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Journal Articles

Radioisotope identification algorithm using deep artificial neural network for supporting nuclear detection and first response on nuclear security incidents

Kimura, Yoshiki; Tsuchiya, Kenichi*

Radioisotopes, 72(2), p.121 - 139, 2023/07

Rapid and precise radioisotope identification in the scene of nuclear detection and nuclear security incidents is one of the challenging issues for the prompt response on the detection alarm or the incidents. A radioisotope identification algorithm using a deep artificial neural network model applicable to handheld gamma-ray detectors has been proposed in the present paper. The proposed algorithm automatically identifies gamma-emitting radioisotopes based on the count contribution ratio (CCR) from each of them estimated by the deep artificial neural network model trained by simulated gamma-ray spectra. The automated radioisotope identification algorithm can support first responders of nuclear detection and nuclear security incidents without sufficient experience and knowledge in radiation measurement. The authors tested the performance of the proposed algorithm using two different types of deep artificial neural network models in application to handheld detectors having high or low energy resolution. The proposed algorithm showed high performance in identifying artificial radioisotopes for actually measured gamma-ray spectra. It was also confirmed that the algorithm is applicable to identifying $$^{235}$$U and automated uranium categorization by analyzing estimated CCRs by the deep artificial neural network models. The authors also com-pared the performance of the proposed algorithm with a conventional radioisotope identification method and discussed promising ways to improve the performance of the algorithm using the deep artificial neural network.

Journal Articles

Fixed point observations and characterization of radioactive caesium in Tama river

Hagiwara, Kenta*; Ochi, Kotaro; Koike, Yuya*

Radioisotopes, 70(4), p.227 - 237, 2021/05

Behavior of radioactive caesium in river water and sediment in Tama river was investigated during 2012-2016. Concentrations of radioactive caesium in river water and sediment were decreased with time exponentially. Concentrations of suspended radioactive caesium, and radioactive caesium in sediment temporarily increased when sediments were resuspended due to rain. On the other hand, dissolved radioactive caesium was not easily impacted by this factor. Sequential extraction, elemental and crystal phase analysis were performed on the sediments and examined the chemical state of radioactive caesium as well as the adsorption mechanism. Radioactive caesium in sediment was present in a stable chemical form, and there is possibility that radioactive caesium was incorpolated in biotite.

Journal Articles

Recent evolution of fission-track chronometry; Advanced analytical methods, understanding of annealing kinetics, and developments of new dating systems

Sueoka, Shigeru; Shimada, Koji; Hasebe, Noriko*; Tagami, Takahiro*

Radioisotopes, 70(3), p.189 - 207, 2021/03

no abstracts in English

Journal Articles

Ultra-low-temperature thermochronology using optically stimulated luminescence (OSL)

Ogata, Manabu; Sueoka, Shigeru

Radioisotopes, 70(3), p.159 - 172, 2021/03

no abstracts in English

Journal Articles

Basics of fission-track geo- and thermo-chronometry; Revisiting its history to explore future potential

Hasebe, Noriko*; Sueoka, Shigeru; Tagami, Takahiro*

Radioisotopes, 70(3), p.117 - 130, 2021/03

no abstracts in English

Journal Articles

Thermochronometric studies of mountains in island arc settings based on fission-track method; A Review

Fukuda, Shoma; Sueoka, Shigeru; Tagami, Takahiro*

Radioisotopes, 70(3), p.173 - 187, 2021/03

Thermochronometric studies (e.g., fission-track thermochronometry) on major orogenic belts, such as collision zones and/or cratons have been successfully conducted since 1970s. However, such studies in arc-trench systems were limited so far. According to the development of thermochrology in three decades, the applicability for these regions has been identified. Thus, recent thermochronometric studies in an island arc setting have been proceeding. This paper introduces the current status of thermochronometric studies for mountain building process on arc-trench settings, especially in island arcs.

