of the generic method described by Adams (1981) and by Leggett et al. (1984). Strontium-90 Several models have been developed over the years to estimate the cycling and retention of 90Sr in the body as a function of age to calculate age-dependent dose conversion factors (Kulp and Schulert, 1962; Rivera, 1967; Bennett, 1973, 1977, 1978; Klusek, 1979; Papworth and The calculation for photon emissions is more complex because the entire energy of the photon is not absorbed in the source organ. As the body 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 transformation for a radionuclide like 137Cs that has both charged-particle and photon Vennart, 1973; Leggett et al., 1982). previously used both the model developed at EML (Rivera, 1967; Bennett, 1973, 1977, 1978; Klusek, 1979) and that of Papworth and Vennart (1973). However, this procedure can be used for 137Cs_ for a quick, conservative approach to the relative dose from 137Cs asa function of the ageat intake. Leggett et al. (1984) and Cristy and Ekerman (1987a to 1987g) have calculated age- dependent energy deposition factors (S factors) that account for changes in deposition of photon energy as a function of size (i.e., age). The results are based on Monte Carlo calculations in tee ee 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 measurements of %9Sr in the diet and corresponding measurements of 90r in autopsy bone samples. The retentions and turnoverrates and discrimination factors in the models are determined by regression analysis or equation solution-fitting of the observed data. No particular correlation is made with bone emissions, the actual dose for infants and children will be overestimated. We have compartments, as outlined by the ICRP (1972, various sizes of computer-generated phantoms; 1¢79), in the EML model, but Papworth and the S factors are presented for newborn, 1-y-old, Vennart's model does include the two compartments of compact and cancellous bone. A recent model developed by Leggett etal. 5-y-old, 10-y-old, 15-y-old males, and adult females and adult males. Values for other ages are obtained by linear interpolation. We have combined the age-dependent modifications to the ICRP model for chargedparticle emissions for the beta-particle emissions (E = 0.51 meV) from 137Cs and the methods of Leggett et al. (1984) and Cristy and Ekerman (1987a to 1987g) for the photon emission (E = 0.66 meV) associated with 137Cs decay to generate.the final age-dependent dose conversion factors. (1982) is based on the structure and function of bone compartments as generally outlined in the ICRP model (1972, 1979). The bone is assumed to be composed of a structural component associated with bone volume, which includes the compact cortical bone, a large portion of the cancellous (trabecular) bone, and a metabolic component associated with bone surfaces. In effect, three compartments are then identified, two within _ the bone volumeand one within the bone surface. The biological half-life of 137Cs is The bone volumeis associated with mechanical determined as a function of mass(i.e., age) by the methods described in the "Retention" section. The age-dependent energy deposition factors and biological half-life are combined to adjust the ICRP dosimetry methods for !37Cs_ to an age-dependent model. 2000170 structure and integrity of the bone, and the bone surface is involved with the metabolic regulation of extracellular calcium. Much use is made of general data about age-dependent bone formation within these compartments and, consequently, this model is not as dependent on radionuclide-specific data as the other models. . 16