• Nuclear Engineering and Technology
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• 제19권2호
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• pp.115-121
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• 1987

SNU 1.5MV 직렬형 반데그라프 가속기의 고전압 안정화 계통을 설치하여 그 동작 특성을 파악하고 최적화하였다. 이온빔 수송계통의 최적 운전 조건을 단계적인 실험을 통하여 결정하였으며 적절한 운전 조건하에 표적함에서 350nA의 가속된 양성자빔을 얻었다. 고전압을 안정화하지 않았을 때의 고전압 변동은 이온빔을 가속하지 않을 때와 가속할 때 각각 $\Delta$V/V=5.2$\times$$10^{-3}$, 7.2$\times$$10^{-3}$이었으며 그 변동 주파수는 3Hz 이하였다. 터미날 전압 247.3kV에서 고전압 안정화 계통의 최적 운전을 통하여 터미날 전압의 변동은 $\Delta$V/V=2.45$\times$$10^{-4}$ 으로 줄었고 에너지 안정도는 $\Delta$E/E=2.44$\times$$10^{-4}$ 으로 유지되었으며 이 때의 안정화 계수는 29.4였다.

• Nuclear Engineering and Technology
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• 제55권5호
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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.

• Journal of Radiation Protection and Research
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• 제48권4호
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• pp.184-196
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• 2023

Background: Radiation protection is crucial in various fields due to the harmful effects of radiation. Shielding is used to reduce radiation exposure, but gamma radiation poses challenges due to its high energy and penetration capabilities. Materials and Methods: This work investigates the radiation shielding properties of polyvinylidene fluoride (PVDF) samples containing different weight fraction of tungsten carbide (WC), tungsten trioxide (WO₃), and tungsten disulfide (WS₂). Parameters such as the mass attenuation coefficient (MAC), half-value layer (HVL), mean free path (MFP), effective atomic number (Z_eff), and macroscopic effective removal cross-section for fast neutrons (Σ_R) were calculated using the Phy-X/PSD software. EpiXS simulations were conducted for MAC validation. Results and Discussion: Increasing the weight fraction of the additives resulted in higher MAC values, indicating improved radiation shielding. PVDF-xWC showed the highest percentage increase in MAC values. MFP results indicated that PVDF-0.20WC has the lowest values, suggesting superior shielding properties compared to PVDF-0.20WO₃ and PVDF-0.20WS₂. PVDF-0.20WC also exhibited the highest Z_eff values, while PVDF-0.20WS₂ showed a slightly higher increase in Z_eff at energies of 0.662 and 1.333 MeV. PVDF-0.20WC has demonstrated the highest Σ_R value, indicating effective shielding against fast neutrons, while PVDF-0.20WS₂ had the lowest Σ_R value. The Monte Carlo N-Particle Transport version 5 (MCNP5) simulations showed that PVDF-xWC attenuates gamma radiation more than pure PVDF, significantly decreasing the dose equivalent rate. Conclusion: Overall, this research provides insights into the radiation shielding properties of PVDF mixtures, with PVDF-xWC showing the most promising results.

• Nuclear Engineering and Technology
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• 제56권1호
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• pp.301-308
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• 2024

Ceramic materials are being explored as alternatives to toxic lead sheets for radiation shielding due to their favorable properties like durability, thermal stability, and aesthetic appeal. However, crafting effective ceramics for radiation shielding entails complex processes, raising production costs. To investigate local viability, this study evaluated Malaysian ceramic tiles for shielding in diagnostic X-ray rooms. Different ceramics in terms of density and thickness were selected from local manufacturers. Energy Dispersive X-ray Fluorescence (EDXRF) and X-ray Fluorescence (XRF) characterized ceramic compositions, while Monte Carlo Particle and Heavy Ion Transport code System (MC PHITS) simulations determined Linear Attenuation Coefficient (LAC), Half-value Layer (HVL), Mass Attenuation Coefficient (MAC), and Mean Free Path (MFP) within the 40-150 kV energy range. Comparative analysis between MC PHITS simulations and real setups was conducted. The C3-S9 ceramic sample, known for homogeneous full-color structure, showcased superior shielding attributes, attributed to its high density and iron content. Notably, energy levels considerably impacted radiation penetration. Overall, C3-S9 demonstrated strong shielding performance, underlining Malaysia's potential ceramic tile resources for X-ray room radiation shielding.

