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Journal Articles

A Phoswich alpha/beta detector for monitoring in the site of Fukushima Daiichi Nuclear Power Station

Morishita, Yuki; Takasaki, Koji; Kitayama, Yoshiharu; Tagawa, Akihiro; Shibata, Takuya; Hoshi, Katsuya; Kaneko, Junichi*; Higuchi, Mikio*; Oura, Masatoshi*

Radiation Measurements, 160, p.106896_1 - 106896_10, 2023/01

 Times Cited Count:0 Percentile:0.04(Nuclear Science & Technology)

This study proposes a newly developed phoswich alpha/beta detector that can discriminate alpha and beta particles emitted from the alpha and beta contaminations in the FDNPS site. The phoswich alpha/beta detector is made up of two layers of scintillators that detect alpha and beta particles. The pulse shape discrimination (PSD) method was used to detect alpha particles in high beta particle and high gamma-ray (comparable to gamma-ray dose rate near the FDNPS reactor building) environments. Due to a 23.3% full width at half maximum (FWHM) energy resolution for alpha particles, the detector can be used to distinguish between nuclear fuel materials such as plutonium and its radon progeny (Po-214). Moreover, the detector could distinguish alpha particles from $$^{137}$$Cs gamma rays with a dose rate background up to 9.0 mSv/h. It is the first to demonstrate that the developed phoswich detector can be used to discriminate and measure alpha and beta particles of the actual contaminated FDNPS samples.

JAEA Reports

Examination of exposure management method for the eye lens at Oarai Research and Development Institute

Matsuoka, Amane; Yasumune, Takashi; Kojima, Nobuhiro; Miyauchi, Hideaki; Takasaki, Koji; Hashimoto, Makoto

JAEA-Review 2021-055, 11 Pages, 2021/12


The dose limit for the eye lens was lowered on April 1 2021, and a 3 mm dose equivalent was added to the calculation. The guidelines require that lens dosimeters be worn and managed when there is a risk of exceeding control standards. In this report, in order to examine future management methods, we investigated whether work that might exceed the equivalent dose limit was performed in the past. As a result of the investigation, the exposure dose for all works after fiscal year 2008 was sufficiently low compared to the equivalent dose limit. For this reason, it is considered that there is no need for additional management of wearing a personal dosimeter near the eyes for the work that is normally performed. In the future, as in the past, the basic management method will be to wear a dosimeter only on the basic part of the trunk under uniform exposure conditions, and to wear a dosimeter on the basic part of the trunk and the maximum dose part under nonuniform exposure conditions. When performing work with a high exposure dose to the eye lens, a dosimeter should be worn near the eye to measure the 3 mm dose equivalent.

JAEA Reports

Activity median aerodynamic diameter relating to contamination at Plutonium Fuel Research Facility in Oarai Research and Development Center; Particle size analysis for plutonium particles using imaging plate

Takasaki, Koji; Yasumune, Takashi; Hashimoto, Makoto; Maeda, Koji; Kato, Masato; Yoshizawa, Michio; Momose, Takumaro

JAEA-Review 2019-003, 48 Pages, 2019/03


June 6, 2017, at Plutonium Fuel Research Facility in Oarai Research and Development Center of JAEA, when five workers were inspecting storage containers containing plutonium and uranium, resin bags in a storage container ruptured, and radioactive dust spread. Though they were wearing a half face mask respirator, they inhaled radioactive materials. In the evaluation of the internal exposure dose, the aerodynamic radioactive median diameter (AMAD) is an important parameter. We measured 14 smear samples and a dust filter paper with imaging plates, and estimated the AMAD by image analysis. As a result of estimating the AMAD, from the 14 smear samples, the AMADs are 4.3 to 11 $$mu$$m or more in the case of nitrate plutonium, and the AMADs are 5.6 to 14 $$mu$$m or more in the case of the oxidized plutonium. Also, from the dust filter paper, the AMAD is 3.0 $$mu$$m or more in the case of nitrate plutonium, and the AMAD is 3.9 $$mu$$m or more in the case of the oxidized plutonium.

