• 자원환경지질
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• 제56권5호
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• pp.547-555
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• 2023

분석 기기의 발달과 더불어 자연 우라늄 동위원소 비(²³⁸U/²³⁵U)와 분별작용에 대한 연구가 점차 증가하고 있다. MC-ICP-MS을 이용한 우라늄 동위원소의 정밀한 분석이 가능해지면서 137.88의 고정된 값으로 여겨졌던 자연 물질의 ²³⁸U/²³⁵U 비가 우라늄 동위원소 분별작용에 의해 최대 수 퍼밀까지 변화할 수 있다는 것이 밝혀졌다. 본 고찰에서는 우라늄 동위원소의 분석과 표기에 대해 간략하게 설명한 후, 지구 상 주요 물질들의 우라늄 동위원소 값(δ²³⁸U)의 변화와 지구화학적 특징을 살펴본다. 특히, 우라늄 광상의 유형과 특징에 따른 우라늄 동위원소 조성 연구 사례를 소개하고, 상대적으로 큰 δ²³⁸U 범위를 야기하는 우라늄 동위원소 분별작용에 대해 논의한다. 이를 바탕으로 고준위 방사성 폐기물 처분장의 모의 실험을 위한 자연 유사 모델로서 우라늄 광상이 갖는 연구 의의에 대해 고찰한다.

• Nuclear Engineering and Technology
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• 제1권1호
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• pp.33-38
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• 1969

Determinations of the isotopic contents of U$^{235}$ and U$^{238}$ in ten uranium samples containing 0.72-89.70 at % U$^{235}$ were carried out in two ways utilizing high resolution Ge (Li) gamma-ray spectrometer. One method is based upon the fact that the intensity of 185.5 kev gamma-ray vary linearly with U$^{235}$ content for a given geometry. Another method applied for the direct determination of the U$^{235}$ / U$^{238}$ isotopic ratios is the precision gamma-ray spectrometric analysis of reactor irradiated uranium samples after allowing a fixed cooling time for one hour. The results obtained by both methods well agree with the values calculated from the isotopic contents of highly enriched original uranium samples measured by mass spectrometer. The precision obtained was well below 5% for most of the isotopic ratios investigated.

• Nuclear Engineering and Technology
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• 제54권12호
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• pp.4636-4643
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• 2022

A time-of-flight and energy (TOF-E) detection system for the measurement of ²³⁶U accelerator mass spectrometry (AMS) has been developed to improve the ²³⁶U/²³⁸U sensitivity at Micro Analysis Laboratory, Tandem accelerator (MALT), The University of Tokyo. With observing TOF distribution of ²³⁵U, ²³⁶U and ²³⁸U, this TOF-E detection system has clearly separated ²³⁶U from the interference of ²³⁵U and ²³⁸U when measuring three kinds of uranium standards. In addition, we have developed a novel method combining kernel-based density estimation method and multi-Gaussian fitting method to estimate the ²³⁶U/²³⁸U sensitivity of the TOF-E detection system. Using this new estimation method, 3.4 × 10^-12 of ²³⁶U/²³⁸U sensitivity and 1.9 ns of time resolution are obtained. ²³⁶U/²³⁸U sensitivity of TOF-E detection system has improved two orders of magnitude better than that of previous gas ionization chamber. Moreover, unknown species other than uranium isotopes were also observed in the measurement of a surface soil sample, which has demonstrated that TOF-E detection system has a higher sensitivity in particle identification. With its high sensibility in mass determination, this TOF-E detection system could also be used in other heavy isotope AMS.

• 분석과학
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• 제20권6호
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• pp.460-467
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• 2007

자연계에 존재하는 $^{238}U$, $^{235}U$, $^{232}Th$ 그리고 $^{40}K$의 감마선과 베타선에 대해 토양의 흡수선량을 평가하기 위한 유효 흡수선량 환산인자를 계산하였다. 이 때 감마선과 베타선에 대한 붕괴당 에너지, 반감기, 분기율등의 핵자료들은 National Nuclear Data Center (NNDC)의 최근 자료들을 이용하였다. 본 연구에서 계산한 흡수선량 인자 및 이를 이용하여 얻은 $^{238}U$, $^{232}Th$ 그리고 $^{40}K$의 베타선과 감마선에 유효흡수선량은 1998년 Aitken의 결과와 비교적 잘 일치하였지만, $^{235}U$의 경우는 많은 차이가 있음을 확인하였다. 한국 충북 청원군 오성에 있는 선사유적지(만수리) 내의 토양에 대해 고 분해능 감마선 분광 분석 장치(HP Ge 검출기)로 지각 방사선의 감마선 스펙트럼을 측정하고, 계산된 유효 흡수선량 환산인자를 이용하여 연간방사선량을 평가하였는데, 연간방사선량이 3.8~5.9 mGy/year으로 평가되었다. 또한 Rn 이하의 붕괴 핵종을 포함하여 연간방사선량을 평가하는 경우와, 이를 포함하지 않고 연간방사선량을 평가하는 경우는 9~30 % 차이를 나타내었다. 이 흡수선량 환산인자로 토양에 존재하는 자연 방사성 동위원소들의 베타선과 감마선에 대한 유효 흡수선량 평가법이 확립하였다.

