Relative activities of 212Bi (thorium-C) and 228Ra (mesothorium-1) in former radium dial workers

From analyses of bones, estimates were made of the relative intakes of 228Ra and 226Ra by the employees of a dial-painting studio that used luminous compounds activated with technical mesothorium. These data, in turn, were used to derive estimates of 228Ra activity from activities of 226Ra in living colleagues whose body contents of 226Ra and 212Bi had been measured. The indirectly determined 212Bi to 228Ra activity ratios in the living workers averaged 1.56 +- 0.10 (S.E.) at a median of 42 yr post intake. If no 228Ra decay products are excreted, the expected 212Bi to 228Ra activity ratio at 42 yr after intake is 1.59 according to the simple power function of radium retention of Norris et al., and 1.72 according to the alkaline earth model of ICRP No. 20. 15 references, 2 tables