Analysis of the Radiation Environment on Board the International Space Station Using Data from the SilEye-3/Alteino Experiment

University dissertation from Stockholm : KTH Royal Institute of Technology

Abstract: This thesis presents an analysis of the radiation environment on board the Russian section of the International Space Station (ISS) using data from the SilEye-3/Alteino experiment. As part of the analysis the efficiency and response of the SilEye-3/Alteino detector was studied. The relative nuclear abundance is generally in agreement with expected results. The presence of odd Z nuclei is significantly increased when compared with measurements outside the ISS. However, in ISS-y (Starboard-Ports) and z (Nadir-Zenith) directions an underabundance of carbon and oxygen nuclei is seen, whereasin x (Forward-Aft) there seemes to be an overabundance. One possible explanation is the absence of high-Z material in the ISS module wall for y and z . Whereas in x, most of the main body of the ISS is in front of the detector and the amount of high-Z material (i.e. aluminium) is large. The nalysis of fragmentation of iron into a range of secondary nuclei (15?Z ?25) indicates an aluminium hull equivalent thickness of 8-9 cm in y- and z-directions. For x the aluminium hull equivalence amounts to about 17 cm. Flux, LET, dose and dose equivalent rates present a clear anisotropy in the different orthogonal directions of the ISS, with rates consistently lower in x. This effect is more pronounced for the heavy-ion component (LET >50 keV/?m). Measureddose rates vary from 25 ?Gy/day to 75 ?Gy/day, depending on location, orientationand configuration of the detector. The dose equivalent varies from 50 ?Sv/day toalmost 470 ?Sv/day.The shielding effect of the polyethylene amounts to 25-37% dependent on loca-tion and orientation inside the ISS. The majority of the reduction occurs duringpassages through the SAA. A Geant4 comparison with the Phits simulations code have been preformed as an initial survey into the treatment of hadronic physics for heavy ions in Geant4.