• Bulletin of the Korean Chemical Society
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• 제32권12호
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• pp.4327-4331
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• 2011

A new method in thermal ionization mass spectrometry (TIMS) was developed to correct peak tailing backgrounds in the isotope ratio measurements of uranium in ultra trace levels for higher accuracy. Two different uranium standard reference materials (U005 and U030) were used to construct databases of signal intensities at mass 234 u and mass 236 u, which correspond to the two uranium minor isotopes, and signal intensity of $^{238}U$. Correlations between peak tailing backgrounds and $^{238}U$ were obtained by least-squares regression on calculated backgrounds at mass 234 u and mass 236 u with respect to the signal intensity of $^{238}U$ followed by separation of the peak tails of the two major isotopes of uranium ($^{235}U$ and $^{238}U$), which enables us to obtain a master equation for peak tailing background correction on all kinds of samples. Verification of the correction method was carried out using U010 and IRMM-040a.

• Journal of Radiation Protection and Research
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• 제24권4호
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• pp.187-193
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• 1999

국내 석탄화력발전소에서 발생되는 비산석탄회의 방사능 농도 분석을 수행하였고 재활용을 위한 방사능 함량의 유해도를 평가하였다. TBP 용매추출법과 알파스펙트로베타를 사용하여 비산석탄회에 존재하는 우라늄 동위원소($^{238}U,\;^{235}U,\;^{234}U$)의 방사능 농도를 측정하였으며, 감마스펙트로메타를 사용하여 $^{226}Ra,\;^{232}Th,\;^{40}K$ 등의 방사능 농도를 결정하였다. 우라늄 동위원소의 농도측정 결과 $^{238}U,\;^{235}U,\;^{234}U$의 방사능 농도는 평균적으로 각각 116.1, 5.01, 및 121.2 Bq $kg^{-1}$으로 나타났으며, $^{234}U/^{238}U$의 방사능 농도비는 $1.04\;{\pm}\;0.03$ 로서 자연상태의 토양중 방사능 농도 비인 1.14 와 유사하였다. 동일시료에 대한 감마측정 결과 $^{226}Ra,\;^{292}Th$ 및 $^{40}K$의 방사능 농도는 각각 $101.7\;{\sim}\;113.9,\;39.5\;{\sim}\;54.2$, 및 $315.0\;{\sim}\;990.6$ Bq $kg^{-1}$ 으로 나타났다. $^{226}Ra,\;^{292}Th$ 및 $^{40}K$ 동위원소의 농도를 사용하여 재활용 목적으로서의 비산석탄회의 방사능 함량 유해도를 평가하였고, 그 결과 본 연구의 대상물질인 비산석탄회의 방사능 함량은 허용기준치 이하로 나타났다.

• 분석과학
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• 제30권5호
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• pp.252-261
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• 2017

천연방사성핵종을 함유한 물질들은 인간 활동에 의해 인위적인 조작과정을 거치면서 농축되는 경우 방사선 노출에 따른 위해를 증가시킬 수 있다. 본 연구는 다양한 전처리 방법 및 분석 방법 간 비교를 통해 분석정확도를 평가하고 실내 건축자재 중 $^{232}Th$, $^{235}U$, $^{238}U$의 천연방사성핵종을 분석하기 위한 최적의 분석 방법을 확립하고자 하였다. ICP-MS를 이용한 실내 건축자재 중 천연방사성핵종 분석방법을 확립하기 위하여, 인증표준물질 5종을 왕수, 불산, 과염소산의 습식산화법과 용융법의 전처리법에 따른 U, Th의 분석 정확도 및 정밀도를 평가하였고, 최적의 전처리법으로써 용융법과 $Fe(OH)_3$ 공침법을 선정하였다. 확립된 분석방법을 석고보드, 벽돌, 시멘트, 페인트, 타일과 벽지 총 51 종의 실내 건축자재 시료에 적용하여 천연방사성핵종의 농도를 정량 분석하였다. 또한 동일한 시료에 대해 감마분광분석법 중 간접측정법을 사용하여 $^{238}U$, $^{232}Th$의 농도를 정량하고 ICP-MS 분석 결과와 비교하였다.

