The application of least squares analysis for the estimation of low atmospheric concentrations of short-lived radon daughters and studies on their disequilibrium

The application of the weighted and unweighted least-squares method to the analysis of the individual concentrations of short-lived radon daughters in the open atmosphere, where, unlike in the mines the levels are low, is discussed. The method can be optimized to give minimum counting errors by proper choice of collection times and counting periods. By analysing a large number of samples it is shown that the least squares method gives better accuracy than the simultaneous equations method generally in use. The calculation can be simplified by using the unweighted least-squares analysis without significant loss in accuracy. The levels of RaA, RaB and RaC in surface air at Bombay during the period January-June 1975, calculated using the least-square method, are presented. The activity ratios of RaC/RaB are shown to have an average value around 0.6–0.9 even at 18 m height. The RaB/RaA activity ratios however show a much larger scatter than the RaC/RaB values. The possible reasons for these differences are discussed. The application of the least-squares method to the analysis of Th-B and Th-C is also described.