Michiya Sasaki

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Role and Collaboration of Radiation Protection Experts: Summary of Discussions between the Japan Health Physics Society and the Korean Association of Radiation Protection Related to Tritiated Water

방사선방어학회지, Jul 6, 2022

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SUMRAY: R and Python Codes for Calculating Cancer Risk Due to Radiation Exposure of a Population

Journal of Radiation Protection and Research

Background: Quantitative risk assessments should be accompanied by uncertainty analyses of the ri... more Background: Quantitative risk assessments should be accompanied by uncertainty analyses of the risk models employed in the calculations. In this study, we aim to develop a computational code named SUMRAY for use in cancer risk projections from radiation exposure taking into account uncertainties. We also aim to make SUMRAY publicly available as a resource for further improvement of risk projection.Materials and Methods: SUMRAY has two versions of code written in R and Python. The risk models used in SUMRAY for all-solid-cancer mortality and incidence were those published in the Life Span Study of a cohort of the atomic bomb survivors in Hiroshima and Nagasaki. The confidence intervals associated with the evaluated risks were derived by propagating the statistical uncertainties in the risk model parameter estimates by the Monte Carlo method.Results and Discussion: SUMRAY was used to calculate the lifetime or time-integrated attributable risks of cancer under an exposure scenario (bas...

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Role and Collaboration of Radiation Protection Experts: Summary of Discussions between the Japan Health Physics Society and the Korean Association of Radiation Protection Related to Tritiated Water

Journal of Radiation Protection and Research

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Characterisation of a Real-time Personal Neutron Dosemeter with Two Silicon Detectors

Radiation Protection Dosimetry, Sep 1, 1999

ABSTRACT We have developed a new real-time personal neutron dosemeter containing two neutron sens... more ABSTRACT We have developed a new real-time personal neutron dosemeter containing two neutron sensors, a fast and a slow neutron sensor. The former sensor is a p-type silicon semiconductor detector. The slow neutron sensor is also a p-type silicon semiconductor detector and natural boron is doped on the aluminum electrode to produce 10B(n,α) reactions. A thin polyethylene radiator is contacted on the front surface of each sensor to produce recoil protons. The neutron detection efficiencies of these sensors were measured in a thermal neutron field and monoenergetic neutron fields from 8keV to 22MeV. By taking the weighted sum of counts given by the two sensors, the detection efficiency could be made to approach to the fluence-to-dose equivalent conversion factor given by ICRP 51. Field tests of the performance of this neutron dosemeter were performed in the radiation environments around several nuclear facilities, including reactor, accelerator, radioisotope and nuclear fuel handling facilities. Based on the results of these field tests, we conclude that our dosemeter is able to provide a reading of the neutron dose equivalent within a factor of 2 margin of accuracy.

Trends and Issues on the Current Drafts of IAEA DS499 and DS500: General Discussion in the 2021 Symposium Organized by the International Correspondence Committee

Japanese Journal of Health Physics

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Conclusions and Suggestions on Low-Dose and Low-Dose Rate Radiation Risk Estimation Methodology

Journal of Radiation Protection and Research

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Development of Waste Monitor of Clearance Level to Ensure Social Reliance on Recycled Metal From Nuclear Facilities

9th ASME International Conference on Radioactive Waste Management and Environmental Remediation: Volumes 1, 2, and 3

Metal and concrete wastes in the decommissioning of nuclear facilities are classified according t... more Metal and concrete wastes in the decommissioning of nuclear facilities are classified according to their radioactivity level after decontamination. Radioactive waste below the clearance level (e.g., 0.4Bq.g−1 for Co-60 in Japan) can be disposed of as general industrial waste or recycled. Metal wastes mainly originate from equipment in buildings, except for the metal bars in reinforced concrete. Since contaminated equipment must be decontaminated after dismantling, the main target of measurement would be fragments of equipment, of various shapes, numbers and sizes. In order to transport such metallic fragments out of controlled areas, a surface contamination survey must be performed to confirm that the contamination level is below the legal standard level (e.g., 4Bq.cm−2 for beta or gamma emitters in Japan) in addition to satisfying the clearance level. Taking account of social reliance on recycled metal after inspection of the clearance level and the surface contamination level, it ...

Impressions of the International Correspondence Committee Session “Recent International Trends in Radiological Protection” in the 53rd Annual Meeting of JHPS

Japanese Journal of Health Physics

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New Surface Contamination Measurement Method at Nuclear Power Plants -Demonstration of Applicability of Clearance Automatic Laser Inspection System for Surface Contamination Measurement

86 Background In the clearance level inspection*1 of solid materials such as metal and concrete s... more 86 Background In the clearance level inspection*1 of solid materials such as metal and concrete scrap generated from nuclear power plants, the activity level of waste must be compared with not only the clearance level (0.1 Bq/g for Co-60) but also the surface contamination density standard (4 Bq/cm2 for beta or gamma emitter). Usually, a manual GM survey meter based on beta-ray detection is used for surface contamination density inspection at present. Recently, the clearance automatic laser inspection system (CLALIS) has been developed for low-level radioactive waste measurement. The radiation detection ability for scrap metals and concrete segments has been clarified in a large number of experiments using mock metal and concrete waste samples and standard radioactive sources. It has been experimentally shown that the detection limit of CLALIS is approximately 100 Bq for Co-60, which is sufficiently low not only for clearance measurement, but also for surface contamination density m...

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Activity evaluation system using shape measurement and Monte-Carlo methods

Transactions of the American Nuclear Society, 2006

JHPS International Symposium: How Do We Find the Solution to Radiological Protection of Tritium Water?