• Nuclear Engineering and Technology
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• 제52권7호
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• pp.1532-1536
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• 2020

For ensuring nuclear safeguards, we report the analytical signal-detection performance of thermal ionization mass spectrometry (TIMS) with continuous heating for the measurement of isotopic ratios in samples containing ultra-trace amounts of uranium. As methods for detecting uranium signals, peak-jumping mode using a single detector and static mode using multiple detectors were examined with U100 (10% ²³⁵U-enriched) uranium standard samples in the femtogram-to-picogram range. Uranium isotope ratios, n(²³⁵U)/n(²³⁸U), were measured down to levels of 1 fg and 3 fg in static and peak-jumping modes, respectively, while n(²³⁴U)/n(²³⁸U) and n(²³⁶U)/n(²³⁸U) values were measured down to levels of 100 fg in both modes. In addition, the dependency of the ²³⁸U signal intensity on sample quantity exhibited similar tendencies in both modes. The precisions of the isotope ratios obtained in the static mode over all sample ranges used in this study were overall slightly higher than those obtained in peak-jumping mode. These results indicate that isotope ratio measurements by TIMS with continuous heating are almost independent of the detection method, i.e., peak-jumping mode or static mode, which is characteristic of isotope-ratio measurements using the TIMS method with continuous heating. TIMS with continuous heating is advantageous as it exhibits the properties of multiple detectors within a single detector, and is expected to be used in various fields in addition to ensuring nuclear safeguards.

• Nuclear Engineering and Technology
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• 제50권6호
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• pp.929-936
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• 2018

A basic characterization of uranium samples was performed using gamma- and X-ray spectroscopy. The studied uranium samples were eight types of certified reference materials with $^{235}U$ enrichments in the range of 1-97%, and the measurements were performed over 24 h using a high-resolution and high-purity planar germanium detector. A general peak analysis of the spectrum and the $XK_{\alpha}$ region of the uranium spectra was carried out by using HyperGam and HyperGam-U, respectively. The standard reference sources were used to calibrate the spectroscopy system. To obtain the absolute detection efficiency, an effective solid angle code, EXVol, was run for each sample. Hence, the peak activities and isotopic activities were determined, and then, the total U content and $^{234}U$, $^{235}U$, and $^{238}U$ isotopic contents were determined and compared with those of the certified reference values. A new method to determine the model age based on the ratio of the activities of $^{223}Ra$ and $^{235}U$ in the sample was studied, and the model age was compared with the known true age. In summary, the present study developed a method for basic characterization of uranium samples by nondestructive gamma-ray spectrometry in 24 h and to obtain information on the sample age.

• Nuclear Engineering and Technology
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• 제50권1호
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• pp.140-144
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• 2018

Isotopic analyses of plutonium and low-enriched uranium mixtures with particle sizes of $0.6-3.3{\mu}m$ were performed using thermal ionization mass spectrometry with a continuous heating method to verify its effectiveness for the accurate analysis of minor isotopes without sample pretreatment. The mixed particles used in this study were prepared from a mixed solution of plutonium (SRM 947) and uranium (U010, $^{235}U$ 1% enriched) reference materials. The isotope ratios for plutonium in the individual mixed particles, including $^{238}Pu/^{239}Pu$, $^{241}Pu/^{239}Pu$ as well as $^{240}Pu/^{239}Pu$, and $^{242}Pu/^{239}Pu$, were in good agreement with the certified values despite the isobaric interference of $^{238}U$ and $^{241}Am$. The isotope ratios for uranium in the mixed particles also agreed well with the certified values within the range of error. However, the isotope ratios for minor isotopes, such as $^{234}U$ and $^{236}U$, in the particles with diameters of less than approximately $1.8{\mu}m$ could not be measured because numbers of $^{234}U$ and $^{236}U$ atoms in analyzed particles are too low. These results indicate that thermal ionization mass spectrometry with a continuous heating method is applicable for the analysis of trace amounts of plutonium isotopes, including $^{238}Pu$ and $^{241}Pu$, despite the presence of the respective isobars $^{238}U$ and $^{241}Am$ in the microsamples.