Radiological Characteristics of the Havar Foil in the Cyclotron Target

Dong gun Jang,Sang hwa Shin,Chang lak Kim,Gyeong hyeon Gwak2 한국방사성폐기물학회 2023 한국방사성폐기물학회 학술논문요약집 Vol.21 No.2

The cyclotron is an apparatus used for the production of radioactive isotopes through nuclear reactions, resulting in the inevitable emission of neutrons. Consequently, surrounding components become activated. The purpose of this study was to investigate the radiological characteristics of Havar foil, a periodic replacement part of the Targetry system. In this study, radioactivity and radiation dose were calculated based on the time of Havar foil replacement and equipment dismantling. The time to dismantle the equipment was set at one year after the equipment was shut down, based on the recently used 1g of Havar foil. All simulations were performed using the FLUKA program. First, in the simulation results, 11 elements (Re, W, Tc, Nb, Cu, Ni, Co, Fe, Mn, Cr, V) were converted into 36 radioisotopes by activation based on the replacement period. Based on radioactivity levels, major isotopes included 52Mn (77.63%), 56Co (13.36%), 96Tc (2.4%), and 95Tc (1.80%). Based on radiation dose rates, 52Mn (82.66%) and 56Co (13.45%) exhibited the highest levels. Furthermore, the dose rates at distances of 10 cm, 50 cm, and 100 cm were found to be 1.36E+1 mSv/hr, 2.24E+00 mSv/hr, and 8.80E-01 mSv/hr, respectively. Second, as of the time the equipment was dismantled, 20 radioactive isotopes of 10 elements, excluding short-lived nuclides, were generated. In terms of radioactivity, 56Co (45.83%), 55Fe (19.73%), 57Co (14.48%), and 54Mn (13.50%) were prominent. Regarding radiation dose rates, 56Co (92%) and 54Mn (7.32%) exhibited higher levels. Dose rates at distances of 10 cm, 50 cm, and 100 cm were calculated at 5.31E-01 mSv/hr, 8.80E-02 mSv/hr, and 3.47 E-02 mSv/hr, respectively. Third, according to the radioactive waste classification standards in the replacement and decommissioning stages, Havar foil was predicted to be low-level radioactive waste in terms of radioactivity. In addition, it was derived that a cooling period of approximately 12 years is necessary to satisfy the allowable dose for clearance level waste. In conclusion, Havar foil, which is periodically generated as radioactive waste, can cause radiation exposure to replacement workers. Therefore, special and careful management is required for the Havar foil of the cyclotron.

Silver nanoplate-pillared mesoporous nano-clays for surface enhanced raman scattering

Gyeong-Hyeon Gwak,Tetsuo Yamaguchi,Min-Kyu Kim,박진균,Jae-Min Oh 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.89 No.-

Due to characteristic properties of silver (Ag), Ag nanoparticles have attracted unprecedented attention invarious scientificfields such as sensors, catalysts, antibacterial materials, and so on. To obtain tailor-madefunctionalities of Ag nanoparticles with desired physicochemical properties, proper fabrication process isneeded to control their sizes, morphologies or arrangements by hybridization with different components,immobilization on solid struts, and etc. Herein, we suggest a facile synthetic route to obtain Ag-pillaredmesoporous nanoclays through simultaneous crystal growth and arrangement of Ag nanoplates with thehelp of a 2-dimensional inorganic template. To obtain Ag-pillars, layered silver-thiolate self-assemblywas exfoliated to monolayers (Ag precursor) and then in-situ hybridized with layered double hydroxidein a layer-by-layer manner. Through reductive calcination, silver thiolate transformed to Ag-pillars whichgrew in nanoplate morphology with well-arrangement in confined space of nanoclays. Crystal structure,morphology, and pore structure of Ag-pillars in nanoclays were systematically characterized. Surfaceenhanced Raman scattering effect of arranged Ag-pillars on metal oxide substrate obtained uponcalcination was also investigated with rhodamine 6 G.

Nanocomposites of Magnetite and Layered Double Hydroxide for Recyclable Chromate Removal

Gwak, Gyeong-Hyeon,Kim, Min-Kyu,Oh, Jae-Min Hindawi Limited 2016 Journal of nanomaterials Vol.2016 No.-

