Verification of shielding effect by the water-filled materials for space radiation in the International Space Station using passive dosimeters

•Dose reduction effect for space radiation by water shielding material was verified.•Absorbed dose and dose equivalent were evaluated with passive dosimeters.•Observed dose reduction rate was found to be 37±7% in dose equivalent.•It will effectively reduce the annual dose for space crews and long-term mission. The dose reduction effects for space radiation by installation of water shielding material (“protective curtain”) of a stack board consisting of the hygienic wipes and towels have been experimentally evaluated in the International Space Station by using passive dosimeters. The averaged water thickness of the protective curtain was 6.3g/cm2. The passive dosimeters consisted of a combination of thermoluminescent detectors (TLDs) and plastic nuclear track detectors (PNTDs). Totally 12 passive dosimeter packages were installed in the Russian Service Module during late 2010. Half of the packages were located at the protective curtain surface and the other half were at the crew cabin wall behind or aside the protective curtain. The mean absorbed dose and dose equivalent rates are measured to be 327μGy/day and 821μSv/day for the unprotected packages and 224μGy/day and 575μSv/day for the protected packages, respectively. The observed dose reduction rate with protective curtain was found to be 37±7% in dose equivalent, which was consistent with the calculation in the spherical water phantom by PHITS. The contributions due to low and high LET particles were found to be comparable in observed dose reduction rate. The protective curtain would be effective shielding material for not only trapped particles (several 10MeV) but also for low energy galactic cosmic rays (several 100MeV/n). The properly utilized protective curtain will effectively reduce the radiation dose for crew living in space station and prolong long-term mission in the future.