• 방사성폐기물학회지
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• 제18권2_spc호
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• pp.317-325
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• 2020

한국원자력환경공단은 처분시설 내 1단계 인수·저장구역의 인수검사 공간 및 드럼 취급 공간 부족에 대한 문제를 해결하기 위하여 방폐물검사건물을 건설하여 저장·처리능력을 확충할 예정이다. 본 연구에서는 MCNP 코드를 이용하여 방폐물검사건물 내 저장구역에서 취급하는 해체 방사성폐기물 대상 신형처분용기를 대상으로 작업종사자의 피폭선량을 평가하였다. 평가결과, 시설 내 저장 가능한 최대 용기 개수(304개)와 방사선작업에 대한 연간 예상 작업시간(약 306시간)에 대하여 연간 집단선량은 총 84.8 man-mSv로 계산되었다. 시설 내 총 304개의 신형처분용기(소형/중형 타입)가 저장 완료된 시점에서 인수검사, 처분검사를 위한 작업종사자의 투입인력은 총 25명, 작업종사자 당 예상피폭선량은 연평균 3.39 mSv로 산출되었다. 소형용기 취급 시 작업종사자의 고방사선량 작업에 따른 작업효율과 방사선적 안전성 확보를 위해서는 콘크리트 라이너의 두께를 증가시키는 추가적인 차폐가 필요할 것으로 평가되었다. 향후 본 연구를 바탕으로 실측기반의 해체폐기물의 선원항과 특성을 활용하여 방사선작업 당 작업시간 및 투입인력을 산출함으로써 작업종사자의 최적의 방사선작업조건을 도출할 수 있을 것으로 사료된다.

• Journal of Astronomy and Space Sciences
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• 제5권1호
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• pp.1-8
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• 1988

Electron beam propagation in a fully ionized plasma has been studied using a one-dimensional particle simulation model. We compare the results of electrostatic simulations to those of electromagnetic simulations. The electrostatic results show the essential features of beam-plasma interactions. It is found that the return currents are enhanced by the beam-plasma instability which accelerates ambinet plasmas. The results also show the heating of ambient plasmas and the trapping of plasmas due to the locally generated electric field. The electromagnetic simulations show much the same results as the electrostatic simulations do. The level of the radiation generated by the same non-relativistic beam is slightly higher than the noise level. We discuss the results in context in context of the heating of coronal plasma during solar flares.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 1998년도 Proceedings of International Symposium on Remote Sensing
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• pp.355-360
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• 1998

A small package of plasma instruments, Space Physics Sensor, will monitor the space environment and its effects on microelectronics in the low altitude region as it operates on board the KOMPSAT-1 from 1999 over the maximum of the solar cycle 23. The Space Physics Sensor (SPS) consists of two parts: the Ionospheric Measurement Sensor (IMS) and the High Energy Particle Detector (HEPD). IMS will make in situ Measurements of the thermal electron density and temperature, and is expected to provide a global map of the thermal electron characteristics and the variability according to the solar and geomagnetic activity in the high altitude ionosphere of the KOMPSAT-t orbit. HEPD will measure the fluxes of high energy protons and electrons, monitor the single event upsets caused by these energetic charged particles, and give the information of the total radiation dose received by the spacecraft. The continuous operation of these sensors, along with the ground measurements such as incoherent scatter radars, digital ionosondes and other spacecraft measurements, will enhance our understanding of this important region of practical use for the low earth orbit satellites.

• 한국항공우주학회지
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• 제40권9호
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• pp.737-744
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• 2012

유한체적법을 이용하여 설정된 가상의 노즐 조건에 따라 비행체 배기플룸의 SE와 PE에 의한 열복사 저부가열 해석 연구를 수행하였다. 저부면에서의 복사열유속을 얻기 위해 배기플룸은 흡수, 방사 및 산란하는 매질을 고려하였다. 저부면은 차가운 흑체이고 비회색가스와 입자의 복사 물성치는 회색가스가중합법(WSGGM)을 사용하였다. 후방 몬테카를로 방법을 사용한 기존의 연구와 비교하여 검증한 후, 입자의 농도, 온도, 그리고 등방성 또는 이방성 산란에 따른 복사저부가열을 해석하였다. 그 결과, 복사열유속은 노즐 출구와의 거리가 멀어지거나 비행 고도가 증가할수록 감소하고 입자의 온도가 높아질수록 복사열유속은 증가한다. 또한 전방산란은 PE를 증가시키고 후방산란은 SE를 증가시켰다.

