• Nuclear Engineering and Technology
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• v.53 no.4
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• pp.1289-1296
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• 2021

In this study, an electron-scattering device was fabricated to practically use the ultra-high dose rate electron beams for the FLASH preclinical research in Dongnam Institute of Radiological and Medical Sciences. The Dongnam Institute of Radiological and Medical Sciences has been involved in the investigation of linear accelerators for preclinical research and has recently implemented FLASH electron beams. To determine the geometry of the scattering device for the FLASH preclinical research with a 6-MeV linear accelerator, the Monte Carlo N-particle transport code was exploited. By employing the fabricated scattering device, the off-axis and depth dose distributions were measured with radiochromic films. The generated mean energy of electron beams via the scattering device was 4.3 MeV, and the symmetry and flatness of the off-axis dose distribution were 0.11% and 2.33%, respectively. Finally, the doses per pulse were obtained as a function of the source to surface distance (SSD); the measured dose per pulse varied from 4.0 to 0.2 Gy/pulse at an SSD range of 20-90 cm. At an SSD of 30 cm with a 100-Hz repetition rate, the dose rate was 180 Gy/s, which is sufficient for the preclinical FLASH studies.

• Journal of Radiation Protection and Research
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• v.47 no.3
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• pp.134-142
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• 2022

Background: This study investigated the characteristics of optically stimulated luminescence dosimeters (OSLDs) with fully filled deep electron/hole traps in the kV energy ranges. Materials and Methods: The experimental group consisted of InLight nanoDots, whose deep electron/hole traps were fully filled with 5 kGy pre-irradiation (OSLD_exp), whereas the non-pre-irradiated OSLDs were arranged as a control group (OSLD_cont). Absorbed doses for 75, 80, 85, 90, 95, 100, and 105 kVp with 200 mA and 40 ms were measured and defined as the unit doses for each energy value. A bleaching device equipped with a 520-nm long-pass filter was used, and the strong beam mode was used to read out signal counts. The characteristics were investigated in terms of fading, dose sensitivities according to the accumulated doses, and dose linearity. Results and Discussion: In OSLD_exp, the average normalized counts (sensitivities) were 12.7%, 14.0%, 15.0%, 10.2%, 18.0%, 17.9%, and 17.3% higher compared with those in OSLD_cont for 75, 80, 90, 95, 100, and 105 kVp, respectively. The dose accumulation and bleaching time did not significantly alter the sensitivity, regardless of the filling of deep traps for all radiation qualities. Both OSLD_exp and OSLD_cont exhibited good linearity, by showing coefficients determination (R²) > 0.99. The OSL sensitivities can be increased by filling of deep electron/hole traps in the energy ranges between 75 and 105 kVp, and they exhibited no significant variations according to the bleaching time.

• Applied Microscopy
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• v.40 no.2
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• pp.117-123
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• 2010

This study has examined experimentally the Beer's law which is a precondition for quantitative electron tomography. We used carbon support film and latex spheres, which have similar absorption coefficients with biological samples, as the test samples to take a tilt-series of images for electron tomography. First, the 3D information of carbon film and latex spheres was obtained by electron tomography. Then, the regression analysis on the relationship between the intensities of the incident and the transmitted beams in a tilt series was carried out to examine the Beer's law. The regression results with RMS error of 0.976 show the linear intensity variations of the transmitted beam as the tilt angles were increased. In addition, the relative absorption coefficients of carbon support film and latex spheres calculated experimentally through the Beer's law were 1.71 (5) and 2.67 (6)/${\mu}m$, respectively. The absorption coefficients remained constant within a full tilt range. Therefore, it is expected that quantitative electron tomography could be performed for biological samples by applying Beer's law provided the exact intensity of incident beam can be obtained under the thoroughly controlled experimental conditions.

