APPENDIX TECHNICAL CONSIDERA TIONS Spatial Resolution Spatial resolution is controlled by altitude, flight speed, data accumulation time and gamma-ray energy. The detectors exhibit a cosine angular response for low energy gamma-rays such as the 60 keVline from Am 241. Inherent spatial resolution is approximately 125 ft at 100 ft altitude for this energy. Inherent spatial resolution is degraded for higher energy gamma-rays due to the decrease in air attenuation and the transmission of gamma-rays by the shielding around the sides of the crystals. The assumption of isotopic angular response and no air attenuation for high energy gamma-rays gives a spatial resolution of 200 ft at an altitude of 100 ft. Data accumulation time can be adjusted to be consistent with inherent spatial resolution and flight speed. Sensitivity Sensitivity is controlled by survey rate, spatial resolution and background count rates under the photopeaks of interest. Sensitivities can be estimated by assuming background spectra in the region of interest to be identical to that taken over typical U. S. Soil with an array of 4- by 4-inch crystals. Amplitude of the spectra are scaled according to crystal surface area and radiation levels three feet above the ground. The following sensitivities are estimated with these assumptions and the additional assumptions of 100 ft/sec flight speed, spatial resolution of 150 ft, survey speed 15000 ft? /sec, and cosine angular response for the detector system