<P>Nanocomposites containing magnetic iron oxide (magnetite) nanoparticles and layered double hydroxide (LDH) nanosheets were prepared by two different methods, exfoliation-reassembly and coprecipitation, for aqueous chromate adsorbent. According to X-ray diffraction, scanning electron microscopy, and atomic force microscopy, both nanocomposites were determined to develop different nanostructures; LDH nanosheets well covered magnetite nanoparticles with house-of-cards-like structure in exfoliation-reassembly method, while coprecipitation resulted in LDH particle formation along with magnetite nanoparticles. Zeta-potential measurement also revealed that the magnetite surface was effectively covered by LDH moiety in exfoliation-reassembly compared with coprecipitation. Time, pH, concentration dependent chromate adsorption tests, and magnetic separation experiments exhibited that both nanocomposites effectively adsorb and easily collect chromate. However, exfoliation-reassembly nanocomposite was determined to be slightly effective in chromate removal by ~10%. Chromate adsorbed nanocomposites could be regenerated by treating with bicarbonate and the regenerated nanocomposites preserved ~80% of chromate adsorption efficacy after three times of recycling.</P>

Controlled Crystal Growth of Two-Dimensional Layered Nanomaterials in Hydrogel via a Modified Electrical Double Migration Method

Gwak, Gyeong-Hyeon,Kwon, Na Kyung,Lee, Won-Jae,Paek, Seung-Min,Kim, So Youn,Oh, Jae-Min The American Chemical Society 2017 CRYSTAL GROWTH AND DESIGN Vol.17 No.12

<P>Layered double hydroxide (LDH) nanomaterials of uniform size and homogeneous distribution are successfully developed in agarose hydrogel through the electrical double migration method. To grow LDH crystals in agarose matrix, both cationic (Ni<SUP>2+</SUP>, Ga<SUP>3+</SUP>) and anionic precursors (OH<SUP>–</SUP> and CO<SUB>3</SUB><SUP>2–</SUP>) of LDH are simultaneously transported from solution to agarose hydrogel through electric potential, resulting in the in situ crystal growth of LDH. X-ray diffraction patterns, X-ray absorption spectra, and high-resolution transmission electron microscopic images confirm that the developed LDH is ∼15 nm in size and had a well-defined crystal structure. Scanning electron microscopy and small-angle X-ray scattering spectroscopy showed homogeneous arrays of LDH nanocrystals along agarose sheets with homogeneous distribution. On the basis of the characterization results, we suggest that crystal nuclei are first developed on the agarose chain, and then LDHs homogeneously grow along sheets of agarose matrix.</P><P>Layered double hydroxides (LDHs) of uniform size and homogeneous distribution are developed in agarose hydrogel through the electrical double migration method. Developed LDH had a well-defined crystal structure and homogeneous arrays along agarose sheets with homogeneous distribution. Thus, we suggest that crystal nuclei are first developed on the agarose chain, and then LDHs homogeneously grow along sheets of agarose matrix.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cgdefu/2017/cgdefu.2017.17.issue-12/acs.cgd.7b01252/production/images/medium/cg-2017-01252b_0009.gif'></P>

의료용 소재를 위한 고분자-무기 하이브리드

곽경현(Gyeong Hyeon Gwak),오제민(Jae Min Oh),최진호(Jin Ho Choy) 한국고분자학회 2012 고분자 과학과 기술 Vol.23 No.3

Electrophoretic Preparation of an Organic–Inorganic Hybrid of Layered Metal Hydroxide and Hydrogel for a Potential Drug‐Delivery System

Gwak, Gyeong‐,Hyeon,Paek, Seung‐,Min,Oh, Jae‐,Min Wiley-VCH 2012 European journal of inorganic chemistry Vol. No.

<P><B>Abstract</B></P><P>We have prepared organic–inorganic hybrid materials consisting of layered metal hydroxides and hydrogel polymers for potential use as a drug delivery system. The hybrid materials were synthesized by an electrophoretic method; anionic precursors, OH<SUP>–</SUP>/CO<SUB>3</SUB><SUP>2–</SUP>, and cationic metal Zn<SUP>2+</SUP> were migrated into hydrogel by applying an electrical potential of 25 V for 20 min to form inorganic nanocrystals inside the hydrogel matrix. Hydrozincite [Zn<SUB>5</SUB>(OH)<SUB>8</SUB>(CO<SUB>3</SUB>)] nanoparticles, a kind of layered metal hydroxide, were determined to develop inside the hydrogel according to powder X‐ray diffraction, FTIR, and X‐ray absorption spectroscopy. Scanning electron microscopic images showed that the prepared hybrid materials have well‐dispersed inorganic nanoparticles in the hydrogel matrix. In order to evaluate the potential of the thus prepared hybrid materials as a drug‐delivery system, the well‐known antioxidant ferulic acid was incorporated and their time‐dependent release profile was obtained by HPLC.</P>

Synthesis of hydrotalcite type layered double hydroxide with various Mg/Al ratio and surface charge under controlled reaction condition

Lee, Ji-Yeong,Gwak, Gyeong-Hyeon,Kim, Hyoung-Mi,Kim, Tae-il,Lee, Gyeong Jin,Oh, Jae-Min Elsevier 2016 Applied clay science Vol.134 No.1

