• Nuclear Engineering and Technology
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• 제56권10호
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• pp.3993-4006
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• 2024

Compton imaging excels at visualizing gamma rays in the range of several hundred kiloelectronvolts to several megaelectronvolts. However, this technique has limitations in the imaging of low-energy gamma rays. In contrast, collimatorless imaging technique determines the location of a source by analyzing the distribution of interactions. Because the collimatorless imaging technique excels at imaging low-energy gamma rays that are easily shielded by detector components, it can compensate for the shortcomings of the Compton imaging technique. In this study, we propose a dual-mode imaging technique that selects the imaging method depending on the target gamma-ray energy and fuses them during reconstruction. The collimatorless imaging method demonstrated high angular resolution at low energy levels, whereas the Compton image surpasses it starting from 200 keV within its reconstructible range. The angular resolution of the dual-mode image was between those of the two methods. The trend of the positional error of gamma ray energy was similar to that of the angular resolution, and the dual-mode method exhibited the lowest average error of 0.7°. The dual imaging method exhibited higher efficiency, figure of merit, and signal-to-noise ratio by utilizing events from both imaging modalities. In addition, we investigated the geometrical effects of various structures.

• Journal of Radiation Protection and Research
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• 제43권2호
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• pp.39-49
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• 2018

Background: A model to assess the activity concentration of agricultural products and the public ingestion dose as result of a nuclear accident is necessarily required to manage the contaminated agricultural systems by the accident, or to estimate the effects of chronic exposure due to food ingestion at a Level 3 PSA. Materials and Methods: A dynamic compartment model, which is composed of three sub-modules, namely, an agricultural plant contamination assessment model, an animal product contamination assessment model, and an ingestion dose assessment model has been developed based on Korean farming characteristics such as the growth characteristics of rice and stockbreeding. Results and Discussion: The application study showed that the present model can predict well the characteristics of the activity concentration for agricultural products and ingestion dose depending on the deposition date. Conclusion: The present model is very useful to predict the radioactivity concentration of agricultural foodstuffs and public ingestion dose as consequence of a nuclear accident. Consequently, it is expected to be used effectively as a module for the ingestion dose calculation of the Korean agricultural contamination management system as well as the Level 3 PSA code, which is currently being developed.

• 대한환경공학회지
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• 제39권7호
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• pp.385-390
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• 2017

응집 침전기술인 방사능 오염물질의 처리장치의 용존성 Cs 처리특성을 평가하였다. 방사능 오염물질 처리장치는 전흡착부, 고형물침전부, 후흡착부로 구성하였다. 흡착제는 천연광물 일라이트를 입자크기에 따라 LPI (Large Particle Illite), SPI (Small Particle Illite)로 구분하여 사용하였고, 응집제는 고염기도 PAC (poly aluminum chloride)을 사용하였다. 흡착제는 판상구조형태로 주로 석영, 조장석, 백운모로 구성되었으며, LPI, SPI의 Surface area는 각각 $4.201m^2/g$, $4.227m^2/g$으로 나타났고 입자크기는 각각 $197.4-840.9{\mu}m$, $3.28-53.57{\mu}m$로 나타났다. 천연광물인 일라이트의 흡착효율은 LPI는 82.8%, SPI는 85.6%로 나타났고 흡착제 회수에 대한 간접적인 지표인 탁도의 제거율은 96.4%, 98.3%로 나타났다.

• 한국환경농학회지
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• 제7권1호
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• pp.1-7
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• 1988

토양중(土壤中)에 존재(存在)하는 제초제(除草劑) Bentazon 잔류량(殘留量)이 농작물(農作物)에 의하여 어느 정도 흡수(吸收)되는지를 구명(究明)하기 위하여 $^{14}C-Bentazon$을 재배(栽培) 직전(直前)에 처리(處理)한 토양(Fresh Bentazon 토양)과 추출(抽出)이 불가능(不可能)한 토양흡착(土壤吸着) 잔류물(殘留物)함 형태(形態)의 $^{14}C-Bentazon$을 함유한 토양(Bound Bentazon 토양)에 콩과 무우를 심고 28일간 생육(生育)시켜 다음과 같은 결과를 얻었다. 1. $^{14}C-Bentazon$을 토양에 처리하고 6개월 동안 전배양(前培養(pre-incubation))하는 동안 발생된 총 $^{14}CO_2$량(量)은 처리 방사능의 14.79% 이었다. 2. 28일간 작물(作物)을 재배하는 동안 토양 중의 $^{14}C-Bentazon$이 $^{14}CO_2$로 무기화(無機化)되는 량(量)은 Bound Bentazon 토양보다 Fresh Bentazon토양에서 훨씬 많았으며 콩에서보다 무우에 있어서 훨씬 많았다. 3. 콩과 무우에 의하여 흡수된 $^{14}C-Bentazon$ 및 그 대사산물의 량(量)은 Fresh Bentazon 토양에서 각각 45.41%와 21.48%이었으며 Bound Bentazon 토양에서는 각각 3.92%와 1.23%이 었다. 흡수(吸收)된 방사능(放射能)이 뿌리로부터 지상부(地上部)로 이행(移行)되는 비률(比率)은 콩에서보다 무우에 있어서 훨씬 높았다. 4. 콩과 무우에 의하여 흡수(吸收)된 Fresh Bentazon 대(對) Bound Bentazon의 비율은 각각 12 : 1과 17 : 1 이었다. 5. 작물(作物)의 존재(存在)는 $^{14}C-Bentazon$의 $^{14}CO_2$로의 무기화(無機化)와 극성대사산물(極性代謝産物)로의 변화를 증진(增進)시킴이 입증(立證)되었다.

