Strontium-90 Dose Equivalent intake beginning as adults always exceeds that calculated for intake beginning at any other age. To determine the consequence of equal Strontium-90 is primarily deposited in the boneafter ingestion, and the two major organs receiving exposure are the bone marrow and the bone surface cells. The annual dose equivalent from the ingestion of 9°Sr beginning at different ages is shownin Fig. 4. The maximum annual dose equivalent to the bone marrow is about intake of 137Cs_ for each age, the dose equivalent for an initial intake of 1000 pCi/d was calculated for each age group. Theresults are listed in Table 8. Even for the extreme case of equal, continuous intake for each age group (which does not occur under real dietary conditions) with the annual intake declining at a rate determined by the radiological half-life 2mrem/y, and this occurs when 99Sr intake begins at ages 12 and 18. of 137Cs, the integral 30-, 50- or 70-y dose The integral 30-, 50-, and 70-y dose equivalent to bone marrow and bonesurface are listed in Table 9. The integral dose equivalent equivalents are very similar regardless of when ‘the age intake begins. The results for the integral 50-y dose equivalent for intake beginning at each age rangeare birth, 688 mrem; is very similar for all ages. 4 months, 690 mrem; 9 months, 619 mrem; 1.5 y, 619 mrem; 4 y, 622 mrem; 12 y, 633 mrem; and 18 y, 640 mrem. Recent changes in the modeling and dosimetry for 13’Cs used by the United Kingdom show that the effective committed dose equivalent per single unit intake of 137Cs is the same regardless of the age of intake (Kendall et al., 1986). | intake begins at age 12. The integral 30-, 50-, and 70-y effective dose equivalent due to the intake of Sris also listed in Table 9 and ranges from 8.6 to 10 mrem for 30 y, 12.9 to 14.4 mrem for 50 y, ard 15.7 to 17.3 mrem for70 y. Table 8. The integral 30-, 50-, and 70-y effective dose equivalent for equal (1000 pCi/d) initial and continuous intake of 137Cs starting at various ages. Total (mrem) 50 y 70 y 513 688 794 4 months 515 690 801 9 months 444 619 729 Birth 30y 15y 444 619 729 4y 447 622 732 i2y 458 633 743 18 y 465 640 750 9000173 Effective (137Cs + 90Sr) ) Dose Equivalent The total integral 30-, 50-, and 70-y effective doses from the ingestion of 137Cs and 90Sr at Rongelap Island are listed in Table 10. The integral 30-y effective dose ranges from about 370 mrem to about 510 mrem,the integral 50-y effective dose ranges from about 560 mrem to about 700 mrem, and the integral 70-y effective dose ranges from about 630 mrem to about 830 mrem. Of the total estimated dose equivalent due to the ingestion of 90Sr and 137Cs, the 90Sr contributes only 2 or 3%, while !37Cs contnbutes 97 to 98%. Integral dose equivalent, Age intake begins For example, the 50-y integral dose equivalent ranges from 60 to 70 mrem for bone marrow and from 150 to 200 mrem for bone surface depending on when the age intake begins. The highest dose comes when 19