• Journal of Radiation Protection and Research
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• v.34 no.4
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• pp.176-183
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• 2009

Maintenance on the water chamber of steam generator during outage in nuclear power plants (NPPs) has a likelihood of high radiation exposure to whole body of workers even short time period due to the high radiation exposure rates. In particular, it is expected that hands would receive the highest radiation exposure because of its contact with radiation materials. In this study, characteristic analysis of inhomogeneous radiation fields for contact operations was conducted using thermoluminescent dosimeter (TLD) readouts from the application tests of two-dosimeter algorithm to Korean NPPs in 2004. It is regarded that inhomogeneous radiation fields for contact operations in NPPs are dominated by high energy photons. In addition, field tests for workers who participated in maintenance on the steam generator during outage at Ulchin NPPs in 2009 and pressure tube replacement at Wolsong NPPs in 2009 were conducted to analyze radiation fields and to estimate the extremity dose. As a result, radiation fields were dominated by high energy photons.

• Korean Journal of Optics and Photonics
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• v.11 no.1
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• pp.37-42
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• 2000

We have numerically solved rate-equations of semiconductor optical amplifier (SOA) to understand the characteristics of SOA. The rate-equations we have used can describe injection carrier density, amplified spontaneous emission and signal photon density in spatial and time domain by dividing the cavity into multi-section. We have investigated injection carrier density, amplified spontaneous emission and signal photon density as a function of position and time in the case of single channel input in the form of square pulse. Also we have analyzed the non-linear phenomena of SOA in the case of injecting multi-channel wavelengths as in WDM. Intermodulation distortion (IMD) caused by beat among channels has significant effects on the signal distortion as the channel spacing becomes narrower, and channel crosstalk becomes larger as the power of signals increases. In the case of the injection of another CW laser whose wavelength is far enough from the signal wavelengths, the crosstalk and the output signal distortion can be significantly reduced. duced.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.264-267
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• 2005

A subregional slicing method (SSM) is proposed to increase the nanofabrication efficiency of a nano-stereolithography (NSL) process based on two-photon polymerization (TPP). The NSL process can be used to fabricate 3D microstructures via the accumulation of layers of uniform thickness; hence, the precision of the final 3D microstructure depends on the layer thickness. The use of a uniform layer thickness means that, to fabricate a precise microstructure, a large number of thin slices is inevitably required. leading to long processing times. In the SSM proposed here, however, the 3D microstructure is divided into several subregions on the basis of the geometric slope, and then each of these subregions is uniformly sliced with a layer thickness determined by the geometric slope characteristics of each subregion. Subregions with gentle slopes are sliced with thin layer thicknesses, whereas subregions with steep slopes are sliced with thick layer thicknesses. Here, we describe the procedure of the SSM based on TPP, and discuss the fabrication efficiency of the method through the fabrication of a 3D microstructure.

• Dementia and Neurocognitive Disorders
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• v.16 no.3
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• pp.72-77
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• 2017

Background and Purpose Although sleep disturbances are common and considered a major burden for patients with Alzheimer's disease (AD), the fundamental mechanisms underlying the development and maintenance of sleep disturbance in AD patients have yet to be elucidated. The aim of this study was to examine the correlation between regional cerebral blood flow (rCBF) and sleep disturbance in AD patients using technetium-99m hexamethylpropylene amine oxime single-photon emission computed tomography (SPECT). Methods A total of 140 AD patients were included in this cross-sectional study. Seventy patients were assigned to the AD with sleep loss (SL) group and the rest were assigned to the AD without SL group. SL was measured using the sleep subscale of the Neuropsychiatric Inventory. A whole-brain voxel-wise analysis of brain SPECT data was conducted to compare the rCBF between the two groups. Results The two groups did not differ in demographic characteristics, severity of dementia, general cognitive function, and neuropsychiatric symptoms, with the exception of sleep disturbances. The SPECT imaging analysis displayed decreased perfusion in the bilateral inferior frontal gyrus, bilateral temporal pole, and right precentral gyrus in the AD patients with SL group compared with the AD patients without SL group. It also revealed increased perfusion in the right precuneus, right occipital pole, and left middle occipital gyrus in the AD with SL group compared with the AD without SL group. Conclusions The AD patients who experienced sleep disturbance had notably decreased perfusion in the frontal and temporal lobes and increased rCBF in the parietal and occipital regions. The findings of this study suggest that functional alterations in these brain areas may be the underlying neural correlates of sleep disturbance in AD patients.

