calculation of internal dose commitments is based on an intake at 9 hours after Shot Bravo, with large-particle dose conversion factors applied to the radionuclide inventory to that time. The inventory, which is based on radiochemical analysis of Bravo, is normalized to the activity level of iodine-131. Intake of this radionuclide is determined from the body metabolism of iodine that led to a measured activity of I-131 in urine samples taken 17 days after Bravo. The calculated thyroid dose commitment of 190 rem is by far the largest organ dose commitment, and the dose is accrued comparatively rapidly. Short-lived radio- nuclides dominate the thyroid dose, which is seven times that from I-131 alone. If the intake had been at 13 hours after Bravo, the thyroid dose would be six times that from I-131 (based on the Reference 11 radionuclide inventory). Thus, the thyroid dose is not sensitive to actual time of intake within the fallout deposition period. é The only other dose commitments that exceed the dose from external gamma_ radiation are for the sections of the large intestine. Actinide emitters, produced by the neutron activation of U-238 during the detonation, are significant to these doses. Because GI tract doses are dominated by the ingested contents in transit rather than by absorbed radionuclides, these doses are also accrued rapidly. Caution is advised in interpreting these calculated internal doses for specific individuals. Based on a pooled urine sample, the calculated doses represent an average Or nominal dose estimate and do not necessarily pertain to a specific individual. However, limited individual urine sampling reported by indicated only a modest spread of results. Dr. Harris (Reference 9) The counts of the individual samples were consistent to within 40 percent of their mean. Also, the implied intake of I-131 agreed well with that from the pooled sample. 5.2 COMPARISON WITH PREVIOUS DOSE DETERMINATIONS Dose determinations for personnel on atolls downwind of CASTLE Bravo have been principally of two types: the initial estimates developed in the mid-1950s, shortly after the event, and the long-term, continuing followup by Brookhaven 26 GL