Correlation of indoor concentrations between radon and its daughters

Concentrations of radon and its daughters are measured simultaneously in a ferroconcrete building. Concentrations of radon are obtained with a plane multiwire-electrode ionization chamber. The filter method is used to estimate the concentrations of respective daughters. It is also used for obtaining the apparent daughter concentration by assuming the radioactive equilibrium between radon daughters. The ratios of concentrations of daughters to that of radon are found to increase with the radon concentration. The equilibrium factor F that is calculated from the concentrations of individual daughters depends consequently on the radon concentration. The apparent daughter concentration is nearly equal to that of respective daughters. A simplified equilibrium factor F' is derived from the apparent daughter concentration. The value of F' agrees well with F within statistical errors. (author)