Effects of neutron radiation generated in deep space-like environments on food resources.

The impact of deep space cosmic rays on food resources is as important as the risks of cosmic rays to the human body. This study demonstrates the potential for neutrons as secondary radiation in deep space spacecraft to cause meat activation and oxidative modification of proteins and lipids. We conducted a series of experiments such as the neutron irradiation experiment, the radioactivation analysis and the biochemical analysis. Neutrons with energies from 1 to 5 MeV with doses from 0.01 Gy to 4 Gy were irradiated by the RIKEN accelerated-driven neutron source (RANS). Radioactive nuclei, 24Na, 42K, and 38Cl, were detected in the neutron-irradiated meat. The modification products of the proteins by oxidative nitration, 6-nitrotryptophan (6NO2Trp), and by a lipid peroxidation, 4-hydroxy-2-nonenal (4-HNE), were detected in several proteins with neutron dose dependent. The proteome analysis showed that many oxidative modifications were detected in actin and myosin which are major proteins of myofibrils. This study is of crucial importance not only as risk factors for human space exploration, but also as fundamental effects of radiation on the components of the human body.

[Optical Computed Tomography for Polymer Gel Dosimetry].

This article describes an optical computed tomography (OCT) for polymer gel dosimetry, focusing on two systems recently constructed by us. The first OCT system, which is categorized as a first-generation system, comprised a single He-Ne laser, photodiode, and mechanical stages for moving and turning gel dosimeter. Projection data per angle are acquired from turned gel dosimeter. In this system, the reconstructed image is obtained using filtered back-projection (FBP) method from projection data. The second OCT system is a 2D-OCT scanner that utilizes a light panel and a camera detector. The dose-response relationship between the optical density and radiation dose reconstructed from the scanning images is comparable to that obtained using magnetic resonance imaging. Although there is much room for improvement in the image artifacts due to reflection and refraction of light and so on, OCT is expected as a modality for the future polymer gel dosimetry as the rapid, high-resolution, highly accurate evaluation tool.