(1) AFSWP data (2) NYOO Fall-out Data (3) Approximated from Lamont Laboratory SUNSHINE Data. It can be seen that the 40 MI of fission yield released thus far has resulted in one-third of the expected body burden in human bone that would be predicted by the SUNSHINE model. Further examina- tion of the table shows that only 2.6 per cent of the amount predicted by the model has actually fallen out in the United States as determined by cumulative soil analysis date. This indicates further that there 4s 12 times as much strontium-90 in human bone, based on the actual amounts available for uptake, as the SUNSHINE model would predict. Mention should be made here that the strontium-90 soil figure of 1.08 me/sq mi reported by the New York Operations Office of the Atomic Energy Commission is a theoretical figure based on the Hunter- Ballou table. Because of the known phenomenon of fractionation, a factor of 3 increase in the strontium-90 available for world-wide dis- tribution from surface or tower bursts over the value that would be predicted on the basis of a gross fission product sample from the upper atmosphere appears reasonable and has been suggested by the New York Operations Office 2/ If the above calculations are corrected for fractionation of strontium, then instead of transport to bone being 12 times the ex- pected value it is perhaps closer to 4 times this value. This is in agreement with experimental data suggesting that much of the early fall-out material is mechanically transported by plants rather than going through the soil-plant-animal biospheric chain. This factor of a four-fold increase in deposition of strontium90 in bone over the theoretically expected amount is not important if only a small total of the available strontium-90 is available for mechanical transport. ha/ But if the bulk of the strontium-90 which still Eisenbud, M. and Harley, J.H., Radioactive Fall-out in the United States, Science 121:677, 1955 (May 13) 113