• Journal of Soil and Groundwater Environment
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• v.20 no.6
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• pp.62-72
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• 2015

This study investigates the in-situ implementation of bio-regenerated iron mineral catalyst to remove explosive compounds in ground water at a military shooting range in operation. A bio-regenerated iron mineral catalyst was synthesized using lepidocrocite (iron-bearing soil mineral), iron-reducing bacteria Shewanella putrefaciens CN32, and electron mediator (riboflavin) in the culture medium. This catalyst was then injected periodically in the ground to build a redox active zone acting like permeable reactive barrier through injection wells constructed at a live fire military shooting range. Ground water and core soils were sampled periodically for analysis of explosive compounds, mainly RDX and its metabolites, along with toxicity analysis and REDOX potential measurement. Results suggested that a redox active zone was formed in the subsurface in which contaminated ground water flows through. Concentration of RDX as well as toxicity (% inhibition) of ground water decreased in the downstream compared to those in the upstream while concentration of RDX reduction products increased in the downstream.

• Journal of Powder Materials
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• v.20 no.6
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• pp.474-478
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• 2013

The most general photocatalyst, $TiO_2$ and $WO_3$, are acknowledged to be ineffective in range of visible light. Therefore, many efforts have been directed at improving their activity such as: band-gap narrowing with non-metal element doping and making composites with high specific surface area to effectively separate electrons and holes. In this paper, the method was introduced to prepare a photo-active catalyst to visible irradiation by making a mixture with $TiO_2$ and $WO_3$. In the $TiO_2-WO_3$ composite, $WO_3$ absorbs visible light creating excited electrons and holes while some of the excited electrons move to $TiO_2$ and the holes remain in $WO_3$. This charge separation reduces electron-hole recombination resulting in an enhancement of photocatalytic activity. Added Ag plays the role of electron acceptor, retarding the recombination rate of excited electrons and holes. In making a mixture of $TiO_2-WO_3$ composite, the mixing route affects the photocatalytic activity. The planetary ball-mill method is more effective than magnetic stirring route, owing to a more effective dispersion of aggregated powders. The volume ratio of $TiO_2(4)$ and $WO_3(6)$ shows the most effective photocatalytic activity in the range of visible light in the view point of effective separation of electrons and holes.

• Journal of the Korean Vacuum Society
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• v.7 no.s1
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• pp.57-77
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• 1998

Heteroepitaxial $Y_2O_3$ films were grown on a Si(111) substrate by ionized cluster beam deposition(ICBD) in ultra high vacuum, and its qualities such as crystllitnity, film stress, and morphological characteristics were investigated using the various measurement methods. The crystallinity was investigated by x-ray diffraction (XRD) and reflection high energy electron diffraction (RHEED). Interface crystallinity was also examined by Rutherford backscattering spectroscopy(RBS) channeling, transmission electron microscopy(TEM). The stress of the films was measured by RBS channeling and XRD. Surface and interface morphological characteristics were investigated by atomic force microscopy (AFM) and x-ray scattering method. Comparing the interface with the surface characteristics, we can conclude that many defects at the interface region were generated by interface reaction between the yttrium metal and SiO2 layer and by ion beam characteristic such as shallow implantation, so that they influenced the film qualities. The film quality was dominantly depended on the characteristic temperature range. In the temperature range from $500^{\circ}C$ to $600^{\circ}C$, the crystallinity was mainly improved and the surface roughness was drastically decreased. On the other hand, in the temperature range from $600^{\circ}C$ to $700^{\circ}C$, the compressive stress and film density were dominantly increased, and the island size was more decreased. Also the surface morphological shape was transformed from elliptical shape to triangular. The film stress existed dominantly at the interface region due to the defects generation.

