Reducing Errors in Airborne Gamma Ray Spectrometry

The effect on stripping factors of the air between aircraft and ground can be determined by counting at various altitudes over pure sources of uranium and thorium. One published set of spectra from a small crystal indicates that stripping factors vary with altitude, and ground determined values are probably too low at 100 metres altitude. The ability of various window systems to separate uranium and thorium series radiation differs, even for identical crystal volumes and ideal conditions. The systems can be compared if complete calibration is available. The narrow window systems are most precise and in addition they offer practical advantages because they are highly specific for the radiation from natural radionuclides.