Toshiso Kosako

The University of Tokyo, Tōkyō, Japan

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Publications (61)54.6 Total impact

  • Journal of Nuclear Science and Technology 08/2014; 37(sup1):522-525. DOI:10.1080/00223131.2000.10874942 · 1.45 Impact Factor
  • Journal of Nuclear Science and Technology 08/2014; 37(sup1):655-659. DOI:10.1080/00223131.2000.10874970 · 1.45 Impact Factor
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    ABSTRACT: Monitoring preparation for internal contamination with actinides (e.g. Pu and Am) is required to assess internal doses at nuclear fuel cycle-related facilities. In this paper, the authors focus on skull counting in case of single-incident inhalation of (241)Am and propose an effective procedure for skull counting with an existing system, taking into account the biokinetic behaviour of (241)Am in the human body. The predicted response of the system to skull counting under a certain counting geometry was found to be only ∼1.0 × 10(-5) cps Bq(-1) 1y after intake. However, this disadvantage could be remedied by repeated measurements of the skull during the late stage of the intake due to the predicted response reaching a plateau at about the 1000th day after exposure and exceeding that in the lung counting. Further studies are needed for the development of a new detection system with higher sensitivity to perform reliable internal dose estimations based on direct measurements.
    Radiation Protection Dosimetry 06/2014; 163(3). DOI:10.1093/rpd/ncu189 · 0.86 Impact Factor
  • K Tani, S Iwai, T Kosako
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    ABSTRACT: Measurements for internal dose assessment are required to be conducted based on the distribution of radionuclides in the body, which may change depending on the lapsed time. In this study, a biokinetic analysis code, which can be used in practical radiation control is developed, and the results of (60)Co and (137)Cs biokinetics are visualised as examples by drawing the depositions for each organ and tissue in a figure of the body as a function of lapsed time. In addition, based on visualised biokinetics, precautions for in vivo measurements are also discussed. These discussions led to the conclusion that the information of visualised biokinetics is useful for actual measurements in practical radiation control.
    Radiation Protection Dosimetry 06/2013; 157(3). DOI:10.1093/rpd/nct153 · 0.86 Impact Factor
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    ABSTRACT: Reaction rate distributions were measured inside a 60-cm thick concrete pile placed at the lateral position of a thick (stopping length) iron target that was bombarded with heavy ions, 400 MeV/u C and 800 MeV/u Si. Foils of aluminum and gold, as well as gold, tungsten and manganese covered with cadmium were inserted at various locations in the concrete pile to serve as activation detectors. Features of reaction rate distribution, such as the shape of the reaction rate profile, contribution of the neutrons from intra-nuclear cascade and that from evaporation to the activation reactions are determined by the analysis of measured reaction rates. The measured reaction rates were compared with those calculated with radiation transport simulation codes, FLUKA and PHITS, to verify their capability to predict induced activity. The simulated reaction rates agree with the experimental results within a factor of three in general. However, systematic discrepancies between simulated reaction rates and measured reaction rates attributed to the neutron source terms are observed.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 01/2012; Volume 271:65-71. DOI:10.1016/j.nimb.2011.11.008 · 1.19 Impact Factor
  • Kazumasa Shimada, Takeshi Iimoto, Toshiso Kosako
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    ABSTRACT: Personal neutron dosimeters are necessary for radiation protection of nuclear workers in high energy accelerator facilities. To improve sensitivity for high energy neutrons above 10 MeV, a new personal neutron dosimeter was designed using a solid state nuclear track detector (CR-39) covered with Multi-Layer radiator consisting of polyethylene, polyamide and iron/aluminum sheets. In this work, we investigated various radiator combinations and thicknesses in order to detect high energy neutrons above 10 MeV. Energy response of each radiator was calculated using the multi-purpose Monte Carlo simulation code, Particle and Heavy Ion Transport System (PHITS). To evaluate the accuracy of our calculations, the energy response of each radiator was measured in a mono-energetic neutron field at the Facility of Radiation Standard (FRS) of the Japan Atomic Energy Agency (JAEA). The energy response of each radiator calculated by PHITS was in good agreement with our experimental results. The results obtained in this research indicate that PHITS is a useful software tool for the design of new personal neutron dosimeters using CR-39 and using Multi-layer radiator approach.
