APPLICATION OF AIRBORNE GAMMA SPECTROMETRIC SURVEY DATA TO ESTIMATINGTERRESTRIAL GAMMA-RAY DOSE-RATES - AN EXAMPLE IN CALIFORNIA

We examine the applicability of radioelement data from the National Ae rial Radiometric Reconnaissance, an element of the National Uranium Re source Evaluation, to estimate terrestrial gamma-ray absorbed dose rat es, by comparing dose rates calculated from aeroradiometric surveys of uranium, thorium, and potassium concentrations with dose rates calcul ated from a radiogeologic data base and the distribution of lithologie s in California. Gamma-ray dose rates increase generally from north to south following lithological trends, with low values of 25-30 nGy h(- 1) in the northernmost 1 x 2 degrees quadrangles between 41 and 42 deg rees N to high values of 75-100 nGy h(-1) in southeastern California. Lithologic-based estimates of mean dose rates in the quadrangles gener ally match those from aeroradiometric data, with statewide means of 63 and 60 nGy h(-1), respectively. These are intermediate between a popu lation-weighted global average of 51 nGy h(-1) reported in 1982 by UNS CEAR and a weighted continental average of 70 nGy h(-1), based on the global distribution of rock types. The concurrence of lithologically a nd aeroradiometrically determined dose rates in California, with its v aried geology and topography encompassing settings representative of t he continents, indicates that the National Aerial Radiometric Reconnai ssance data are applicable to estimates of terrestrial absorbed dose r ates from natural gamma emitters.