Manabe, Kentaro; Koyama, Shuji*
Radiation Protection Dosimetry, 189(4), p.489 - 496, 2020/05
It is important for radiation protection in diagnostic nuclear medicine to estimate organ absorbed doses in consideration of person-specific parameters. This study proposes a straightforward method for estimating organ doses which reflect an individual organ masses by scaling the reference doses based on the reference human models using the inverse ratio of the individual masses to the reference organ masses. The method was tested for the administration cases of Tc-labelled colloids and I-labelled sodium iodine to confirm the effectiveness of the method. The discrepancies of the doses estimated by the method were sufficiently small in terms of solid organs.
Furuta, Hiroshige*; Tsujimura, Norio; Nishide, Akemi*; Kudo, Shinichi*; Saegusa, Shin*
Radiation Protection Dosimetry, 189(3), p.371 - 383, 2020/05
Kowatari, Munehiko; Nishino, Sho; Romallosa, K. M. D.*; Yoshitomi, Hiroshi; Tanimura, Yoshihiko; Oishi, Tetsuya
Radiation Protection Dosimetry, 189(4), p.436 - 443, 2020/05
The anisotropic emission of neutrons from a cylindrical X1 Cf source with the spherical external casing was experimentally determined. The influence of metal materials and shapes of the external casing to the anisotropy factor, () was assessed by the Monte Carlo calculation, before performing the measurement. The results of the calculation result implied that light and spherical-shaped external casing decreases the anisotropic emission of neutrons from a cylindrical source and the nature of the material does not affect the anisotropic emission to a large extent. The experimental results obtained when a spherical-shaped aluminum protection case was employed also revealed that the anisotropy factor was close to 1.0 with a wide zenith angle range.
Morishita, Yuki; Usami, Hiroshi; Furuta, Yoshihiro; Aoki, Katsunori; Tsurudome, Koji; Hoshi, Katsuya; Torii, Tatsuo
Radiation Protection Dosimetry, 189(2), p.172 - 181, 2020/04
We developed a remote continuous air monitoring (RCAM) system. The RCAM system consisted of a personal air monitor and a robot. The personal air monitor (poCAMon, SARAD, Germany) had a 400 mm ion-injected silicon detector and a membrane air filter with 25 mm-diameter. The personal air monitor provides the alpha energy spectra for any measurement time interval. Demonstration measurements were taken underground at the Mizunami Underground Research Laboratory (MIU) and at a poorly ventilated concrete building. The RCAM system was remotely operated and successfully measured the Rn progeny even though the relative humidity (RH) was almost 100%. In the measured alpha spectra, the peaks of Po (6.0 MeV alpha) and Po (7.7 MeV alpha) were clearly identified. Our developed monitor is promising for alpha dust monitoring in a high gamma-ray environment or contaminated areas where a worker cannot safely physically enter.
Yoshitomi, Hiroshi; Kowatari, Munehiko
Radiation Protection Dosimetry, 188(2), p.191 - 198, 2020/02
Takai, Shizuka; Shimada, Asako; Sawaguchi, Takuma; Takeda, Seiji; Kimura, Hideo
Radiation Protection Dosimetry, 188(1), p.1 - 7, 2020/01
After the Fukushima Nuclear Power Plant accident, most of radiocesium-contaminated soil generated from decontamination activities outside Fukushima prefecture has been stored at decontamination sites such as schools, parks and residential lands (storage at sites) according to the Decontamination Guidelines. However, additional exposure due to the present storage has not been evaluated. Moreover, entering storage sites, which is not restricted for storage at sites, was not considered in safety assessment conducted in the guidelines. To continue the storage and confirm the effectiveness, understanding of present possible exposures is important. In this study, we evaluated exposure doses for residents and users of storage sites based on the present situation. As a result, annual doses due to residence were 10 to 10 mSv y and doses due to annual entries were of the order of 10 mSv y. Hence, we confirmed that the exposure due to present storage outside Fukushima is significantly less than 1 mSv y.
Kowatari, Munehiko; Yoshitomi, Hiroshi; Nishino, Sho; Tanimura, Yoshihiko; Oishi, Tetsuya; Kessler, P.*; Neumaier, S.*; Rttger, A.*
Radiation Protection Dosimetry, 187(1), p.61 - 68, 2019/12
Nakanishi, Takahiro; Sato, Seiji; Matsumoto, Takumi*
Radiation Protection Dosimetry, 184(3-4), p.311 - 314, 2019/10
There has been significant concern about an increase of exposure dose in living sphere due to the accumulation of radiocesium discharged from contaminated mountainous forest in Fukushima. In this study, we investigated the history of radiocesium deposition on some floodplains in Fukushima. Radiocesium concentrations of river suspended particles and air dose rates at floodplains were also observed continuously. In many situations, annual sediment accumulation at floodplains was only several kg m and its radiocesium concentration was gradually decreasing in line with that of suspended particle. Simultaneously, air dose rates on floodplains were decreasing with time. In 2015 with heavy flood discharge, several hundred kg m of sediment accumulation and sharply decrease of air dose rate was observed at rivers without reservoir. Conversely, radiocesium accumulation at floodplain was significant reduced due to deposition on upstream reservoir.
