• Journal of Radiation Protection and Research
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• 제42권1호
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• pp.26-32
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• 2017

Background: Ionizing radiation is known to be harmful to human health. The shielding of ionizing radiation depends on the attenuation which can be achieved by three main rules, i.e. time, distance and absorbing material. Materials and Methods: The mass attenuation coefficient, linear attenuation coefficient, Half Value Layer (HVL) and Tenth Value Layer (TVL) of X-rays (32 keV, 74 keV) and gamma rays (662 keV) are measured in Barium compounds. Results and Discussion: The measured values agree well with the theory. The effective atomic numbers ($Z_{eff}$) and electron density (Ne) of Barium compounds have been computed in the wide energy region 1 keV to 100 GeV using an accurate database of photon-interaction cross sections and the WinXCom program. Conclusion: The mass attenuation coefficient and linear attenuation coefficient for $BaCO_3$ is higher than the $BaCl_2$, $Ba(No_3)_2$ and BaSO4. HVL, TVL and mean free path are lower for $BaCO_3$ than the $BaCl_2$, $Ba(No_3)_2$ and $BaSO_4$. Among the studied barium compounds, $BaCO_3$ is best material for x-ray and gamma shielding.

• Nuclear Engineering and Technology
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• 제36권1호
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• pp.1-11
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• 2004

Two approximate methods for a cosmic radiation shielding calculation in low earth orbits were developed and assessed. Those are a sectoring method and a chord-length distribution method. In order to simulate a change in cosmic radiation environments along the satellite mission trajectory, IGRF model and AP(E)-8 model were used. When the approximate methods were applied, the geometrical model of satellite structure was approximated as one-dimensional slabs, and a pre-calculated dose-depth conversion function was introduced to simplify the dose calculation process. Verification was performed with mission data of KITSAT-1 and the calculated results were also compared with detailed 3-dimensional calculation results using Monte Carlo calculation. Dose results from the approximate methods were conservatively higher than Monte Carlo results, but were lower than experimental data in total dose rate. Differences between calculation and experimental data seem to come from the AP-8 model, for which it is reported that fluxes of proton are underestimated. We confirmed that the developed approximate method can be applied to commercial satellite shielding calculations. It is also found that commercial products of semi-conductors can be damaged due to total ionizing dose under LEO radiation environment. An intensive shielding analysis should be taken into account when commercial devices are used.

• 방사선산업학회지
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• 제5권1호
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• pp.1-5
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• 2011

Since proteomics can be employed to compare changes in the expression levels of many proteins under particular genetic and environmental conditions, using mass spectrometry to establish radiation stimulon, we performed two-dimensional gel electrophoresis and identified E. coli proteins whose expressions are affected by high dose of ionizing radiation. After exposure to 3 kGy, it was found that 6 proteins involved in carbon and energy metabolism were reduced. Although 4 of 7 protein spots showing a significant increase in expression level were neither identified nor classified, uridine phosphorylase (Udp), superoxide dismutase (SodB), and thioredoxin-dependent thiol peroxidase (Bcp) were proven to be up-regulated after irradiation. This suggests that E. coli subjected to high doses of radiation (3 kGy) may operate a defense system that is able to detoxify reactive oxygen species and stimulate the salvage pathway of nucleotide synthesis to replenish damaged DNA.

• 천문학회보
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• 제44권1호
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• pp.75.1-75.1
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• 2019

The universe has been ionized in the post-reionization by several photon contributors. The dominant source to produce the hydrogen ionizing photons is not revealed so far. Faint quasars have been expected to generate UV photon budgets required to maintain ionization state of universe. Observational limits, however, hinder to discover them despite their higher number density than bright one. Consequently, the influence of faint quasars on post-reionization are not considered sufficiently. Therefore, a survey to find faint quasars at z ~ 5 is crucial to determine the main ionizing source in the post-reionization era. Deep images from the Hyper Suprime-Cam Subaru Strategic Program (HSC SSP) allow us to search for quasar swith low luminosities in the ELAIS-N1 field. J band information are obtained by the Infrared Medium-deep Survey (IMS) and the UKIRT Infrared Deep Sky Survey (UKIDSS) - Deep ExtragalacticSurvey (DXS). Faint quasar candidates were selected from several multi-band color cut criteria based on simulated quasars on color-color diagram. To choose the reliable candidates with possible Lyman break, we have performed medium-bands observations. Whether a candidate is a quasar or a dwarf star contamination was decided by results from chi-square minimization of quasar/dwarf model fitting. Spectroscopic follow-up observations confirm three quasars at z ~ 5. 100% spectral confirmation success rate implies that the medium-band observations effectively select faint quasars with strong Lyman alpha emission.

• 대한의생명과학회지
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• 제26권4호
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• pp.249-255
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• 2020

Radiation therapy is one of the primary options for the treatment of malignant tumors. Even though it is an effective anti-cancer treatment, it can cause serious complications owing to radiation-induced damage to the normal tissue around the tumor. It was recently reported that normal stem cell response to the genotoxic stress of ionizing radiation can boost the therapeutic effectiveness of radiation by repairing damaged cells. Therefore, we focused on annexin A-1 (ANXA1), one of the genes induced by low-dose irradiation, and assessed whether it can protect adipose-derived stem cells (ADSCs) against oxidative stress-induced damage caused by low-dose irradiation and improve effectively cell survival. After confirming ANXA1 expression in ADSCs transfected with an ANXA1 expression vector, exposure to hydrogen peroxide (H2O2) was used to mimic cellular damage induced by a chronic oxidative environment to assess cell survival under oxidative conditions. ANXA1-transfected ADSCs demonstrated that increased viability compared with un-transfected cells and exhibited enhanced anti-oxidative properties. Taken together, these results suggest that ANXA1 could be used as a potential therapeutic target to improve the survival of stem cells after low-dose radiation treatment.

