o INTRODUCTION AND CONCLUSIONS WORLDWIDE EFFECTS OF ATOMIC WEAPONS We assumehere high-altitude bursts, with the immediate area of ground zero receiving no more than its proportional share of the fallout debris. Exchange of debris between the earth's hemispheresis also neglected. The over-all assumption is pessimistic. 2. Atmospheric or other natural storage mechanisms that might allow appreciable Sr°° decay before it becomes available to humans. Whether Sr®® is stored in the atmosphere or in the biosphere, this con- sideration is not likely to increase’ our estimate by more than a factor of two. 3. Availability of Sr°° in debris for transfer to the biosphere. We believe that the bulk of the Sr°° is plated out on the surface of the debris particles and that it is also scavenged out in solution by rainfall. Thus it should be readily available for take-up by the biosphere. If our reasoning is incorrect and the Sr°° ts contained inside insoluble particles, the calculation given below should then be regarded as highly pessimistic. 4. Availability of natural strontium in soils. The parameter used here is 60 lb of agriculturally available strontium per acre. We feel that over a period of time such as we are considering, more fixed strontium in the soil will become available. The better value lies somewhere between one and twenty times this amount. Having used the lower limit, our estimate in this respect is also pessimistic. 5. Redistribution of Sr°° by plowing, fertilizer, etc. Fallout debris deposited on untilled soil is not leached down very effectively by rainfall. In agricultural areas (the areas of interest), however, the soil is constantly well mixed to an effective depth by the efforts of man. We also assume wash-off as relatively low. These considerations, in themselves, make our calculation pessimistic. 6. Content of natural strontium in bone. The average U.S. adult, normalized to the “Standard Man,” contains 0.7 gm total strontium in his bones. This figure is probably rather accurate. On the basis of the above assumptions and other phystcal parameters, 7 the preliminary SUNSHINEestimate of the nuclear bomb yield required to bring the population of the world up to Maximum Permissible Concen- tration 15 larger than 2.5 X 10‘ megatons (MT). We have taken the liberty of normalizing the GABRIEL models to an MPCof1 pc and have corrected the Sryield factor. For comparison with the preliminary SUNSHINE estimate, the GABRIEL gauge lies between 20 MT and 9 X 10* MT. An estimate developed on a calcium-strontium modelhas indicated an 800 MTlimit; the uncertainty of this limit is unknown, butit is probably pessimistic, since parameters similar to the strontium-ratio type ofcalculation are involved. Thus, the SUNSHINE methodology achieves minima that lie close to the maxima of all previous models. RECOMMENDATIONS It is seen that a number of physical and biological parameters remain to be determined to greater exactitude; many are unknown to several magnitudes. Until comparatively recently it would have been extremely difficult, if not impossible, to obtain a measure of a numberof the param- eters. Today we are afforded the opportunity of doing a radioactive-tracer chemistry experiment on a worldwidescale. The release in the world of several kilograms (kg) of Sr°° within less than a decade has probably disseminated enough of the contaminantto provide amounts that are probably now detectable in samples of inert and biological materials throughout the world. An analysis of these materials for St? will provide us with much of the information that is now lacking. For our model we will also require an analysis of the ordinary strontium content of soils, waters, and biological materials. Other requirements may appeay_as the program develops. It is rather striking that the last comprehensive measurements of souls for natural strontium were made in 1914-1917.The strontium cycle in the biosphere is almost completely unknown, and unknown meteorological factors abound. We submit, therefore, that the adoption of a sampling