The source and full nature of cosmic rays are still largely undetermined. Direct observations from outside the Earth's atmosphere of Galactic cosmic rays do not extend beyond energies of 1014 eV. Particles with larger energies, up to 1020 eV, are detected indirectly by ground-based air-shower detectors and such measurements are affected by the large uncertainties implicit in this experimental method. The Advanced Cosmic-ray Composition Experiment for the Space Station (ACCESS) will measure the elemental composition and energy spectra of cosmic-ray particles to energies of over 1015 eV. The experimental apparatus of ACCESS includes a transition radiation detector and a thin ionization calorimeter. The calorimeter will measure the spectra of cosmic-ray protons and helium and identify cosmic-ray electrons. The design of a space-based calorimeter differs significantly from ground-based detectors. A hadronic calorimeter for space must necessarily be thin in order to meet the stringent mass requirements of a space mission. Its design is ultimately a tradeoff between desired energy resolution and required collecting power. Several concepts have been proposed for the structure of the ACCESS calorimeter. This work describes the design of the Silicon-Tungsten imaging calorimeter for ACCESS, developed as part of a NASA-sponsored mission concept and detector assessment study. A reduced version of this detector was developed and flown by the WiZard collaboration in balloon-borne and in a few satellite-based cosmic-ray experiments, primarily to search for primordial antimatter in the cosmic radiation. In this dissertation, we study the optimization of the Silicon-Tungsten calorimeter design for ACCESS, and then verify the performance of the final structure for the measurement of high-energy cosmic-ray protons, alpha-particles and electrons. Our results show that the Silicon-Tungsten calorimeter is an ideal detector for ACCESS, and offers the best possible performance achievable within the strict constraints imposed on the structure of this experiment.
- Pub Date: