the Effects of Atomic Radiafjon > and are equivalent to a bone-marrow dose on calcium in bone and an endosteal cell dose rate of 1.4 mrad/y per pCi rate of 1. § mrad/y per pCi 7¥Sr/g calcium in bone. They are based upon the ggtake of 24Sr relative to the intake of calcium, ihe residence time of Sr in bone and the mean effective energy of the Y beta particles. These conversion factors for endosteal cell and bone-marrow (32555) and dose rates are calculated 1g two steps. used to correlate the bone. First, the model of Bennett\ 20Sr concentrations’ in diet with r36+ in mineral Second, the dosimetric model developed by Spiers(29) is used to calculate the bone-marrow dose rate from the concentration in mineral bone. Bennett's empirical model is developed from 90Sr concentrations from world-wide fallout found-in foods and autopsy bone samples from New York and San Francisco. It also includes age-dependent variations that allow us to make dose estimates for children as well as adults. An estimate of the calcium content of the normal Marshallese diet peyover 0.8 g/d, which 1S very Similar to the 0.9 g/d estimated for U.S. diets Thus, the 7*Sr uptake and retention would be essentially the same as those developed by Bennett. Using Spiers' model the dose rate D, to a small, tissue- filled cavity in bone is calculated from the 90Sr concentration in mineral bone. Then from geometrical considerations, the dose rates to the bone marrow D,, and endosteal cells D, are calculated using conversion factors 0,/D, = 0.31 and 0./D, = 0.62 respectively. This is equivalent to a bone marrow dose rate of q. 4 mrad/pCi-y/g Ca and an endosteal dose rate of 1-8 mrad/pCi-y/g Ca. The above models and Gonversion factors are used to calculate the dose conversion constant for 7¥Sr in Table 6. 137 The dose equation relating the various factors is similar to that for C s but it is more difficult to determine the integrated pCi-d because the 90s model requires a numerical integration. The base parameters are: the average effective energy of 90s~ -90y beta particles = 1.13 Mev and is included in the W term defined below. f1; = the gut transfer factor = 0.3 for 30 years. E W= the conversion factor from pCi of 90s in bone to the rad dose in bone marrow = 1.4 mrad pti-y g Ca = 1.4 x 1073 rad pCi-y g Ca Z = the ratio of bone mass to calcium mass = 5g bone/g Ca. Q= the term for the time 3integration representing the retention of 90s r in the bone = 7.9 x103 pCi(pCi 7H) Intake M= the mass of mineral bone = 5000 g fF = the quality factor for beta particles = 1.0 rem rad 9000113 0-8