Characterization of Bubble Detectors for Space Application

Abstract A passive neutron-bubble dosimeter, developed by Bubble Technology Industries, has been used for space applications. This study provides a means to characterize the response of these detectors to various particle types in support of bubble-detector measurements made on a board the International Space Station (ISS) in Low Earth Orbit. An analysis of the radiation environment onboard the ISS in the Service Module with the OLTARIS code indicates that neutrons, protons, and lower atomic mass particles are the more abundant particles. Based on a Monte Carlo treatment with the Stopping Range of Ions in Matter (SRIM) code, the response functions of the lighter ions were determined. This assessment considered the maximum linear energy transfer of these ions at the end of their path (Bragg peak) in the detector that exceeded the minimum threshold to cause bubble nucleation. The model was benchmarked against previous heavy-ion measurements in ground-based accelerator studies. The model was able to successfully predict, for a beam oriented along the detector axis, the observed energies at which the ions penetrated and exited the detector as well as the relative scaling of the response curves. By folding in the calculated particle fluxes with both the predicted light-ion response functions, as well as using experimental responses for neutrons, protons and alpha particles measured in previous accelerator studies, the contribution of particles in space to the bubble count was evaluated. This analysis shows that for an isotropic-irradiation geometry in space, neutrons are the major contributors to the bubble count with a much smaller contribution from protons.