Search results for: Ayako Okubo

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The application of radiochronometry during the 4th collaborative materials exercise of the nuclear forensics international technical working group (ITWG)

Michael J. Kristo, Ross Williams, Amy M. Gaffney, Theresa M. Kayzar-Boggs, more

Journal of Radioanalytical and Nuclear Chemistry > 2018 > 315 > 2 > 425-434

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...

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Overall approaches and experiences of first-time participants in the Nuclear Forensics International Technical Working Group’s Fourth Collaborative Material Exercise (CMX-4)

Doris M. L. Ho, Aubrey N. Nelwamondo, Ayako Okubo, Henrik Ramebäck, more

Journal of Radioanalytical and Nuclear Chemistry > 2018 > 315 > 2 > 353-363

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. Each of the laboratories had their strategic role to play in its respective country, analyzing real-world samples using their in-house...

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Uranium age-dating using in-situ isotope ratios by thermal ionization mass spectrometry for nuclear forensics

Ayako Okubo, Nobuo Shinohara, Masaaki Magara

Journal of Radioanalytical and Nuclear Chemistry > 2017 > 314 > 1 > 231-234

The model dates of two enriched uranium materials were determined using a new method for nuclear forensics investigation. In this method, without spike addition, the ²³⁰Th/²³⁴U ratio was calculated from the measured ratios of ²³⁰Th/²³⁴Th and ²³⁴U/²³⁸U and from calculated ²³⁴Th/²³⁸U ratio in secular equilibrium. The model date obtained for the low-enriched uranium material was in agreement with the...

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Round-robin ²³⁰Th–²³⁴U age dating of bulk uranium for nuclear forensics

Amy M. Gaffney, Amélie Hubert, William S. Kinman, Masaaki Magara, more

Journal of Radioanalytical and Nuclear Chemistry > 2016 > 307 > 3 > 2055-2060

In an inter-laboratory measurement comparison study, four laboratories determined ²³⁰Th–²³⁴U 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...

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Precise determination of dissolved platinum in seawater of the Japan Sea, Sea of Okhotsk and western North Pacific Ocean

Asami Suzuki, Hajime Obata, Ayako Okubo, Toshitaka Gamo

Marine Chemistry > 2014 > 166 > C > 114-121

Platinum is among the least abundant elements in the earth's crust and is now widely used in various products such as catalytic converters in automobiles and anticancer drugs. Consequently, the concentration of Pt in urban aquatic environments is increasing. However, little is known about the distributions and geochemical cycles of Pt in the ocean owing to its low concentrations in seawater (<0...

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Path Dependence and Paradigm Shift: How Cetacean Scientists Learned to Develop Management Procedures that Survived the Controversial Whaling Regime

Atsushi Ishii, Ayako Okubo

Review of Policy Research > 31 > 4 > 257 - 280

The transformation of the International Whaling Commission (IWC) into a preservationist regime met with extremely fierce opposition from the prowhaling countries and created an unprecedented and famous polarization of the IWC parties into pro and antiwhaling camps, which can be observed even today. In such a bipolar and harsh process, it would be typically argued that scientific advice would be powerless...

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Rapid collection of iron hydroxide for determination of Th isotopes in seawater

Ayako Okubo, Hajime Obata, Masaaki Magara, Takaumi Kimura, more

Analytica Chimica Acta > 2013 > 804 > Complete > 120-125

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 co-precipitated with iron hydroxide, and this precipitate was sent to chelating resin column. Ferric ions in the iron hydroxide were bonded...

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Atmospheric deposition of trace metals to the western North Pacific Ocean observed at coastal station in Japan

Ayako Okubo, Shigenobu Takeda, Hajime Obata

Atmospheric Research > 2013 > 129-130 > Complete > 20-32

To understand the atmospheric input of trace metals to surface seawaters, the total deposition samples were collected simultaneously from three coastal stations in Japan. The trace metal concentrations (Al, Sc, Ti, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb, and Th) were then determined for particulate and dissolved fractions using a high-resolution ICP-MS. The observed total Fe flux (average, 194μg/m ² ...

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Ultrasound Can Improve the Accuracy of the 2010 American College of Rheumatology/European League Against Rheumatism Classification Criteria for Rheumatoid Arthritis to Predict the Requirement for Methotrexate Treatment

Daiki Nakagomi, Kei Ikeda, Ayako Okubo, Taro Iwamoto, more

Arthritis & Rheumatology > 65 > 4 > 890 - 898

ObjectiveThe 2010 American College of Rheumatology/European League Against Rheumatism (ACR/EULAR) classification criteria for rheumatoid arthritis (RA) refer to a possible use of ultrasound “for confirmation of the clinical findings.” We undertook this study to determine the optimized definition of ultrasound‐detected synovitis for the 2010 ACR/EULAR criteria and to assess the impact of its use on...

