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Ho, D. M. L.*; Nelwamondo, A. N.*; Okubo, Ayako; Rameb
ck, H.*; Song, K.*; Han, S.-H.*; Hancke, J. J.*; Holmgren, S.*; Jonsson, S.*; Kataoka, Osamu; et al.
Journal of Radioanalytical and Nuclear Chemistry, 315(2), p.353 - 363, 2018/02
Times Cited Count：2 Percentile：16.65(Chemistry, Analytical)The Fourth Collaborative Material Exercise (CMX-4) of the Nuclear Forensics International Technical Working Group (ITWG) registered the largest participation for this exercise in nuclear forensics, with seven of the 17 laboratories participating for the first time. In this paper, participants from five of the first-time laboratories shared their individual experience in this exercise, from preparation to analysis of samples. The exercise proved to be highly useful for testing procedures, repurposing established methods, exercising skills, and improving the understanding of nuclear forensic signatures and their interpretation trough the post-exercise review meeting.
Kristo, M. J.*; Williams, R.*; Gaffney, A. M.*; Kayzar-Boggs, T. M.*; Schorzman, K. C.*; Lagerkvist, P.*; Vesterlund, A.*; Ramebck, H.*; Nelwamondo, A. N.*; Kotze, D.*; et al.
Journal of Radioanalytical and Nuclear Chemistry, 315(2), p.425 - 434, 2018/02
Times Cited Count：20 Percentile：83.09(Chemistry, Analytical)In a recent international exercise, 10 international nuclear forensics laboratories successfully performed radiochronometry on three low enriched uranium oxide samples, providing 12 analytical results using three different parent-daughter pairs serving as independent chronometers. The vast majority of the results were consistent with one another and consistent with the known processing history of the materials. In general, for these particular samples, mass spectrometry gave more accurate and more precise analytical results than decay counting measurements. In addition, the concordance of the 
U-
Pa and 
U-
Th chronometers confirmed the validity of the age dating assumptions, increasing confidence in the resulting conclusions.
Okubo, Ayako; Shinohara, Nobuo; Magara, Masaaki
Journal of Radioanalytical and Nuclear Chemistry, 314(1), p.231 - 234, 2017/10
Times Cited Count：3 Percentile：23.33(Chemistry, Analytical)The model date of two enriched uranium materials were determined using a new method for nuclear forensics investigation. In this method, the Th/U ratio was calculated without spike addition from measured ratios of Th/Th and U/
U, and calculated Th/U ratio in secular equilibrium. The obtained model date for the low-enriched uranium material was agreed with the known production date within uncertainty. For the highly enriched uranium material, slightly younger model date than the known production date was obtained. The U interference on Th counting in thermal ionization mass spectrometry measurement was suspected as a potential cause.
Tamai, Hiroshi; Okubo, Ayako; Kimura, Yoshiki; Shinohara, Nobuo; Tazaki, Makiko; Shimizu, Ryo; Suda, Kazunori; Tomikawa, Hirofumi
Proceedings of INMM 58th Annual Meeting (Internet), 6 Pages, 2017/07
Nuclear forensics is a technical measure to analyse and collate samples of illegally used nuclear materials, etc., to clarify their origins, routes, etc. and contribute to criminal identifications. Close collaboration with police and judicial organizations is essential. The national response framework is being built up with international cooperation. Discussions on promoting technical capability and regional cooperation are presented.
Tamai, Hiroshi; Okubo, Ayako; Kimura, Yoshiki; Kokaji, Lisa; Shinohara, Nobuo; Tomikawa, Hirofumi
Dai-37-Kai Kaku Busshitsu Kanri Gakkai Nihon Shibu Nenji Taikai Rombunshu (CD-ROM), 8 Pages, 2017/02
Nuclear Forensics capability has been developed under the international collaborations. For its effective function, technical development in analysis of seized nuclear materials as well as the institutional development in comprehensive response framework are required under individual national responsibility. In order to keep the "chain of custody" in the proper operation of sample collection at the event scene, radiological analysis at the laboratory, storage of the samples, and further inspection and trial, close cooperation and information sharing between relevant organisations are essential. IAEA issues the Implementing Guide to provide the model action plan and assists individual national development. International cooperation for the technical improvement and awareness cultivation is promoted. Examples in such national developments will be introduced and prospective technical/institutional prerequisite for nuclear forensics response framework will be studied.
