Report on participation in the 6th Asian and Oceanic Congress on Radiation Protection

Yoshitomi, Hiroshi; Manabe, Kentaro; Ochi, Kotaro; Kono, Takahiko; Sasaki, Michiya*; Yoshida, Hiroko*

Hoken Butsuri (Internet), 58(2), p.105 - 111, 2023/08

https://doi.org/10.5453/jhps.58.105

This article gives the report on participation in the 6th Asian and Oceanic Congress on Radiation Protection (AOCRP6), which was held in Mumbai, India on between February 7th and 11th, 2023.

Effective dose coefficients for internal exposure dose assessment in accordance with ICRP 2007 recommendations (Contract research)

Takahashi, Fumiaki; Manabe, Kentaro; Sato, Kaoru

JAEA-Review 2020-068, 114 Pages, 2021/03

JAEA-Review-2020-068.pdf:2.61MB

Radiation safety regulations have been currently established based on the 1990Recommendation by the International Commission on Radiological Protection (ICRP) in Japan. Meanwhile, ICRP released the 2007 Recommendation that replaces the 1990 Recommendation. Thus, the Radiation Council, which is established under the Nuclear Regulation Authority (NRA), has made discussions to incorporate the purpose of the 2007 Recommendation into Japanese regulations for radiation safety. As ICRP also has published effective dose coefficients for internal exposure assessment in accordance with the 2007recommendation, the technical standards are to be revised for the internal exposure assessment method in Japan. Currently, not all of the effective doses have been published to revise concentration limits for internal exposure protections of workers and public. The published effective dose coefficients are applied to radionuclides which are important in radiation protection for internal exposure of a worker. Thus, we review new effective dose coefficients as well as basic dosimetry models and data based upon Occupational Intakes of Radionuclides (OIR) parts 2, 3 and 4 that have been published from 2016 to 2019 by ICRP. In addition, issues are sorted out to provide information for revision of the technical standards for internal exposure assessment based on the 2007 Recommendations in future.

Organ absorbed dose estimation reflecting specific organ masses with simple scaling of reference doses using the organ masses

Manabe, Kentaro; Koyama, Shuji*

Radiation Protection Dosimetry, 189(4), p.489 - 496, 2020/05

AA2019-0343.pdf:0.67MB

https://doi.org/10.1093/rpd/ncaa058

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.

Estimating internal dose coefficients of short-lived radionuclides in accordance with ICRP 2007 Recommendations

Manabe, Kentaro; Sato, Kaoru; Takahashi, Fumiaki

Journal of Nuclear Science and Technology, 56(5), p.385 - 393, 2019/05

https://doi.org/10.1080/00223131.2019.1585988

At high energy accelerator facilities, various radionuclides are produced by nuclear reactions of high energy particles with structure and/or ambient air of the facilities. Consequently, the radionuclides are potential sources of internal exposure for works of the facilities. However, the International Commission on Radiological Protection (ICRP) do not provide dose coefficients, which are committed effective doses per intake, for the short-lived radionuclides whose half-lives are shorter than 10 minutes in accordance with the ICRP 2007 Recommendations. Then, we estimated the dose coefficients for inhalation and ingestion of these short-lived radionuclides in accordance with the ICRP 2007 Recommendations. In addition, we compared the dose coefficients with those in accordance with the ICRP 1990 Recommendations. As a result, a decreasing tendency was shown in the dose coefficients for inhalation cases; an increasing tendency was observed in those for ingestion cases. It was found that these changes in dose coefficients were mainly caused by the revision of the dose calculation procedures, alimentary tract models. The result of this study will be useful for planning of radiation protection at the high energy facilities.

Impressions of Health Physics Seminar 2016

Manabe, Kentaro

Hoken Butsuri, 52(1), p.35 - 38, 2017/03

https://doi.org/10.5453/jhps.52.35

Health Physics Seminar 2016 was held at the Osaka Science & Technology Center with 150 participants on Nov. 2, 2016. The seminar was consisted of three themes: "current movements of protection and operational quantities", "future risk communications inspired by the Fukushima accident", and "effects of low dose radiation on human". Eminent specialists gave lectures about the news in their particular fields and suggestions to problems. In addition, a special lecture entitled "recent movements of issues about Act on Prevention of Radiation Hazards due to Radioisotopes, etc." was given by a specialist of the Secretariat of Nuclear Regulation Authority. This lecture introduced the examples of trouble incidents, reports on implementation status of inspections, results of Integrated Regulatory Review Service by IAEA, etc. There were vigorous questioning and discussions through the seminar. This document reported the summary of the lectures and discussions, and the author's impressions of the seminar.

Assessment of specific absorbed fractions for photons and electrons using average adult Japanese male phantom

Manabe, Kentaro; Sato, Kaoru; Takahashi, Fumiaki

JAEA-Data/Code 2014-017, 60 Pages, 2014/10

JAEA-Data-Code-2014-017.pdf:15.4MB
JAEA-Data-Code-2014-017-appendix(CD-ROM).zip:0.62MB

International Commission on Radiological Protection (ICRP) determined reference phantoms based on physique and organ masses (physical characteristics) of Caucasian for dose assessment in the 2007 Recommendations. In internal dosimetry, the reference phantoms are used for calculation of specific absorbed fractions (SAFs). On the other hand, adult Japanese have smaller build than adult Caucasian, and organ masses are different from each other. SAFs depend on physical characteristics. Therefore, differences in physical characteristics between both races can influence dose coefficients. Then, SAFs of average adult Japanese male phantom, JM-103, were calculated by incorporating JM-103 into the general purpose radiation transport code, MCNPX2.6.0, and electron and photon SAFs were evaluated for 25 energies from 10 keV to 10 MeV and for combinations of 67 source regions and 41 target organs. The effect of the difference in build and organ masses between adult Japanese and Caucasian on SAFs was also examined by comparison between the calculated SAFs in this study and SAFs of the reference adult male phantom of ICRP. The SAFs of JM-103 calculated in this study are basic data for assessment of influence of difference in physical characteristics between the races on dose coefficients.

