WORLDWIDE EFFECTS OF ATOMIC WEAPONS DISTRIBUTION OF RADIOACTIVE DEBRIS SUNSHINE hazard is that the radioactive isotope Sr"? in nuclear weapons is the mostlikely to constitute the long-term hazard for man. Consequently, it is of interest to examinethe quantities of Sr°° that may be produced by the detonation of nuclear weapons and the range of concentrations that This concentration is probably reduced even more on land because of the rainfall carrying the Sr°° into the ocean or into deep underground 34 may be encountered at various places on earth. Extension of the data given in Appendix V of this report indicates that a megaton of fission will produce 1 me of Sr°°/mi’, if the fission products from a nuclear detonation are evenly distributed over the earth’s surface." However, as we have seen from the TUMBLER/SNAPPER and Ivy fallout measurements, the fallout from individual explosions varies by a factor of 200, either way, from the average for stations outside the test sites. Consequently, we can expect that even if all the Sr°° from the A-bomb explosions has fallen out, the concentration of Sr’ will vary over the earth’s surface within this factor. Because of this possible extreme variation of Stdeposition—localized, but long-range—St"’ contamination may well be the most important aspect of the SUNSHINE project. It was also seen that for high-yield, air burst, weapons the greater per- centage of the activity may be suspended tn the upper atmosphere for long periods of time. Also, it is known’ that Sr*’ has a tendency to fractionate in the cloud, so that its concentration becomes higher as the cloud becomes older. The Sr” should exhibit a similar behavior because of its gaseous precursor Kr". This would have two effects; namely, the fallout of Sr°° would tend to be spread out over greater areas than the total fissionproduct activity, and the Sr°® would have a greater tendency to stay in the upper atmosphere than the total activity fallout measurements have indicated. Because of the uncertainties concerning the collection efficiency of the gummed paper and the lack of information concerning the fraction of Sr°* that may stay suspended in the atmosphere and for what lengths of time, all we can say, at present, is that the range of concentration of Sr°° may be of the order of a thousandth of the limiting concentration | ae defined in the next chapter), but with a large margin of uncertainty. * These figures ace derived from data as known in 1953. See the Preface to this report for more recent (1956) values. eee meha + Verbal communication, R. W. Spence, Los Alamos Scientific Laboratory. 35 waters. RECOMMENDATIONS FOR FUTURE STUDY From the above considerations it is clear that additional data are required in order to determine more exactly the quantities of Sr°° that may be available for human consumption. If it is practicable to do so, the following additional data should be obtained in futuretests. 1. A thorough investigation should be made of the collection efficiency of the NYOO program's gummed paper for radioactive debris from A-bombs. This should include both the dry fallout and the material brought down with rainfall. If possible, it should also be determined if this efficiency changes with distance of travel and with the age of the debris being collected, since the average particle size may be a function of these parameters. 2. While it is obviously difficult or impossible to sample large areas of the earth's surface for the fallout of radioactive debris, more samples covering areas in the southern hemisphere and islands in the oceans should be obtained. Since the polar regions have not been sampled, advantage should be taken of any polar expeditions to obtain such samples. Also, samples should be collected near the test sites, or at least some method of survey should be used, such as that used in TUMBLER/SNAPPER, to make possible an estimate of the total fallout in these important areas. 3. After CASTLE (the next series of Pacific proving-ground tests) an effort should be made to continue the sampling during the whole period before the next test series to see if fallout from material suspended in the atmosphere will continue to be observed for longer periods than the dura- tion of past sampling programs.* There are obvious difficulties involved because of the fission-product decay and the large number of samples that ing the sampling periods and increasing the number of square feet of paper exposed at each station would solve these difficulties. *The NYOO is collecting fallout data at some stations during the period between UPSHOT/KNOTHOLE and CASTLE,