• 천문학회보
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• 제46권2호
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• pp.57.4-58
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• 2021

Asteroids have undergone various processes such as impacts, space weathering, and thermal evolution. Because they expose their surfaces to space without atmosphere, these evolutional processes have been recorded directly on their surfaces. The remote-sensing observations have been conducted to reveal these evolutional histories of the target asteroids. For example, crater and boulder distributions are unambiguous evidence for past nondestructive impacts with other celestial bodies. Multiband and spectroscopic observations have revealed space-weathering history (as well as compositions). Whereas most physical quantities have been examined intensively using spacecraft and telescopes, only a little has been studied on "the grain size". It is one of the fundamental physical quantities for diagnosing the collisional and thermal history of asteroids. Our group has conducted polarimetric research of asteroids (as well as Moon [1]) to determine the particle size and further investigate the evolutional histories of target asteroids [2],[3]. For example, the existence of regolith on an S-type asteroid, Toutatis, was suggested almost twenty years before space exploration [4]. Moreover, we reported that near-Sun asteroids indicate a signature of submillimeter grains, which could be created by a thermal sintering process by solar radiation [5]. However, it is important to note that in-situ polarimetry has not been reported on the asteroid surface, although the Korean Lunar Exploration Program aims to do polarimetry on the lunar surface [6]. Therefore, it is expected that the polarizer mounted on the Korean Apophis spacecraft can make the first estimate of the grain size and its regional variation over the Apophis surface. In this presentation, we outline research of S-type asteroid surfaces through remote-sensing observations and consider the role of polarimetry. Based on this review, we consider the purpose, potentiality, and strategy of the polarimetry using the onboard device for the Apophis spacecraft. We will report a possible polarization phase curve of Apophis estimated from ordinary chondrites and past observational data of S-type asteroids, taking account of the space weathering effect. Based on this estimation, we will consider the strategy of how to determine the particle size (and space weathering degree) of the Apophis surface. We will also mention the detectability of dust hovering on the surface.

• 천문학회보
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• 제39권2호
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• pp.113.1-113.1
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• 2014

We propose a three-year Key Science Program (KSP) consisting of VLBI monitoring observations and single dish (SD) rapid response observations (RRO). The VLBI monitoring observations are comprised of ten 24-hr observations per year (every month) of about 30 gamma-ray brigt active galactic nuclei (AGNs) with Korea VLBI Network (KVN) at 22, 43, 86, and 129 GHz. The SD RROs may consist of twelve 7-hr observations per source (every week for 3 months after triggering) of gamma-ray flaring sources with two KVN SD telescopes at 22, 43, and 86 GHz in dual polarization. We expect one or two sources per year for the SD RROs. Gamma-ray flares of AGNs are known to be occured in innermost regions of relativistic jets which radiate in whole ranges of electromagnetic spectra due to synchrotron radiation, syschrotron self absorption, inverse-compton scttering, doppler boosting etc. Possible explanations of the gamma-ray flares in AGNs are a) shocks-in-jets propagating within jet flow and b) bending of the whole jets. For both cases, we should expect changes in polarization, luminosity, particle distribution, and structures of jets at mas-scale. The multifrequency simultaneous VLBI/SD observations with KVN are the best tool for detecting such changes correlated with gamma-ray flares. This KSP proposal aims to answer the fundamental questions about the basic nature of the flares of AGNs.

• 천문학회보
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• 제38권2호
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• pp.93.1-93.1
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• 2013

The Earth's radiation belts consist of an inner belt and an outer belt, being separated by the slot region. It is well known that the variations of the inner edge of the outer belt and the location of the plasmapause (Lpp) are closely related to each other. Different waves exist inside and outside the plasmasphere, playing different roles in the particle dynamics. The plasmapause is well known to be influenced by solar wind conditions and geomagnetic disturbances. Therefore, it is important to precisely determine the location of the plasmapause and develop a prediction scheme. In this study, we identified the location of the plasmapause using the plasma density data from the Time History of Events and Macroscale Interactions During Substorms (THEMIS). The plasmapause is determined by requiring density gradient of a factor of 15 within L-change = 0.5. We statistically determined Lpp as a function of preceding geomagnetic indices. Also, we determined the relations between Lpp and preceding solar wind conditions by estimating correlation coefficients. These relations give us predicting models of Lpp as a function of preceding solar wind parameters and geomagnetic indices. As our database covers a period over the ascending phase from near-sunspot minimum, our statistical results differ somewhat from previous works that cover near-sunspot maximum. Finally, we give some comparative examples obtained from the Van Allen Probes data.