    Radiation Measurements 12/2011; 46(12). DOI:10.1016/j.radmeas.2011.10.001 · 1.14 Impact Factor
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    ABSTRACT: Spallation and neutron capture reaction rate distributions were measured using activation detectors inside a 90-cm thick ordinary concrete pile exposed to a field of secondary particles escaping a thick (stopping length) iron target bombarded with various intermediate energy ions, 230 MeV/u He, 400 MeV/u C, and 800MeV/u Si. Activation detectors of aluminum, bismuth, gold, and gold covered with cadmium were inserted at various depths in the concrete pile. In addition, the distributions of activation reaction rate were simulated by FLUKA and PHITS Monte-Carlo codes. Generally, comparison of measured and calculated reaction rates show agreement within a factor of two. The experimental data will be useful for benchmarking Monte-Carlo radiation transport simulation code capabilities in estimating radioactivity induced in accelerator radiation shielding.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 09/2011; 269:1929-1939. DOI:10.1016/j.nimb.2011.05.031 · 1.19 Impact Factor
  • Makoto Hashimoto, Takeshi Iimoto, Toshiso Kosako
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    ABSTRACT: A dose evaluation using multiple radiation detectors can be improved by the convex optimisation method. It enables flexible dose evaluation corresponding to the actual radiation energy spectrum. An application to the neutron ambient dose equivalent evaluation is investigated using a mixed-gas proportional counter. The convex derives the certain neutron ambient dose with certain width corresponding to the true neutron energy spectrum. The range of the evaluated dose is comparable to the error of conventional neutron dose measurement equipments. An application to the neutron individual dose equivalent measurement is also investigated. Convexes of particular dosemeter combinations evaluate the individual dose equivalent better than the dose evaluation of a single dosemeter. The combinations of dosemeters with high orthogonality of their response characteristics tend to provide a good suitability for dose evaluation.
    Radiation Protection Dosimetry 07/2011; 146(1-3):65-8. DOI:10.1093/rpd/ncr113 · 0.86 Impact Factor
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    ABSTRACT: The International Commission on Radiological Protection has recommended that cosmic radiation exposure of crew in commercial jet aircraft be considered as occupational exposure. In Japan, the Radiation Council of the government has established a guideline that requests domestic airlines to voluntarily keep the effective dose of cosmic radiation for aircraft crew below 5 mSv y(-1). The guideline also gives some advice and policies regarding the method of cosmic radiation dosimetry, the necessity of explanation and education about this issue, a way to view and record dose data, and the necessity of medical examination for crew. The National Institute of Radiological Sciences helps the airlines to follow the guideline, particularly for the determination of aviation route doses by numerical simulation. The calculation is performed using an original, easy-to-use program package called 'JISCARD EX' coupled with a PHITS-based analytical model and a GEANT4-based particle tracing code. The new radiation weighting factors recommended in 2007 are employed for effective dose determination. The annual individual doses of aircraft crew were estimated using this program.
    Radiation Protection Dosimetry 05/2011; 146(1-3):123-5. DOI:10.1093/rpd/ncr133 · 0.86 Impact Factor
