Dose Equivalent, Absorbed Dose and Charge Spectrum Measurements Made in the International Space Station Orbit

Particle intensity, dose equivalent and absorbed dose have been measured on board the space shuttles during their visit to the International Space Station (ISS) on STS-108 and STS-112. The dose estimates are based on very accurate measurements of recoils produced in CR-39 by cosmic ray primary and secondary protons and heavier nuclei and by secondary neutrons. The corresponding LET spectra were used to determine dose equivalent and absorbed dose values for both missions. Estimates of the total flux of Z≥2 nuclei have been undertaken and a charge spectrum was measured for both missions. Comparisons are made with the predictions of a cosmic ray transport model. In low earth orbit astronauts are exposed to the radiation fields of galactic cosmic rays (GCR), solar particles, electrons and protons in the Earth’s radiation belts, albedo neutrons and protons coming from interactions in the Earth’s atmosphere. When particles traverse the spacecraft walls, internal structures and equipment, secondary charged particles and neutral particles are produced and a very complex radiation field is then created. Dose contributions for astronauts depend on the orbital inclination and altitude and the stage of solar cycle. LET (Linear Energy Transfer) spectra and charge spectra for STS-108 and STS-112 missions were measured by CR-39 detectors calibrated with heavy ions and at the CERF radiation field at CERN. This paper describes the approach used and presents the observed results and the comparison with theoretical predictions. 2. Experimental Approach and Data Analysis The CR-39 material used by DIAS (Dublin Institute for Advanced Studies) for STS missions was manufactured by American Technical Plastics. The detector thickness is about 600 µm and is covered by a thin plastic film to protect the detector from exposure to radon. A stack of 20 detectors was used for STS108 and each detector had an area of 7 cm × 7 cm. Because of the limited