1967; Lloyd, 1966), to 20 to 50 d for children (Karcher et al., 1969; Boni, 1969; Naversten, 1964; Bengtsson et al., 1964; Lloyd et al., 1966, 1970), and to 110 d and 85 d for adult men and women (Richmond et al., 1962; Van Dilla, 1965; with body weight and age is only significant when infants, juveniles, and teenagers are included and that there is no correlation with either for adult males or adult females (Karcher, 1973; Cryer, 1972). The only Boni, 1969; Lloyd, 1966; Lloyd et al., 1970; ICRP, significant difference in T!/? among adults is indicates that the long-term T!/2 is about 22 d for that between males and females wherethere is a distinct difference in the average body weight 1979; NCRP, 1977). Leggett (Leggett, 1987) newborns, decreases to about 13 d by 1 y, and then begins to increase again to about 30 d by 5 y. In addition to the change in T!/? with age, the fractional deposition of 137Cs in the short- (Lloyd, 1973; NCRP, 1977; ICRP, 1979). The average biological half-life for 137Cs_ in Japanese males, whose average body weight is significantly less than for U.S. and European and long-term compartments also changes (Leggett et al., 1984). The fractional deposition for newborns is 0.5 in the short-term males, was determined to be about 85 d compartment; this gradually changes to 0.10 and commonto age, body weight, and sex. compartment and 0.5 in the long-term 0.90 for the short- and long-term compartments, respectively, for adults. Table 6, abstracted from Leggett (1987), shows the change with age for the total body potassium, fractional deposits, and T!/?. Models have been proposed indicating that the long-term T!/? for 137Cs_is correlated with age (Boni, 1969; McCraw, 1965; Weng and- Beckner, 1973; Fisher and Snyder, 1967), body weight (Eberhardt, 1967; Cryer, 1972), and sex (Clemente et al., 1971; Boni, 1969). However, (Uchiyama et al., 1969; Fujita, 1966). Lloyd indicates that it is more likely that the T?/? for 137Cs is correlated with some other factor Leggett (1986, 1987) has recently shown that the strongest correlation for the biological half-life of 137Cs appears to be with the total amountof potassium (K) in the body. The model — proposed by Leggett is the standard twocompartment model of the form: A(t)=a 0-693 t/T1 4 (1-gjo0-693 t/T2 , where A(t) = the !3’Cs activity in the body at Lloyd (1973) has indicated that the correlation time t after ingestion, Table 6. Estimated compartmental fractions and half-times in the age-dependent retention function for cesium. Age Total-body K Short- plus intermediateterm fraction Short- plus intermediateterm T!/2 (days) Long-term fraction Long-term T!/? (days) Newborn 100 days 1 year 5 years 10 years 15 years 5.2 11.4 20.8 42.7 71.0 131.4 0.60 0.60 0.60 0.45 0.30 0.13 22 16 13 9.1 5.8 2.2 0.40 0.40 0.40 0.55 0.70 0.87 22 16 13 30 50 © 93 Adult 150 0.10 1.6 0.90 107 I000to).