Time profile of cosmic radiation exposure during the EXPOSE-E mission: the R3DE instrument

Abstract

The aim of this paper is to present the time profile of cosmic radiation exposure obtained by the Radiation Risk Radiometer-Dosimeter during the EXPOSE-E mission in the European Technology Exposure Facility on the International Space Station's Columbus module. Another aim is to make the obtained results available to other EXPOSE-E teams for use in their data analysis. Radiation Risk Radiometer-Dosimeter is a low-mass and small-dimension automatic device that measures solar radiation in four channels and cosmic ionizing radiation as well. The main results of the present study include the following: (1) three different radiation sources were detected and quantified-galactic cosmic rays (GCR), energetic protons from the South Atlantic Anomaly (SAA) region of the inner radiation belt, and energetic electrons from the outer radiation belt (ORB); (2) the highest daily averaged absorbed dose rate of 426 μGy d(-1) came from SAA protons; (3) GCR delivered a much smaller daily absorbed dose rate of 91.1 μGy d(-1), and the ORB source delivered only 8.6 μGy d(-1). The analysis of the UV and temperature data is a subject of another article (Schuster et al., 2012 ).

FIG. 1.

External view of the EXPOSE-E facility and R3DE instrument, which is situated in the bottom left corner of the picture. The four photodiodes of the solar irradiance spectrometer can be clearly seen in the center of the R3DE. The ionizing radiation PIN diode with 2 cm² area is behind the aluminum cover and therefore not visible in the picture. Color images available online at www.liebertonline.com/ast

FIG. 2.

Block diagram of the R3DE instrument. The upper part of the figure presents the ionizing radiation block scheme, while the bottom part shows the solar radiation and temperature block scheme.

FIG. 3.

Latitudinal distribution of the dose rates measured with the R3DE instrument against McIlwain's L values. The maximum in the upper left side of the figure denoted by SAA is created by high-energy protons when the ISS crosses the region of the SAA. The maximum in the right side is generated by sporadic high-energy electrons seen mainly at high geographic latitudes (L>3.5). Galactic cosmic rays (GCR) are seen everywhere and at all times on the ISS. Their distribution is spread in the bottom side of the figure. Color images available online at www.liebertonline.com/ast

FIG. 4.

Daily and hourly SAA dose rates and SAA proton energies measured with the R3DE instrument during the EXPOSE-E mission. The space shuttle dockings at the ISS create strong decreases in the hourly and daily dose rates due to the additional shielding effect of the space shuttle body on the R3DE detector. At the same time the energy of the protons in the SAA increases. The space shuttle visits are marked with the STS number of flight. Color images available online at www.liebertonline.com/ast

FIG. 5.

Daily GCR dose rates measured with the R3DE instrument during the EXPOSE-E mission are denoted on the figure by AD. The small positive trend of the GCR doses is compared with the trend in the daily averaged Oulu neutron monitor (NM) counts divided by 60 to be in the same linear scale as the GCR data. Color images available online at www.liebertonline.com/ast

FIG. 6.

ORB dose rates measured with the R3DE instrument during the EXPOSE-E mission (c) are compared with the GOES-11 daily more than 2 MeV electron fluence (b) and global daily Ap index (a). The data for GOES energetic electrons and Ap indexes are taken from the 2008/2009_DPD.txt and 2008/2009_DGD.txt files prepared by the U.S. Department of Commerce, NOAA, Space Weather Prediction Center, available online from http://www.swpc.noaa.gov/ftpmenu/index.html.