[en] Attitude of Democratic People's Republic of Korea towards completing denuclearization of Korean Peninsula is expressed within the global aim of attaining peace and security with the support of international organizations

[en] Gamma spectroscopy is used to determine the identity and quantity of gamma-emitters in nuclear physics, geochemistry and astrophysics. The scintillation detectors are being used as a gamma spectrometer generally, because of their higher gamma-ray detection efficiency and cheaper price than germanium semi-conductor detectors. A typical scintillation detector is composed of a scintillator, a window, and a photodetector. The photomultiplier (PM) tube has been the most widely used as a photodetector because of its advantages like high sensitivity, high signal-to-noise ratio, and wide dynamic range. Recently, the Silicon Photomultiplier (SiPM) is being studied as a substitute of PM tube. The SiPM has almost same performance compared to PM tube but it has additional advantages; low operating voltage, small volume, and cheap production cost. In this research, the gamma spectrometer using SiPM instead of PM tube is developed. The use of SiPM as a photodetector makes the gamma spectrometer smaller, cheaper, easier to use. For photon transport and collection from the large area scintillator to the small area SiPM, a light guide is applied in this gamma spectrometer system. Before fabrication of light guide, DETECT simulation is performed to study and prospect characteristics of light guide structure. And actual light guides are fabricated on the basis of this simulation result. Poly(methyl methacrylate) (PMMA) is chosen as material of light guide, 5 sample light guides are fabricated in different lengths and coatings. As a scintillator crystal, same NaI(Tl) crystal is chosen. For measurement and analysis of gamma spectrometer system, 3 gamma spectrometer systems are composed: PM tube-based system, PM tube-based system with the light guide, SiPM-based system with the light guide. Through comparison between the results of each gamma spectrometer, the performances of gamma spectrometer system are analyzed by each component. Measurement results of the second system is well matched with DETECT simulation results. Degrading of energy resolution due to light guide is 4∼8% at 662 keV. Photon loss during transport in the light guide is the main reason of this degrading. This degrading can be reduced by more reflective coating. When applying the light guide and the SiPM both in the third system, the best energy resolution is 25% at 662 keV. Considering resolution degrading due to light guide, degrading due to SiPM is about 10%. The main cause is the difference between pixels of SiPM array, and summing of signal from each pixel makes noise level high. It can improve through gain adjustment and preamplifier circuit for SiPM array. Developed gamma spectrometer has limited performance for special conditions, but it has possibility to be better and new type of gamma spectrometer

[en] The plastic scintillator has been used for gamma-ray detection in the fields of dosimetry and security because of their advantages including a fast decay time, a low production cost, an easy fabrication method, availability in various shapes and large scale, dose linearity, and tissue-equivalence. Nevertheless, the fundamental characteristics of the plastic scintillator limit its applicability in spectral analysis. Energy calibration and analysis of the spectrum measured with plastic scintillators are not as simple as those on the spectrum measured with inorganic scintillators because only a Compton maximum is observed on the spectrum, and even its energy is not obvious. Several methods have been suggested for energy calibration and description of a spectrum in plastic scintillators but they required additional measurement equipment and many iterations in analyzing processes.In this study, an improved method to describe spectral gamma response in the plastic scintillator is suggested. The proposed method is based on the linear correlation between the energy resolution (σ_R) and the estimated energy broadening at a Compton maximum (σ_CM). The measured gamma spectra of known sources are calibrated first with the assumption on the energy of Compton maxima. After initial calibration, the energy broadening at a Compton maxima (σ_CM) is estimated by Gaussian fitting and the corresponding energy resolution (σ_R) is computed. The Compton spectra for each gamma-ray energy are calculated with the computed energy resolution and compared to the measured spectra. Then, the energy of the Compton maxima are deter-mined and used with the FWHM values for the computation of input parameters for GEB-treated MCNP6 simulation. Through this GEB-treated MCNP6 simulation, the detailed gamma spectra can be described, and the energy information required to the energy calibration can be provided by only the calculation of Compton spectra.The proposed method has been applied to three cases: the 1cm³ polystyrene scintillator for dosimetry, the 2-inch EJ200 scintillator which is the most common size, and the large PVT scintillator for the radiation portal monitor. The effectiveness of the proposed method was verified by showing a great agreement between measured gamma spectra and simulated spectra. This method can describe the gamma spectrum accurately without many iterations so that it is expected to provide a direct way for the energy calibration and spectral analysis in the applications of plastic scintillators

[en] Since the high-temperature superconductor of oxide type was founded, many researches and efforts have been performed for finding its application field. The YBCO superconducting film fabricated on economic metal substrate with uniform critical current density is considered as superconducting fault-current limiter (SFCL). There are physical and chemical processes to fabricate superconductor film, and it is understood that the chemical methods are more economic to deposit large area. Among them, chemical vapor deposition (CVD) is a promising deposition method in obtaining film uniformity. To solve the problems due to the high deposition temperature of thermal CVD, plasma-enhanced chemical vapor deposition (PECVD) is suggested. This report describes the principle and fabrication trend of SFCL, example of YBCO film deposition by PECVD method, and principle of plasma deposition