Th-U age dating of bulk uranium for nuclear forensicsGaffney, A.*; Hubert, A.*; Kinman, W. S.*; Magara, Masaaki; Okubo, Ayako; Pointurier, F.*; Schorzman, K. C.*; Steiner, R. E.*; Williams, R. W.*
Journal of Radioanalytical and Nuclear Chemistry, 307(3), p.2055 - 2060, 2016/03
Times Cited Count：29 Percentile：90.68(Chemistry, Analytical)In and inter-laboratory measurement comparison study, four laboratories (LLNL, LANL, CEA, JAEA) determined Th-U model ages of uranium certified reference material NBL U050 using isotope dilution mass spectrometry. The model dates determined by the participating laboratories range from 9 March 1956 to 19 October 1957, and are indistinguishable given the associated measurement uncertainties. These model ages are concordant with to slightly older than the known production age of NBL U050, indicating unsufficient purification of U050.
Kimura, Yoshiki; Shinohara, Nobuo; Okubo, Ayako
Nihon Genshiryoku Gakkai-Shi ATOMO
, 57(12), p.782 - 786, 2015/12
no abstracts in English
Okubo, Ayako; Kimura, Yoshiki; Shinohara, Nobuo; Toda, Nobufumi; Funatake, Yoshio; Watahiki, Masaru; Sakurai, Satoshi; Kuno, Yusuke
JAEA-Technology 2015-001, 185 Pages, 2015/03
JAEA-Technology-2015-001.pdf:56.65MB
Nuclear forensics is the analysis of intercepted illicit nuclear or radioactive material and any associated material to provide evidence for nuclear attribution by determining origin, history, transit routes and purpose involving such material. Nuclear forensics activity includes sampling of the illicit material, analysis of the samples and evaluation of the attribution by comparing the analyzed data with database or numerical simulation. Because the nuclear forensics technologies specify the origin of the nuclear materials used illegal dealings or nuclear terrorism, it becomes possible to identify and indict offenders, hence to enhance deterrent effect against such terrorism. Worldwide network on nuclear forensics can contribute to strengthen global nuclear security regime. In this paper, the results of research and development of fundamental nuclear forensics technologies performed in Japan Atomic Energy Agency during the fiscal term of 2011-2013 were reported.
Okubo, Ayako; Obata, Hajime*; Magara, Masaaki; Kimura, Takaumi; Ogawa, Hiroshi*
Analytica Chimica Acta, 804, p.120 - 125, 2013/12
Times Cited Count：3 Percentile：10.03(Chemistry, Analytical)This work introduces a novel method of recovery of iron hydroxide using a DIAION CR-20 chelating resin column to determine Th isotopes in seawater with a sector field (SF) inductively coupled plasma mass spectrometer (ICP-MS). Thorium isotopes in seawater were coprecipitated with iron hydroxide, and this precipitate was sent to chelating resin column. The chelating column quantitatively collected 
Th with iron hydroxide in seawater at flow rates of 20-25 mL/min. Based on this flow rate, a 5 L sample was processed within 3-4 h.
Okubo, Ayako; Takeda, Shigenobu*; Obata, Hajime*
Atmospheric Research, 129-130, p.20 - 32, 2013/07
Times Cited Count：43 Percentile：69.84(Meteorology & Atmospheric Sciences)To understand the atmospheric input of trace metals to surface seawaters, the total deposition samples were collected simultaneously from three coastal station in Japan. The observed flux was within the lower limit of the previous estimation based on a model. Except for Sc and Fe, all the elements showed a increasing tendency toward dissolution with decreasing the pH. We calculated the Sc-normalized enrichment factors. The increasing tendency toward dissolution with decreasing the pH was higher for Al than that of Fe.
Th and Th distributions in mid-latitudes of the North Pacific Ocean; Effect of bottom scavengingOkubo, Ayako; Obata, Hajime*; Gamo, Toshitaka*; Yamada, Masatoshi*
Earth and Planetary Science Letters, 339-340, p.139 - 150, 2012/07
Times Cited Count：45 Percentile：71.79(Geochemistry & Geophysics)Vertical distributions of total Th and dissolved Th were determined in the mid-latitudes of the North Pacific Ocean. Th in the Pacific Ocean have been described well using the reversible-scavenging model. However, we observed the depletion of total Th. The enhanced vertical eddy diffusion derived from the complex topography of the western Pacific Ocean might promote bottom scavenging and transport of the low Th in deep water to the upper layers.
