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Yoshizawa, Michio
Nihon Genshiryoku Gakkai-Shi ATOMO
, 64(8), p.439 - 441, 2022/08
no abstracts in English
Takahashi, Masa; Yoshizawa, Michio
Isotope News, (778), p.30 - 33, 2021/12
no abstracts in English
Hirayama, Hideo*; Kawasaki, Masatsugu; Matsumura, Hiroshi*; Okura, Takehisa; Namito, Yoshihito*; Sanami, Toshiya*; Taki, Mitsumasa; Oishi, Tetsuya; Yoshizawa, Michio
Insights Concerning the Fukushima Daiichi Nuclear Accident, Vol.4; Endeavors by Scientists, p.295 - 307, 2021/10
Yonomoto, Taisuke; Nakashima, Hiroshi*; Sono, Hiroki; Kishimoto, Katsumi; Izawa, Kazuhiko; Kinase, Masami; Osa, Akihiko; Ogawa, Kazuhiko; Horiguchi, Hironori; Inoi, Hiroyuki; et al.
JAEA-Review 2020-056, 51 Pages, 2021/03
JAEA-Review-2020-056.pdf:3.26MB
A group named as "The group for investigation of reasonable safety assurance based on graded approach", which consists of about 10 staffs from Sector of Nuclear Science Research, Safety and Nuclear Security Administration Department, departments for management of nuclear facility, Sector of Nuclear Safety Research and Emergency Preparedness, aims to realize effective graded approach (GA) about management of facilities and regulatory compliance of JAEA. The group started its activities in September, 2019 and has had discussions through 10 meetings and email communications. In the meetings, basic ideas of GA, status of compliance with new regulatory standards at each facility, new inspection system, etc were discussed, while individual investigation at each facility were shared among the members. This report is compiled with expectation that it will help promote rational and effective safety management based on GA by sharing contents of the activity widely inside and outside JAEA.
Takasaki, Koji; Yasumune, Takashi; Hashimoto, Makoto; Maeda, Koji; Kato, Masato; Yoshizawa, Michio; Momose, Takumaro
JAEA-Review 2019-003, 48 Pages, 2019/03
JAEA-Review-2019-003.pdf:3.81MB
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 
m or more in the case of nitrate plutonium, and the AMADs are 5.6 to 14 m or more in the case of the oxidized plutonium. Also, from the dust filter paper, the AMAD is 3.0 m or more in the case of nitrate plutonium, and the AMAD is 3.9 m or more in the case of the oxidized plutonium.
Kowatari, Munehiko; Yoshitomi, Hiroshi; Oishi, Tetsuya; Yoshizawa, Michio
Progress in Nuclear Science and Technology (Internet), 6, p.86 - 90, 2019/01
Tanimura, Yoshihiko; Yoshizawa, Michio
Radiation Protection Dosimetry, 180(1-4), p.417 - 421, 2018/08
Times Cited Count：0 Percentile：0.00(Environmental Sciences)A high efficiency proton recoil telescope (PRT), which consists of a radiator, a 
E detector and an E detector, was developed to determine the neutron fluence in the 14.8 MeV mono-energetic neutron field at the FRS. A 2 mm thick plastic scintillation detector was employed as the radiator to increase the detection efficiency and compensate the energy loss of the recoil proton in the radiator. A thin and a thick silicon detectors with 150 m and 3 mm thick sensitive layers were employed as the E and E detectors, respectively. The detection efficiency was evaluated by the neutron measurements in the 14.8 MeV field for the distances from the radiator to E detector of 50 mm, 100 mm and 150 mm. The detection efficiency increases up to 3.7 
10
with the decrease in the distance, which is roughly a few orders of magnitude greater than those of common PRTs. These detection efficiencies are high enough to determine the neutron fluence at the 14.8 MeV field within a few hours.