<P><B>Abstract</B></P> <P>In order to control Mg/Al ratio in hydrotalcite type layered double hydroxide (LDH), LDH was prepared through coprecipitation under varied synthetic parameters such as initial Mg/Al ratio (from 1 to 20) in metal solution and coprecipitation pH (9.5, 10, 10.5 and 11). Phase evolution of hydrotalcite or impurities was examined with powder X-ray diffraction pattern and the Mg/Al ratio in final product was evaluated with inductively coupled plasma-atomic emission spectroscopy. It was found that the nominal Mg/Al ratio did not correspond to the final values, showing narrow correlation range between 1 and 3 at relatively low pH~9.5. By raising coprecipitation pH upto 11, Mg/Al ratio successfully increased in final LDH product upto 15.4. Under controlled initial Mg/Al ratio and coprecipitation pH, various LDHs with Mg/Al ratio between 1 and 16, which corresponded to layer charge density between 0.5 and 6(+)/100Å<SUP>2</SUP>, were obtained. The charge density and surface charge of LDHs exhibited linear correlation, showing zeta potential value 16–40mV at neutral pH.</P> <P><B>Highlights</B></P> <P> <UL> <LI> LDHs with various Mg/Al ratio were prepared. </LI> <LI> Starting Mg/Al ratio and pH was controlled respectively in coprecipitation reaction. </LI> <LI> Mg/Al ratio between 1.44 and 15.43 was obtained under controlled conditions. </LI> <LI> Zeta potential of LDH was highly dependent on the Mg/Al ratio. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Fibrous Silver Particles Prepared from Layered Silver Alkanethiolates and Their Catalytic Property

Kim, Min-Kyu,Gwak, Gyeong-Hyeon,Oh, Jae-Min American Scientific Publishers 2017 Journal of nanoscience and nanotechnology Vol.17 No.5

<P>We have prepared fibrous silver particles (FSPs) by reducing layered silver alkanethiolates (LSTs) having various alkyl chain length. According to powder X-ray diffraction and infrared spectra, LSTs had lamellar structure with different interlayer distance with respect to alkyl chain length. Microscopic study revealed that LSTs particles had flat shape with hundreds of nanometers diameter and tens of nanometers thickness, regardless of alkyl chain length. Upon reductive calcination at 400 degrees C under H-2 flow, LSTs transformed to face centered cubic Ag fiber having bundle of Ag filaments having similar to 1 mu m diameter. Through Scherrer's equation, microscopic analyses and N-2 adsorption-desorption isotherm, it was revealed that silver nanoparticle preferentially aggregated to one direction during reduction to form FSPs, and molecules could access through the inter-particle space in the aggregates. Conversion of 4-nitrophenol to 4-aminophenol catalyzed by FSPs was analyzed with Langmuir-Hinshelwood model. It was found that FSPs had similar or higher catalytic reaction rate compared with Ag nanoparticles. Furthermore, FSPs were found to possess high recyclability by showing continuous catalytic activity after 5 catalytic reactions.</P>

Cam type 대퇴비구 충돌증후군 진단을 위한 Dunn View 검사에서 보조기구의 유용성

전인기(In-Ki Jeon),곽영곤(Yeong-Gon Gwak),임호태(Ho-Tae Lim):오현일(Hyeon-IL O),이경숙(Gyeong-Suk Lee),최진영(Jinyeong Choi),이광원(Gwangwon Lee) 대한영상의학기술학회 2017 대한영상의학기술학회 논문지 Vol.2017 No.1

