Azimuthal dependence of the atmospheric gamma-ray background
Shelton, David Harold
Haymes, Robert C.
Master of Science
On May 15, 1973 a balloon borne gamma-ray detector belonging to Rice University was launched from Palestine, Texas. From 19:4 CDT to 21:25 CDT the atmospheric gamma ray background was observed from 56 KeV to 12.4 MeV in energy. The directional detector was pointed at a constant zenith angle of 13.4° and viewed the atmospheric background at all values of azimuth angle. The experiment was carried out at altitudes of roughly 3.5 gm/cm2 residual atmosphere. The detector consisted of a central crystal of Nal(Tl) which was actively collimated by a shield of the same material. The instrument had a beam width of 15° full width half maximum. Results are consistent with an observed sinusoidal perturbation of the average background count rate between 56 KeV and 375 KeV of the form R = B[1 + (.188 ± .33)sin(Az - (12° ± 22°))] where R is the photon count rate, B is the average photon count rate, and Az is the azimuth angle at which the instrument was pointed. No similar behavior was observed at other energies.