Journal Articles

Spectroscopic measurements of L X-rays with a TES microcalorimeter for a non-destructive assay of transuranium elements

Nakamura, Keisuke; Morishita, Yuki; Takasaki, Koji; Maehata, Keisuke*; Sugimoto, Tetsuya*; Kiguchi, Yu*; Iyomoto, Naoko*; Mitsuda, Kazuhisa*

Journal of Low Temperature Physics, 193(3-4), p.314 - 320, 2018/11

 Times Cited Count:0 Percentile:0(Physics, Applied)

Journal Articles

Improvement of estimation of $$^{131}$$I concentrations in the air using data measured by monitoring posts applied by determination of passing-through time of plume using noble gas counts

Yamada, Junya; Hashimoto, Makoto; Seya, Natsumi; Haba, Risa; Muto, Yasunobu; Shimizu, Takehiko; Takasaki, Koji; Yokoyama, Sumi*; Shimo, Michikuni*

Hoken Butsuri, 52(1), p.5 - 12, 2017/03

The purpose of this study is to improve a quick method for estimation of $$^{131}$$I concentrations in the air using data measured by monitoring posts in case that a nuclear disaster occurs. In this method, $$^{131}$$I concentrations were estimated by multiplying $$^{131}$$I count rates of cloud-shine measured with NaI (Tl) detector by concentration conversion factor. A previous study suggested that it was difficult to determine passing-through time of plume from temporal change of $$^{131}$$I count rates or dose rate. Our study applies the method for estimating passing-through time of plume from temporal change of noble gas counts. The $$^{131}$$I concentrations in the air at Oarai center, Japan Atomic Energy Agency resulting from the accident at the Fukushima Daiichi Nuclear Power Plant were estimated by proposal technique. The result of comparison of this method with sampling method for $$^{131}$$I concentrations in the air were within factor 3.

Journal Articles

Calculation of conversion factor for estimation of $$^{131}$$I concentrations in the air from pulse-height distribution observed by NaI(Tl) detector in monitoring posts

Yamada, Junya; Hashimoto, Makoto; Seya, Natsumi; Haba, Risa; Muto, Yasunobu; Shimizu, Takehiko; Takasaki, Koji; Yokoyama, Sumi*; Shimo, Michikuni*

Radioisotopes, 65(10), p.403 - 408, 2016/10

The purpose of this study is to develop a quick method for estimation of $$^{131}$$I concentrations in the air using data measured by monitoring posts. In this method, $$^{131}$$I concentrations were estimated by multiplying $$^{131}$$I count rates at the full-energy peak measured with a NaI(Tl) detector by a concentration conversion factor. The concentration conversion factor for monitoring posts in JAEA Oarai Center was calculated with an EGS5 Monte Carlo code. As a result, the concentration conversion factor for an infinite-air-source was 25.7 Bq/m$$^{3}$$/cps.

Journal Articles

Applicability of meteorological statistics over a 5-year period to evaluation of annual average of radionuclide concentration in surface air; Based on meteorological statistics for 20 years at Oarai Research and Development Center, JAEA

Seya, Natsumi; Hashimoto, Makoto; Nemoto, Koji*; Shimizu, Takehiko; Takasaki, Koji

Hoken Butsuri, 49(1), p.29 - 38, 2014/03

Evaluation of annual average of radionuclide concentration in surface air obtained from atmospheric dispersion factor is intended to determine a public dose as a primary source for the safety analysis of nuclear facilities in normal operation. Oarai Research and Development Center (ORDC) of the JAEA have used fixed 5-year meteorological statistics for derivation of atmospheric dispersion factors as average conditions. To show that the meteorological statistics for any 5-year period could be used as representative data for evaluation of average conditions, annual average (1-year average) and 5-year average of evaluated radionuclide concentrations derived from the meteorological data observed from 1991 to 2010 at ORDC were analyzed. The fluctuations of evaluated radionuclide concentrations of any 5-year averages were smaller than those of 1-year averages during 20 years, and any 5-year averages contained no rejections by the F-test (5% significance level). It means that any 5-year averages of radionuclide concentration evaluations are well representative for the safety analysis under normal condition in ORDC.

JAEA Reports

Research for spectroscopy of fuel debris using superconducting phase transition edge sensor microcalorimeter; Measurement experiment and simulated calculation (Joint research)

Takasaki, Koji; Yasumune, Takashi; Onishi, Takashi; Nakamura, Keisuke; Ishimi, Akihiro; Ito, Chikara; Osaka, Masahiko; Ono, Masashi*; Hatakeyama, Shuichi*; Takahashi, Hiroyuki*; et al.

