ratio, the current value will be maintained at 1.0 Sunshine Unit if the environment allows strontium-90 to be incorporated at the same rate which provided the current 1.0 Sunshine Unit. If the amount of strontium-90 available decreases with time, then as a child grows it will lay dow relatively more calcium than strontium-90, and the Sunshine Unit value borne by the child will decrease. Thus the uncertainty relative to the continued availability for uptake of the strontium-90 created in past detonations but not yet deposited is still an unsettled problem. Evaluation of the SUNSHINE Model Hazard Calculations. The Sunshine model listed six parameters necessary for assessing the strontium-90 hazard on a world-wide scale. Since the time this model was constructed, additional data have been collected so that it is worth while to re-examine these factors in the light of more recent knowledge. thatdistribution ofstrontium-90, requires drastic correction. tion is as follows: 1. In summary, the situa- : 50-90% of gross fission product fall-out is accounted for locally for land surface bursts. of 60% appears reasonable. For purposes of calculation, a figure It will be recalled that the SUNSHINE model assumed @ high air burst, which would involve a negligible local deposition of fall-out. 2. Less than 2% of the gross fission products created in detonations to date have been accounted for in world-wide fall-out. 3. One-third of the expected amount of strontium-90 on the basis of uniform distribution relative to other fission products was observed 80 miles downwind after the first CASTLE shot. 4. The world-wide gummed peper fall-out collections by the Atomic Energy Commission are, on the average, three times enriched in strontium-90 over the content in a normal gross sample of fission products. 5. A British calculation estimates 20 MI of gross fission 116