Kowatari, Munehiko; Yoshitomi, Hiroshi; Nishino, Sho; Tanimura, Yoshihiko; Oishi, Tetsuya; Yoshizawa, Michio
Proceedings of 14th International Congress of the International Radiation Protection Association (IRPA-14), Vol.3 (Internet), p.1230 - 1238, 2017/11
The Facility of Radiation Standards (FRS) of the Japan Atomic Energy Agency (JAEA) offers various kinds of radiation calibration fields for calibration and testing for over three decades. The FRS-JAEA offers reliable X-ray, 
-ray, beta-ray and neutron calibration fields with a vast range of variety. The quality and a set of neutron calibration fields are particularly mentioned. Neutron calibration fields with energies ranging between 0.025 eV and 19 MeV enable users to check the whole items for performance test. Two different sets of beta-ray calibration fields were established and served for regular calibration of dosimeters mainly used in nuclear industries. Resent research accomplishments on -ray calibration fields can extend the upper limit of the energy up to 6 MeV. In addition to them, a simulated workplace neutron calibration field has been newly established for calibration of neutron dosimeters used inside the nuclear reactors.
-ray spectra measured inside and outside a house in FukushimaTanimura, Yoshihiko; Tomita, Jumpei; Yoshitomi, Hiroshi; Yoshizawa, Michio; Hakozaki, Ryozo*; Takahashi, Sohei*
Hoken Butsuri, 51(3), p.141 - 146, 2016/09
Photon spectra were measured inside and outside a house in Minami-Soma city by using a NaI(Tl) scintillation spectrometer. The photons were categorized into three groups according to their energy. The groups were (1) scattered photons, which include low energy photons, (2) direct photons from 
Cs and 
Cs sources and (3) the other photons. Then the ratios of the ambient dose equivalents H
(10) of the scattered photons to those of the direct photons from the Cs and Cs sources have been evaluated from the measured photon spectra. The ratios are high inside the house compared with those out of the house. It was found that the scattered photons contribute to the H(10) by more than 50
inside the house. The ambient dose equivalent average energies of the scattered photons are around 0.25 MeV both inside and outside the house. These data is worthwhile to design the optimum shielding for the protection against the public radiation exposure.
Am-Be sources in JAEA-FRSNishino, Sho; Tanimura, Yoshihiko; Ebata, Yoshiaki*; Yoshizawa, Michio
Journal of Radiation Protection and Research, 41(3), p.211 - 215, 2016/09
We developed the graphite-moderated neutron calibration fields using Am-Be sources at the Facility of Radiation Standard in the Japan Atomic Energy Agency. The neutron spectra of the fields were evaluated by Monte-Carlo calculation and measurements using the Bonner Multi-sphere Spectrometer. Reference values of fluence rates and dose equivalent rates of H
(10) and H
(10) were determined from neutron spectra by measurements. Currently, our fields are available for calibration or performance test of neutron measuring instruments.
Takahashi, Naoki; Yoshinaka, Kazuyuki; Harada, Akio; Yamanaka, Atsushi; Ueno, Takashi; Kurihara, Ryoichi; Suzuki, Soju; Takamatsu, Misao; Maeda, Shigetaka; Iseki, Atsushi; et al.
Nihon Genshiryoku Gakkai Homu Peji (Internet), 64 Pages, 2016/00
no abstracts in English
Yoshitomi, Hiroshi; Tanimura, Yoshihiko*; Tatebe, Yosuke; Tsutsumi, Masahiro; Kawasaki, Katsuya; Kowatari, Munehiko; Yoshizawa, Michio; Shimizu, Shigeru*; Kim, J.-S.*; Lee, J.-G.*; et al.
Proceedings of 4th Asian and Oceanic Congress on Radiation Protection (AOCRP-4) (CD-ROM), 4 Pages, 2015/07
Li(p,n)Be reactionTanimura, Yoshihiko; Tsutsumi, Masahiro; Yoshizawa, Michio
Radiation Protection Dosimetry, 161(1-4), p.149 - 152, 2014/10
Times Cited Count：2 Percentile：15.22(Environmental Sciences)Mono-energetic neutron calibration fields have been established in the energy range from 8 keV to 19 MeV using an accelerator at FRS. In the 144, 250 and 565 keV fields, mono-energetic neutrons are produced by bombarding a LiF target with accelerated protons in order to cause Li(p,n)Be reactions. Photons mixed in these neutron fields, which are produced by other nuclear reactions, can affect the calibration results. These mixed photon dose should be evaluated. In this paper the photons produced by the nuclear reactions between neutrons and target, its supporting materials and the constructional materials of the irradiation room such as the walls, floor and ceiling. were calculated using the MCNP-ANT code. Then the ambient dose equivalent H*(10) of the photons were evaluated and compared with that of the mono-energetic neutrons.