JAEA-Research 2013-043, 33 Pages, 2014/01


In the Fukushima Daiichi Nuclear Power Plant, it is assumed that the core fuels melted partially or wholly, and the normal technique of accounting for a fuel assembly is not applicable. Therefore, it is necessary to develop the transparent and rational technique of accounting in the process of collection and storage of fuel debris. In this research, an application of the superconducting phase Transition Edge Sensor microcalorimeter (TES microcalorimeter) is studied for the accounting of nuclear materials in the fuel debris. It is expected that the detailed information of nuclear materials and fission products in fuel debris is obtained by using a high-resolution characteristic of TES microcalorimeter. In this report, the principle of TES microcalorimeter, the measurement experiment using TES in JAEA, and the simulated calculation using the EGS5 code system are summarized.

JAEA Reports

Environmental radiation monitoring resulting from the accident at the Fukushima Daiichi Nuclear Power Plant, conducted by Oarai Research and Development Center, JAEA; Results of ambient gamma-ray dose rate, atmospheric radioactivity and meteorological observation

Yamada, Junya; Seya, Natsumi; Haba, Risa; Muto, Yasunobu; Numari, Hideyuki*; Sato, Naomitsu*; Nemoto, Koji*; Takasaki, Hiroichi*; Shimizu, Takehiko; Takasaki, Koji

JAEA-Data/Code 2013-006, 100 Pages, 2013/06


This report presents the results of emergency radiation monitoring, including ambient $$gamma$$-ray dose rate, atmospheric radioactivity, meteorological observation and estimation of internal exposure resulting from the accident at the Fukushima Daiichi Nuclear Power Plant triggered by the earthquake off the pacific coast of Tohoku on 11th March 2011, conducted by Oarai Research and Development Center (ORDC), Japan Atomic Energy Agency (JAEA) from March to May, 2011. ORDC is located in the central part of Ibaraki prefecture and approximately 130 km southwest of the Fukushima Daiichi Nuclear Power Plant. From around 15th to 21st March, 2011, the ambient $$gamma$$-ray dose rate increased and many radioactive nuclides were detected in the atmosphere.

Journal Articles

Development of a microcalorimeter with transition edge sensor for detection of LX rays emitted by transuranium elements

Nakamura, Keisuke; Maeda, Makoto*; Yasumune, Takashi*; Maehata, Keisuke*; Ishibashi, Kenji*; Tanaka, Keiichi*; Umeno, Takahiro*; Takasaki, Koji; Momose, Takumaro

Radiation Protection Dosimetry, 146(1-3), p.88 - 91, 2011/07

 Times Cited Count:1 Percentile:10.97(Environmental Sciences)

A Transition Edge Sensor (TES) microcalorimeter has been developed for use as an energy dispersive X-ray spectrometer. A TES microcalorimeter is a thermal detector used to measure the energy of an incident photon with increase in temperature. In this work, a TES microcalorimeter with a 5$$mu$$m Au absorber was developed for use in measuring LX rays emitted from transuranium elements. Furthermore, as a cooling system a dilution refrigerator utilizing a Gifford-McMahon refrigerator was used, which needs no liquid helium. The performance of the TES microcalorimeter was evaluated by measuring the LX rays emitted by an $$^{241}$$Am source. This system proved effective in the measurement of the LX rays because the full width at half maximum of the L$$_{beta1}$$X ray was about 80 eV.

Journal Articles

An Autoradiographical method using an imaging plate for the analyses of plutonium contamination in a plutonium handling facility

Takasaki, Koji; Sagawa, Naoki; Kurosawa, Shigeyuki; Mizuniwa, Harumi

Journal of Nuclear Science and Technology, 48(6), p.911 - 918, 2011/06

 Times Cited Count:10 Percentile:58.76(Nuclear Science & Technology)

An autoradiographical method using an imaging plate (IP) was developed to analyze the plutonium contamination in the plutonium handling facility and was applied to the monitoring of the workplace in a practical uranium-plutonium mixed oxide (MOX) fuel fabrication facility. A good relationship between the photo stimulated luminescence (PSL) intensities of IP and radioactivities measured by a radiation counter was obtained by the least-square fitting, taking the fading effect into consideration. The $$alpha$$-radioactivities of plutonium contamination were derived from the PSL image in this IP method, and their relative errors were evaluated from exposure time.