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    ABSTRACT: Neutron-induced reaction rate depth profiles inside concrete shield irradiated by intermediate energy neutron were calculated using a Monte-Carlo code and compared with an experiment. An irradiation field of intermediate neutron produced in the forward direction from a thick (stopping length) target bombarded by 400 MeV nucleon(-1) carbon ions was arranged at the heavy ion medical accelerator in Chiba. Ordinary concrete shield of 90 cm thickness was installed 50 cm downstream the iron target. Activation detectors of aluminum, gold and gold covered with cadmium were inserted at various depths. Irradiated samples were extracted after exposure and gamma-ray spectrometry was performed for each sample. Comparison of experimental and calculated shows good agreement for both low- and high-energy neutron-induced reaction except for (27)Al(n,X)(24)Na reaction at the surface.
    Radiation Protection Dosimetry 04/2011; 146(1-3):356-9. DOI:10.1093/rpd/ncr188 · 0.86 Impact Factor
  • Takeshi Iimoto, Toshiso Kosako
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    ABSTRACT: Activities on radon management strategy of international organisations (International Atomic Energy Agency, International Commission on Radiation Protection, etc.) should be carefully and continuously traced to discuss how to control radon in various environments, for example, dwellings, workplace, underground, caves, mines, hot springs, disposal facilities and so on. It is more reasonable in parallel to set radon reference level by effective dose criteria of Sv y(-1) as well as by radon concentration in air of Bq m(-3). How to investigate radon concentration in each environment, and how to make decisions on needed action for radiation protection from natural radon,--these should be discussed for each environmental situation on a case-by-case basis. International discussion as well as domestic discussion is continuously needed, not only among the radon specialists and regulators, but also including stakeholders who are the main users of regulation and guidance.
    Radiation Protection Dosimetry 04/2011; 146(1-3):217-20. DOI:10.1093/rpd/ncr153 · 0.86 Impact Factor
  • Ngoc Toan Tran, Takeishi Iimoto, Toshiso Kosako
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    ABSTRACT: In diagnostic radiology, the tube voltage [peak kilovoltage (kV(p))] is one of the most important parameter affecting both radiation exposure and image contrast. So, an accurate kV(p) meter is necessary to control kV(p) in the medical radiography practice with the overall uncertainty less than ± 5 % according to IEC 61676. Therefore, both invasive and non-invasive calibration methods of kV(p) meter were established and applied to different kinds of commercial quality control instruments for diagnostic radiology. Calibration of kV(p) meter by the invasive method is the most accurate (with uncertainty of 1.67 %, k=2); however, the non-invasive method also provides good results (with uncertainty of 3.12 %, k=2). Due to their detailed design, the commercial kV(p) meters have various responses with X-ray beam, so the working regime of a particular device type must be appropriately selected with a specific X-ray machine used for calibration of kV(p) meter.
    Radiation Protection Dosimetry 03/2011; 148(3):352-7. DOI:10.1093/rpd/ncr037 · 0.86 Impact Factor
  • Tatsuhiko Ogawa, Takeshi Iimoto, Toshiso Kosako
    01/2011; 46:70-75. DOI:10.5453/jhps.46.1a
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    ABSTRACT: Radon adsorption by activated charcoal collectors such as PicoRad radon detectors is known to be largely affected by temperature and relative humidity. Quantitative models are, however, still needed for accurate radon estimation in a variable environment. Here we introduce a temperature calibration formula based on the gas adsorption theory to evaluate the radon concentration in air from the average temperature, collection time, and liquid scintillation count rate. On the basis of calibration experiments done by using the 25 m³ radon chamber available at the National Institute of Radiological Sciences in Japan, we found that the radon adsorption efficiency may vary up to a factor of two for temperatures typical of indoor conditions. We expect our results to be useful for establishing standardized protocols for optimized radon assessment in dwellings and workplaces.
    Journal of Environmental Radioactivity 10/2010; 102(1):60-3. DOI:10.1016/j.jenvrad.2010.09.004 · 3.57 Impact Factor
  • Tenth meeting of the task force on Shielding Aspects of Accelerators, Targets and Irradiation Facilities; 06/2010