Am-Be-encapsulation sourceKowatari, Munehiko; Tanimura, Yoshihiko; Yoshizawa, Michio
Radiation Protection Dosimetry, 161(1-4), p.166 - 170, 2014/10
Times Cited Count：2 Percentile：15.22(Environmental Sciences)An attempt to decrease the anisotropic emissions of neutrons from a cylindrical Am-Be encapsulated X3 source was conducted out by Monte Carlo calculations and experiments. Influence of metal materials and shapes of the external casing to the anisotropy factor were focused on. Results obtained by calculations using MCNP4C implied that a light and spherical-shaped casing decreases the anisotropic emission of neutrons. Experimental results using the spherical-shaped aluminum protection case also revealed that the anisotropy factor was close to 1.0 with wide zenith angle ranges.
Tanimura, Yoshihiko; Tsutsumi, Masahiro; Yoshizawa, Michio
Radiation Protection Dosimetry, 161(1-4), p.144 - 148, 2014/10
Times Cited Count：10 Percentile：57.73(Environmental Sciences)A Long Counter (LC) is the most appropriate detector to measure neutron fluence due to flat response over a wide neutron energy range. Therefore, it is usually employed as a neutron fluence monitor. The weight of the LC used at FRS is 50 kg. It is too heavy to transfer it from one room to another room. Then we developed a new portable long counter whose weight is 15 kg. The portable LC consists of a 
He or BF
counter and a cylindrical moderator. It was designed to have an almost flat response from a few eV to a few MeV. While typical LCs have air gaps in the front surface, which allow lower-energy neutrons to penetrate deeper into the moderator, the portable LC has little space to make such air gaps due to the small size. Then we employed a polystyrene (PS) moderator instead of a polyethylene (PE) one as a front part of the moderator. As the hydrogen density of PS is nearly half that of PE, lower-energy neutrons can penetrate the PS moderator deeper than the PE moderator.
Hirayama, Hideo*; Kawasaki, Masatsugu; Matsumura, Hiroshi*; Okura, Takehisa; Namito, Yoshihito*; Sanami, Toshiya*; Taki, Mitsumasa; Oishi, Tetsuya; Yoshizawa, Michio
Nihon Genshiryoku Gakkai Wabun Rombunshi, 13(3), p.119 - 126, 2014/09
A method of deducing the I-131 concentration in a radioactive plume from the time history of peak count rates determined from pulse height spectra obtained from an NaI(Tl)scintillation detector employed as a detector of a monitoring post was presented. The concentrations of I-131 in the plumes were estimated from the count rates using the calculated response of the NaI(Tl) detector with egs5 for a model of a plume uniformly containing I-131. This method was applied to the data from the monitoring posts at Nuclear Science Research Institutes of Japan Atomic Energy Agency (JAEA). The estimated time history variation of I-131 concentrations in plumes was in fair agreement with those measured directly by an air sampling method. The difference was less than a factor of 4 for plumes that arrived on March 15 and March 21, indicating relatively high I-131 concentrations among the plumes studied in this work.
