The Russian BRADOS experiment onboard the International Space Station (ISS) was aimed at developing methods in radiation dosimetry and radiobiology to improve the reliability of risk estimates for the radiation environment in low-Earth orbit. Experimental data from thermoluminescence detectors (TLDs) and solid state nuclear track detectors (SSNTDs) gathered during the BRADOS-1 (24 February–31 October 2001) mission are reviewed and convolved to obtain absorbed dose and dose equivalent from primary and secondary cosmic-ray particles. Absorbed dose rates in the ISS Russian Segment (Zvezda) ranged from 208 ± 14 to 275 ± 14 μ Gy d – 1 . Dose equivalent rates were determined to range from 438 ± 29 to 536 ± 32 μ Sv d – 1 , indicating a quality factor between 1.95 ± 0.15 and 2.11 ± 0.20 . The contribution of densely ionizing particles ( LET ⩾ 10 keV μ m – 1 ) to dose equivalent made up between 54% and 64%.
Research Containing: SSNTD
Cosmic ray detection on the ISS by a 3 axes track etch detector stack and the complementary calibration studies
The complex radiation field inside the International Space Station (ISS) as well as the dose received by its crew was studied for several years in the BRADOS ( 1 – 5 ) projects organized by the Institute for Biomedical Problems (IBMP, Moscow) with the participation of different laboratories. The results of the measurements performed during the BRADOS-5 project by a 3 axes solid state nuclear track detector (SSNTD) stack as LET spectra and dose values are presented. According to the results, no remarkable directional dependence could be observed in the radiation field. The averaged absorbed dose rate and dose equivalent rate values above ∼ 12 keV μ m – 1 were 27.0 ± 1.6 μ Gy d – 1 and 211.4 ± 14.4 μ Sv d – 1 , respectively, resulting in an averaged quality factor of 7.9 ± 0.1 .
The aim of the study was to investigate the contribution of secondary neutrons to the total dose inside the International Space Station (ISS). For this purpose solid-state nuclear track detector (SSNTD) stacks were used. Each stack consisted of three CR-39 sheets. The first and second sheets were separated by a Ti plate, and the second and third sheets sandwiched a Lexan polycarbonate foil. The neutron and proton responses of each sheet were studied through MC calculations and experimentally, utilising monoenergetic protons. Seven stacks were exposed in 2001 for 249 days at different locations of the Russian segment ‘Zvezda’. The total storage time before and after the exposure onboard was estimated to be seven months. Another eight stacks were exposed at the CERF high-energy neutron field for calibration purposes.The CR-39 detectors were evaluated in four steps: after 2, 6, 12 and 20 h etching in 6 N NaOH at 70°C (VB = 1.34 µm h−1). All the individual tracks were investigated and recorded using an image analyser. The stacks provided the averaged neutron ambient dose equivalent (H*) between 200 keV and 20 MeV, and the values varied from 39 to 73 μSv d−1, depending on the location. The Lexan detectors were used to detect the dose originating from high-charge and high-energy (HZE) particles. These results will be published elsewhere.