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[en] TRIGA Mark II, the first research reactor in Korea operated since 1962, and TRIGA Mark III, operated since 1972, have phased out their operation due to their operating lives in 1995. The Ministry of Science and Technology (MOST) and the Korea Atomic Energy Research Institute (KAERI) then decided the decontamination and decommissioning (D and D) of these two research reactors in 1996. The D and D project of these two reactors has started at the beginning of 1997 and will last until the end of 1999. KAERI has no experience on the D and D of a nuclear facility. KAERI has so decided to it be done by a Korean company which has large experiences on nuclear fields other than D and D. Korean company should be so associated with a foreign company which has experiences on D and D of similar research reactors up to stage 3. On the other hand, KAERI has launched the real related Research and Development (R and D) for the D and D of nuclear facilities in 1997 under auspices of the long-term R and D program for nuclear energy. These R and D results should be applied or demonstrated when the D and D field works of TRIGA Mark II and III will start. This paper summarizes the current status of the decommissioning project of the TRIGA Mark II and III research reactors and also its future plan to be done. 9 refs., 2 tabs., 2 figs
[en] We studied the transmission of the electromagnetic waves through subwavelength slit arrays in terahertz (THz) and optical frequency regions, respectively. In the optical frequency regime, the influences of surface plasmon polaritons on the near-field distribution and on the far-field transmittance are discussed. The near-field electro-optic sampling technique combined with fast Fourier transformation is applied in measuring the THz near-field distribution in time and spectral domains. From these, we discuss the existence of highly confined surface waves in the perfect conductor regime (THz) in comparison with the finite conducting case (visible range) in metallic multi-slit arrays. Our studies provide an integrated view of surface plasmons in the optical regime, and surface-bound waves mimicking surface plasmons in the THz region.
[en] We report on a near-field amplification in a transmission metallic grating, whereby the spatially and spectrally resolved near-field intensity reaches ∼20 times the incident intensity at the surface plasmon polariton resonance. The amplified value is maintained up to ∼2 μm away from the surface. Our experiments show that the near-field amplification in the transmission grating, which is strongly implied in a recent superlens design, indeed occurs at the surface plasmon polariton resonance. Theoretical calculation shows good agreement with experiment and also reveals that the horizontal magnetic field is predominantly amplified. Our results suggest that a grating-assisted superlens should have its optimal functional wavelength right around the surface plasmon resonance
[en] In radiotherapy, a variety of detectors such as ionization chambers, films, TLDs, diodes, and OSL, are being used for quality assurance (QA). Owing to its high sensitivity and feasibility to operate at low voltages, silicon (Si) photoconductors, which are used as detection material of a diode, are currently being used as relative dosimeters. In addition, other materials such as amorphous selenium (a-Se), cadmium telluride (CdTe), lead iodide (PbI2), and mercury iodide (HgI2) were also being investigated for their feasibility as diagnostic radiation detector. Among these materials, HgI2 has been reported to show remarkable properties including high spatial resolution and high stopping power. Hence In this study, we have verified the feasibility of HgI2 dosimeter for quality assurance of radiotherapy. In order to fabricate the detector, HgI2 was mixed with TiO2 to minimize the signal reduction. Following this, the resulting mixture was deposited onto indium tin oxide (ITO) coated glass by particle-in binder (PIB) method. Finally, the top ITO electrode was coated by magnetron sputterring system. Subsequently, we measured the electrical properties generated by high-energy radiation from linear accelerator (LINAC), and analyzed the reproducibility, linearity, and percent depth dose (PDD) of the fabricated detoctor. In addition, we have determined the build-up materials in experimental setup, since the thickness of build-up region, where the secondary electron emission equilibrium occurs, changes depending on radiation energy. It was observed that the relative variations measured as standard deviation divided by the average value among repeated measurements was approximately 1%. Deviations from linearity are smaller than 5%. Finally, we compared the experimental data of the detector fabricated in this study with those of the farmer-type ionization chamber. Base on the results obtained from this study, it could be realized that HgI2 could be used as dosimeter for QA of radiotherapy.
[en] The conical band structure is the cornerstone of graphene’s ultra-broadband optical conductivity. For practical use of graphene in nonlinear photonics, however, substantial increases of the light–matter interaction strength will be required while preserving the promising features of monolayers, as the interaction of light with a single atomic layer is limited due to the extremely short interaction length and low density of state, particularly for the long-wavelength region. Here, we report that this demand can be fulfilled by random stacking of high-quality large-area monolayer graphene up to a requested number of layers, which leads to the electronic interaction between layers being effectively switched off due to turbostratic disorder. The nonlinear characteristics of randomly stacked multilayer graphene (RSMG), which originates from a thermo-modulational feedback mechanism through ultrafast free-carrier heating and temperature-dependent carrier-phonon collisions, show clear improvements in the terahertz (THz) regime with increasing layer numbers, whereas as-grown multilayer graphene (AGMG) exhibits limited behaviors due to strong interlayer coupling. This controllable nonlinearity enhancement provides an ideal prerequisite for developing efficient graphene-based THz photonic devices. (paper)
[en] The purpose of this study was to measure the accuracy of a three-dimensional surface imaging system (3-D SIS) in comparison to a 3-laser system by analyzing the setup errors obtained from a RANDO Phantom and head and neck cancer patients. The 3-D SIS used for the evaluation of the setup errors was a C-RAD Sentinel. In the phantom study, the OBI setup errors without the thermoplastic mask of the 3-laser system vs. the 3-D SIS were measured. Furthermore, the setup errors with the thermoplastic mask of the 3-laser system vs. the 3-D SIS were measured. After comparison of the CBCT, setup correction about 1 mm was performed in a few cases. The probability of the error without the thermoplastic mask exceeding 1 mm in the 3-laser system vs. the 3-D SIS was 75.00% vs. 35.00% on the X-axis, 80.00% vs. 40.00% on the Y-axis, and 80.00% vs. 65.00% on the Z-axis. Moreover, the probability of the error with the thermoplastic mask exceeding 1 mm in the 3-laser system vs. the 3-D SIS was 70.00% vs. 15.00% on the X-axis, 75.00% vs. 25.00% on the Y-axis, and 70.00% vs. 35.00% on the Z-axis. These results showed that the 3-D SIS has a lower probability of setup error than the 3-laser system for the phantom. For the patients, the setup errors of the 3-laser system vs. the 3-D SIS were measured. The probability of the error exceeding more than 1 mm in the 3-laser system vs. the 3-D SIS was shown to be 81.82% vs. 36.36% on the X-axis, 81.82% vs. 45.45% on the Y-axis, and 86.36% vs. 72.73% on the Z-axis. As a result, the 3-D SIS also exhibited a lower probability of setup error for the cancer patients. Therefore, this study confirmed that the 3-D SIS is a promising method for setup verification