• Journal of Astronomy and Space Sciences
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• 제41권3호
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• pp.195-208
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• 2024

As human exploration goals shift from missions in low Earth orbit (LEO) to long-duration interplanetary missions, radiation protection remains one of the key technological issues that must be resolved. The low Earth orbit space radiation dosimeter (LEO-DOS) instrument to measure radiation levels and create a global dose map in the LEO on board the the next generation small satellite-2 (NEXTSat-2) was launched successfully on May 25, 2023 using the Nuri KSLV-III in Korea. The NEXTSat-2 orbits the Earth every 100 minutes, in an orbit with an inclination of 97.8° and an altitude of about 550 km above sea level. The LEO-DOS is equipped with a particle dosimeter (PD) and a neutron spectrometer (NS), which enable the measurement of dosimetric quantities such as absorbed dose (D), dose equivalent (H) for charged particles and neutrons. To verify the observations of LEO-DOS, we conducted a radiation dose estimation study based on the initial results of LEO-DOS, measured from June 2023 to September 2023. The study considered four source categories: (i) galactic cosmic ray particles; (ii) the South Atlantic Anomaly region of the inner radiation belt (IRB); (iii) relativistic electrons and/or bremsstrahlung in the outer radiation belt (ORB); and (iv) solar energetic particle (SEP) events.

• Journal of the Korean Physical Society
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• 제80권
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• pp.1-12
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• 2022

Over the past few decades, tetrafluoroethane (TFE, R134a Freon)-based gases have been widely used in the operation of phenolic resistive plate chambers (RPCs) in many high-energy experiments. However, TFE has a high global warming potential (GWP); therefore, a search for new eco-friendly gases to replace traditional TFE-based ones is now unavoidable. In this research, we present cosmic-ray test results of a prototype RPC for the SHiP (search for hidden particles) experiment using 1.6- and 1.4-mm-thick RPC electrodes containing mixtures of various gases, including 1,3,3,3-tetrafluoropropene (HFO1234ze), CO₂, iC₄H₁₀ and SF₆. We compare the performance data gathered with these new gas mixtures with those gathered with a traditional TFE-based gas used for RPCs in compact muon solenoid (CMS) and a toroidal LHC apparatus (ATLAS) experiments. The addition of CO₂ to the HFO1234ze-based gas was found to be fairly effective in reducing the working-point high voltage (HVWP) for RPC operation. The results of our experiments lead us to the conclusion that adding 40% CO₂ or less, when combined with HFO1234ze-based gas, is conducive to reliable detector performance for SHiP single-gap phenolic RPCs.

• Journal of Astronomy and Space Sciences
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• 제36권1호
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• pp.21-33
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• 2019

This paper focuses on the interpretation of radiation fluxes from active galactic nuclei. The advantage of positron annihilation spectroscopy over other methods of spectral diagnostics of active galactic nuclei (therefore AGN) is demonstrated. A relationship between regular and random components in both bolometric and spectral composition of fluxes of quanta and particles generated in AGN is found. We consider their diffuse component separately and also detect radiative feedback after the passage of high-velocity cosmic rays and hard quanta through gas-and-dust aggregates surrounding massive black holes in AGN. The motion of relativistic positrons and electrons in such complex systems produces secondary radiation throughout the whole investigated region of active galactic nuclei in form of cylinder with radius R= 400-1000 pc and height H=200-400 pc, thus causing their visible luminescence across all spectral bands. We obtain radiation and electron energy distribution functions depending on the spatial distribution of the investigated bulk of matter in AGN. Radiation luminescence of the non-central part of AGN is a response to the effects of particles and quanta falling from its center created by atoms, molecules and dust of its diffuse component. The cross-sections for the single-photon annihilation of positrons of different energies with atoms in these active galactic nuclei are determined. For the first time we use the data on the change in chemical composition due to spallation reactions induced by high-energy particles. We establish or define more accurately how the energies of the incident positron, emitted ${\gamma}-quantum$ and recoiling nucleus correlate with the atomic number and weight of the target nucleus. For light elements, we provide detailed tables of all indicated parameters. A new criterion is proposed, based on the use of the ratio of the fluxes of ${\gamma}-quanta$ formed in one- and two-photon annihilation of positrons in a diffuse medium. It is concluded that, as is the case in young supernova remnants, the two-photon annihilation tends to occur in solid-state grains as a result of active loss of kinetic energy of positrons due to ionisation down to thermal energy of free electrons. The single-photon annihilation of positrons manifests itself in the gas component of active galactic nuclei. Such annihilation occurs as interaction between positrons and K-shell electrons; hence, it is suitable for identification of the chemical state of substances comprising the gas component of the investigated media. Specific physical media producing high fluxes of positrons are discussed; it allowed a significant reduction in the number of reaction channels generating positrons. We estimate the brightness distribution in the ${\gamma}-ray$ spectra of the gas-and-dust media through which positron fluxes travel with the energy range similar to that recorded by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) research module. Based on the results of our calculations, we analyse the reasons for such a high power of positrons to penetrate through gas-and-dust aggregates. The energy loss of positrons by ionisation is compared to the production of secondary positrons by high-energy cosmic rays in order to determine the depth of their penetration into gas-and-dust aggregations clustered in active galactic nuclei. The relationship between the energy of ${\gamma}-quanta$ emitted upon the single-photon annihilation and the energy of incident electrons is established. The obtained cross sections for positron interactions with bound electrons of the diffuse component of the non-central, peripheral AGN regions allowed us to obtain new spectroscopic characteristics of the atoms involved in single-photon annihilation.