[en] By the direct coprecipitation of the aqueous solution of iron salt and tetramethylammonium hydroxide solution the stable iron ferrite nanoparticles were formulated. These nanoparticles were found to have uniform sizes of about 7 nm, and also showed no coalescence in the aqueous solution for a few months. The superparamagnetic behavior of these nanoparticles was checked by a vibrating sample magnetometer. Also, the temperature dependence of saturation magnetization of nanoparticles was observed using a superconducting quantum interface device magnetometer. The relaxation times of T₁ and T₂ of hydrogen proton in the colloidal aqueous solution of magnetic nanoparticles were measured using a nuclear magnetic resonance spectrometer for the wide range of concentration of nanoparticles in the aqueous solution. The inverse of relaxation times was observed to be directly dependent on the concentration of nanoparticles

[en] Vertebral artery loop formation is an anatomic variation that possibly causes cervical nerve root compression, leading to cervical radiculopathy. A few cases of vertebral artery loop formation depicted with conventional sagittal magnetic resonance imaging (MRI) have been reported, but cases of vertebral artery loop formation depicted with oblique sagittal MRI have been less frequently reported. We present a case of vertebral artery loop formation depicted on oblique sagittal MRI.

[en] A Stockbridge damper system can control the aeolian vibrations in a transmission line by dissipating excitation energy through the self-excitation of the damper system. Therefore, locating these resonant frequencies is a critical design consideration for a Stockbridge damper to determine the efficiency of spectral energy dissipation. In this study, the design strategy of a damper was investigated after conducting a design sensitivity analysis of the resonant frequency of a Stockbridge damper that considered several design parameters, including length of the messenger wire, inertia of the counterweight, and gyration radius of the counterweight. The formulation of the design sensitivity analysis was performed using partial derivatives of the eigenvalues with respect to each design parameter over two resonant frequencies. The sensitivity formulations were validated through a case study of eigenvalues that considered a variation of up to ±30 % in the values of the design parameters. The design guidelines for a Stockbridge damper were derived from the sensitivity analysis results.

[en] Very High Temperature gas-cooled Reactor (VHTR) that is one of the concepts of GEN-IV reactor adopts Reactor Cavity Cooling System (RCCS) as a passive safety system removing the decay heat from the reactor vessel. RCCS is comprised of vertical rectangular riser channels, which surround the reactor vessel to remove the afterheat emitted from it. To ensure the integrity of the reactor vessel, an accurate prediction of heat removal rate through the RCCS riser is essential, and understanding of the heat transfer phenomena in the RCCS riser is required. This phenomenon, especially in a vertical rectangular duct, has not been sufficiently investigated due to the lack of experimental data and insufficient understanding of the local flow structure. Several researches on the performance of RCCS riser have been conducted with reduced-scale experiment facilities, and the results implied that the overall heat transfer rate through the experiment facilities and prototype RCCS riser would be different depending on the thermal boundary conditions and convective heat transfer regime. To enhance the understanding of the heat transfer mechanism in the rectangular riser duct, an investigation on the local flow structure is required for the different thermal boundary conditions. In this study, local flow structure was measured in a strongly heated rectangular riser duct with Particle Image Velocimetry (PIV) method. Outer wall temperature distribution of the test section was obtained by infrared (IR) thermometry for the boundary condition of CFD calculation. By comparing the experimental data and CFD analysis results, prediction capabilities of turbulence models were assessed in a heated rectangular riser duct for natural convection. Finally, planned activities for further investigation were introduced. Local flow structure and turbulence quantities were obtained in a heated rectangular riser duct in natural convection condition using PIV method, and the data was compared with the CFD analysis results to assess the prediction capabilities of two turbulence models; V2F turbulence model and realizable k-ε turbulence model.

[en] To fabricate the second generation superconductor wire, coated conductor, we selected MOCVD (Metal organic chemical vapor deposition) method which is commercially available and whose growth rate is very high. The first buffer layer CeO₂ was successfully deposited on the Ni tape. The thick Y-stabilized ZrO₂ layer was thus inserted between two CeO₂ layers by MOCVD method. The c-axis growth of the first CeO₂, the inserted YSZ and top CeO₂ layer was achieved by optimized the deposition condition for the three buffers. It was found that the YBCO deposition was fairly dependant on the depostion temperature, time, oxygen partial pressure, amount of the source supplied. Especially the thickness of the YBCO films was linearly dedendant on the deposition temperature and time, but current properties was not linearly dependant on the film thickness. The critical current (Ic) of the YBCO film grown on SrTiO₃ and IBAD template were over 100 A/cm-width and 50 A/cm-width at 77 K and 0 field. To establish the MOCVD process, collaboration work with several organizations was made

[en] Current carrying capacity is one of the most important issues in the consideration of superconductor bulk materials for engineering applications. There are numerous applications of Y-Ba-Cu-O (YBCO) bulk superconductors e.g. magnetic levitation train, flywheel energy storage system, levitation transportation, lunar telescope, centrifugal device, magnetic shielding materials, bulk magnets etc. Accordingly, to obtain YBCO materials in the form of large, single crystals without weak-link problem is necessary. A top seeded melt growth (TSMG) process was used to fabricate single crystal YBCO bulk superconductors. The seeded and infiltration growth (IG) technique was also very promising method for the synthesis of large, single-grain YBCO bulk superconductors with good superconducting properties. 5 wt.% Ag doped Y211 green compacts were sintered at 900 .deg. C ∼ 1200 .deg.C and then a single crystal YBCO was fabricated by an infiltration method. A refinement and uniform distribution of the Y211 particles in the Y123 matrix were achieved by sintering the Ag-doped samples. This enhancement of the critical current density was ascribable to a fine dispersion of the Y211 particles, a low porosity and the presence of Ag particles. In addition, we have designed and manufactured large YBCO single domain with levitation force of 10-13 kg/cm² using TSMG processing technique