Date of Award
Doctor of Philosophy (PhD)
Since the discovery of cosmic rays, Earth's upper atmosphere at depths of 1-10 g cm2 has been used for balloon-borne observations probing the high-energy universe. However, the interaction of cosmic rays with the earth atmosphere generates numerous particles, each with their own flux and interaction physics that contribute to instrument background. In Fall 2014, the X-Calibur X-ray polarimeter designed and built at Washington University in St. Louis was launched from Ft. Sumner, New Mexico. While no astrophysical observation was performed as a result of a failure in telescope mechanisms, X-Calibur was able to record hours of instrument background with an energy resolution of E ~keV at a depth of 3.45 g cm2.
Using the 2014 X-Calibur data, existing observations of atmospheric gamma-rays, hadrons, and leptons, and the MEGAlib/GEANT particle transport simulation environments, I develop and perform preliminarily validation of detailed background models in the regime of 1 keV-100 GeV. The models are generally constructed by involving experimental data with atmospheric mass and composition models rather than integration of source/emission functions or complete Monte Carlo simulation of cosmic rays entering at the top of the atmosphere. Notably, these models are derived as functions of energy, off-zenith angle to degree precision, geomagnetic latitude, and solar modulation factor enabling predictions of instrument background for future X-Calibur flights.
These background models are also used to optimize the shielding conguration through
additional passive material or active components as constrained by the existing active shield.
Chair and Committee
James Buckley, Henry Garrett, Martin Israel, Ryan Ogliore
Amini, Rashied Baradaran, "Modern Assessment of the High-Energy Background Environment at Small Atmospheric Depths Using the X-Calibur X-Ray Polarimeter and Its Implications" (2016). Arts & Sciences Electronic Theses and Dissertations. 983.