• Journal of the Korean Society of Industry Convergence
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• v.25 no.6_3
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• pp.1147-1154
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• 2022

Now that the development of autonomous driving is progressing, LiDAR has become an indispensable element. However, LiDAR is a device that uses lasers, and laser side effects may occur. One of them is the much-talked-about eye-safety, and developers have been satisfying this through laser characteristics and operation methods. But eye-safety is just one of the problems lasers pose. For example, irradiating a laser with a specific energy level or higher in a dusty environment can cause deterioration of the dust particles, leading to a sudden explosion. For this reason, the dust ignition proof regulations clearly state that "a source with a pulse period of less than 5 seconds is considered a continuous light source, and the average energy does not exceed 5 mJ/mm 2 or 35 mW" [2]. Energy of output optical power is limited by the law. In this way, the manufacturer cannot define the usage environment of the LiDAR, and the development of a LiDAR that can be used in such an environment can increase the ripple effect in terms of use in application fields using the LiDAR. In this paper, we develop a LiDAR with low optical power that can be used in environments where high power lasers can cause problems, evaluate its performance. Also, we discuss and present one of the directions for the development of LiDAR with laser power limited by dust ignition proof regulations.

• Nuclear Engineering and Technology
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• v.55 no.5
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• pp.1734-1741
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• 2023

This work presents the synthesis and preparation of a new glass system described by the equation of (70-x) B₂O₃-5TeO₂ -20SrCO₃-5ZnO -xBi₂O₃, x = 0, 1, 5, 10, and 15 mol. %, using the melt quenching technique at a melting temperature of 1100 ℃. The photon-shielding characteristics mainly the linear attenuation coefficient (LAC) of the prepared glass samples were evaluated using Monte Carlo (MC) simulation N-particle transport code (MCNP-5) at gamma-ray energy extended from 59 keV to 1408 keV emitted by the radioisotopes Am-241, Ba-133, Cs-137, Co-60, Na-22, and Eu-152. Furthermore, we observed that the Bi₂O₃ content of the glasses had a significantly stronger impact on the LAC at 59 and 356 keV. The study of the lead equivalent thickness shows that the performance of fabricated glass sample with 15 mol.% of Bi₂O₃ is four times less than the performance of pure lead at low gamma photon energy while it is enhanced and became two times lower the perforce of pure lead at high energy. Therefore, the fabricated glasses special sample with 15 mol.% of Bi₂O₃ has good shielding properties in low, intermediate, and high energy intervals.

• Radiation Oncology Journal
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• v.9 no.1
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• pp.131-141
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• 1991

A comprehensive set of dosimetric measurements has been made on the Varian Clinac 1800 15 MV photon beam. Beam quality, percentage depth dose, dose in the build up region, output, symmetry and flatness, transmission through iead (Cerrobend), tray attenuation, isodose curves for the open and wedged fields were measured using 3 dimensional water phantom dosimetry system (including film densitometer system) and polystyrene phantoms. These dosimetric measurements sufficiently characterized the beam to permit clinical use. The depth dose characteristics of photon beam is $d_{max}$ of 3.0 cm and percentage depth dose of $76.8\%$ at 10 cm,100 cm source-surface distance, field size of $10\times10\;cm^2$ for 15 MV X-ray beam. The Output factors ranged 0.927 for $4\times4\;cm^2$ field to 1,087 for $35\times35\;cm^2$ field. The build-up level of maximum dose was at 3.0 cm and surface dose was approximately $15.5\%$ for a field size $10\times10\;cm^2$ The stability of output is $within\pm1\%$ and flatness and symmetry are $within\pm3\%$. The half value thickness (HVL) of lead is 13 mm, which corresponds to an attenuation coefficient of $0.053\;mm^{-1}$. These figures compare facorably with the manufacturesr`s specifications.

