or sickness and other factors. Regardless of the cause of individual differ- ences from the mean, a smooth description of the body burden and activity ingestion rate for the population could be adopted. On this basis a declining contin- uous uptake model was used. Internal Dose Equivalent Rates The approximate instantaneous dose equivalent rates for the total body were determined from the body burden data illustrated in Figures 7 and 8 and from the following equation H = ql, (4) where H = the total body dose equivalent rate, mRem yt, I = equilibrium dose equivalent rate to the total body per unit body burden, mRem y7l uci7!, q = instanteous body burden, uCi. The approximate nature of the estimate was due to the assumption that the radioactive atoms were distributed among the body tissues as they would be following constant continuous uptake for periods of time much greater than the mean residence time for the total body. assumed. In the case of 90.., 86% of equilibrium was These assumptions were not used in the estimate of the total dose equivalent. In addition, since mean adult body burdens were computed, a factor of 1.2 was needed to adjust for differences in body mass relative to a 70 kilogram adult. Table 5 lists values of I which were determined from information given in ICRP59 and corrected for body mass differences.