1 Scientific RepoRts | 7: 1644 | DOI:10.1038/s41598-017-01707-2 www.nature.com/scientificreports performances of Kevlar and polyethylene as radiation shielding on-board the International space station in high latitude radiation environment Livio Narici 1,2 , Marco Casolino 2 , Luca Di Fino 1 , Marianna Larosa 1 , Piergiorgio picozza 1,2 , Alessandro Rizzo 1,2 & Veronica Zaconte 1 passive radiation shielding is a mandatory element in the design of an integrated solution to mitigate the efects of radiation during long deep space voyages for human exploration. Understanding and exploiting the characteristics of materials suitable for radiation shielding in space fights is, therefore, of primary importance. We present here the results of the frst space-test on Kevlar and Polyethylene radiation shielding capabilities including direct measurements of the background baseline (no shield). Measurements are performed on-board of the International Space Station (Columbus modulus) during the ALTEA-shield ESA sponsored program. For the frst time the shielding capability of such materials has been tested in a radiation environment similar to the deep-space one, thanks to the feature of the ALTEA system, which allows to select only high latitude orbital tracts of the International Space Station. Polyethylene is widely used for radiation shielding in space and therefore it is an excellent benchmark material to be used in comparative investigations. In this work we show that Kevlar has radiation shielding performances comparable to the Polyethylene ones, reaching a dose rate reduction of 32 ± 2% and a dose equivalent rate reduction of 55 ± 4% (for a shield of 10 g/cm 2 ). Mitigation of radiation risk is one of the most important issues to be addressed to allow human exploration of deep space 1 . Radiation in a deep space habitat is composed by the Galactic Cosmic Rays (GCR), the radiation associated with solar events, such as the Solar Particle Events (SPEs), and the secondary radiation produced by the interaction of GCR and SPEs with the space habitat hull and/or other intervening material (such as a space suit or an experiment rack). Understanding the radiation shielding features of materials is therefore an important step toward an integrated solution for radiation countermeasures in space, where passive shielding will play a major role. Te goal of such studies is to reduce the radiation risk for the crew to a level As Low As Reasonably Achievable (ALARA), down to the ideal case where the risk for radiation exposure in space is comparable to the one on Earth, not to afect the allowable mission duration. As this goal is still out of reach of the available technology, future mission plans consider ‘additional’ radiation risk, which must lie below some pre-determined threshold. Te study of the radiation shielding performances for a given material to be used in space missions generally follows three main steps. First, shielding capabilities of the material are validated by a Monte Carlo simulation. If results are promising, then the material properties may be evaluated by ions irradiation in particle accelerator facilities. Te ions used in these test are expected to be the most abundant ones in space. Finally, a characteriza- tion in space are performed only for materials which have shown the best characteristics in the previous two steps. Measurements in Low Earth Orbit (LEO) at high latitude allow the investigation of a radiation feld similar to the deep-space one, with the correct ions spectrum, needed to evaluate the material characteristics as radiation shield. However, these measurements are much more resource demanding than the ground based ones. For this 1 Department of Physics, University of Rome Tor Vergata, via della Ricerca Scientifca 1, 00133, Roma, Italy. 2 INFN Roma Tor Vergata, via della Ricerca Scientifca 1, 00133, Roma, Italy. Correspondence and requests for materials should be addressed to L.N. (email: narici@roma2.infn.it) Received: 25 January 2017 Accepted: 31 March 2017 Published: xx xx xxxx opeN