• Environmental Analysis Health and Toxicology
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• 제31권
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• pp.1.1-1.13
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• 2016

Objectives To investigate the accuracy and scientific validity of the current very low risk factor for hereditary diseases in humans following exposures to ionizing radiation adopted by the United Nations Scientific Committee on the Effects of Atomic Radiation and the International Commission on Radiological Protection. The value is based on experiments on mice due to reportedly absent effects in the Japanese atomic bomb (A-bomb) survivors. Methods To review the published evidence for heritable effects after ionising radiation exposures particularly, but not restricted to, populations exposed to contamination from the Chernobyl accident and from atmospheric nuclear test fallout. To make a compilation of findings about early deaths, congenital malformations, Down's syndrome, cancer and other genetic effects observed in humans after the exposure of the parents. To also examine more closely the evidence from the Japanese A-bomb epidemiology and discuss its scientific validity. Results Nearly all types of hereditary defects were found at doses as low as one to 10 mSv. We discuss the clash between the current risk model and these observations on the basis of biological mechanism and assumptions about linear relationships between dose and effect in neonatal and foetal epidemiology. The evidence supports a dose response relationship which is non-linear and is either biphasic or supralinear (hogs-back) and largely either saturates or falls above 10 mSv. Conclusions We conclude that the current risk model for heritable effects of radiation is unsafe. The dose response relationship is non-linear with the greatest effects at the lowest doses. Using Chernobyl data we derive an excess relative risk for all malformations of 1.0 per 10 mSv cumulative dose. The safety of the Japanese A-bomb epidemiology is argued to be both scientifically and philosophically questionable owing to errors in the choice of control groups, omission of internal exposure effects and assumptions about linear dose response.

• 분석과학
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• 제13권6호
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• pp.743-750
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• 2000

라듐 및 라돈과 같은 환경 방사성 핵종의 분석 방법 중 HPGe 검출기를 이용한 감마선 분광 분석법은 대부분 플라스틱 용기를 많이 이용하고 있다. 그러나 플라스틱 용기는 대기 중 라돈 딸 핵종의 흡착에 의해 백그라운드가 증가할 뿐만 아니라 방사 평형 과정에서 생성된 기체 상의 라돈의 손실에 의하여 완전한 방사 평형에 도달하지 않는다는 것이다. 이러한 문제점을 해결하기 위하여 알루미늄 재질의 측정 용기를 제작하였고, 그 특성을 조사하였다. 알루미늄 용기를 이용하여 방사 평형 과정을 조사한 결과, 고체 및 액체 시료 모두 기체 상태의 라돈 손실 없이 라듐과 그 딸핵종들이 측정 용기 안에서 완전한 방사 평형에 도달하는 것을 알았다. 또한 감마선 분광 분석법을 이용한 고체 및 액체 시료 중의 라듐 및 라돈의 비파괴 분석이 가능함을 확인하였다.

• Nuclear Engineering and Technology
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• 제52권10호
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• pp.2370-2378
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• 2020

Building materials contribute significantly to the indoor radon and thoron levels. Therefore, parameters that influence the exhalation rates of radon and thoron from building material need to be analyzed closely. As a preliminary study, the effects of humidity on exhalation rates were measured using a system with an accumulation chamber and RAD7 detector for Korean brick, Korean soil, and Indonesian brick. Resulting doses to a person who resides in a room constructed from the building materials were assessed by UNSCEAR method for different air exchange rates. The measurements have revealed that Korean brick exhaled the highest radon and thoron while Indonesian brick exhaled the lowest thoron. Results showed that for a typical low dense material, radon and thoron exhalation rate will increase until reached its maximum at a certain value of humidity and will remain saturated above it. Analysis on concentration and effective dose showed that radon is strongly affected by air exchange rate (ACH). This is showed by about 66 times decrease of radon dose from 0.00 h^-1 to those of 0.50 h^-1 ACH and decrease by a factor of 2 from 0.50 h^-1 to those of 0.80 h^-1. In case of thoron, the ACH doesn't have significant effects on effective dose.