• Journal of the Korean Society of Food Science and Nutrition
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• v.37 no.11
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• pp.1529-1533
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• 2008

The detection characteristics of gamma-irradiated ($0{\sim}10.0\;kGy$) medicinal herbs (Platycodon grandiflorum, Acanthopanax chiisanensis) were investigated by photostimulated luminescence (PSL), thermoluminescence (TL), and electron spin resonance (ESR). The results of the PSL, a first screening method in comparison with the TL, showed photon counts greater than 5,000 counts/60 s (positive) in the irradiated samples, while the non-irradiated samples yielded photon counts less than 700 counts/60 s (negative). The TL was also applied for the detection method of irradiated medicinal herbs and showed that the non-irradiated sample revealed a glow curve with a low intensity, while the irradiated samples showed a higher intensity. These results were normalized by re-irradiating the mineral grains with a irradiation dose of 1.0 kGy, and a second glow curve was recorded. The ratio of the intensity of the first glow curve ($TL_1$) to that after the normalization dose ($TL_2$) was determined and compared with the recommended threshold values. TL ratio ($TL_1/TL_2$) was below 0.007 for the non-irradiated sample and higher than 0.1 for all irradiated samples (above 1.0 kGy). ESR spectroscopy revealed specific signals (6.065 mT) derived from free radicals in cellulose containing irradiated medicinal herbs. The P. grandiflorum showed clearer signals than A. chiisanensis. From the results of our studies, the PSL, TL, and ESR determinations were found to be suitable for the detection of irradiated medicinal herbs such as P. grandiflorum and A. chiisanensis.

• Korean Journal of Medicinal Crop Science
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• v.6 no.1
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• pp.51-56
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• 1998

This study was carried out to evaluate environmental and ecological characteristics of natural habitat for cultivation of Epimedium koreanum. Habitat of E. koreanum was the slope foot of mountain descending gradually toward mostly northwest from top of mountain with slope of $2{\sim}20%$ and the altitude ranged from 60 to 400m above the sea level. Some physiochemical characteristics of habitat soil were as follows: pH, $4.1{\sim}5.8$, organic matters content, $4.9{\sim}6.6%$ and cation exchange capacity, $14.8{\sim}34.3\;me/100g$ soil, respectively. Habitats were shaded by deciduous broad-leaved tree mainly, and compared with those of naked area, relative photon flux density was $3.5{\sim}13.1%$ and relative luminance was $3.3{\sim}11.9%$ due to shading. Air temperature of habitat under shade was $4.3{\sim}6.5^{\circ}C$ lower than that of naked area. Habitat soil temperature was lower than that of naked area but temperature range was smaller than that of naked area. E. koreanum plants were growing with semishading plants under shade of tree leaf. From investigation of natural characteristics of habitat, it was concluded that E. koreanum plant would grow at place with a little change in temperature and moisture of soil which was caused by shading and mulching with litterfall of broad-leaved tree.

• JSTS:Journal of Semiconductor Technology and Science
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• v.7 no.3
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• pp.196-208
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• 2007

An analytical model is proposed for an optically controlled Metal Semiconductor Field Effect Transistor (MESFET), known as Optical Field Effect Transistor (OPFET) considering the diffusion fabrication process. The electrical parameters such as threshold voltage, drain-source current, gate capacitances and switching response have been determined for the dark and various illuminated conditions. The Photovoltaic effect due to photogenerated carriers under illumination is shown to modulate the channel cross-section, which in turn significantly changes the threshold voltage, drainsource current, the gate capacitances and the device switching speed. The threshold voltage $V_T$ is reduced under optical illumination condition, which leads the device to change the device property from enhancement mode to depletion mode depending on photon impurity flux density. The resulting I-V characteristics show that the drain-source current IDS for different gate-source voltage $V_{gs}$ is significantly increased with optical illumination for photon flux densities of ${\Phi}=10^{15}\;and\;10^{17}/cm^2s$ compared to the dark condition. Further more, the drain-source current as a function of drain-source voltage $V_{DS}$ is evaluated to find the I-V characteristics for various pinch-off voltages $V_P$ for optimization of impurity flux density $Q_{Diff}$ by diffusion process. The resulting I-V characteristics also show that the diffusion process introduces less process-induced damage compared to ion implantation, which suffers from current reduction due to a large number of defects introduced by the ion implantation process. Further the results show significant increase in gate-source capacitance $C_{gs}$ and gate-drain capacitance $C_{gd}$ for optical illuminations, where the photo-induced voltage has a significant role on gate capacitances. The switching time ${\tau}$ of the OPFET device is computed for dark and illumination conditions. The switching time ${\tau}$ is greatly reduced by optical illumination and is also a function of device active layer thickness and corresponding impurity flux density $Q_{Diff}$. Thus it is shown that the diffusion process shows great potential for improvement of optoelectronic devices in quantum efficiency and other performance areas.