Strontium-90 of the generic method described by Adams(1981) and by Leggettet al. (1984). Several models have been developed over the years to estimate the cycling and retention Thecalculation for photon emissions is more complex because the entire energy of the photon of 99Sr in the body as a function of age to is not absorbed in the source organ. As the body calculate age-dependent dose conversion factors (Kulp and Schulert, 1962; Rivera, 1967; Bennett, and organ size become smaller,.a larger portion of the energy escapes the source organ and the relative position of the organs is significant. Consequently, if the charged-particle-emission concept is used for making age-dependent adjustments for the total energy released per 1973, 1977, 1978; Klusek, 1979; Papworth and Vennart, 1973; Leggett et al., 1982). We have previously used both the model developed at EML (Rivera, 1967; Bennett, 1973, 1977, 1978; Klusek, 1979) and that of Papworth and Vennart transformation for a radionuclide like 137Cs that has both charged-particle and photon (1973). The two models give very similar results, with the biggest difference in results occurring for persons between ages 5 and 15 y. Both models are empirical models based on emissions, the actual dose for infants and children will be overestimated. However, this procedure can be used for 137Cs_ for a quick, measurements of 29Sr in the diet and conservative approachto the relative dose from 137Cs asa function ofthe ageat intake. Leggett et al. (1984) and Cristy and corresponding measurements of 9°Sr in autopsy that account for changes in deposition of photon solution-fitting of the observed data. No Vennart's model does include -the two bone samples. The retentions and turnoverrates and discrimination factors in the models are determined by regression analysis or equation Ekerman (1987a to 1987g) have calculated agedependent energy deposition factors (S factors) energy as a function of size (i.e., age). The particular correlation is made with bone compartments, as outlined by the [CRP (1972, 1979), in the EML model, but Papworth and _ Tesults are based on Monte Carlo calculations in various sizes of computer-generated phantoms; the S factors are presented for newborn, 1-y-old, 5-y-old, 10-y-old, 15-y-old males, and adult females and adult males. Values for other ages are obtained bylinear interpolation. compartments of compact and cancellous bone. A recent model developed by Leggett etal. (1982) is based on the structure and function of We have combined the age-dependent modifications to the ICRP model for charged- particle emissions bone compartments as generally outlined in the ICRP model (1972, 1979). The bone is assumed to be composed of a structural componentassociated with bone volume, which includes the compact cortical bone, a large portion of the cancellous for the beta-particle emissions (E = 0.51 meV) from 137Cs and the methodsof Leggett et al. (1984) and Cristy and Ekerman (1987a to 1987g) for the photon (trabecular) bone, and a metabolic component emission (E = 0.66 meV) associated with 137Cs associated with bone surfaces. In effect, three decay to generate the final age-dependent dose conversion factors. compartments are then identified, two within the bone volumeandonewithin the bonesurface. The biological half-life of 137Cs_ is The bone volumeis associated with mechanical structure and integrity of the bone, and the bone surface is involved with the metabolic determined as a function of mass(i.e., age) by the methods described in the "Retention" section. regulation of extracellular calcium. Much use is The age-dependent energy deposition factors and biological half-life are combined to madeof general data about age-dependent bone formation within these compartments and, consequently, this model is not as dependent on adjust the ICRP dosimetry methods for !37Cs to an CC an age-dependent model. radionuclide-specific data as the other models. 16