Tanimura, Yoshihiko; Kowatari, Munehiko; Yoshitomi, Hiroshi; Nishino, Sho; Yoshizawa, Michio
IAEA-TECDOC-1743, Annex (CD-ROM), p.133 - 138, 2014/07
Mono-energetic neutron calibration fields have been developed in the energy range of 8 keV to 19 MeV using a 4 MV Pelletron accelerator at the FRS in the JAEA. Protons or deuterons are accelerated and transported to bombard various targets for neutron production. The targets are prepared by depositing Sc, LiF or TiT on the backing disks for 
Sc(p,n)Ti, 
Li(p,n)Be and, 
H(p,n)He and H(d,n)
He reactions, respectively. For 
H(d,n)He reaction, a gas target is prepared by filling a target cell with D
gas. A pulsed beam with a minimum width of 2 ns can be derived with the pulsing system. Neutron fluence rates were measured with a Bonner sphere, a Li glass detector, a Si-SSD with a polyethylene radiator and a BC501A detector. Though the maximum fluence rates should not be high enough to obtain the nuclear data using an activation method, they can be available to obtain the nuclear data by using the prompt ray analysis.
Tanimura, Yoshihiko; Fujii, Katsutoshi; Tsutsumi, Masahiro; Yoshizawa, Michio
Progress in Nuclear Science and Technology (Internet), 4, p.388 - 391, 2014/04
Mono-energetic neutron calibration fields have been developed at Facility of Radiation Standards (FRS) using a 4 MV Pelletron accelerator. The neutron energies are available between 8 keV and 19 MeV for determining the energy responses of neutron dosemeters. The neutron energies are well adjusted to the energy points specified in the international standard (ISO 8529-1) and Japanese standard (JIS Z4521). Precise neutron fluence is the most important parameter for the calibration. In order to determine the fluence a Long Counter (hereinafter LC) is installed in the field for monitoring the neutron emission rate from the target. The fluence can be precisely determined using the output counts of the LC, the distance from the target, calibration coefficient of the LC and the air attenuation factor. This presentation describes the neutron monitors, outline of our monitoring system, determination of the air attenuation factor and procedure to determine the neutron fluence.
Tanimura, Yoshihiko; Tsutsumi, Masahiro; Yoshizawa, Michio
Progress in Nuclear Science and Technology (Internet), 4, p.392 - 395, 2014/04
1.2 and 2.5 MeV Mono-energetic neutron calibration fields have been developed at Facility of Radiation Standards (FRS) by using a 4MV Pelletron accelerator and employing H(p,n)He reaction. For the calibration, neutron fluence should be precisely evaluated. A silicon semiconductor detector with a polyethylene converter (hereinafter CH
-SSD) was developed to determine the neutron fluence. The detection efficiency of a common CH-SSD is not large enough to determine the neutron fluence. Then we developed a CH-SSD with high efficiency by using a large silicon semiconductor detector with 3,000 mm
sensitive area. This makes it possible to determine the neutron fluence with satisfactory accuracy. The detection efficiency of the CH-SSD was calculated with NRESP-ANT code and PHITS code. The maximum neutron fluence at 1 m from the target were evaluated to be about 1,000 and 2,000 cm
s
in the 1.2 and 2.5 MeV neutron fields, especially.
Yamada, Katsunori; Fujii, Katsutoshi; Kanda, Hiroshi; Higashi, Daisuke; Kobayashi, Toshiaki; Nakagawa, Masahiro; Fukami, Tomoyo; Yoshida, Keisuke; Ueno, Yumi; Nakajima, Junya; et al.
JAEA-Review 2013-033, 51 Pages, 2013/12
JAEA-Review-2013-033.pdf:2.73MB
After the accident at Fukushima Dai-ichi Nuclear Power Plant, various numerical criteria relevant to radiation protection were defined. We surveyed these criteria through internet. As a result of survey, the following 13 items were identified: (1) criteria for taking stable iodine tablets, (2) criteria for the screening of surface contamination, (3) evacuation area, sheltering area, etc., (4) activity concentrations in food, drinking water, etc., (5) dose limit for radiation workers engaged in emergency work, (6) guideline levels of radioactive substances in bathing areas, (7) criteria for use of school buildings and schoolyards, (8) restriction on planting rice, (9) acceptable activity concentrations in feedstuff, (10) acceptable activity concentrations in compost, (11) criteria for export containers and ships, (12) criteria for contaminated waste, (13) standards for radiation workers engaged in decontamination work. In this report, the basis of and issues on these criteria are summarized.