Comparison of internal doses calculated using the specific absorbed fractions of the average adult Japanese male phantom with those of the reference computational phantom-adult male of ICRP publication 110

Manabe, Kentaro; Sato, Kaoru; Endo, Akira

Physics in Medicine & Biology, 59(5), p.1255 - 1270, 2014/03

https://doi.org/10.1088/0031-9155/59/5/1255

The International Commission on Radiological Protection (ICRP) decided to use reference phantoms based on physical characteristics of basic Caucasian in evaluation of effective doses in the ICRP 2007 Recommendations. Specific absorbed fractions (SAFs), which are essential data for internal dosimetry, depend on physical characteristics of a phantom used in calculating the SAFs. The body size and amount of adipose tissue of adult Japanese are generally smaller than that of Caucasian. Then, we studied the effects of differences in physical characteristics on internal doses. The electron and photon SAFs of the average adult Japanese male phantom (JM-103) were calculated with the Monte Carlo method, MCNPX. The electron SAFs of the ICRP reference computational phantom-adult male (RCP-AM) were taken from published data. The photon SAFs of the RCP-AM were calculated in the same way as JM-103. Then, the values corresponding to effective dose coefficients for intakes of radionuclides were calculated using the SAFs of these phantoms. As a result of a comparison for 2894 cases of 923 radionuclides, the maximum discrepancy in the effective dose coefficients between the JM-103 and RCP-AM was about 40%. However, the discrepancies were smaller than 10% in 97% of all cases. Information obtained in this study is helpful in applying the dose coefficients of the ICRP to races other than Caucasian.

Impact of a revision of nuclear decay data on internal dose coefficients for workers

Manabe, Kentaro; Endo, Akira

Radioisotopes, 60(9), p.375 - 384, 2011/09

https://doi.org/10.3769/radioisotopes.60.375

The impact of revisions of nuclear decay data on internal dose coefficients for workers was studied using revised data of ICRP Publication 107 (ICRP107) and existing data of ICRP Publication 38 (ICRP38). At first, two sets of ingestion dose coefficients for workers based on ICRP107 and ICRP38 were calculated using the dose and risk calculation software DCAL for 876 chemical forms of 774 nuclides. Ingestion dose coefficients based on ICRP107 increased by over 10% compared with those based on ICRP38 in 61 chemical forms, and decreased by over 10% in 28 chemical forms. It was revealed that the differences in ingestion dose coefficients mainly originated from the revision of energy data as is the case in inhalation dose coefficients. And, the revisions of the proportion of energy of electrons to that of photons, decay modes and half-lives also resulted in changes in the dose coefficients. Then, the extent and causes of changes in ingestion and inhalation dose coefficients were also compared with each other in light of our previous work concerning inhalation dose coefficients. As a result of comparing the dose coefficients for ingestion and inhalation, it was found that the change in proportion of energy of electrons to that of photons impacted on dose coefficients in ingestion more significantly than in inhalation. On the other hand, the change in shape of energy spectrum, which was one of the causes of change in inhalation dose coefficients, did not impact on ingestion dose coefficients.

Influence of water concentrations to chemical forms of tritium generated in mercury through a nuclear reaction

Manabe, Kentaro; Yokoyama, Sumi

Applied Radiation and Isotopes, 68(3), p.418 - 421, 2010/03

https://doi.org/10.1016/j.apradiso.2009.08.020

Influence of water content to chemical forms of tritium generated in mercury was evaluated for assessment of potential internal exposure in the Japan Spallation Neutron Source (JSNS) using a mercury target. In order to simulate the condition of tritium production in the mercury target, mercury samples containing a small amount of metallic lithium as a source of tritium and water were irradiated with a thermal neutron beam. It was found that the ratio of HTO to the sum of HTO and HT increased with the water content in the mercury samples.

Research on release of tritium and iodine formed in mercury to gas-phase

Yokoyama, Sumi; Manabe, Kentaro

JAEA-Research 2008-057, 29 Pages, 2008/06

JAEA-Research-2008-057.pdf:3.24MB

At Material and Life Science facility of J-PARC, a mercury target as spallation neutron source is used. In the mercury target, airborne radionuclides such as tritium and iodine are formed by spallation reaction with high energy and intensity proton beam. There is possibility that the airborne radionuclides leaked from the target vessel to the air of the facilities may cause internal exposure. However, there is insufficient information about these chemical forms and behavior in mercury to estimate internal doses. We clarified chemical forms and release rates of tritium and iodine from mercury by experiments and discussed from the viewpoint of internal radiation protection. In this study, we found that most tritium formed in mercury is released to the gas-phase as HTO, while iodine is not released under the condition of gas phase in the mercury target.