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Sakai, Akihiro; Okoshi, Minoru
Radiation Risk Assessment Workshop Proceedings, p.175 - 186, 2003/00
To establish the clearance levels, the Nuclear Safety Commission (NSC) has been discussing the clearance levels since May 1997. The NSC derived the unconditional clearance levels for the solid materials, namely concrete and metal, arising from the operation and dismantling of nuclear reactors and post irradiation examination (PIE) facilities. Two destinations of the cleared materials, namely disposal and recycle/reuse, were considered. Deterministic calculation models were established to assess individual doses resulting from 73 exposure pathways, and realistic parameter values were selected considering the Japanese natural and social conditions. The clearance levels for 21 radionuclides of nuclear reactors and for 49 of PIE facilities were derived as radioactivity concentration equivalent to the individual doses of 10 
Sv/y. Most of calculated clearance levels were nearly the same as those shown in IAEA-TECDOC-855. Some, however, were different. It is considered that the major reasons depend on differences of fixed scenarios and of selected values of parameters.
Takahashi, Fumiaki; Yamaguchi, Yasuhiro
Radiation Risk Assessment Workshop Proceedings, p.71 - 78, 2003/00
Conversion from tooth enamel dose to organ doses against external photon exposure were studied in order to develop a method that can retrospectively estimate organ doses by the Electron Spin Resonance (ESR) dosimetry using tooth samples. Monte Carlo calculations using EGS4 code were performed to obtain dose to tooth enamel and organ doses by using a modified MIRD-type phantom. The Electron Spin Resonance (ESR) dosimetry using tooth samples and dose measurements using thermo-luminescence dosimeters (TLDs) were also carried out to examine dose to teeth region with a realistic physical phantom. A Voxel-type phantom was constructed from CT images of the physical phantom. Monte Carlo calculations with the Voxel-type phantom were performed to verify the results of the experiments and enamel doses calculated by use of the modified MIRD-type phantom. The obtained data are to be useful for the retrospective assessment of individual dose in past exposure events by the ESR dosimetry with tooth enamel.
Endo, Akira; Yamaguchi, Yasuhiro; Takahashi, Fumiaki
Radiation Risk Assessment Workshop Proceedings, p.151 - 156, 2003/00
We have developed a new system using numerical simulation technique for analyzing dose distribution in various postures by neutron, photon and electron exposures. The system consists of mathematical human phantoms with movable arms and legs and Monte Carlo codes MCNP and MCNPX. This system was applied to the analysis of dose distribution for the heavily exposed workers in the Tokai-mura criticality accident. The paper describes the simulation technique employed and a summary of the dose analysis.
Yokoya, Ritsuko; Saito, Kimiaki
Radiation Risk Assessment Workshop Proceedings, p.48 - 55, 2001/00
no abstracts in English
Kinase, Sakae; Zankl, M.*; Kuwabara, Jun; Sato, Kaoru; Noguchi, Hiroshi; Funabiki, Jun*; Saito, Kimiaki
Radiation Risk Assessment Workshop Proceedings, p.118 - 127, 2001/00
There exists a need to calculate specific absorbed fractions (SAFs) in voxel phantoms for internal dosimetry. For the purpose, an EGS4 user code for calculating SAFs using voxel phantoms was developed on the basis of the EGS4 user code (UCPIXEL). In the developed code, the transport of photons, electrons and positrons in voxel phantoms can be simulated, particularly the transport simulations of secondary electrons in voxel phantoms can be made. The evaluated SAFs for the GSF "Child" voxel phantom using the developed code were found to be in good agreement with the GSF evaluated data. In addition, SAFs in voxel phantoms developed at JAERI were evaluated using the developed code and were compared with several published data. It was found that SAFs depend on the organ masses and would be affected by differences in the structure of the human body.
Pinak, M.
Radiation Risk Assessment Workshop Proceedings, p.30 - 39, 2001/00
no abstracts in English
Sato, Kaoru; Noguchi, Hiroshi; Saito, Kimiaki; Emoto, Yutaka*; Koga, Sukehiko*
Radiation Risk Assessment Workshop Proceedings, p.102 - 110, 2001/00
For calculating doses due to radioactivity taken in a body, Specific Absorbed Fractions (SAFs) are used. In recent years, more realistic phantoms called voxel (volume pixel) phantoms have been developed on the basis of CT or MRI images of actual persons. The voxel phantoms can accurately describe sizes, shapes and locations of organs, which would affect SAFs. We are now developing Japanese adult voxel phantoms for internal dosimetry by using CT images. Until now, CT scans for three healthy Japanese male volunteers were performed under supine or upright positions to study the effect of body size and position on SAFs. The height and weight of the middle size man is almost coincident with the averages for Japanese adult. So far the development of voxel phantom has been almost finished for the middle size man (voxel-phantom-MM). The voxel size is 0.98
0.981.0 mm
. It was found that even small size organs such as thyroid were realistically modeled. The result showed that voxel-phantom-MM had realistic structure which would enable us to calculate reliable SAFs
Nakayama, Teruyuki; Kato, Shohei
Radiation Risk Assessment Workshop Proceedings, p.140 - 150, 2001/00
no abstracts in English