Development and validation of a Medaka fish voxel-based model for internal ionizing radiation dosimetry.

In this paper, we present a voxel-based phantom of Medaka fish that can be used to assess the internal radiation doses that would be absorbed by different organs of this fish species if exposed to radioactive wastewater released into the ocean. The geometric model for fish was generated based on available Wavefront Object files for smooth-bodied Medaka fish organs, whereas due to the lack of Medaka fish material specification, the material model was constructed using material data appropriate to ICRP 110 adult male voxel-based phantom. Absorbed Fractions (AFs) and Specific Absorbed Fractions (SAFs) were calculated for eight organs of major interest as sources and for each organ as target at a set of discrete photon, electron, alpha and neutron energies. To validate the present model the calculated AFs in the studied organs were compared to ones obtained in similar organs in a voxel-based phantom of another teleost fish species called Limanda limanda. The results presented are consistent with the reference dosimetric data. We concluded that the Medaka model can be used in radioecology research to improve marine radiation protection.

InterDosi Monte Carlo study of radiation exposure of a reference crab phantom due to radioactive wastewater deposited in marine environment following the Fukushima nuclear accident.

S-values are typically used to quantify internal doses of biota internally due to the incorporation of radionuclides. In this study, the InterDosi 1.0 Monte Carlo code was used to estimate S-values in five main organs of a crab phantom as well as in surrounding seawater for eleven radionuclides, namely 3H, 14C, 134Cs, 137Cs, 60Co, 125Sb, 90Sr, 129I, 99Tc, 106Ru, and 238Pu. After the Fukushima accident, these radionuclides have been detected in wastewater by the Japan Nuclear Regulatory Authority. In this work, S-values were calculated for all crab organs and the surrounding seawater. These values can be used in conjunction with any measured activities in water, to determine internal doses absorbed by crab organs. Furthermore, it is shown that for a self-absorption condition the studied radionuclides can be classified into five main categories, with 238Pu showing the highest S-values for any organ. Moreover, the results demonstrate that the obtained S-values decrease with increasing organ mass. In contrast, for a cross-absorption condition, the studied organs can be classified into seven main categories. In addition, by taking seawater as a source of irradiation, 238Pu had the highest cross-absorption S-values in two organs of particular biological relevance, the heart and gonads, when compared to the remaining radionuclides. It is concluded that due to the pre-calculated S-value database of a reference crab, it will become easier to use this organism as a bio indicator to study any radiation-induced effects on the marine environment.