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Ambient dose equivalent rates were measured in the environment of the Fukushima prefecture using NaI(Tl)/CsI(Tl) scintillation detectors and CdZnTe/Ge semiconductor detectors. The dose rates obtained at the same locations varied beyond uncertainty (1σ). By replacing the spectrum-dose conversion operators obtained from the anterior–posterior geometry with those from the rotational geometry, the dose rates agreed with each other within uncertainties, except for a CsI(Tl) scintillation detector with a considerably flat crystal configuration, due to its excessive directional dependence. [ABSTRACT FROM AUTHOR]

In nuclear emergencies, it is especially important to carry out a wide range of environmental monitoring and provide the data immediately so as to understand the current distribution of radionuclides and investigate countermeasures. Therefore, it is indispensable for a nuclear emergency response to establish a system that supports rapid provision of these data. The authors have been developing the software platform by integrating technologies of environmental monitoring, information processing and network communication, based on the experience of the Fukushima Daiichi Nuclear Accident. It was discovered that the platform is effective in reducing the time needed to publish the monitoring data. Reducing the cost and workload for publishing the monitoring data is also important because monitoring should be continued over a few decades in the case of the Fukushima accident. The authors' platform is expected to help to mitigate the problem, too. [ABSTRACT FROM AUTHOR]

In nuclear emergencies, it is especially important to carry out a wide range of environmental monitoring and provide the data immediately so as to understand the current distribution of radionuclides and investigate countermeasures. Therefore, it is indispensable for a nuclear emergency response to establish a system that supports rapid provision of these data. The authors have been developing the software platform by integrating technologies of environmental monitoring, information processing and network communication, based on the experience of the Fukushima Daiichi Nuclear Accident. It was discovered that the platform is effective in reducing the time needed to publish the monitoring data. Reducing the cost and workload for publishing the monitoring data is also important because monitoring should be continued over a few decades in the case of the Fukushima accident. The authors' platform is expected to help to mitigate the problem, too. [ABSTRACT FROM AUTHOR]

A Japanese voxel phantom in upright posture, JM2, has been developed on the basis of CT images of a healthy Japanese adult male. Body characteristics of JM2 were compared with those of the supine voxel phantom, JM, previously developed using CT images of the same person. Differences were found in the shapes of the spine and lower abdomen and the locations of several organs such as kidneys, liver and stomach between the two phantoms. Specific absorbed fractions (SAFs) for 24 target and II sources organs were calculated for monoenergetic photon ranging from 0.01 to 4 MeV. It was found that the SAFs for the kidneys as source organ and the lower large intestine wall as target organ in JM2 were significantly higher than those in JM for all photon energies. The differences of the SAFs between the two phantoms were attributed to the differences in the organ distance and organ geometry depending on the posture. [ABSTRACT FROM AUTHOR]

Voxel phantoms and Monte Carlo methods are of considerable interest in calibrating in vivo counting applications for radioactive body burden such as whole-body counters. At the Japan Atomic Energy Research Institute (JAERI), a calculation code—UCWBC code—for whole-body counter calibrations using voxel phantoms has been developed as an EGS4 Monte Carlo user code. To validate the UCWEC code for calibrating whole-body counters at JAERI, response functions and counting efficiencies of a p-type high-purity Ge (HPGe) semiconductor detector used for the whole-body counter were evaluated for a water-filled block-shape phantom by use of UCWBC code and were measured by experiments. The voxel version of the water-filled block-shape phantom based on an actual phantom was used for the calculations. Furthermore, counting efficiencies of the Ge semiconductor detector for the male and female voxel phantoms developed at JAERI were evaluated in the photon energy range from 60 to 1836 keV by the UCWBC code in order to examine the differences between the counting efficiencies for voxel phantoms. In conclusion, it was found that the response functions and counting efficiencies of the Ge semiconductor detector found by the UCWBC code for the water-filled block-shape phantom are in good agreement with measured data. The UCWBC code was validated by those comparisons. It was also found that the counting efficiencies of the Ge semiconductor detector depend on the size of the phantoms and the effective distance between phantom and detector. The calibration of whole-body counters using voxel phantoms and Monte Carlo methods would be quite useful for the improvement in the accuracy of measurement results. [ABSTRACT FROM AUTHOR]

