In the frame of the EXPOSE-R mission outside the Russian Zvezda Module of the International Space Station (ISS) passive thermoluminescence dosimeters were applied to measure the radiation exposure of biological samples. The detectors were located beneath the sample carriers to determine the dose levels for maximum shielding. The dose measured beneath the sample carriers varied between 317 ± 10 and 230 ± 2 mGy, which amount to an average dose rate of 381 ± 12 and 276 ± 2 μGy d−1. These values are close to those assessed for the interior of the ISS and reflect the high shielding of the biological experiments within the EXPOSE-R facility. As a consequence of the high shielding (several g cm−2), the biological samples were predominantly exposed to galactic cosmic heavy ions and trapped protons in the Earth's radiation belts, whereas the trapped electrons did not reach the samples.
