In the on-going project absorbed dose rates are measured in the direct vicinity of the dried lymphocytes and bone marrow cell samples in three different modules of the Russian segment, on-board the International Space Station. These compartments have different shielding thicknesses; the Service module is frequently used by cosmonauts, thus it is the most shielded location, while the MRM-2 (Poisk) and the Pirs module are less protected. The latter segment is applied as a docking port, equipped with an airlock as well, therefore the highest dose was expected to be measured in this location. The one-by-one recovery of the dosimeter packages was planned to be performed after four half-year-long sessions. Applying this method it is possible to follow the changes in the radiation field during the decreasing phase of the 24th solar cycle. After the first 199-day-long session the results were ready to be published in 2016 [1]. The dosimetry groups including the researchers of MTA EK applied passive detectors – which require no energy input – such as solid state nuclear track detectors and thermoluminescent dosimeters. These devices are able to detect particles having different linear energy transfer (LET), thus posing a different health effect. With the convolution of the results obtained by these dosimeters it is possible to measure the cosmic radiation in a wide energy range.
As a result of the first session of detectors exposed between the end of 2014 and the beginning of 2015 accompanied by intensive solar activity, we obtained higher doses than it was published for the same locations in a quieter solar period. Compared to the measurements near the end of the 23rd solar cycle [2] and the beginning of the 24th cycle [3] we detected 25% higher dose rate in the Service module (265±36 µGy/day) and more than twice as high dose rate in the much less shielded Pirs module (732±2 µGy/day). In the MRM-2 (Poisk) segment the dose rate was between these two (413±13 µGy/d). Differences in the radiation fields compared to previous observations can be explained by the complex effect caused by the changing of solar activity and the altitude of the ISS, while the dose differences between the modules are caused by the dissimilar shielding thicknesses. The preliminary results show a good survival of human cell nuclei and it was noticed that the degree of DNA fragmentation depends on the dose rate directly [4].
Andrea Strádi
[1] Strádi, A.,Szabó, J., Inozemtsev, K. O.,Kushin, V. V., Tolochek, R. V., Shurshakov, V. A., Alchinovad, A. B., Karganov, M. Yu., Comparative Radiation Measurements in the Russian Segment of the International Space Station by Applying Passive Dosimeters, Radiat. Meas. 2017, doi: 10.1016/j.radmeas.2017.01.018
[2] Ambrozova, I., Brabcova, K., Spurny, F., et al., 2011. Monitoring on board spacecraft by means of passive detectors. Radiat. Prot. Dosim. 144 (1e4), 605e610.
[3] Kodaira, S., Kawashima, H., Kitamura, H., et al., 2013. Analysis of radiation dose variations measured by passive dosimeters onboard the International Space Station during the solar quiet period (2007-2008). Radiat. Meas. 49, 95e102.
[4] Karganov, M. Yu, Alchinova, I. B., Yakovenko, E. N., et al., 2017. The “PHOENIX” space experiment: study of space radiation impact on cells genetic apparatus on board the international space station. J. Phys.: Conf. Series 784, 012024.