S. Usuda
Japan Atomic Energy Agency
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by S. Usuda.
Talanta | 2007
Fumitaka Esaka; Konomi T. Esaka; Chi-Gyu Lee; Masaaki Magara; S. Sakurai; S. Usuda; Kazuo Watanabe
A new technique to measure (234)U/(238)U and (236)U/(238)U isotope ratios for individual particles in environmental samples was developed, which was a combination of particle isolation under scanning electron microscope (SEM) and secondary ion mass spectrometry (SIMS). The technique was verified by measuring (234)U/(238)U and (236)U/(238)U isotope ratios in individual particles in a simulated environmental sample containing uranium standard (NBL CRM U010) and Pb metal particles. When the uranium particles were not isolated, the relative deviations of the measured isotope ratios from the reference values increased with increasing the signal intensity ratio of (208)Pb to (238)U, which was due to the molecular ion interferences by the Pb particles co-existing in the sputtered area. By the isolation of individual uranium particles, the interferences were eliminated and the measured isotope ratios were in good agreement with the reference values. The maximum relative deviations among 20 particles were 8.9% for (234)U/(238)U and 13.1% for (236)U/(238)U isotope ratios, respectively. The technique was also successfully applied to the analysis of a real swipe sample containing various kinds of elements.
Talanta | 2009
Fumitaka Esaka; Masaaki Magara; Chi-Gyu Lee; S. Sakurai; S. Usuda; Nobuo Shinohara
The determination of uranium isotope ratios in individual particles is of great importance for nuclear safeguards. In the present study, an analytical technique by inductively coupled plasma mass spectrometry (ICP-MS) with a desolvation sample introduction system was applied to isotope ratio analysis of individual uranium particles. In ICP-MS analysis of individual uranium particles with diameters ranging from 0.6 to 4.2 microm in a standard reference material (NBL CRM U050), the use of the desolvation system for sample introduction improved the precision of (234)U/(238)U and (236)U/(238)U isotope ratios. The performance of ICP-MS with desolvation was compared with that of a conventionally used method, i.e., secondary ion mass spectrometry (SIMS). The analysis of test swipe samples taken at nuclear facilities implied that the performance of ICP-MS with desolvation was superior to that of SIMS in a viewpoint of accuracy, because the problems of agglomeration of uranium particles and molecular ion interferences by other elements could be avoided. These results indicated that ICP-MS with desolvation has an enough ability to become an effective tool for nuclear safeguards.
Journal of Environmental Radioactivity | 2008
Yoko Saito-Kokubu; Kenichiro Yasuda; Masaaki Magara; Yutaka Miyamoto; S. Sakurai; S. Usuda; Hideo Yamazaki; Shusaku Yoshikawa; S. Nagaoka; M. Mitamura; J. Inoue; A. Murakami
In a sediment core of Nishiyama reservoir at Nagasaki city, depth profiles of (240)Pu/(239)Pu isotopic ratio, (239+240)Pu and (137)Cs activities were determined. Sediments containing plutonium and (137)Cs, which were deposited immediately after a detonation of Nagasaki atomic bomb, were identified in the core. Observed below the sediments were macroscopic charcoals, providing evidence for initial deposit of the fallout of the Nagasaki atomic bomb. This is the first entire depositional records of plutonium and (137)Cs released from the Nagasaki atomic bomb together with those from atmospheric nuclear tests.
Journal of Nuclear Science and Technology | 2009
Chi-Gyu Lee; Daisuke Suzuki; Fumitaka Esaka; Masaaki Magara; Nobuo Shinohara; S. Usuda
A method to selectively detect uranium particles with high 235U enrichment has been developed; this method can contribute to improving particle analysis on nuclear safeguards environmental samples. The newly developed method involves three key components: (1) a two-step filtration system for particle recovery from swipe samples, (2) a system for controlling the etching time of fission track (FT) detector, and (3) a system for comparing the FT morphologies and particle sizes. The method to screen uranium particles according to their enrichment is focused on detecting highly enriched uranium particles preferentially in various particles recovered from swipe sample; this is one of the most important tasks involved in nuclear safeguards. In order to verify the effectiveness of the screening method developed, a mixture sample containing uranium particles with natural composition and those with 10% enrichment is used. It was shown that enrichment-based screening of uranium particles is possible by comparing the FT morphologies and particle sizes, in addition to controlling the etching time. The developed method uses the etching behaviors of the FT detector mainly; thus, it can be applied to real swipe samples easily.
Journal of Nuclear Science and Technology | 2006
Mitsutoshi Suzuki; Masato Hori; Ryoji Asou; S. Usuda
The multiscale statistical process control (MSSPC) method is applied to clarify the elements of material unaccounted for (MUF) in large scale reprocessing plants using numerical calculations. Continuous wavelet functions are used to decompose the process data, which simulate batch operation superimposed by various types of disturbance, and the disturbance components included in the data are divided into time and frequency spaces. The diagnosis of MSSPC is applied to distinguish abnormal events from the process data and shows how to detect abrupt and protracted diversions using principle component analysis. Quantitative performance of MSSPC for the time series data is shown with average run lengths given by Monte-Carlo simulation to compare to the non-detection probability β. Recent discussion about bias corrections in material balances is introduced and another approach is presented to evaluate MUF without assuming the measurement error model.
Spectrochimica Acta Part B: Atomic Spectroscopy | 2007
Xiao Zhi Zhang; Fumitaka Esaka; Konomi T. Esaka; Masaaki Magara; S. Sakurai; S. Usuda; Kazuo Watanabe
Journal of Radioanalytical and Nuclear Chemistry | 2007
Chi-Gyu Lee; K. Iguchi; Jun Inagawa; Daisuke Suzuki; Fumitaka Esaka; Masaaki Magara; S. Sakurai; Kazuo Watanabe; S. Usuda
Applied Radiation and Isotopes | 2007
Yoko Saito-Kokubu; Fumitaka Esaka; Kenichiro Yasuda; Masaaki Magara; Yutaka Miyamoto; S. Sakurai; S. Usuda; Hideo Yamazaki; Shusaku Yoshikawa; S. Nagaoka
Applied Surface Science | 2008
Fumitaka Esaka; Kazuo Watanabe; Takashi Onodera; Chi-Gyu Lee; Masaaki Magara; S. Sakurai; S. Usuda
Journal of nuclear and radiochemical sciences | 2009
Yutaka Miyamoto; Kenichiro Yasuda; Masaaki Magara; Takaumi Kimura; S. Usuda