Journal Articles

JAEA Reports

Application of imaging plate to the radiation protection in the MOX fuel fabrication facility

Sagawa, Naoki; Yamazaki, Takumi; Kurosawa, Shigeyuki*; Izaki, Kenji; Mizuniwa, Harumi; Takasaki, Koji

JAEA-Technology 2010-051, 35 Pages, 2011/03


The image analysis method using a imaging plate (IP) is recent technique, and this method can get the information of radioactivity distribution by the unit of Photo Simulated Luminescence (PSL). We have investigated the PSL images obtained by measuring some plutonium samples which are radiation protection samples in order to apply imaging plate to the radiation protection at the MOX fuel facility. Plutonium spots were extracted from the PSL image extracted by the threshold, in which about 99% of the back ground was excluded, and identified by the additional requirement that the spot size is more than 40 pixels. The average background is subtracted from PSL strength of the spot area identified as Pu, and the radioactivity of the Pu spot was evaluated by multiplying the conversion calculation that is in consideration of fading.

Journal Articles

Wide-range krypton gas monitor using a plastic scintillation detector operated in current mode with a gate circuit

Takasaki, Koji; Kobayashi, Hirohide; Suzuki, Hideki; Ushigome, Sadaharu*

Journal of Nuclear Science and Technology, 47(3), p.255 - 261, 2010/03

 Times Cited Count:3 Percentile:24.76(Nuclear Science & Technology)

The wide-range krypton-85 detector was developed for monitoring of krypton-85 gas, which was discharged from the stack of a nuclear fuel reprocessing plant and varied largely in concentration. The detector combined a current-mode-operated plastic scintillation counter with a gated photomultiplier. The discrimination voltage of gated photomultiplier was determined, and the effects of temperature and humidity were examined on the background measurement. The detector was calibrated by krypton-85 gas and the decision threshold was estimated. These examinations showed that the wide-range krypton-85 detector worked in the measurement range as wide as 10$$^{-3}$$-10$$^{2}$$ Bq/cm$$^{3}$$ in linearity and the decision threshold of krypton-85 concentration was 1.3$$times$$10$$^{-3}$$ Bq/cm$$^{3}$$ for 10-minute measurement. The parallel measurement was made between this detector and a GM counter in the reprocessing laboratory. Both concentrations showed a good agreement with each other.

Journal Articles

Development of a TES microcalorimeter for spectroscopic measurement of LX-rays emitted by transuranium elements

Maehata, Keisuke*; Nakamura, Keisuke*; Yasumune, Takashi*; Ishibashi, Kenji*; Takasaki, Koji; Tanaka, Keiichi*; Odawara, Akikazu*; Nagata, Atsushi*

Journal of Nuclear Science and Technology, 47(3), p.308 - 313, 2010/03

 Times Cited Count:5 Percentile:36.7(Nuclear Science & Technology)

A phase transition edge sensor (TES) microcalorimeter was developed for the energy dispersive measurement of LX-ray photons emitted from transuranium elements. The phase transition temperature of the TES was designed to be 200 mK by using bilayer structure of Au of 120 nm thick and Ti of 50 nm thick. The Au layer of 5.0 $$mu$$m thick was deposited on the Au/Ti bilayer for absorption efficiency of 50% and counting rate of 100 counts per second in the detection of LX-ray photons with the energy from 10 to 20 keV. The TES microcalorimeter was operated for the detection of LX-ray photons emitted from $$^{241}$$Am, $$^{238}$$Pu and $$^{239}$$Pu sources. The decay time constant of 180 $$mu$$s of detection signal pulses allowed the TES microcalorimeter operating with the counting rate higher than 100 counts per second. The energy resolution was obtained to be 50 eV of FWHM value for a peak corresponding to $$^{237}$$Np L$$beta$$$$_{1}$$ X-ray of 17.75 keV.

JAEA Reports

Examination of fabric of protective clothing suitable for sweltering radiation work; Influence on survey of contamination (MOX) in wet condition with sweat

Horikoshi, Yoshinori; Nemoto, Norio; Kurosawa, Shigeyuki*; Takasaki, Koji; Mizuniwa, Harumi

JAEA-Testing 2008-003, 29 Pages, 2008/04


In the Plutonium Fuel Technical Development Center, protective clothing suitable for sweltering radiation work was examined. Since it worried about the influence of wet protective clothing with sweat on detection of MOX powder contamination, Detection situations, the diffusion of contamination, and the osmosis and penetrability to wet protective clothing were examined about the present fabric and other new fabrics. As a result of examination, it was confirmed that the influence of detection on alpha ray in the wet condition of new fabrics was smaller than the current fabric. This report compiled the result of examination and points in the fabric selection suitable for protective clothing.

