• Journal of Radiation Protection and Research
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• v.12 no.1
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• pp.54-60
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• 1987

The quasi-exposure rate and the quasi-effective energy of the natural radiation in the field at 47 monitoring points around nuclear power plants have been studied with the pair filter thermoluminescence dosimeter system. The results of the six years observation showed that the relationship between the quasi-exposure rate $X_q$, and quasi-effective energy $E_q$ can be represented as a hyperbolic function: $X_q=A+C/(E_q-B)$, where the constants A and B correspond to the quasi-exposure rate of cosmic-rays and the minimum quasi-effective energy of natural radiation, respectively. Furthermore, the constant A is in close agreement with the values obtained by using ionization chambers and scintillation detectors. The constant B is approximately 0.68 MeV, closely corresponding to the mean energy of the photons emitted from natural uranium.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.109.1-109.1
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• 2011

Shock waves are ubiquitous in astrophysical environments. In particular, shocks formed by merger of subclumps, infall of matter and internal flow motion in intracluster media (ICMs) and cluster outskirts are relatively weak with Mach number M ${\lesssim}$ a few. At such weak shocks, it has been believed that the diffusive shock acceleration (DSA) of cosmic rays is rather inefficient. Yet, the presence of nonthermal phenomena, such as radio halos and relics, suggests that contrary to the expectation, DSA as well as magnetic field amplification should operate at weak shocks in cluster environments. We recently initiated a study of weak, collisionless, astrophysical shocks using a PIC(Particle-in-Cell) code. The PIC code describes the motion of electron and ion particles under the electromagnetic field which is represented in grid zones. Here, we present a preliminary work of one-dimensional simulations. We show how shocks are set up as the turbulent electromagnetic field is developed in the shock transition layer, and discuss the implication on DSA and magnetic field amplification.

• The Bulletin of The Korean Astronomical Society
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• v.34 no.1
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• pp.188.2-188.2
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• 2009

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.423-427
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• 2015

Recognition of the role of radio galaxies in the universe has been increasing in recent years. Their colossal energy output over huge volumes is now widely believed to play a key role not only in the formation of galaxies and their supermassive black holes, but also in the evolution of clusters of galaxies and, possibly, the cosmic web itself. In this regard, we need to understand the inflation of radio bubbles in the hot gas atmospheres of clusters and the importance of the role that radio galaxies play in the overall energy budget of the intracluster medium. Here, we present results from X-ray and radio band observations of the hot gas atmospheres of powerful, nearby radio galaxies in poor clusters.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.64-64
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• 2012

Supernova remnants (SNRs) are beautiful and diverse. Individual SNRs have their own distinctive features. The morphology and physical characteristics of young SNRs result from the interaction of supernova (SN) ejecta with circumstellar medium, while those of old SNRs result from the interaction of SN blast wave with the interstellar medium. The diversity of SNRs reflects different types of SN and the broad physical conditions in their environments, which are ultimately related to the formation and evolutionary history of progenitor stars. The importance of SNe and SNRs as the sources of heavy elements, cosmic rays, dusts, hot coronal gases, and interstellar turbulences depends on their types and environments. In this talk, I discuss the connections among SNRs, SNe, and their progenitors, and the consequences on the characteristics and astrophysical roles of SNRs.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.78.1-78.1
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• 2011

현재 국내에는 약 30여 개의 종합(관측실과 투영관이 있는) 천문시설이 운영 중에 있으며 매년 2-3개의 시설이 추가로 건설 되고 있다. 대부분의 천문시설에서는 별자리 설명, 천체투영관에서의 영상물 상영, 그리고 천체망원경을 이용한 관측실습 등 한정된 소재와 일관된 형식의 천문교육 프로그램을 운영 하고 있다. 하지만 천문학은 일반 대중들이 많은 흥미와 관심을 가지는 분야이기 때문에 여러 가지 다양한 소재와 형식의 교육프로그램 및 콘텐츠 개발이 필요하다. 특히 최근 언론에 자주 등장하는 UFO, 황도 13궁, 태양 폭발, 우주선(Cosmic Rays)이 지구에 미치는 영향 등의 소재들은 일반인들이 잘못된 개념을 가지기 쉬운 분야이기 때문에 여기에 대한 올바른 과학내용을 일반인들이 이해하기 쉽도록 전달하는 것이 필요하다. 교육 콘텐츠는 디지털 천체투영기를 이용한 스크립트 프로그램 개발, 관측실습 전 후의 이론 교육 등 다양한 형태가 될 수 있다. 각 천문시설 운영자들이 직접 다양한 교육 콘텐츠를 개발하는 데에는 한계가 있으므로 기관협력체나 천문연구원 등의 체계적인 천문교육 콘텐츠 개발 및 보급이 절실하다.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.45.1-45.1
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• 2011

