>(Ce) scintillators, which actively collimate the radiation and are used as the 1st detector of an electronic collimator to reconstruct a Compton image. A detector box made from six planar LaCl<SUB>3</SUB>(Ce) scintillators was positioned behind the active collimator. The LaCl<SUB>3</SUB>(Ce) scintillator arrays used as the active collimator and box detector consisted of voxels, each 2 mm × 2 mm × 5 mm<SUP>3</SUP> in size. A combination of active collimators and box detectors can produce multiple modalities for both mechanical and electronic collimation. The information from each modality was combined effectively using the maximum likelihood expectation maximization (MLEM) method. Therefore, a reconstructed image from multiple modalities has inherently higher efficiency than each conventional modality. The reconstructed images were evaluated using the resolution-variance curve as a quantitative method. Although mechanical collimation is effective at low γ-ray energy and electronic collimation shows high performance at high γ-ray energy, multiple modalities are superior to the conventional single modalities for intermediate γ-ray energies (364 keV). The angular resolution and absolute efficiency were calculated for each modality and source energy.</P>
( Hye Ryoun Jang ),( Ajin Jo ),( Ji Hyeon Park ),( Jung Eun Lee ),( Woo Seong Huh ),( Dae Joong Kim ),( Ha Young Oh ),( Yoon Goo Kim ) 대한신장학회 2011 Kidney Research and Clinical Practice Vol.30 No.6
Purpose: Urinary angiotensinogen (AGT) has been reported as an important marker reflecting the activity of intrarenal renin-angiotensin system (RAS) in chronic glomerulonephritis patients. We investigated urinary AGT excretion and intrarenal AGT expression in patients with minimal change disease (MCD). Methods: In 20 patients with biopsy-proven MCD, urinary and plasma AGT was measured using a sandwich ELISA and intrarenal AGT expression was measured with immunohistochemistry. Urine samples from normal healthy volunteers and patients with biopsy-proven thin basement membrane disease (TBM) were used as control groups. Results: MCD patients showed a wide range of natural logarithm of the urinary AGT/creatinine [ln (urinary AGT/Cr)] and the ln (urinary AGT/Cr) was higher in MCD patients compared with normal controls and TBM controls (normal control vs. TBM vs. MCD, 1.2±0.25 vs. 0.9±0.34 vs. 3.2±0.40). Intrarenal AGT expression was diverse in MCD patients (intrarenal AGT, arbitrary unit, 27.39-78.52 in TBM, 0.00-145.80 in MCD). Ln (urinary AGT/Cr) did not show a direct correlation with intrarenal AGT expression, plasma AGT, or urinary protein/creatinine ratio. Conclusion: Urinary AGT excretion and intrarenal AGT expression are enhanced in some MCD patients, suggesting that intrarenal RAS is activated in these patients.