• 대한방사선기술학회지:방사선기술과학
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• 제40권4호
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• pp.633-638
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• 2017

방사선 진료기술의 발전에 따라 의료분야에서 발생하는 방사성폐기물이 급속히 증가하고 있다. 최근의 경향을 보면, 갑상선암 진료 목적의 I-131을 비롯하여 PET/CT 조영제로 사용하는 F-18, 핵의학검사에 폭 넓게 적용하는 Tc-99m 등의 방사성동위원소 사용이 일반화 되고 있다. 사용과정에서 이러한 핵종에 오염된 방사성폐기물이 발생하게 되는데, 일정기간 보관한 후에 방사능이 규제해제(Clearance) 수준으로 감쇠하면 소각 등의 방법으로 자체처분하게 된다. 국제원자력기구(IAEA)에서는 $10{\mu}Sv/y$의 개인선량 및 1man-Sv/y의 집단선량과 함께 핵종별 농도에 근거하여 방사성폐기물의 규제해제기준을 제시하였다. 이 연구에서는 IAEA의 핵종별 방사능농도기준에 따른 규제해제 시점을 확인하기 위하여, Tc-99m과 방사화학상유사한 성질을 가지고 있는 Re-186 관련 방사성폐기물을 수집하여 방사능을 측정하였다. Re-186은 반감기가 3.8일로 방사성의약품으로는 비교적 길고, 베타선 및 감마선을 방출하여 방사성의약품 치료와 영상에 모두 사용된다. Re-186 사용과 관련하여 발생하는 오염된 일회용장갑(Poly Glove)의 방사능측정을 위하여 다중파고분석기(Multi Channel Analyzer; MCA)를 이용하였으며, 이를 위하여 표준물질을 제작하여 MCA를 교정한 이후 감마방사능 측정절차에 따라 수행하였다. 측정결과를 근거로 방사능 감쇠 유도식을 산출하여 이론식과 대비하여 고찰하였는바, Re-186 핵종의 유도반감기(3.6일)는 이론적 반감기(3.8일)에 비해 다소 짧은 것으로 나타났다. 따라서 측정결과에 근거한 유도반감기를 적용한다면, 다소 줄어든 기간 동안 Re-186 핵종 폐기물을 보관하였다가 자체처분을 할 수 있을 것으로 확인하였다. 이 연구 결과는 현재 추진하고 있는 국제표준화기구(International Organization for Standardization) 국제표준에 포함될 예정이다.

• 자원환경지질
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• 제30권6호
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• pp.587-601
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• 1997

This study had three purposes: (1) to investigate the enrichment levels and dispersion patterns of potentially toxic elements in the rock-soil-plant system; (2) to evaluate the uptake ratios of heavy metals from soils into plants and (3) to assess the chemical speciation of heavy metals in soils. Rock, surface soil and plant samples were collected in the Boeun area underlain by black shales of the Okchon Zone. These samples were analyzed for multi-elements using INAA, ICP-AES and AAS. The maximum abundance of U in black shales is 16 mg/kg and radioactivity counts up to 300 cpm. In particular, Mo, V, Ba, Cd, Pb and U are enriched in black shales. Most of soils derived from black shales show high concentrations of U, As, Mo, Ba, Cu, Cd, Pb, Zn and mean concentrations of As and Mo in soils (20 mg/kg of As and 6.6 mg/kg of Mo) are higher than the permissible level suggested by Kloke (1979). Enrichment index values of soils are calculated and higher than 1.0 in the black shale area with the highest value of 6.4. Mean concentration of Cd in plants is higher than those of Cu, Pb and Zn. The concentration of Cd in plant species decreases in the order of Chinese cabbage > red pepper > soybean=sesame > rice stalk > com > rice grain. The biological absorption coefficients (BAC) in plants are in the order of Cd > Zn=Cu > Pb, which suggests that Cd is more bioavailable to plants than Cu, Pb and Zn. From the results of sequential extraction analysis of soils, relatively high proportion of Cu, Pb and Zn are present as residual fractions whereas that of Cd as non-residual fractions. Cadmuim occurs predominantly as exchangeable/water-acid soluble phase in soils, and Cd is more mobile and bioavailable than Cu, Pb and Zn.

• 자원환경지질
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• 제29권4호
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• pp.495-508
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• 1996

This study had three purposes: (1) to investigate dispersion and enrichment level of potentially toxic elements; (2) to identify uranium-bearing minerals in black shales; and (3) to assess the chemical speciation of heavy metals in soils and sediments. Rock, surface soil and stream sediment samples were collected in the Chungjoo area covered with black shales in Korea. These samples were analyzed for multi-elements using INAA and ICP-AES. The maximum abundance of U in black shales is 56 ppm and radioactivity counts up to 240CPM. Molybdenum, V, Ba, Cu, and Pb are enriched in black shales and most of soils show high concentrations of U, Mo, Ba, Cu, Pb and Zn. Concentrations of potentially toxic elements decrease in the order of mountain soil > farmland soil > paddy soil. Enrichment index of soils and sediments are calculated and higher than 1.0 in the black shale area with the highest value of 6.1. In order to identify U-bearing minerals, electron probe micro analysis was applied, and uraninite and brannerite in black shale were found. Uraninite grains are closely associated with monazite or pyrite with the size of $2{\mu}m$ to $10{\mu}m$ in diameter whereas brannerite occurs as $50{\mu}m$ euhedral grains. With the results of sequential extraction scheme, residual fractions of Cu, Pb and Zn in soils are mainly derived from weathering of black shale but Cu, Pb and Zn in sediments are present as non-residual fractions. Lead is predominantly present as oxidizable phase in soils whereas Zn is in exchageable/water-acid soluble phase in sediments.