Comparisons of High-Linear Energy Transfer Spectra on the ISS and in Deep Space

In deep space, personnel and equipment are exposed to the space radiation environment in the form of energetic particles, specifically galactic cosmic rays and sporadic solar energetic particle events. Radiation fields resulting from these particles are modified by shielding, but most radiation measurements in deep space have been made with detectors that were unshielded or very lightly shielded. In contrast, the space radiation environment on the International Space Station (ISS) is more complicated, with time-dependent modification of the incident flux by the geomagnetic field and complex bulk shielding distributions; measured particle spectra inside the ISS are affected by both types of shielding. The geomagnetic field is also responsible for the existence of the South Atlantic Anomaly, a region of trapped energetic protons and electrons, and hence enhanced radiation dose, through which the ISS travels several times per day on average. Here our primary aim is to compare charged-particle spectra at high linear energy transfer obtained by the Anomalous Long-Term Effects in Astronauts instrument on ISS during high-latitude portions of the orbit to data acquired at the same time by the Cosmic Ray Telescope for the Effects of Radiation and Radiation Assessment Detector instruments, both in deep space. The hypothesis being tested is that these spectra are the same, modulo shielding differences, since the effects of the geomagnetic field are expected to be minimal at high latitudes.