Radiation of cosmic rays in leo in the solar cycle 23

Radiation in LEO (Low Earth Orbit) is mainly composed of primary particles: GCR (Galactic Cosmic Rays), SEP (Solar Energetic Particles), SAA (South Atlantic Anomaly) particles and albedo neutrons and protons from the Earth's atmosphere. When the primary particles enter/pass through the space vehicle shielding and the internal instruments/equipment/detectors, the secondary particles (charged and neutrons) are produced and then a very complicated radiation environment is generated. One of the remarkable characteristics of space radiation is that the radiation varies with the solar activities, in the solar minimum period the radiation is maximum. The solar minimum of solar cycle 23 was between 2008 and 2010. ISS-Expedition 18-19/ULF2 was conducted in this solar minimum (15 Nov. 2008-31 July 2009, total 258.6 days). NASA-SRAG (Space Radiation Analysis Group) has been using both active dosimeters TEPC (Tissue Equivalent Proportional Counter) sensitive to all LET (Linear Energy Transfer) and passive dosimeters TLDs (Thermo Luminescent Dosimeters) and OSLDs (Optically Stimulated Luminescent Dosimeters) sensitive to low LET (≤10 keV/μm water) and CR-39 PNTDs (Plastic Nuclear Track Dosimeters) sensitive to high LET (≥10 keV/μm water) to measure radiation for astronauts and for the selected locations inside the ISS (International Space Station). For the passive methods, the total radiation quantities for all LET can be obtained by combining results measured with TLDs/OSLDs and CR-39 PNTDs. This paper introduces the methods of radiation measurements using TEPC, TLDs/OSLDs and CR-39 PNTDs and the LET spectrum method for CR-39 detectors; presents radiation LET spectra measured with TEPC and CR-39 detectors and radiation quantities measured with TEPC, TLDs/OSLDs and CR-39 PNTDs for the ISS-Expedition 12 and 18-19/ULF2; and compares radiation quantities measured with active and passive dosimeters in the different stages of solar activities.