Radium regionalization in California

The amount of {sup 222}Rn that enters a house depends to a large extent on the concentration of radon's parent, {sup 226}Ra in the soil. With the assumption that radium is in radioactive equilibrium with its ultimate parent, {sup 238}U, the authors used the National Aerial Radiometric Reconnaissance (NARR) data and a database covering the concentration and distribution of uranium in California rocks to estimate the regional distribution of radium. A north-to-south increase in radium occurs between 42{degree} and 36{degree}N, then radium decreases southward. This pattern is explained by the distribution of rock types. The overall mean radium concentrations estimated from the aeroradiometric and lithologic data are similar, but there is a significant discrepancy between aeroradiometric and lithologic-estimated radium in central California. Ground measurements suggest that the radium values from aeroradiometric measurements that the radium values from aeroradiometric measurements there are erroneously high, pointing out the necessity of verifying aeroradiometrically-determined data before they are used to help predict radon production.