• Bulletin of the Korean Chemical Society
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• v.33 no.9
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• pp.2966-2970
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• 2012

Fullerene/polystyrene ($C_{60}$/PS) nano particle was prepared by using emulsion polymerization. Styrene and fullerene were emulsified in aqueous media in the presence of poly(N-vinyl pyridine) as an emulsion stabilizer, and polymerization was initiated by water soluble radical initiator, potassium persulfate. The obtained nano particles have an average diameter in the range of 400-500 nm. The fullerene contents in the nano particle can be controlled up to 15 wt % by varying the feed ratio, which was confirmed by themogravimetric analysis (TGA) and elemental analysis (EA). The structure and morphologies of the $C_{60}$/PS nano particles were examined by various analytical techniques such as dynamic light scattering (DLS), scanning electron microscope (SEM), transmission electron microscope (TEM), electron diffraction (ED) pattern, X-ray powder diffraction (XRD), and UV spectroscopy. Unlike conventional $C_{60}$/PS particles initiated by organic free radical initiators, in which the fullerene is copolymerized forming a covalent bond with styrene monomer, the prepared $C_{60}$/PS nano particles contain pristine fullerene as secondary particles homogeneously distributed in the polystyrene matrix.

• Korean Journal of Agricultural Science
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• v.39 no.3
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• pp.341-347
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• 2012

The objective of this study was to investigate the combined effect of electron beam irradiation (EB) and onion peel extracts and selected flavorings on microbiological and sensory quality of pork jerky. Total aerobic bacteria were detected in the range of $3.87{\pm}0.30{\sim}4.60{\pm}0.12$ log CFU/g in all samples. Addition of both onion peel extract and flavoring showed the decrease of total aerobic bacterial count in pork jerky. No viable cells were observed after EB at 4 kGy. Sensory evaluation indicated that the EB-treated pork jerky with 0.5% barbecue flavoring did not show any difference in overall acceptability compared with the control. Therefore, combined use of EB with onion peel extracts and barbecue flavoring may enhance the safety of pork jerky with proper sensory quality.

• JSTS:Journal of Semiconductor Technology and Science
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• v.1 no.1
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• pp.40-49
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• 2001

We have developed a repeatable process of forming uniform, small-size and high-density self-assembled Si nano-crystals. The Si nano-crystals were fabricated in a conventional LPCVD (low pressure chemical vapor deposition) reactor at $620^{\circ}c$ for 15 sec. The nano-crystals were spherical shaped with about 4.5 nm in diameter and density of $5{\times}l0^{11}/$\textrm{cm}^2$. More uniform dots were fabricated on nitride film than on oxide film. To take advantage of the above-mentioned characteristics of nitride film while keeping the high interface quality between the tunneling dielectrics and the Si substrate, nitride-oxide tunneling dielectrics is proposed in n-channel device. For the first time, the single electron effect at room temperature, which shows a saturation of threshold voltage in a range of gate voltages with a periodicity of ${\Delta}Ｖ_{GS}\;{\approx}\;1.7{\;}V$, corresponding to single and multiple electron storage is reported. The feasibility of p-channel nano-crystal memory with thin oxide in direct tunneling regime is demonstrated. The programming mechanisms of p-channel nano-crystal memory were investigated by charge separation technique. For small gate programming voltage, hole tunneling component from inversion layer is dominant. However, valence band electron tunneling component from the valence band in the nano-crystal becomes dominant for large gate voltage. Finally, the comparison of retention between programmed holes and electrons shows that holes have longer retention time.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.207-207
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• 2016

plasma group velocities of neon with oxygen admixture (ug) are obtained by intensified charge coupled device (ICCD) camera images at fixed gate width time of 5 ns. The propagation velocities outside interelectrode region are in the order of 104 m/s.The plasma ambipolar diffusion velocities are calculated to be in the order of 102 m/s. Plasma jet is generated by all fixed sinusoidal power supply, total gas flow and repetition frequency at 3 kV, 800 sccm and 40 kHz, respectively. The amount of oxygen admixture is varied from 0 to 2.75 %. By employing one dimensional convective wave packet model, the electron temperatures in non-thermal atmospheric-pressure plasma jet are estimated to be in a range from 1.65 to 1.95 eV.