Shock waves form in the intergalactic medium as a consequence of accretion, merger, and turbulent motion during the structure formation of the universe. They not only heat gas but also govern non-thermal processes through the acceleration of cosmic rays (CRs), production of magnetic fields, and generation of vorticity. We examine diffusive shock acceleration of the pre-existing as well as freshly injected populations of nonthermal, CR particles at weak cosmological shocks. Since the injection is extremely inefficient at weak shocks, the pre-existing CR population dominates over the injected population. If the pressure due to pre-existing CR protons is about 5 % of the gas thermal pressure in the upstream flow, the downstream CR pressure can absorb typically a few to 10 % of the shock ram pressure at shocks with the Mach number M<3. Yet, the re-acceleration of CR electrons can result in a substantial synchrotron emission behind the shock. The implication of our findings for observed bright radio relics is discussed.

• Journal of Radiation Industry
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• v.4 no.3
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• pp.285-288
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• 2010

Polyimide films have excellent thermal stability, reliable mechanical properties and low dielectric constant. Therefore, this material is widely used in many industrial fields such as microelectronics, flexible circuits, semiconductor products and aerospace materials. In space applications, earth-orbiting hardware operates in environments that generally include neutral particles, charged particles such as trapped protons and electrons, solar protons, and cosmic rays. Under these conditions, polyimide films were changed in the optical, electrical and mechanical properties. Therefore, in this study, we evaluated the effects of electron beam irradiation on polyimide. The O-H functional groups were created on the polyimide film surface in the results of FT-IR spectra. And it was found that the dielectric constants were changed as a function of electron beam dose.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.39.2-39.2
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• 2021

To investigate the acceleration of ultra-high energy cosmic rays (UHECRs) in relativistic jets of FR-II galaxies, we simulate high-power jets with jet powers of Q~10^46erg/s in a stratified galaxy cluster halo using a state-of-art relativistic hydrodynamic (RHD) code we have recently developed. With the simulated jet-induced flow profiles, we then perform Monte-Carlo simulations, where the transport of high-energy particles is followed assuming large-angle scatterings in the flow-rest frame. We estimate the energy gains and acceleration times in the acceleration processes by shocks, shear, and turbulence. We present the results and discuss implications on the acceleration of UHECRs in FR II radio jets.

• Journal of the Korean Geographical Society
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• v.38 no.3
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• pp.389-399
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• 2003

CRN (Cosmogenic radionuclide) methodology has been a versatile tool applicable to a wide range of geomorphology. This study was underiaken to ascertain the rate of erosion and exposure age of mountain-top detritus (tors and block streams) on Mt. Maneo by employing the concentrations of in-situ produced cosmogenic $^{10}$ Be and $^{26}$ Al from bedrock surfaces that are exposed to cosmic rays. The results suggest that tors on the summit were positioned here during the glacial period but no later than 65ka and block streams have been stabilized also since the last glacial period but no later than 38ka. The tors on the summit have been eroded at a slower rate (9m/Ma) than blocks on the hillslope (15m/Ma) since the initial abrupt exposure of each landform to cosmic rays, suggesting that there is a slight difference in the rate of erosion between the summit and the hillslope, and that the local relief between the two areas has been increased. When the $^{26}$ Al/$^{10}$ Be-$^{10}$ Be concentrations from samples are plotted in Lal's steady-state erosion island, one sample (from a for) has complex exposure histories, which can be explained by the occurrence of multiple chipping event of 5cm to 60cm in length on the surface of the rock.