Characterization of the radiation shielding properties of US and Russian EVA suits using passive detectors

Radiation measurements using passive detectors were carried out to assess the shielding properties of the US Extravehicular Mobility Unit (EMU) space suit and the Russian Orlan-M suit during irradiations of the suits and a tissue-equivalent phantom by monoenergetic proton and electron beams at the Loma Linda University Medical Center (LLUMC). During irradiations of 6 MeV electrons and 60 MeV protons, absorbed dose as a function of depth was measured using thermoluminescent detector (TLD) exposed behind swatches of the two suit materials and inside the two extravehicular activity (EVA) helmets. Considerable reduction in electron dose was measured behind all suit materials on exposure to 6 MeV electrons. Slowing of the proton beam in the suit materials led to an increase in dose measured on exposure to 60 MeV protons. During 232 MeV proton irradiations, measurements were made with TLD and CR-39 plastic nuclear track detector (PNTD) at five organ locations inside a tissue-equivalent phantom, exposed both with and without the two EVA suits. The EVA helmets produced a 13% to 27% reduction in total absorbed dose and a 0% to 25% reduction in dose equivalent when compared to measurements made in the phantom head alone. Differences in absorbed dose and dose equivalent between the suit and non-suit irradiations for the lower portions of the two EVA suits tended to be smaller. Proton-induced target fragmentation was found to be a significant source of increased dose equivalent, especially within the two EVA helmets, and average quality factor inside the EMU and Orlan-M helmets was 2% to 14% greater than that measured in the bare phantom head.