Japanese Journal of Health Physics, 2020

Radiation Protection in the World : The International Commission on Radiological Protection and the Accident at the Fukushima Nuclear Power Stations

Radiation dose estimation at the high background radiation area in Indonesia

Atomic Energy Society of Japan, 2019

Daily variation of radiation dose at the high background radiation area in Indonesia

Applicability of Clearance Automatic Laser Inspection System to Clearance Measurement of Concrete Segments -9129

In the decommissioning of a nuclear power plant, large amounts of metal scrap and concrete segmen... more In the decommissioning of a nuclear power plant, large amounts of metal scrap and concrete segments require disposal when dismantling the nuclear reactor and surrounding facilities. When their activity level is negligible or sufficiently small, they can be regarded as general industrial waste. To distinguish between radioactive and nonradioactive materials, the clearance level for each radionuclide has been determined in units of activity concentration. These clearance levels are indicated in the International Atomic Energy Agency (IAEA) Safety Standards Series No. RS-G-1.7. The Japanese regulatory authority decided in 2005 to adopt the values given in RS-G-1.7 as clearance levels in legislation. Recently, a Clearance Automatic Laser Inspection System (CLALIS) has been developed utilizing gamma-ray measurement, automatic laser shape measurement and Monte Carlo calculation. CLALIS comprises four laser scanners and eight large plastic scintillation detectors surrounded by a 5-cm-thick...

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Comprehensive exposure assessments from the viewpoint of health in a unique high natural background radiation area, Mamuju, Indonesia

Scientific Reports

Mamuju is one of the regions in Indonesia which retains natural conditions but has relatively hig... more Mamuju is one of the regions in Indonesia which retains natural conditions but has relatively high exposure to natural radiation. The goals of the present study were to characterize exposure of the entire Mamuju region as a high natural background radiation area (HNBRA) and to assess the existing exposure as a means for radiation protection of the public and the environment. A cross-sectional study method was used with cluster sampling areas by measuring all parameters that contribute to external and internal radiation exposures. It was determined that Mamuju was a unique HNBRA with the annual effective dose between 17 and 115 mSv, with an average of 32 mSv. The lifetime cumulative dose calculation suggested that Mamuju residents could receive as much as 2.2 Sv on average which is much higher than the average dose of atomic bomb survivors for which risks of cancer and non-cancer diseases are demonstrated. The study results are new scientific data allowing better understanding of hea...

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Natural Radiation Exposure and Carotid Intima-media Thickness Among Women in Karunagappally, Kerala, India

Background: A cross-sectional study was conducted to examine the relationship between natural rad... more Background: A cross-sectional study was conducted to examine the relationship between natural radiation exposure and intima-media thickness (IMT), an atherosclerosis indicator, among female residents in Karunagappally, Kerala, South India, which is known to have areas with high natural background radiation (HNBR) derived mainly from thorium.Methods: Cumulative radiation doses received during childhood, adulthood, and entire life were estimated on the basis of annual indoor and outdoor radiation doses and hours spent indoors and outdoors. In 2013-2014, IMT of the carotid artery was measured with ultrasonography among 400 women aged 29-60 years in Karunagappally. Since there were three subjects with outlying maximum IMT values, corrected IMT values excluding those outliers were calculated. For statistical analysis, raw and corrected IMT values were used. Results: The regression analysis adjusting for age and religion showed a statistically significant association of mean and maximum I...

Quantitative evaluation of conservativeness in the concept of committed dose from internal exposure for radiation workers

Journal of Radiological Protection

For compliance with dose limits, the International Commission on Radiological Protection (ICRP) r... more For compliance with dose limits, the International Commission on Radiological Protection (ICRP) recommends that the committed dose be assigned to the year in which radionuclide intake occurred in the case of internal exposure. For radiation workers, the committed dose is evaluated over the 50 year period following the intake, which is a rounded value for the working-life expectancy of a young person entering the workforce. In this study, we develop an approach to the quantitative evaluation of the conservatism in the concept of the committed dose from internal exposure for radiation workers from the viewpoint of radiological risk. Actual annual doses due to an intake of radionuclides for strontium-90 (90Sr), caesium-137 (137Cs), and plutonium-239 (239Pu) were simulated. Risks of fatal cancer, i.e. unconditional death probability rates, were calculated in accordance with the risk estimation method in ICRP Publication 60. It was found that the conservatism ranged from 1.1 to 1.6 for 9...

Case Study of the Minimum Provable Risk Considering the Variation in Background Risk: Effect of Residual Risk on Epidemiological Studies and a Comparative Assessment of Fatal Disease Risk Due to Radiation Exposure

Health Physics

Abstract In order to prove a small increment in a risk of concern in an epidemiological study, a ... more Abstract In order to prove a small increment in a risk of concern in an epidemiological study, a large sample of a population is generally required. Since the background risk of an end point of interest, such as cancer mortality, is affected by various factors, such as lifestyle (diet, smoking, etc.), adjustment for such factors is necessary. However, it is impossible to inclusively and completely adjust for such factors; therefore, uncertainty in the background risk remains for control and exposed populations, indicating that there is a minimum limit to the lower bound for the provable risk regardless of the sample size. In this case study, we developed and discussed the minimum provable risk considering the uncertainty in background risk for hypothetical populations by referring to recent Japanese statistical information to grasp the extent of the minimum provable risk. Risk of fatal diseases due to radiation exposure, which has recently been the focus of radiological protection, was also examined by comparative assessment of the minimum provable risk for cancer and circulatory diseases. It was estimated that the minimum provable risk for circulatory disease mortality was much greater than that for cancer mortality, approximately five to seven times larger; circulatory disease mortality is more difficult to prove as a radiation risk than cancer mortality under the conditions used in this case study.

Estimated Risks of Radiation-induced Solid Cancers from Various Exposure Conditions and the Effects of Age and Follow-up Period on These Risks

Japanese Journal of Health Physics

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