Miwa, Kazuji; Takeda, Seiji; Iimoto, Takeshi*
Radiation Protection Dosimetry, 184(3-4), p.372 - 375, 2019/10
The Ministry of the Environment has indicated the policy of recycling the contaminated soil generated by decontamination activity after the Fukushima accident. By recycling to coastal reclamation which is one of effective recycling application, dissolved radiocesium and absorbed radiocesium on soil particles will flow out to the ocean by construction, therefore evaluating radiocesium transition in ocean considering the both types of radiocesium is important for safety assessment. In this study, the radiocesium outflow during constructing and after constructing is modeled, and radiocesium transition in ocean is evaluated by Sediment model suggested in OECD/NEA. The adaptability of sediment model is confirmed by reproducing evaluation of the coastal area of Fukushima. We incorporate the sediment model to PASCLR2 code system to evaluate the doses from radiocesium in ocean.
Yoshimura, Kazuya; Fujiwara, Kenso; Nakama, Shigeo
Radiation Protection Dosimetry, 184(3-4), p.315 - 318, 2019/10
Sasaki, Miyuki; Sanada, Yukihisa; Yamamoto, Akio*
Radiation Protection Dosimetry, 184(3-4), p.400 - 404, 2019/10
The maximum-likelihood expectation maximization (ML-EM) method is expected to improve the accuracy of airborne radiation monitoring using an unmanned aerial vehicle. The accuracy of the ML-EM method depends on various parameters, including detector efficiency, attenuation factor, and shielding factor. In this study, we evaluate the shielding factor of trees based on several field radiation measurements. From the actual measurement, the shielding factors were well correlated with the heights of the trees. The evaluated shielding factors were applied to the ML-EM method in conjunction with the measured data obtained from above the Fukushima forest. Compared with the conventional methods used for calculating the dose rate, the proposed method is found to be more reliable.
Tamakuma, Yuki*; Yamada, Ryohei; Suzuki, Takahito*; Kuroki, Tomohiro*; Saga, Rikiya*; Mizuno, Hiroyuki*; Sasaki, Hiroyuki*; Iwaoka, Kazuki*; Hosoda, Masahiro*; Tokonami, Shinji*
Radiation Protection Dosimetry, 184(3-4), p.307 - 310, 2019/10
After the Fukushima Daiichi Nuclear Power Plant accident, the radiation dose for first responders was not evaluated accurately due to lack of the monitoring data. It has been important to evaluate a radiation dose for workers in emergency response at a nuclear accident. In this study, a new device which can evaluate both of external and internal exposure doses was developed and the performance of various environmental radiation monitors including commercially available monitors were tested and compared from the viewpoint of an environmental monitoring at emergency situation. Background counts of the monitors and the ambient dose equivalent rate were measured in Fukushima Prefecture. The detection limit for beta particles was evaluated by the method of ISO11929. The sensitivity for gamma-rays of the dust monitor using a ZnS(Ag) and a plastic scintillator was high, but that of the external exposure monitor using a silicon photodiode with CsI(Tl) crystal was relatively low. The detection limit ranged 190-280 Bq m at 100 Sv h, exceeding the detection limit of 100 Bq m in the minimum requirement by the National Regulation Authority in Japan. Use of the shielding with lead is necessary to achieve the minimum requirement. These results indicate that the dust monitor using a ZnS(Ag) scintillator and a plastic scintillator is suitable for the external exposure monitor and the developed internal exposure monitor is for the internal exposure monitor at emergency situation among the evaluated monitors. In the future study, the counting efficiency, the relative uncertainty and the performance of the detection for alpha particles will be evaluated, and it will be considered which type of a monitor is suitable after taking the portability into account.
Yoshitomi, Hiroshi; Kowatari, Munehiko; Hagiwara, Masayuki*; Nagaguro, Seiji*; Nakamura, Hajime*
Radiation Protection Dosimetry, 184(2), p.179 - 188, 2019/08
Sato, Tatsuhiko; Masunaga, Shinichiro*; Kumada, Hiroaki*; Hamada, Nobuyuki*
Radiation Protection Dosimetry, 183(1-2), p.247 - 250, 2019/05
As an application of Particle and Heavy Ion Transport code System PHITS, We have developed the stochastic microdosimetric kinetic (SMK) model for estimating the therapeutic effects of various kinds of radiation therapy. In this study, we improved the SMK model for estimating the therapeutic effect of boron neutron capture therapy, BNCT. The improved SMK model can consider not only the intra- and intercellular heterogeneity of B-10 distribution but also the dose rate effect. The accuracy of the model was well verified by comparisons made between calculated and measured surviving fractions of tumor cells, which we previously determined in vivo in mice with B-10 compounds exposed to reactor neutron beam. Details of the improved SMK model together with the verification results will be presented at the meeting.