• 천문학회지
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• 제23권1호
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• pp.71-82
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• 1990

Theoretical calculations of the combined radiative transfer and statistical equilibrium equation including the charge-particle conservations have been earned out for a multilevel hydrogen atom in quiescent prominences. Cool and dense models show the steep changes of population and radiation field in the vicinity of the surface, while these physical quantities remain unchanged for models with temperature of 7,300K, regardless of total densities. Ionization rate of hydrogen atom related with metallic line formation varies in considerable amounts from the surface to the center of model prominences cooler than 6,300K. However, such cool models cannot release enough hydrogen line emissions to explain observed intensities. Prominence models with a temperature higher than 8,000K can yield the centrally reversed Lyman line profiles confirmed by satellite EUV observations. We find that queiscent prominence with a density between $2{\times}10^{11}$ and $10^{12}cm^{-3}$ should be in temperature range between 6,300K and 8,300K, in order to explain consistently observed H alpha, beta line emissions and $n_p/n_l$ ratio.

• Journal of Astronomy and Space Sciences
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• 제29권1호
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• pp.51-55
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• 2012

A few high-mass X-ray binaries-consisting of an OB star plus compact companion-have been observed by Fermi and ground-based Cerenkov telescopes like High Energy Stereoscopic System (HESS) to be sources of very high energy (VHE; up to 30 TeV) ${\gamma}$-rays. This paper focuses on the prominent ${\gamma}$-ray source, LS 5039, which consists of a massive O6.5V star in a 3.9-day-period, mildly elliptical ($e{\approx}0.24$) orbit with its companion, assumed here to be an unmagnetized compact object (e.g., black hole). Using three dimensional smoothed particle hydrodynamics simulations of the Bondi-Hoyle accretion of the O-star wind onto the companion, we find that the orbital phase variation of the accretion follows very closely the simple Bondi-Hoyle-Lyttleton (BHL) rate for the local radius and wind speed. Moreover, a simple model, wherein intrinsic emission of ${\gamma}$-rays is assumed to track this accretion rate, reproduces quite well Fermi observations of the phase variation of ${\gamma}$-rays in the energy range 0.1-10 GeV. However for the VHE (0.1-30 TeV) radiation observed by the HESS Cerenkov telescope, it is important to account also for photon-photon interactions between the ${\gamma}$-rays and the stellar optical/UV radiation, which effectively attenuates much of the strong emission near periastron. When this is included, we find that this simple BHL accretion model also quite naturally fits the HESS light curve, thus making it a strong alternative to the pulsar-wind-shock models commonly invoked to explain such VHE ${\gamma}$-ray emission in massive-star binaries.

• Journal of Astronomy and Space Sciences
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• 제17권1호
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• pp.107-116
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• 2000

본 연구는 지구 공전 궤도 근처의 Leonid의 출현 빈도와 속도 등을 예측하기 위한 연구의 초기 단계로서 meteoroid에 대한 기초 자료 조사와 더붙어 기존에 알려져 있는 meteoroid 입자의 분출 속도 모텔과 섭동 모델로부터 meteoroid의 운동 방향과 속도를 컴퓨터로 계산하기 위한 프로그램을 개발하고 이것을Leonid stream에 적용해 보았다. 입자의 초기 속도 모델로는Jones의 분출속도 분포모델을 사용하였으며, meteoroid의 궤도 운동 모델에는 태양과 달, 지구를 비롯한 각 행성들의 섭동 모델이 포함되었다. 태양계 천체들의 Ephemeris를 구하기 위해 JPL (Jet Propulsion L Laboratory)의 SSD (Solar System Dynamics) Laboratory에서 개발된 DE405 Solar System E Ephemeris 데이터 파일을 사용하였다. 이외에 중요한 섭동 요소로써 태양 복사압을 고려하였으며, 적분 알고리즘으로는 8차 Runge-Kutta 방법을 사용하였다.