A computerized method of least squares has been used to analyze the /sup 228/Ac and /sup 212/Pb-/sup 212/Bi and daughter ..gamma..-ray spectra obtained in vivo from 133 former workers at a thorium refinery. In addition, the exhalation rate of /sup 220/Rn was determined for each subject and expressed as pCi of emanating /sup 224/Ra. This value was added to the /sup 212/Pb value determined from the ..gamma..-ray measurements to obtain the total /sup 224/Ra present, and the ratio of /sup 224/Ra to /sup 228/Ac was calculated. Values of the ratio ranged from 0.52 +- 0.32 to 2.1 +- 1.7, with a weighted mean of 0.92 +- 0.17. However, it appears that the ratio observed in a given case is characteristic for that case alone; the computed mean value may not be meaningful. The least squares fitting procedure and the overall calibration of the counting system were validated by measurements of /sup 224/Ra in the lungs of one subject postmortem, compared with results obtained from the same subject in vivo. 6 references, 5 figures.
