• Bulletin of the Korean Chemical Society
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• v.11 no.5
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• pp.435-438
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• 1990

Primary and secondary ${\alpha}$-deuterium kinetic isotope effects are determined with deuterated aniline nucleophiles in the nucleophilic substitution reactions of benzyl benzenesulfonates and 1-phenylethyl benzenesulfonates in acetonitrile at 30.0^{\circ}C. The $k_H/k_D$ values support our previous conclusions regarding the transition state structures proposed for the two reactions based on the cross-interaction constants ${\rho}_{ij}$; the former is a typical $S_N2$ reaction whereas in the latter the four-center transition state may be involved.

• The Journal of the Petrological Society of Korea
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• v.23 no.3
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• pp.229-237
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• 2014

The Lu-Hf isotope system, coupled with the advent of multiple collector inductively coupled plasma source mass spectrometry, is now widely utilized as a tracer for geological processes. The paper presents a comprehensive review on the principles of the Lu-Hf isotopes, and its current and potential applications to both geochronology and petrogenesis. Finally, based on the Lu-Hf isotopic data from Korean mafic and ultramafic rocks, its has been discussed evolution of the mantle beneath the Korean Peninsula.

• Journal of the Korean Chemical Society
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• v.65 no.5
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• pp.309-312
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• 2021

The solvolysis of (1s)-(+)-menthyl chloroformate (1) were studied kinetically in 28 pure and various mixed solvents. The analysis using the extended Grunwald-Winstein equation in the solvolysis of 1 obtained the l value of 2.46 ± 0.18, the m value of 0.91 ± 0.07, and the correlation coefficient of 0.950. The solvolysis of 1 might proceed via an associative S_N2 mechanism enhancing bond making than bond breaking in the transition state (TS). The value of l/m is 2.7 within the ranges of value found in associative S_N2 reaction. This interpretation is further supported by a relatively large solvent kinetic isotope effect (SKIE, 2.16).

• Journal of the Korean Chemical Society
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• v.63 no.4
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• pp.233-236
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• 2019

In this study, the solvolysis of cyclohexanesulfonyl chloride (1) was studied by kinetics in ethanol-water, methanol-water, acetone-water, and 2,2,2-trifluoroethanol (TFE)-water binary solvent systems. The rate constants were applied to the extended Grunwald-Winstein equation, to obtain the values of m = 0.41 and l = 0.81. These values suggested $S_N2$ mechanism in which bond formation is more important than bond breaking in the transition state (TS). Relatively small activation enthalpy values (11.6 to $14.8kcal{\cdot}mol^{-1}$), the large negative activation entropy values (-29.7 to $-38.7cal{\cdot}mol^{-1}{\cdot}K^{-1}$) and the solvent kinetic isotope effects (SKIE, 2.29, 2.30), the solvolyses of the cyclohexanesulfonyl chloride (1) proceeds via the $S_N2$ mechanism.

• Journal of Conservation Science
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• v.35 no.1
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• pp.81-89
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• 2019

The extensive archaeological remains at the Baekje Kingdom site of Wanggung-ri, Iksan, in the South Jeolla Province, Korea, include a seventh century workshop area that was later covered by the construction of a Buddhist temple. Remains of glass, gold, and bronze artefacts, and the ceramic crucibles used in the working of these materials, provide evidence for a multi-craft, high-temperature technology. We will report the results of both chemical compositional and lead isotope analyses for Wanggung-ri glass, which is among the earliest lead-silica glass type in East Asia, as well as review the evidence for primary glass production at Wanggung-ri.

• Nuclear Engineering and Technology
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• v.52 no.12
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• pp.2867-2873
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• 2020

In reprocessed uranium, derived from an impoverished fuel of light-water moderated reactors, there are isotopes of ^{232, 234, 236}U, which make its recycling remarkably difficult. A method of concentration of ²³⁵U target isotope in cascade's additional product was proposed to recover the isotopic composition of reprocessed uranium. A general calculation procedure is presented and a parameters' optimization of multi-flow cascades with additional products. For the first time a numeric model of a cascade that uses the cuts of partial flows of stages with relatively high separation factors was applied in this procedure. A novel computing experiment is carried out on separation of reprocessed uranium hexafluoride with providing a high concentration of ²³⁵U in cascade's additional product with subsequent dilution. The parameters of cascades' stages are determined so as to allow reducing the ^{232, 234, 236}U isotope content up to the acceptable. It was demonstrated that the dilution of selected products by the natural waste makes it possible to receive a low enriched uranium hexafluoride that meets the ASTM C996-15 specification for commercial grade.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.18 no.1
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• pp.40-46
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• 2013

The isotope ratios of $^{13}C/^{12}C$ and $^{18}O/^{16}O$ for a sample in a mass spectrometer are measured relative to those of a pure $CO_2$ reference gas (i.e., laboratory working standard). Thus, the calibration of a laboratory working standard gas to the international isotope scales (Pee Dee Belemnite (PDB) for ${\delta}^{13}C$ and Vienna Standard Mean Ocean Water (V-SMOW) for ${\delta}^{18}O$) is essential for comparisons between data sets obtained by other groups on other mass spectrometers. However, one often finds difficulties in getting well-calibrated standard gases, because of their production time and high price. Additional difficulty is that fractionation processes can occur inside the gas cylinder most likely due to pressure drop in long-term use. Therefore, studies on laboratory production of pure $CO_2$ isotope standard gas from stable solid calcium carbonate standard materials, have been performed. For this study, we propose a method to extract pure $CO_2$ gas without isotope fractionation from a solid calcium carbonate material. The method is similar to that suggested by Coplen et al., (1983), but is better optimized particularly to make a large amount of pure $CO_2$ gas from calcium carbonate material. The $CaCO_3$ releases $CO_2$ in reaction with 100% pure phosphoric acid at $25^{\circ}C$ in a custom designed, evacuated reaction vessel. Here we introduce optimal procedure, reaction conditions, and samples/reactants size for calcium carbonate-phosphoric acid reaction and also provide the details for extracting, purifying and collecting $CO_2$ gas out of the reaction vessel. The measurements for ${\delta}^{18}O$ and ${\delta}^{13}C$ of $CO_2$ were performed at Seoul National University using a stable isotope ratio mass spectrometer (VG Isotech, SIRA Series II) operated in dual-inlet mode. The entire analysis precisions for ${\delta}^{18}O$ and ${\delta}^{13}C$ were evaluated based on the standard deviations of multiple measurements on 15 separate samples of purified $CO_2$. The pure $CO_2$ samples were taken from 100-mg aliquots of a solid calcium carbonate (Solenhofen-ori $CaCO_3$) during 8-day experimental period. The multiple measurements yielded the $1{\sigma}$ precisions of ${\pm}0.01$‰ for ${\delta}^{13}C$ and ${\pm}0.05$‰ for ${\delta}^{18}O$, comparable to the internal instrumental precisions of SIRA. Therefore, we conclude the method proposed in this study can serve as a way to produce an accurate secondary and/or laboratory $CO_2$ standard gas. We hope this study helps resolve difficulties in placing a laboratory working standard onto the international isotope scales and does make accurate comparisons with other data sets from other groups.

• Bulletin of the Korean Chemical Society
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• v.31 no.5
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• pp.1403-1406
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• 2010

• Bulletin of the Korean Chemical Society
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• v.32 no.11
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• pp.4095-4098
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• 2011

• Bulletin of the Korean Chemical Society
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• v.33 no.8
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• pp.2769-2772
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• 2012