Th/Th ratiosOkubo, Ayako; Shinohara, Nobuo; Magara, Masaaki
no journal, ,
The uranium age-dating is a nuclear forensics analysis techniques, by measuring the Th / U isotope ratio in uranium sample, to estimate the elapsed time from being separated and purified. We have determined Th and U using isotope dilution mass spectrometry method, it has conducted for uranium age-dating. Act to perform the isotope analysis after the addition a known quantity of the isotope (spike) to the sample, after spiking, analytical sample is assumed to be in the state of isotopic equilibrium. However, the samples which have complex speciation of uranium and thorium are analyzed, may not sufficiently reach to the state of isotopic equilibrium has been suggested from the experimental results. In this study, without the addition of a spike, from the measurement results of the uranium isotope ratios and thorium isotope ratio in the sample, it was investigated a method for calculating the Th / U isotope ratio. The state of radioactive equilibrium between U and Th in the sample was utilized in the Th / Th method. The Th / U ratio was calculated using measured Th / Th isotope ratio, U / U isotope ratio and Th / U ratio in the radioactive equilibrium.
Okubo, Ayako; Shinohara, Nobuo; Magara, Masaaki
no journal, ,
As an effort of strengthening nuclear security in the world, capacity building of nuclear forensics in each state have been required. The age-dating of nuclear material is to estimate an elapsed time since the final purified day of the nuclear material. Because age-dating result could enable us to better constrain the origin of unidentified material, which is recognized as an important parameter for nuclear forensics. The isotope dilution mass spectrometry (ID-MS) method is recognized as the most reliable method to estimate U/Th ratio for uranium age-dating. Uranium-234 and Th amounts in a uranium material were respectively measured by ID method using spikes (
U and 
Th). The isotopic equilibrium between the isotopes in-situ the sample and added spikes is assumed in ID method. In order to obtain the accurate concentrations of U and Th, precise determination of sample weight and control of spike concentration are required. We have developed a new method to estimate U/Th ratio without spike addition for uranium age-dating. In this method, using secular equilibrium between U and Th (Th/U = 1.45 E-11), U/Th ratio is calculated from measured isotope ratios of U and Th. This new method does not require precise sample weighing and control spike concentration, and is suitable for routine analysis in developing of nuclear forensics database.
Tamai, Hiroshi; Kimura, Yoshiki; Okubo, Ayako; Shinohara, Nobuo; Tomikawa, Hirofumi
no journal, ,
Nuclear forensics is effective measure for strengthening nuclear security through the analysis of origin and characteristics of nuclear materials or radio-isotopes collected at the crime scene inspections. In the development of nuclear forensics laboratory/library, "Chain of Custody" should be kept in mind on the view point of juridical process. Each nation should develop own national response plan to stipulate the framework for integrated nuclear forensics activities. Good practices for stipulating national frameworks for nuclear forensics are investigated in advancing nations such as US, EU and Canada. Issues and measures are proposed aiming at improving its framework.
Okubo, Ayako; Shinohara, Nobuo; Umino, Yuji; Hara, Mikiya
no journal, ,
Okubo, Ayako
no journal, ,
no abstracts in English
Okubo, Ayako; Mayer, K.*
no journal, ,
Under the collaboration between EC-JRC and JAEA, the in-situ age dating method was subject to joint validation, and six different uranium materialswere used for this purpose. The age dating result by in-situ isotope method was consistent with known production dates of the respective samples. The uncertainty evaluation according to GUM for the in-situ isotope method indicates that the measured Th/Th ratio provides the highest contribution. The accuracy of in-situ isotope method can be improved by higher precision in Th/Th measurement.
Kimura, Yoshiki; Tsuchiya, Kenichi*; Okubo, Ayako*; Tanabe, Kosuke*; Kakuda, Hidetoshi*; Akiba, Norimitsu*; Tomikawa, Hirofumi
no journal, ,
Kimura, Yoshiki; Okubo, Ayako; Tomikawa, Hirofumi; Matsumoto, Tetsuya*; Umino, Yuji*; Hosoi, Masaharu*
no journal, ,
Tomikawa, Hirofumi; Kimura, Yoshiki; Okubo, Ayako
no journal, ,