• Nuclear Engineering and Technology
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• 제56권9호
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• pp.3558-3565
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• 2024

The linear attenuation coefficients (LAC) of four soils (Black cotton (S1), Sandy (S2), Clay (S3), and Sandy (S4)) samples were measured at photon energies released from radioisotopes Co⁵⁷ (122 keV), Ba¹³³ (356 keV), ²²Na (511 and 1275 keV), Cs¹³⁷ (662 keV), Mn⁵⁴ (840 keV), and Co⁶⁰ (1330 keV) using a gamma spectrometer includes a NaI (Tl) scintillation detector. The experimental measurements were confirmed utilizing the Monte Carlo N-particle transport code. The linear attenuation coefficient values enhanced from 0.256 cm^-1 to 0.296 cm^-1 (at E_γ of 122 keV), from 0.126 cm^-1 to 0.142 cm^-1 (at E_γ of 662 keV), and from 0.0938 cm^-1 to 0.105 cm^-1 (at E_γ of 1275 keV), raising the (Fe + Mn) concentration from 0.912 wt% to 11.214 wt%, as well as raising the soil samples density from 1.62 g/cm³ to 1.79 g/cm³. The study also shows an enhancement in the half value thickness, transmission factor, radiation protection efficiency and lead's equivalent thickness due to the enrichment of Fe + Mn concentrations within the studied soils. The results show that the Black cotton soil exhibits better shielding properties for γ-ray than the other soils.

• 방사성폐기물학회지
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• 제10권1호
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• pp.37-43
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• 2012

IAEA 및 국내의 방사성물질 운반 관련 규정에 따라 중 저준위 방사성폐기물 드럼 8개를 운반할 수 있는 IP-2형 운반용기를 개발하였다. IP-2형 운반용기는 낙하시험 및 적층시험을 거친 후 내용물의 유실 또는 분산과 운반용기 외부표면에서의 방사선량률이 20 % 이상 증가할 수 있는 차폐능력의 상실이 없어야 한다. 본 연구의 목적은 적층시험조건에 대한 시험방법 및 절차를 수립하고 IP-2형 운반용기의 적층조건에 대한 구조적 건전성을 평가하는데 있다. 운반용기의 원형시험모델을 이용하여 운반용기 중량의 5배 하중으로 24시간 동안 압축하는 적층조건에 대한 시험 및 전산해석을 수행하였다. 적층시험 시 운반용기의 모서리기둥에서의 변형률 및 변위를 측정하였으며, 측정된 변형률 및 변위는 해석결과와 서로 일치하였다. 컨테이너 바닥부의 처짐량은 측정이 어렵기 때문에 전산해석 방법으로 구하였다. 모서리기둥의 최대 변위와 컨테이너 바닥의 최대 처짐은 법규에서 규정하는 허용치에 비하여 낮게 나타났다. 적층시험 전 후에는 운반용기의 외형치수, 차폐체 두께, 볼트토크 등을 측정하였으며, 그 값들을 비교분석한 결과 운반용기는 내용물의 유실 및 분산, 차폐체 두께의 감소가 나타나지 않았다. 따라서 적층시험조건에서 IP-2형 운반용기의 구조적 건전성이 입증되었다.

• 방사성폐기물학회지
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• 제11권4호
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• pp.281-291
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• 2013

KURT(KAERI Underground Research Tunnel) 부지 부근에 가상의 처분장을 설정하고, 해당 부지의 세 지점에서 방사성폐기물로부터 누출된다고 가정한 방사성 핵종의 이동 시간을 계산하였다. 핵종의 이동 경로는 핵종 누출 지점에서 천부 지하수대까지로 설정하고 KURT 주변 지하수 유동계 모의를 통해 결정하였다. 세 지점은 지하수가 빠르게 유동하는 구조(highly water-conductive feature)를 지나가기 때문에 천부 지하수까지 도달하는데 상대적으로 적은 시간이 걸리는 지점으로 선정되었다. 핵종의 이동 시간은 TDRW(Time-Domain Random Walk) 기법을 통해 계산하였다. 지하수 내의 핵종의 이동 시간을 계산하기 위해, 이류(advection)와 분산(dispersion) 이외에 암반 기질(rock matrix)로의 확산(diffusion)과 기질 내부에서의 흡착(sorption)이 고려되었고, 핵종의 붕괴 및 변환에 의한 영향도 몇 개의 붕괴 사슬(decay chain)을 이용하여 계산에 반영하였다. 계산 결과를 보면, 지표 부근의 천부 지하수에 도달하는 핵종의 시간당 이동량(mass flux)은 복수의 이동 경로뿐만 아니라 핵종의 반감기와 암반 기질 내에서의 핵종의 흡착 분배 계수에 크게 영향을 받는 것으로 나타났다. 따라서 보다 안정적이고 불확실성이 감소된 심지층 처분장의 안전성 평가를 위해 우선적으로 필요한 사항으로는, 장반감기 핵종에 대한 평가가 이동 과정 이외에 저장 용기에 들어있는 상태에서부터 면밀하게 이루어져야 하고, 암반 기질에서 발생하는 핵종의 흡착 과정이 심부 현장 조건을 반영하여 평가되어야 할 것으로 생각된다.

