AIRBORNE GAMMA-RAY SPECTROMETRIC BACKGROUND ESTIMATION USING FULL SPECTRUM ANALYSIS

We have developed a new technique for estimating airborne gamma-ray spectrometric backgrounds. The background comes from three sources, namely aircraft, cosmic and atmospheric (radon) radiation. The aircraft and cosmic components are independently estimated by suitable calibration and the monitoring of a 3-6 MeV "cosmic" channel. Multichannel observations of the spectra are used to estimate the atmospheric background directly based on the observation that for gamma-ray counts above the Compton continuum, the low energy Bi-214 photopeak at 0.609 MeV for atmospheric radiation suffers far less attenuation relative to the Bi-214 peak at 1.76 MeV than is the case for radiation from uranium in the ground. Since thorium and potassium sources do not contribute appreciably to these peak countrates, they can be used to calculate the contributions of radon and uranium to the observed spectrum. The technique appears to be less susceptible to errors due to the effects of variations in the vertical distribution of airborne radon and its daughters than upward-looking detector techniques.