목 적:일반영상 검사 중 전방 대퇴비구 충돌을 일으키는 대퇴 경부의 pistol grip 변형을 확인하고, 추적, 관찰 하는 영상인 Dunn view 에서 자체 개발한 보조기구를 이용하여 검사의 정확도를 유지하고 환자가 느끼는 검사자세의 만족도를 향상시키고자 하였다. 대상 및 방법:2015년 1월부터 2016년 12월까지 고관절 관절경(Hip Arthroscopy) 예정인 환자 중 Dunn view (45도, 90도 flextion)로 검사 의뢰 되어 2회 이상 추적, 관찰된 31명(남 20명 평균연령 39.2세 ,여 11명 평균연령 43세)을 대상으로 자체개발한 보조기구를 사용 전, 후로 나누어 일반영상을 검사하였고 이후 MRI로 경사축상면 영상을 획득 하여 각각의 장비에서 검사된 영상을 토대로 10년 이상 경력을 가진 방사선사 2인이 측정방법에 대한 엄격한 협의를 거쳐서 일치된 α-angle과 femoral Head–Neck offset을 측정하였고, 측정을 통해 얻어진 자료는 대응 T검정으로 유의한 차이를 분석하였다. 결 과:MRI 영상과 Dunn 45°, 90°에 대한 보조기구 사용 전,후의 영상에서 α-angle을 측정하고 분석한 결과 45°에서는 통계적으로 유의하지 않았고(P>0.05), 90°에서는 통계적으로 유의하다고 나타났다.(P<0.05) 그리고 MRI 영상과 Dunn 45°, 90°에 대한 보조기구 사용 전, 후의 영상에서 Femoral head-neck offset 을 측정하고 분석한 결과 45°와 90°모두 통계적으로 유의한 결과가 도출되었다.(P<0.05) 결 론:Dunn view 검사에서 자체 제작한 보조기구를 사용하여 검사함으로써 Cam type의대퇴비구 충돌증후군 진단 시 일반영상 검사에서 진단능력을 향상시키고, 향후 추적 관찰 검사에서 정확하고 일관된 진단가치가 높은 영상을 제공함을 기대할 수 있으며 동시에 환자가 느끼는 검사 자세의 만족도를 향상 시켰다는 점에서 의의를 둘 수 있어 앞으로의 dunn view 검사에서 좋은 참고자료가 될 수 있을 것 이라고 사료된다. Purpose:Through Dunn view, we can check, follow-up and observe the pistol grip transform of femoral neck that induce Femoro Acetabular Impingement. We developed our own device that was used during Dunn view. So the purpose of this study was, using the self developed device, to maintain accuracy and to improve the feeling of satisfaction, while the patient was examined. Materials and Methods:We had traced and observed 31 people (20 men average age 39.2, 11 women average age 43) more than 2 times. They were requested to have Dun view (45°, 90° flextion) and supposed to Hip Arthroscopy from January 2015 to December 2016. We examined a general image using self developed device and without using self developed device. After that, we got oblique transverse image through MRI. Based on these things, 2 radiologists who have more than 10-year career discussed measurement method and measured corresponding α-angle and femoral head-neck offset. We analyzed the difference of measured data by the t-test. Result:An analysis of α-angle showed that it was statistically significant in 90°(P>0.05), but not statistically significant in 45°(P<0.05). And an analysis of femoral head-neck offset showed it was statistically significant in both 45° and 90°(P<0.05). Conclusion:By examination with self developed device in Dunn view, it is expected that it improves diagnostic ability in FAI diagnosis of Cam type. And we can get highly valued accurate and consistent images in follow-up examination. It is also expected that it improves the feeling of satisfaction of patient. It may be good references in Dunn view forward.

Zn-Fe mixed metal oxides from metal hydroxide precursor: Effect of calcination temperature on phase evolution, porosity, and catalytic acidity

Kim, Bo-Kyung,Lee, Do-Yeon,Gwak, Gyeong-Hyeon,Han, Yang-Su,Oh, Jae-Min Elsevier 2019 Journal of solid state chemistry Vol.269 No.-

<P><B>Abstract</B></P> <P>Mixed metal oxides consisting of Zn and Fe were prepared by calcining ZnFe-mixed metal hydroxide at respective temperature of 400, 500 and 600 °C. According to X-ray diffraction, the calcination resulted in the evolution of wurtzite ZnO partially with ZnFe<SUB>2</SUB>O<SUB>4</SUB> spinel at high temperature. The local structure around Fe and Zn measured by X-ray absorption spectroscopy did not show difference upon temperature, suggesting the intimate association between zinc oxide and iron oxide. The magnetic property of mixed metal oxide was paramagnetic for calcination temperature of 400 and 500 °C; whereas superparamagnetism was observed in 600 °C calcined sample. The specific surface area and pore volume was the highest for mixed metal oxide calcined at 500 °C showing 66.4 m<SUP>2</SUP>/g and 0.908 cm<SUP>3</SUP>/g, respectively. Temperature programmed desorption of ammonia revealed that the ZnFe-mixed metal oxide had majorly strong Lewis acid site compared with previously reported ZnOs. The acid strength was proportional to the calcination temperature, and however, total acidity decreased for 600 °C calcined oxide. Taking into account the phase, porosity and acidity, the ZnFe-mixed metal oxide prepared at 500 °C could be the most advantageous as acid catalysts.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Mixed metal oxides were obtained by calcining metal hydroxides at various temperatures. </LI> <LI> Specific surface area and pore volume were the highest at moderate temperature. </LI> <LI> Acid strength of metal oxides increases upon temperature. </LI> <LI> High calcination temperature negatively affect total acidity of metal oxides. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Structures and catalytic properties of mixed metal oxides are dependent on calcination temperature.</P> <P>[DISPLAY OMISSION]</P>