Journal Articles

Study on method for simultaneous determination of ambient dose equivalent rates and activity concentration in air for environmental radiation monitoring

Kowatari, Munehiko; Tanimura, Yoshihiko; Kessler, P.*; Neumaier, S.*; R$"o$ttger, A.*

Radioisotopes, 70(1), p.1 - 18, 2021/01

Journal Articles

True coincidence summing correction for cylindrical volume samples in $$gamma$$-ray spectrometry

Yamada, Takashi*; Asai, Masato; Yonezawa, Chushiro*; Kakita, Kazutoshi*; Hirai, Shoji*

Radioisotopes, 69(9), p.287 - 297, 2020/09

We have confirmed that the commercially available Japanese "standard" gamma-ray analysis programs do not consider the effect of sample volume in calculating true coincidence summing (TCS) corrections, which results in underestimation of $$^{134}$$Cs radioactivity in cylindrical volume samples. In this work, we have developed and examined a practical TCS correction method for general Ge detectors which consider the effect of sample volume properly, and have confirmed that this method can reduce the $$^{134}$$Cs radioactivity underestimation to less than 1%.

Journal Articles

Nuclear fallout encountered by oceanographic observation vessel Takuyo

Tsujimura, Norio

Radioisotopes, 69(8), p.253 - 261, 2020/08

The Japan Coast Guard observation vessel Takuyo encountered nuclear fallout originating from a U.S. nuclear weapon test detonated at Bikini Atoll on July 12, 1958. The exposure occurred two days after the detonation when the vessel was sailing southbound, about 300 km west of the danger area set up around the test site. From a small amount of rain sampled at the beginning of a rainsquall, a gross beta radioactivity of 16 kBq/L was observed, but no total precipitation measurement was made at that time. Therefore, the total amount of gross beta activity surface deposition density was alternatively derived based on an indication of a NaI(Tl) scintillation detector placed 0.3-m above the after deck of the Takuyo. By combining the maximum measured dose rate of 3.1 $$mu$$Sv/h aboard with the results of Monte Carlo simulations, the surface deposition density on the Takuyo was estimated to be 2 PBq/km$$^{2}$$, about 10 times higher than the past maximum observed in Japan in 1966. The resultant effective dose to crew members was also estimated to be below 100 $$mu$$Sv over the entire period of the voyage.

Journal Articles

Electrochemistry of actinide

Kitatsuji, Yoshihiro

Radioisotopes, 67(10), p.483 - 493, 2018/10

Electrochemical reactions and redox properties of actinides such as uranium and neptunium are outlined. The flow electrolysis enables rapid and high-efficient treatment. It was demonstrated to measure slow processes of actinide redox. Experimental results of electrolysis of actinide ions and the preparation method of oxidation state of the ions based on the fundamental data are described. Mediator reaction and catalysis observed in the process of electrolysis of actinide ions are also explained.

Journal Articles

Liquid-phase chemistry of rutherfordium (Rf), dubnium (Db) and seaborgium (Sg)

Nagame, Yuichiro

Radioisotopes, 67(10), p.507 - 526, 2018/10

Recent studies of the chemical separation and characterization experiments of the first three transactinide elements, rutherfordium (Rf), dubnium (Db) and seaborgium (Sg), conducted atom-at-a-time in liquid phases, are reviewed. A short description on experimental techniques based on partition methods, specifically automated rapid chemical separation systems, as well as on assessment of role of relativistic effects is also given. Perspectives for liquid phase chemistry experiments on heavier elements are briefly discussed.

Journal Articles

NMR study of actinide compounds; Case of actinide dioxides

Kambe, Shinsaku

Radioisotopes, 67(8), p.389 - 401, 2018/08

no abstracts in English

Journal Articles

Science of heavy and superheavy elements (nuclear physics); Experimental studies on shell structure of superheavy nuclei

Asai, Masato

Radioisotopes, 67(6), p.291 - 298, 2018/06

Stability and limit of existence essentially depend on nuclear shell structure. It is theoretically predicted that stable doubly-closed-shell spherical superheavy nuclei should exist around the region of the proton number 114 to 126 and the neutron number 172 to 184, although their locations and degree of stability have not been established because of large variety of theoretical predictions. On the other hand, recent advances on experimental techniques have made it possible to accumulate experimental data concerning the shell structure of superheavy nuclei, such as half-lives and nuclear masses. In addition, some pioneering experiments have been performed to directly establish the level structure of superheavy nuclei through spectroscopic methods. This paper introduces the current status of experimental studies on nuclear shell structure of superheavy nuclei.

