recommended earlier (ICRP 2, 1959). The effects of variations in 7? or exposure period are much smaller, for the range of parameter values of interest, being less than a factor of 2. Table 5. Ratio of *39Pu Burden in Bone. f° Rate Which 239py Reaches Blood (yp/r,) Fraction From Blood to Bone (fa pw Biological Half-Time for Bone (re), Years 70 100 130 160 200 50-Year Exposure 0.45 0.5 0.6 0.7 0.8 6477°9) 7197 8636 10076 11515 | 6940 7712 9254 10796 12339 7209 8010 9612 11214 12816 7384 7540 8204 9845 11486 13127 8378 10054 11729 13405 9918 11020 13224 15428 17632 10209 11343 13612 15881 18150 70-Year Exposure 0.45 0.5 0.6 0.7 0.8 (a) 8294 9215 11058 12901 14744 9110 10122 12146 14170 16195 9596 10662 12794 14927 17059 Units of ratio are day. CONCLUSIONS The results of this analysis are not surprising. Soil concentration is the most significant source term and is subject to a great deal of variation. The parameter for relating the soil concentration to the concentration in air is also very significant and also subject to wide variations. It is, perhaps, surprising to see the variation in estimated dose rates that could result from uncertainties in the size and chemical/ physical properties of plutonium-bearing particles. However, dose variations due to particle size are much less than those due to variations in soil concentration and mass loading factor, and it is generally assumed that the plutonium-bearing particles at NTS are of such a chemical and physical nature that they are always in the year translocation class. 534