Results of measurements on shuttle missions to the ISS of the neutron component of the radiation field

Abstract

Secondary neutrons can be a major contributor to dose equivalent and effective dose inside a spacecraft for the altitude range and inclination of the International Space Station. The exact proportion is very dependent on the amount of shielding of the primary galactic cosmic radiation and trapped particles, but is likely to lie in the range of 10–60%. Neutron personal dosemeters of simple design, processed using simple techniques developed for routine personal dosimetry, have been used to determine the neutron component, including the neutron-like interactions of high energy protons. For the etch regime employed, the combination of high LET threshold (there is little response below a restricted LET 200 in PADC of 30–40 keV/μm) and poor angle dependence of response to high-energy charged particles results in a much reduced overall response of the neutron dosemeter to the HZE component of the field in spacecraft and no response to protons of energy greater than about 1 MeV. A correction of 10–20% is necessary to account for the detector HZE response. Alternatively, an additional chemical etch can be carried out which allows discrimination.