• Journal of Astronomy and Space Sciences
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• 제22권4호
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• pp.385-392
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• 2005

천구상에서 빠르게 움직이는 인공위성, 우주잔해물 및 빠른 속도의 지구접근천체 등과 같은 고속이동천체들은 별들을 추적하며 관측한 영상에서 선 형태의 궤적으로 나타나게 된다. 이 논문에서는 이러한 궤적을 검출해내기 위해 개발한 궤적탐지 알고리즘에 대한 소개와, 개발된 알고리즘을 이용한 YSTAR-NEOPAT 영상분석결과에 대해 기술하였다. 알고리즘은 기본적으로 외곽선 추적방법을 이용하였으며, 벌들이 밀집한 곳에서의 검출효율을 높이기 위해 차감영상기법을 사용하였다. 알고리즘의 수행속도 테스트 결과, 궤적탐지에 소요되는 시간은 1초 미만으로 대용량 자료의 실시간 분석에도 사용이 가능한 것으로 나타났다. 또한, 검출 결과를 GIF 영상으로 저장함으로써, 눈으로 직접 확인할 수 있도록 하였다. 총 7,000여 장의 YSTAR-NEOPAT 영상을 분석한 결과, 약 700개의 궤적을 발견하였으며 발견된 궤적들 중 고속이동천체는 시계열 영상에서 여러 장에 걸쳐 연속적으로 나타나는 특성을 이용하여 기타 다른 궤적들과 구별해 낼 수 있었다. 이렇게 발견된 고속이동천체는 모두 인공위성 혹은 우주잔해물인 것으로 나타났으며, 기타 궤적들은 우주선 및 유성인 것으로 분류되었다.

• 한국지역지리학회지
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• 제18권3호
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• pp.253-267
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• 2012

본 연구는 무등산에 분포하는 암괴류의 유형과 특징을 파악하고자 하였다. 무등산의 암설지형은 암괴노출형, 노출혼합형, 거력잠재형, 기후단구 노출혼합형으로 분류할 수 있으며, 암괴노출형의 대부분은 암괴류의 형태를 보인다. 암설지대 암괴의 공급은 암질에 따라 다른 양상을 보이고 있다. 안산암질이 우세한 암설은 암설지대 상부의 주상절리 또는 단애에서 암괴의 이동이 있었을 것으로 판단되고. 화강암질은 심층풍화된 암괴가 사면이동하였던 것으로 추정된다. 암괴의 이동방식은 암괴의 낙하보다는 미끄러짐이 우세했던 것으로 추론된다. 그 이유는 단애와 암설지대 사이에 $10^{\circ}$ 내외의 완만한 사면에서 암괴의 장거리 이동이 불가능하고, 거력을 이동시킬만한 수류가 없고, 암설의 장축 방향성은 사면 최대경사방향과 일치하기 때문이다. 화강암과 안산암질 암설이 만나는 지역에서는 화강암이 하부에 안산암질이 상부에 있으며, 솔리플럭션과 동결포행이 활발한 시기에 화강암질 매트릭스가 평탄성이 현저한 사면을 형성한 후 안산암질 거력이 그 위를 덮었을 것으로 판단된다. 현재 기후환경을 고려할 때 무등산 암설지대의 암괴는 이동이 거의 없다. 우주기원 동위원소 36Cl 연대측정 결과로 추론할 때, 최소 50,000년 전 암괴가 단애로부터 떨어져 나와 하부에 이동되었음을 의미하고 있다. 상부는 각력이 우세하고, 하부는 원마도가 좀 더 높은 아원력이 우세한 점을 고려할 때, 암설은 상부에서 하부로 이동되어졌을 것으로 추론되며, 노출연대를 고려했을 때, 안정화된 화석지형이라고 추정된다.