Large amounts of anthropogenic radionuclides, such as 134Cs and 137Cs(radiocesium), were released into the atmosphere due to the Fukushima Daiichi Nuclear Power Plant (F1-NPP) accident and were transported into various environments. The soil accumulations of diffused radionuclides are marked by large differences in their horizontal distributions, and the vertical air dose rates vary depending on the topography, altitude and other factors. In this study, soil activity concentrations of eight islands in the Izu Islands, ~334-563 km south of the F1-NPP, were analyzed from both horizontal and vertical perspectives. Soil samples were collected over a 4-y period from 2012 to 2016, and their activity concentrations of radiocesium were measured. The activity concentrations in the soil were categorized for intervals of a 100-m altitude above sea level, and the relationship between the maximum activity concentration in each category and the distance from the F1-NPP was analyzed. The correlation was good at the lower altitudes., (© The Author(s) 2022. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

To enable precise assessment of health impacts following a nuclear power plant accident, extensive and detailed data on environmental radiation levels are needed. This study was undertaken to investigate the air and the soil radiation levels using a car-borne survey on the main island of Taiwan where no extensive environmental radiation distribution survey had been conducted before. The mean air absorbed dose rate on this island was 57 ± 10 nGy h-1. The measured dose rate distribution varied depending on the geology of the soils, and ranged from 22 to 113 nGy h-1. The mean radiation level in soil was 539 ± 124 Bq kg-1 for 40K, 23 ± 8 Bq kg-1 for 238U and 41 ± 22 Bq kg-1 for 232Th. The air absorbed dose rate (58 nGy h-1) calculated from these data of mean radiation level in soil was comparable to that determined by the car-borne survey method. Thus, this study yielded detailed data on air absorbed dose rate depending primarily on the geology of the soils on the main island of Taiwan., (© The Author(s) 2020. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Internal dosimetry in non-human biota is desirable from the viewpoint of radiation protection of the environment. The International Commission on Radiological Protection (ICRP) proposed Reference Animals and Plants using simplified models, such as ellipsoids and spheres and calculated absorbed fractions (AFs) for whole bodies. In this study, photon and electron AFs in whole bodies of voxel-based rat and frog models have been calculated and compared with AFs in the reference models. It was found that the voxel-based and the reference frog (or rat) models can be consistent for the whole-body AFs within a discrepancy of 25%, as the source was uniformly distributed in the whole body. The specific absorbed fractions (SAFs) and S values were also evaluated in whole bodies and all organs of the voxel-based frog and rat models as the source was distributed in the whole body or skeleton. The results demonstrated that the whole-body SAFs reflect SAFs of all individual organs as the source was uniformly distributed per mass within the whole body by about 30% uncertainties with exceptions for body contour (up to -40%) for both electrons and photons due to enhanced radiation leakages, and for the skeleton for photons only (up to +185%) due to differences in the mass attenuation coefficients. For nuclides such as (90)Y and (90)Sr, which were concentrated in the skeleton, there were large differences between S values in the whole body and those in individual organs, however the whole-body S values for the reference models with the whole body as the source were remarkably similar to those for the voxel-based models with the skeleton as the source, within about 4 and 0.3%, respectively. It can be stated that whole-body SAFs or S values in simplified models without internal organs are not sufficient for accurate internal dosimetry because they do not reflect SAFs or S values of all individual organs as the source was not distributed uniformly in whole body. Thus, voxel-based models would be good candidates for dosimetry in non-human biota if further accuracy in environmental dosimetry is desired.

A Japanese adult male voxel (volume pixel) phantom (hereinafter referred to as the JM phantom) was constructed on the basis of CT images of a healthy Japanese adult male volunteer. Body characteristics of the JM phantom were compared with those of a voxelised MIRD5 type phantom and a Japanese adult male voxel phantom which was previously developed. The voxel size of the JM phantom is 0.98 x 0.98 x 1 mm(3). The shapes of the organs of the JM phantom, even for small or complicated organs, such as thyroid and stomach, are more realistically reproduced as compared with the previous Japanese voxel phantom (voxel size: 0.98 x 0.98 x 10 mm(3)). Photon self-absorbed fractions (self-AFs) for brain, kidneys, spleen, pancreas, thyroid and urinary bladder wall of JM were evaluated and were compared with those of the other phantoms. In consequence, it was suggested that the mass, shape and thickness of organs are important factors for the determination of self-AFs.