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    ABSTRACT: Reaction rate distribution in concrete with/without boron dopant up to a thickness of 60 cm was measured using Yayoi fast reactor located at University of Tokyo. The 7 reaction rates such as (197)Au(n,gamma), (59)Co(n,gamma), (115)In(n,n'), (55)Mn(n,gamma), (23)Na(n,gamma), (94)Zr(n,gamma) and (96)Zr(n,gamma) were measured at 12 different depths, and the reduction of the reaction rate as a result of boron doping was quantitatively analysed. These reaction rates were also used to determine epithermal neutron spectrum shape parameter. Monte Carlo simulations of the experimental setup were performed using the MCNP-5 code. Simulated depth profiles of reaction rates and the epithermal neutron spectrum shape parameter agreed with the experimental results with fair accuracy. This experimental results provide useful data to benchmark the accuracy of neutron transport codes in the prediction of transmission and neutron spectrum distortion in boron-doped concrete.
    Radiation Protection Dosimetry 02/2010; 140(1):89-95. DOI:10.1093/rpd/ncq034 · 0.86 Impact Factor
  • Takuya Abe, Toshiso Kosako, Kazuhisa Komura
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    ABSTRACT: In order to investigate the applicability of (212)Pb as a tracer for atmospheric transport in the sub-regional scale (few hundred kilometers in horizontal direction and up to approximately 1km by height), we measured the air concentrations of the short-lived radionuclide (212)Pb along with the long-lived (7)Be and (210)Pb near the ground surface. For this purpose, simultaneous observations were continued for several days at three locations: a reference point representative for standard land surface atmosphere conditions, a second location at an altitude 650 m near the reference point, and on a solitary island approximately 180 km from the reference point. Measurements of radioactivity in aerosol particle samples collected at intervals of 2-3h with a high-volume air sampler were performed by extremely low background gamma-ray spectrometry with the use of Ge detectors located at the Ogoya Underground Laboratory. Concentration of (7)Be or (210)Pb and their variation patterns was found to be similar among the three points during the whole observation period except for moment of the passage of a cold front. The results indicate that distributions of concentrations of the long-lived nuclides were uniform in this range. On the other hand, concentration levels and the variation patterns of the short-lived (212)Pb differed greatly from one location to another, reflecting differences in geographical location and altitude of the observation points. Additionally, there were certain indications that observed concentration of (212)Pb contained two components: an autogenous component from sources nearby and a heterogenous one from faraway sources carried by atmospheric horizontal transport. Results of this study provide experimental proof that (212)Pb can be used as a tracer of sub-regional atmospheric transport.
    Journal of Environmental Radioactivity 11/2009; 101(2):113-21. DOI:10.1016/j.jenvrad.2009.09.004 · 3.57 Impact Factor
  • Makoto Hashimoto, Takeshi Iimoto, Toshiso Kosako
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    ABSTRACT: A novel neutron dose measurement method that flexibly responds to variations in the neutron field is being developed by Japan Atomic Energy Agency. This is an implementation of the multi-detector method (first introduced in 1960s) for neutron dose evaluation using a convex hull in the response space defined for multiple detectors. The convex hull provides a range of possible neutron dose corresponding to the incident neutron spectrum. Feasibility of the method was studied using a simulated response of mixed gas proportional counter. Monochromatic neutrons are shown to be fundamentally suitable for mapping the convex. The convex hull can be further reduced taking into consideration a priori information about physically possible incident neutron spectra, for example, theoretically derived moderated neutron spectra originated from a fission neutron source.
    Radiation Protection Dosimetry 08/2009; 136(1):1-10. DOI:10.1093/rpd/ncp134 · 0.86 Impact Factor
  • Radioisotopes 01/2009; 58(5):195-207. DOI:10.3769/radioisotopes.58.195
  • 01/2009; 44(1):112-115. DOI:10.5453/jhps.44.112

Publication Stats

85 Citations
54.60 Total Impact Points

Institutions

  • 1981–2013
    • The University of Tokyo
      • • Nuclear Professional School
      • • Department of Nuclear Engineering and Management
      • • Faculty & Graduate School of Engineering
      Tōkyō, Japan
  • 1985
    • National Institute of Radiological Sciences
      Tiba, Chiba, Japan