EVA space suit proton and electron threshold energy measurements by XCT and range shifting

Construction of the International Space Station (ISS) will require more than 1000 h of extravehicular activity (EVA). Outside of the ISS during EVA, astronauts and cosmonauts are likely to be exposed to a large fluence of electrons and protons. Development of radiation protection guidelines and mitigation of risks requires the determination of the minimum energy of electrons and protons that penetrate the astronaut EVA suits at various locations. Measurements of the water equivalent thickness of both United States (US) and Russian EVA suits were obtained by performing X-ray computed tomography (XCT) scans. Selected regions of interest of the suits were further evaluated using a “differential range shift” technique. This technique involved measuring thickness ionization curves for 6 MeV electron and 155 MeV proton beams with ionization chambers using a constant source-to-detector distance. The thicknesses were obtained by stacking polystyrene slabs immediately upstream of the detector. The thicknesses of the 50% ionizations relative to the maximum ionizations were determined. The detectors were then placed within the suit and the stack thickness adjusted until the 50% ionization was re-established. The difference in thickness between the 50% thicknesses was then used with standard range tables to determine the threshold energy for penetration. This paper provides a detailed description of the experimental arrangement and the obtained results.