JAEA Reports

Development of image-analysis method of plutonium samples by imaging plate; Measurement of plutonium samples in mixed oxide fuel fabrication facility

Takasaki, Koji; Sagawa, Naoki; Kurosawa, Shigeyuki*; Shioya, Satoshi; Suzuki, Kazunori; Horikoshi, Yoshinori; Mizuniwa, Harumi

JAEA-Technology 2008-028, 73 Pages, 2008/03


Recently, an imaging plate (IP) was developed. Pu analysis by an IP was studied in the JAEA Cooperative Research Scheme on the Nuclear Fuel Cycle, and the availability about detection of Pu and discrimination with radon progenies was shown. In order to apply these results to the radiation control, this research aims at evaluation of radioactivity, discrimination with radon progenies, and evaluation of AMAD by an IP. In the conventional autoradiography (ARG) by a ZnS and Polaroid film, Contamination of Pu can only be grasped by viewing. Since the digital data of the radiation and location is obtained by an IP, Pu can be detected quantitatively and radioactivity can be evaluated. As a result of this research, the image of alpha emitter on an IP is the same as that of the conventional ARG, and can be applied also to the ARG of beta and $$gamma$$ emitter. In measurement of Pu, the function of Image J (image-analysis software) was very available. Pu radioactivity was evaluated by an IP.

Journal Articles

Practical action levels for chelation therapy in plutonium inhalation using nose swab

Kurihara, Osamu; Takada, Chie; Takasaki, Koji; Ito, Kimio; Momose, Takumaro; Miyabe, Kenjiro

Radiation Protection Dosimetry, 127(1-4), p.411 - 414, 2007/11

 Times Cited Count:7 Percentile:48.2(Environmental Sciences)

Practical action levels for beginning chelation therapy to remove plutonium in the body are now under discussion in Japan since there has been no experience in administrating agents to a subject in accidental intake in Japan although a first commercial reprocessing plant is about to start operation. Recently, International Commission on Radiological Protection (ICRP) proposed some medical intervention levels for chelation therapy on ICRP Publication 96. These levels are determined based on internal dose however common monitoring methods such as lung counting or excreta analysis are not necessarily suitable in terms of both sensitivity and promptness. As an alternative, the authors paid attention to nose swabs and introduced the practical action levels.

Journal Articles

REIDAC; A Software package for retrospective dose assessment in internal contamination of radionuclides

Kurihara, Osamu; Hato, Shinji; Kanai, Katsuta; Takada, Chie; Takasaki, Koji; Ito, Kimio; Ikeda, Hiroshi*; Oeda, Mikihiro*; Kurosawa, Naohiro*; Fukutsu, Kumiko*; et al.

Journal of Nuclear Science and Technology, 44(10), p.1337 - 1346, 2007/10

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

In the case of internal contamination of radionuclides, it is necessary to perform internal dose assessment for radiation protection. For this purpose, the ICRP has given the dose coefficients and the retention and excretion rates for various radionuclides. However, these dosimetric quantities are calculated only in typical conditions, therefore, are not necessarily covered enough in the case of dose assessment in which specific information on the incident or/and individual biokinetic characteristics should be taken into account retrospectively. This paper describes a developed PC-based package of software REIDAC to meet the needs in retrospective dose assessment. REIDAC was verified by comparisons with dosimetric quantities given on the ICRP publications and several examples of practical use were also shown.

Journal Articles

Development of $$^{241}$$Am lung monitoring system using an imaging plate

Hirota, Masahiro*; Kurihara, Osamu; Takada, Chie; Takasaki, Koji; Momose, Takumaro; Deji, Shizuhiko*; Ito, Shigeki*; Saze, Takuya*; Nishizawa, Kunihide*

Health Physics, 93(1), p.28 - 35, 2007/07

 Times Cited Count:4 Percentile:31.91(Environmental Sciences)

A new $$^{241}$$Am lung monitoring system without shielding was devised by using an imaging plate system. The Lawrence Livermore National Laboratory's realistic torso phantom containing a $$^{241}$$Am lung was covered by imaging plates sealed in lightproof bags. The imaging plate system displayed $$^{241}$$Am lung images characteristic of the lung shape of the torso phantom. The imaging plate system's lower detection limits of 14 Bq for 60 min exposure and 6 Bq for 300 min were the same levels as those of the phoswich detectors and the germanium detectors placed in shielded rooms. The imagingplate system for 60 min exposure detected about 2% of the annual limit of 740 Bq for $$^{241}$$Am inhalation. A lung monitoring system using imaging plates is applicable for $$^{241}$$Am lung monitoring.

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