• Journal of Astronomy and Space Sciences
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• 제39권2호
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• pp.51-57
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• 2022

Cosmic radiation exposure of the flight crews in Korea has been managed by Radiation Safety Management around Living Life Act under Nuclear Safety and Security Commission. However, the domestic flight crews are excluded from the Act because of relatively low route dose exposure compared to that of international flight crews. But we found that the accumulated total annual dose of domestic flight crews is far from negligible because of relatively long total flight time and too many flights. In this study, to suggest the necessity of management of domestic flight crews' radiation exposure, we statistically analyzed domestic flight crew's accumulative annual dose by using cosmic radiation estimation models of the Civil Aviation Research Institute (CARI)-6M, Nowcast of Atmospheric Ionizing Radiation for Aviation Safety (NAIRAS), and Korean Radiation Exposure Assessment Model (KREAM) and compared with in-situ measurements of Liulin-6K LET spectrometer. As a result, the average exposure dose of domestic flight crews was found to be 0.5-0.8 mSv. We also expect that our result might provide the basis to include the domestic flight crews as radiation workers, not just international flight attendants.

• 한국시뮬레이션학회논문지
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• 제19권4호
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• pp.123-128
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• 2010

본 논문에서는 우주방사능 환경에서 우주방사능/총 누적 방사선량(TID) 및 이에 대한 시스템 영향과 정지궤도 위성 시스템 설계를 Spenvis 를 사용하여 분석하였다. 우주환경에서 정지궤도 위성 시스템이 겪게 될 우주방사선 환경을 포획된 입자, 태양 양성자 그리고 우주선으로 구분하여 각각 NASA AP8, JPL91 그리고 NRL CREME 모델을 사용하여 전산모사하였다. 임무수명기간 동안 전자부품에 계속적으로 피폭되는 전체 방사량을 알루미늄 차단두께의 함수로 나타내었으며, 이 값들은 디지털채널 처리부의 전자부품의 선택기준 및 위성체 또는 구성품의 구조물 두께를 설정할 수 있는 기준으로 제시한다.

• 한국환경보건학회지
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• 제49권1호
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• pp.1-10
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• 2023

Low-dose radiation exposure has received considerable attention because it reflects the general public's type and level of exposure. Still, controversy remains due to the relatively unclear results and uncertainty in risk estimation compared to high-dose radiation. However, recent epidemiological studies report direct evidence of health effects for various types of low-dose radiation exposure. In particular, international nuclear workers' studies, CT exposure studies, and children's cancer studies on natural radiation showed significantly increased cancer risk among the study populations despite their low-dose radiation exposure. These studies showed similar results even when the cumulative radiation dose was limited to an exposure group of less than 100 mGy, demonstrating that the observed excess risk was not affected by high exposure. A linear dose-response relationship between radiation exposure and cancer incidence has been observed, even at the low-dose interval. These recent epidemiological studies include relatively large populations, and findings are broadly consistent with previous studies on Japanese atomic bomb survivors. However, the health effects of low-dose radiation are assumed to be small compared to the risks that may arise from other lifestyle factors; therefore, the benefits of radiation use should be considered at the individual level through a balanced interpretation. Further low-dose radiation studies are essential to accurately determining the benefits and risks of radiation.

• Nuclear Engineering and Technology
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• 제54권12호
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• pp.4422-4430
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• 2022

Studying the effects of gamma radiation on the instrumentation and control (I&C) system of a nuclear power plant is critical to the successful and reliable operation of the plant. In the accidental scenario, the adverse environment of ionizing radiation affects the performance of the I&C system and it leads to inaccurate and incomprehensible results. This paper reports the effects of gamma radiation on the AT89C51RD2, a commercial-off-the-shelf 8-bit high-performance flash microcontroller. The microcontroller, selected for the device under test for this study is used in the remote terminal unit for a nuclear power plant. The custom circuits were made to test the microcontroller under different gamma doses using a ⁶⁰Co gamma source in both ex-situ and in-situ modes. The device was exposed to a maximum dose of 1.5 kGy. Under this hostile environment, the performance of the microcontroller was studied in terms of device current and voltage changes. It was observed that the microcontroller device can operate up to a total absorbed dose of approximately 0.6 kGy without any failure or degradation in its performance.

• 천문학회보
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• 제44권2호
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• pp.73.2-73.2
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• 2019

The physical origin of low escape fractions of ionizing radiation derived from Lyman-break galaxies (LBGs) at z ~ 3 - 4 is a puzzle in the theory of reionization. We perform idealized disk galaxy simulations to investigate how galactic properties, such as metallicity and gas mass, affect the escape of Lyman continuum (LyC) photons using radiation-hydrodynamic code RAMSES-RT, with strong stellar feedback. We find that the luminosity-weighted escape fraction from a metal-poor (Z=0.002) galaxy embedded in a halo of mass M_h ~ 10¹¹ M_⊙ is 〈f^3D_esc〉 ~ 8%. However, when the gas metallicity is increased to Z=0.02, the escape fraction is significantly reduced to 〈f^3D_esc〉 ~ 1%, as young stars are enshrouded by their birth clouds for a longer period of time. On the other hand, increasing the gas mass by a factor of 5 leads to 〈f^3D_esc〉 ~ 4%, as LyC photons are only moderately absorbed by the thicker disk. Our experiments seem to suggest that high metallicity is primarily responsible for the low escape fractions observed from LBGs, supporting the scenario in which the escape fraction has a negative correlation with halo mass. Indeed, our simulated galaxy with the typical metallicity of LBGs (Z=0.006) shows the relative escape fraction of 8%, consistent with recent observations of galaxies with M₁₅₀₀ = -20.