Journal Articles

Knowledge discovery of suppressive effect of disease and increased anti-oxidative function by low-dose radiation using self-organizing map

Kanzaki, Norie; Kataoka, Takahiro*; Kobashi, Yusuke*; Yunoki, Yuto*; Ishida, Tsuyoshi*; Sakoda, Akihiro; Ishimori, Yuu; Yamaoka, Kiyonori*

Radioisotopes, 67(2), p.43 - 57, 2018/02

We previously reported that low-dose radiation induces the anti-oxidative function in many organ systems of mice. This results in the suppression of several kinds of oxidative stress-induced damage. This study was conducted with the objective of revealing the health effects of low-dose radiation obtained from our previous reports and searching for a new treatment based on low-dose radiation, such as radon therapy. We extracted the characteristics of the effects of low dose radiation suppressing diseases and enhancing the anti-oxidative function using fuzzy answer by self-organizing map (SOM) based on mutual knowledge. The relationship between the suppressive effect and increased antioxidative function was shown in our result, and the concentration dependence of the effect against pain was shown on the output map. Although the effect against other organs depending on concentration was unpredictable, our results indicate that low-dose radiation may also be suitable for treatment of liver disease and brain disease.

Journal Articles

Modern radiation chemistry (Applications), 13; Dose heterogeneity from a viewpoint of microdosimetry

Sato, Tatsuhiko

Radioisotopes, 66(11), p.507 - 512, 2017/11

Absorbed doses are inhomogeneously distributed in microscopic scales such as DNA and cell nucleus. In order to quantify the radiation effect due to this inhomogeneity, the probability density of the absorbed dose should be evaluated. This report reviews the concept of dose inhomogeneity from the viewpoint of microdosimetry, and introduces our established method for calculating the probability density of microscopic doses and its applications to radiation biology.

Journal Articles

Modern radiation chemistry (Applications), 18; Radiation chemistry at solid/water interfaces

Kumagai, Yuta

Radioisotopes, 66(11), p.537 - 541, 2017/11

Radiation effects on the mixtures of inorganic oxides and water have been investigated for understanding radiation chemistry in solid-liquid systems. A number of studies revealed that energy deposition on solid phase stimulates reactions at the interface. This energy/charge transfer has been demonstrated by experiments to affect early stage of the radiation-induced reaction. However, the interfacial reactions subsequent to the energy/charge transfer require further studies. Here, we will see gaps between the basic understanding on the early stage and radiation effects in solid-liquid systems connected to applications, taking zeolite/water and uranium oxide/water interfaces for examples. Understanding of the interfacial reactions subsequent to the energy/charge transfer would bridge the gaps and enable to predict the radiation effects in applications.

Journal Articles

Modern radiation chemistry (Applications), 24; Radiation chemistry and positron annihilation

Hirade, Tetsuya

Radioisotopes, 66(11), p.587 - 593, 2017/11

Positron, anti-particle of electron, annihilates with the lifetime of 100ps to several ns in condensed matter. The energy of the mass of both particles emits as two $$gamma$$-rays. The annihilation rate of energy of $$gamma$$-rays indicate information just before the annihilation. Positrons have some possibility of reaction with excess electrons to form Positronium (Ps). Ps formation occur within ~ps, therefore Ps formation can be a probe of very fast reactions. Moreover, long lived triplet Ps can have reaction with reactive species until the lifetime of ~ns. Here, methods of positron annihilation research for radiation chemistry and some researches done by positron annihilation methods are introduced.

Journal Articles

Modern radiation chemistry (Applications), 16; Computer simulation study of initial process of radiation biological effect

Watanabe, Ritsuko*; Kai, Takeshi; Hattori, Yuya*

Radioisotopes, 66(11), p.525 - 530, 2017/11

To understand the mechanisms of radiation biological effects, modeling and simulation studies are important. In particular, simulation approach is powerful tool to evaluate modeling of mechanisms and the relationship among experimental results in different spatial scale of biological systems such as DNA molecular and cell. This article summarizes our approach to evaluate radiation action on DNA and cells by combination of knowledge in radiation physics, chemistry and biology. It contains newly theoretical approach to estimate physico-chemical process of DNA damage induction in addition to typical method of DNA damage prediction. Outline of the mathematical model for dynamics of DNA damage and cellular response is also presented.

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