Sato, Tatsuhiko; Nagamatsu, Aiko*; Ueno, Haruka*; Kataoka, Ryuho*; Miyake, Shoko*; Takeda, Kazuo*; Niita, Koji*
Radiation Protection Dosimetry, 180(1-4), p.146 - 149, 2018/08
Cosmic-ray dose rates spatially and temporally change very much. In this study, we compared the calculated cosmic-ray environments on the Earth, Moon, and Mars as well as inside spacecraft on low-earth orbit (LEO) and at interplanetary space. In the calculation, a galactic cosmic-ray model developed in DLR and trapped proton/electron models AP9/AE9 were used for determining the incident cosmic-ray fluxes, and the Particle and Heavy Ion Transport code System, PHITS, was employed for the cosmic-ray transport simulation in the Earth, Lunar, and Martian systems as well as spacecraft. The virtual International Space Station (ISS) model developed by JAXA was adopted as the representative of spacecraft in the PHITS simulation. This paper focuses on the comprehensive discussions on the difference of cosmic-ray environments and the effective methods of their shielding in various exposure situations.
Tanimura, Yoshihiko; Yoshizawa, Michio
Radiation Protection Dosimetry, 180(1-4), p.417 - 421, 2018/08
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.
Otto, T.*; Hertel, N. E.*; Bartlett, D. T.*; Behrens, R.*; Bordy, J.-M.*; Dietze, G.*; Endo, Akira; Gualdrini, G.*; Pelliccioni, M.*
Radiation Protection Dosimetry, 180(1-4), p.10 - 16, 2018/08
Report Committee 26 of the ICRU proposes a set of operational quantities for radiation protection for external radiation, directly based on effective dose and for an extended range of particles and energies. It is accompanied by new quantities for estimating deterministic effects to the eye lens and the local skin. The operational quantities are designed to overcome the conceptual and technical shortcomings of those presently in use. This paper describes the proposed operational quantities, and highlights the improvements with respect to the present legal monitoring quantities.
Morishita, Yuki; Yamamoto, Seiichi*; Momose, Takumaro; Kaneko, Junichi*; Nemoto, Norio
Radiation Protection Dosimetry, 178(4), p.414 - 421, 2018/03
Plutonium dioxide (PuO) is used to fabricate a mixed oxide fuel for fast breeder reactors. When a glove box containing PuO fails, such as by rupture of a glove or a vinyl bag, airborne contamination of plutonium (Pu) can occur. If the worker inhale PuO particles, they deposit in the lung and cause lung cancer. The nasal smear and nose blow methods are useful for checking workers for PuO intake in the field. However, neither method can evaluate the quantitative activity of Pu. No alpha-particle detector that can be used for direct measurements in the nasal cavity has been developed. Therefore, we developed a nasal monitor capable of directly measuring the activity of Pu in the nasal cavity to precisely evaluate the internal exposure dose of a worker. Prismatic-shaped 22 acrylic light guides were used to compose a detector block, and a ZnS(Ag) scintillator was adhered to the surface of these light guides. Silicon photomultiplier (SiPM) arrays with 88 channels were used as a photodetector. Actual PuO particles were measured using the nasal monitor. The nasal monitor could be directly inserted in the nasal cavities. The activity distribution of Pu was obtained by the nasal monitor. The average efficiencies in 4 were 11.43% and 11.58% for the left and right nasal cavities, respectively. The effect of and rays on the detection of the alpha particles of Pu was negligible. The difference in the measured Pu activity between the ZnS(Ag) scintillation counter and the nasal monitor was within 4.0%. The developed nasal monitor can solve the uncertainty problem encountered with the nasal smear and the nose blow methods. We expect this monitor to be useful for accurately estimating the internal exposure dose of workers.
Kowatari, Munehiko; Zutz, H.*; Hupe, O.*
Radiation Protection Dosimetry, 178(1), p.48 - 56, 2018/01
In high energy photon reference fields the value of the air kerma rate is determined by using ionization chambers. From the charge collected inside the ionization chamber the dose can be calculated using a set of calibration and correction factors according to ISO 4037-2. A crucial parameter is the correction for the attenuation and scattering of the primary radiation due to the chamber wall. This parameter can be determined using Monte Carlo calculations. The evaluation of the factor was performed for a commercially available ionization chamber of the type Victoreen 550-3 under different build-up conditions. The results were verified by measurements in the R-F high energy photon fields according to ISO 4037-1 at the Physikalisch-Technische Bundesanstalt (PTB) and the Japan Atomic Energy Agency (JAEA).
Radiation Protection Dosimetry, 175(3), p.378 - 387, 2017/07
The International Commission on Radiation Units and Measurements (ICRU) has been discussing to propose a new system of the operational quantities for external radiations based on protection quantities. The aim of this study is to provide a set of conversion coefficients for use in defining personal dose equivalent for individual monitoring. Fluence-to-effective dose conversion coefficients have been calculated for photons, neutrons, electrons, positrons, protons, muons, pions and helium ions for various incident angles of radiations. The data sets comprise effective dose conversion coefficients for incident angles of radiations from 0 to 90 in steps of 15 and at 180. Conversion coefficients for rotational, isotropic, superior hemisphere semi-isotropic and inferior hemisphere semi-isotropic irradiations are also included. The conversion coefficients are used to define the operational quantity personal dose equivalent which is being considered by ICRU and utilized for the design and calibration of dosemeters.