• 한국대기환경학회지
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• 제34권2호
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• pp.321-330
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• 2018

Concentrations of the atmospheric radon and gaseous pollutants were measured at the Gosan site on Jeju Island from 2010 to 2015, in order to observe their time-series variation characteristics and examine the concentration change related to the airflow transport pathways. Based on the realtime monitoring of the atmospheric radon and gaseous pollutants, the daily mean concentrations of radon ($^{222}Rn$) and gaseous pollutants($SO_2$, CO, $O_3$, $NO_x$) were $2,400mBq\;m^{-3}$ and 1.3, 377.6, 41.1, 3.9 ppb, respectively. On monthly variations of radon, the mean concentration in October was the highest as $3,033mBq\;m^{-3}$, almost twice as that in July ($1,452mBq\;m^{-3}$). The diurnal variation of radon concentration shows bimodal curves at early morning (around 7 a.m.) and near midnight, whereas its lowest concentration was recorded at around 3 p.m. Several gaseous pollutants($SO_2$, CO, $NO_x$) showed a similar seasonal variation with radon concentration as high in winter and low in summer, whereas the $O_3$ concentrations had a bit different seasonal trend. According to the cluster back trajectory analysis, the frequencies of airflow pathways moving from continental North China, East China, Japan and the East Sea, the Korean Peninsula, and North Pacific Ocean routes were 36, 37, 10, 13, and 4%, respectively. When the airflow were moved to Jeju Island from continental China, the concentrations of radon and gaseous pollutants were relatively high. On the other hand, when the airflows were moved from North Pacific Ocean and East Sea, their concentrations were much lower than those from continental China.

• 한국결정성장학회지
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• 제26권2호
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• pp.84-88
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• 2016

PVT(Physical vapor transport)법을 이용하여 AlN 단결정을 성장시켰으며 유도 코일의 위치를 변화시켜가면서 핫존의 위치가 달라짐에 따라 변화하는 결과를 비교하였다. 그라파이트 도가니가 사용되었으며 그 규격은 ${\Phi}90{\times}H120$이었다. 온도는 $1950{\sim}2050^{\circ}C$이며 챔버 압력은 150에서 1 Torr까지 사용되었다. 또한 핫존은 실험 회차에 따라 변화를 주었으며 이 결과가 비교되었다. 핫존의 위치가 AlN 단결정 응축 위치에서부터 충분히 아래쪽(> 40 mm)인 경우 성장된 결정 사이즈는 다른 조건들에 비해 양호했지만(${\sim}300{\mu}m/hr$), 조건 재현성은 상당히 떨어졌다. 반대로 핫존과 AlN 성장 위치간의 거리가 가까워질수록 성장된 결정의 크기는 작아지고 결정의 핵이 생성되는 빈도는 낮아지면서 성장된 결정의 질의 안정성은 증가했다. 성장 속도와 품질 두 가지 면에서 초기 핫존 코일의 위치가 결정 성장 위치로부터 20 mm 정도일 때가 가장 우수했다. 핫존의 위치는 매우 민감한 결과를 주었고 이것에서 더 나아가 코일의 이동 속도 또한 최적으로 컨트롤 되어야만 최적의 성장 조건이 설정될 수 있다.

• Animal cells and systems
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• 제1권2호
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• pp.363-370
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• 1997

RNase MRP is a ribonucleoprotein complex with a site-specific endonuclease activity. Its original substrate for cleavage is the small mitochondrial RNA near the mitochondrial DNA replication origin, thus it was proposed to generate the primer for mtDNA replication. Recently, it has been shown to have another substrate in the nucleus, such as pre-S.8S ribosomal RNA in nucleolus. The gene for the RNA component of RNase MRP (MRP RNA) was found to be encoded by the nucleus genome, suggesting an interesting intracellular trafficking of MRP RNA to both mitochondria and nucleolus after transcription in nucleus. In this study, genomic DNA encoding MRP RNA was microinjected into the nucleus of Xenopus oocytes, to analyze promoter regions involved in the transcription. It showed that the proximal sequence element and TATA box are important for basal level transcription; octamer motif and Sp1 binding sites are for elevated level transcription. Most of Xenopus MRP RNA was exported out to the cytoplasm following transcription in the nucleus. Utilizing various hybrid constructs, export of MRP RNA was found to be regulated by the promoter and the 5' half of the coding region of the gene. Interestingly, the transcription in nucleus seems to be coupled to the export of MRP RNA to cytoplasm. Intracellular transport of injected MRP RNA can be easily visualized by whole-mount in situ hybridization following microinjection; it also shows possible intra-nuclear sites for transcription and export of MRP RNA.