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230Th and 232Th distributions in mid-latitudes of the North Pacific Ocean: Effect of bottom scavenging

Ayako Okubo, Hajime Obata, Toshitaka Gamo, Masatoshi Yamada

Earth and Planetary Science Letters > 2012 > 339-340 > Complete > 139-150

Vertical distributions of total ²³⁰ Th and dissolved ²³² Th were determined in the mid-latitudes of the North Pacific Ocean (8°N, 95°W–40°N, 160°E). The observed ²³² Th concentrations are some of the lowest values reported for oceans. Because of low biogenic particle flux, high ²³⁰ Th activity is exhibited in the central gyre. Most vertical distributions of ²³⁰...

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Numerical simulation of piezomagnetic changes associated with hydrothermal pressurization

Ayako Okubo, Wataru Kanda

Geophysical Journal International > 181 > 3 > 1343 - 1361

We have developed a computer program to calculate geomagnetic field changes due to the piezomagnetic effect, which is caused by hydrothermal pressurization. The program uses the distribution of pore fluid pressure that is the result of a numerical simulation for hydrothermal fluid circulation after magma intrusion. First, we present a mathematical formulation of three‐dimensional (3‐D) effective stress...

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Apparent magnetization intensity map on Sakurajima Volcano, Kyushu, Japan, inferred from low-altitude, high-density helicopter-borne aeromagnetic surveys

Ayako Okubo, Wataru Kanda, Yoshikazu Tanaka, Kazuhiro Ishihara, more

Tectonophysics > 2009 > 478 > 1-2 > 34-42

In November 2005, we conducted the first low-altitude, high-density helicopter-borne aeromagnetic survey over Sakurajima Volcano, Kyushu, Japan to provide a baseline for subsequent measurement of changes in magnetic anomalies related to volcanic processes, because previously acquired aeromagnetic data cannot resolve small-scale geological feature. Although the observation error was considered to be...

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Particle flux in the twilight zone of the eastern Indian Ocean: A constraint from 234U–230Th and 228Ra–228Th disequilibria

Ayako Okubo, Hajime Obata, Shangde Luo, Toshitaka Gamo, more

Deep-Sea Research Part I > 2007 > 54 > 10 > 1758-1772

Total ²³⁰ Th and ²²⁸ Th vertical distributions were measured in the eastern Indian Ocean. Based on disequilibria of ²³⁴ U– ²³⁰ Th and ²²⁸ Ra– ²²⁸ Th, we estimated the particle flux from the surface to 950m. The estimated particle flux ranged from 190±60 (150m in the Southern Ocean) to 8.4±2.5mg/m ² /day (950m in the West Australian Basin). The...

article

Scavenging of 230Th in the Sulu Sea

Ayako Okubo, Hajime Obata, Toshitaka Gamo, Hideki Minami, more

Deep-Sea Research Part II > 2007 > 54 > 1-2 > 50-59

Thorium-230 concentrations were determined in the Sulu Sea, a small 5000m deep basin surrounded by the Philippine and Malaysian Islands, and the South China Sea. The mid-water of South China Sea flows into the Sulu Sea through the Mindoro Strait (sill depth 420m). Thorium-230 concentrations in deep waters at two stations (PA-1 in the Sulu Sea and PA-11 in the South China Sea) are considerably lower...

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Aeromagnetic constraits on the subsurface structure of the Unzen Graben, Kyushu, Japan

Ayako Okubo, Tadashi Nakatsuka, Yoshikazu Tanaka, Tsuneomi Kagiyama, more

Earth, Planets and Space > 2006 > 58 > 1 > 23-31

Aeromagnetic analyses have been conducted in and around the Unzen Volcano, Kyushu, Japan, in order to reveal the subsurface structure of the Unzen graben. First, we applied a magnetization intensity mapping method to analyze the aeromagnetic anomalies of the central part of the Shimabara peninsula. Magnetization highs and lows correspond to the Older Unzen (0.15–0.5 Ma) and the Younger Unzen (<0...

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Magnetization intensity mapping on Unzen Volcano, Japan, determined from high-resolution, low-altitude helicopter-borne aeromagnetic survey

Ayako Okubo, Yoshikazu Tanaka, Mitsuru Utsugi, Naoto Kitada, more

Earth, Planets and Space > 2005 > 57 > 8 > 743-753

On September 18, 2002, we conducted a high-resolution, low-altitude helicopter-borne aeromagnetic survey at two flight altitudes, using spiral trajectories for the first time, over Unzen Volcano in the framework of the Unzen Scientific Drilling Project (USDP). This study obtained more detailed and new information than the previous aeromagnetic studies in Unzen volcano about the geological features,...

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