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PubMed2004

Implementation of ALARA radiation protection on the ISS through polyethylene shielding augmentation of the Service Module Crew Quarters.

With 5-7 month long duration missions at 51.6 degrees inclination in Low Earth Orbit, the ionizing radiation levels to which International Space Station (ISS) crewmembers are exposed will be the highest planned occupational exposures in the world. Even with the expectation that regulatory dose limits will not be exceeded during a single tour of duty aboard the ISS, the "as low as reasonably achievable" (ALARA) precept requires that radiological risks be minimized when possible through a dose optimization process. Judicious placement of efficient shielding materials in locations where crewmembers sleep, rest, or work is an important means for implementing ALARA for spaceflight. Polyethylene (CnHn) is a relatively inexpensive, stable, and, with a low atomic number, an effective shielding material that has been certified for use aboard the ISS. Several designs for placement of slabs or walls of polyethylene have been evaluated for radiation exposure reduction in the Crew Quarters (CQ) of the Zvezda (Star) Service Module. Optimization of shield designs relies on accurate characterization of the expected primary and secondary particle environment and modeling of the predicted radiobiological responses of critical organs and tissues. Results of the studies shown herein indicate that 20% or more reduction in equivalent dose to the CQ occupant is achievable. These results suggest that shielding design and risk analysis are necessary measures for reducing long-term radiological risks to ISS inhabitants and for meeting legal ALARA requirements. Verification of shield concepts requires results from specific designs to be compared with onboard dosimetry.

Astronauts↗
PubMedDate not supplied

Near-infrared radiation protects the red cell membrane against oxidation.

The antioxidant effects of near-infrared radiation (NIR) in vitro (700-200 nm) on human erythrocytes was studied as a continuation of our earlier studies. The changes of: ratio of hemolysis, electrokinetic potential, lipids peroxidation, autohemolysis, and fluidity of red cell lipid bilayer were studied for intact, irradiated, ozonated and irradiated, and ozonated erythrocytes. We revealed that, under in vitro condition, the oxidation of red cells by ozone decreased lipids' bilayer fluidity in the vicinity of the 5th carbon and increased fluidity on the 16th carbon level of hydrocarbon chains, induced autohemolysis, oxidized lipids, and changed the electrokinetic potential. However, when erythrocytes were exposed to near-infrared radiation (NIR) and later ozonated, measured parameters were the same as that for control cells kept in darkness or markedly less modified than that ozonated. In conclusion, these observations suggest protective action of NIR radiation on the erythrocyte membrane. The results support the idea that during exposition to NIR, dehydration process induces the photochemical dissociation oxyhemoglobin to deoxyhemoglobin. Deoxygenation leads to phosphorylation of cytoplasmic domain of band 3 at tyrosine 8 that strengthens its association with the spectrin network. An increased association between band 3 and the underlying skeleton elevated the cell membrane mechanical resistance that could protect them before autohemolysis. Also, weakening hydrogen bonds on the surface of erythrocyte membranes moderate the surface charge, lowering the accessibility of charged free radicals from ozone solution into cells.

Electron Spin Resonance Spectroscopy↗