Depth dose measurements with the Liulin-5 experiment inside the spherical phantom of the MATROSHKA-R project onboard the International Space Station J. Semkova a,⇑ , R. Koleva a , St. Maltchev a , N. Bankov a , V. Benghin b , I. Chernykh b , V. Shurshakov b , V. Petrov b , S. Drobyshev b , I. Nikolaev c a Space and Solar-Terrestrial Research Institute, Bulgarian Academy of Sciences, Bulgaria b State Scientific Center of Russian Federation, Institute of Biomedical Problems, Russian Academy of Sciences, Russia c S.P. Korolev Rocket and Space Corporation Energia, Russia Received 26 May 2011; received in revised form 4 October 2011; accepted 6 October 2011 Available online 14 October 2011 Abstract The Liulin-5 experiment is a part of the international project MATROSHKA-R on the Russian segment of the ISS, which uses a tissue-equivalent spherical phantom equipped with a set of radiation detectors. The objective of the MATROSHKA-R project is to pro- vide depth dose distribution of the radiation field inside the sphere in order to get more information on the distribution of dose in a human body. Liulin-5 is a charged particle telescope using three silicon detectors. It measures time resolved energy deposition spectra, linear energy transfer (LET) spectra, particle flux, and absorbed doses of electrons, protons and heavy ions, simultaneously at three depths along the radius of the phantom. Measurements during the minimum of the solar activity in cycle 23 show that the average absorbed daily doses at 40 mm depth in the phantom are between 180 lGy/day and 220 lGy/day. The absorbed doses at 165 mm depth in the phantom decrease by a factor of 1.6–1.8 compared to the doses at 40 mm depth due to the self-shielding of the phantom from trapped protons. The average dose equivalent at 40 mm depth is 590 ± 32 lSV/day and the galactic cosmic rays (GCR) contribute at least 70% of the total dose equivalent at that depth. Shown is that due to the South Atlantic Anomaly (SAA) trapped protons asymmetry and the direction of Liulin-5 lowest shielding zone the dose rates on ascending and descending nodes in SAA are different. The data obtained are compared to data from other radiation detectors on ISS. Ó 2011 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Space radiation dosimetry; International Space Station; Tissue-equivalent phantom; Charged particle telescope 1. Introduction Space radiation is a concern for astronauts’ health and safety and investigation of the radiation influence on space vehicles and their crew has been conducted since the early times of human space flight. Predicting the effects of radia- tion on humans in space flight requires accurate knowledge and modelling of the space radiation environment, calcula- tion of primary and secondary particle transport through the shielding materials and through the human body, and assessment of the biological effect of cosmic particles. The radiation field onboard the ISS is complex, composed of galactic cosmic rays (GCR), trapped radiation of the Earth radiation belts, solar energetic particles, albedo par- ticles from Earth’s atmosphere and the secondary radiation produced in the shielding materials of the spacecraft and in human body. The GCRs, consisting of 99% protons and He nuclei and 1% heavy ions with energies up to tens of GeV/nuc are a permanent source of ionising radiation in ISS. The 0273-1177/$36.00 Ó 2011 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2011.10.005 ⇑ Corresponding author. E-mail addresses: jsemkova@stil.bas.bg (J. Semkova), v_benghin@ mail.ru (V. Benghin), i24.nikolaev@pochta.ru (I. Nikolaev). www.elsevier.com/locate/asr Available online at www.sciencedirect.com Advances in Space Research 49 (2012) 471–478