en reeead ‘ en mee 7 ~~ ee eercersnmempaberenme BO Sonera € One rere eons . . Assuming that comparable fall-out occurred over 100 sq mi of surface from alayer of air 1 mile deep (a 75-micron particle falls 1 mi/hr according to Stokes’ law), a total of 10” large particles carrying 10" yc in the original cloud is required. (This estimate of the number of particles is remarkably well supported by a spot count on radioautographs of the wingfilters from the manned drone flown after George shot. These showed about 0.1 active particles/cu ft of air in the fall-out region.) Supposing that the activity of the large particles was acquired by adsorption of small active particles, the loss of activity from the smallparticle category would have been OM 10” tc out of a total OM 10% uc, a loss which would hardly be noticeable, The existence of 10" large particles in a cloud of 10’* small particles would require the counting of 10° small particles to obtain a 50-50 chance of observing one largeparticle. 2.6.10 Biomedical Investigation Urine samples from 125 individuals present during the Dog shot fall-out were analyzed in the TU 3.1.5 laboratory. By means of spiked samples, it was determined that the method would reveal the presence of 1.5 x 1074 pe of mixed fission products in a urine sample. Three individuals were at first found to have slight activity, but their subsequent samples were negative. Four other individuals had about 2x 1074 uc, and similar results were obtained from their following samples. Animals were sent to Los Alamos for analysis of lungs, liver, spleen, kidney, and bone. All tissues of all animals were found negative. The animals comprised 12 mice, 3 cats, and 2 dogs from Japtan and 1 dog from Parry shipped on D+2 day; 2 dogs from Eniwetok and 3 dogs from Parry and 2 dogs and 1 cat from Japtan shipped on E+2 day. 2.6.11 Conclusions a. Very strong evidence was obtained that the Dog shot radioactive fall-out on Japtan, Parry, and Eniwetok islands, and on neighboring vessels, consisted of large particles, mostly 100 microns in diameter or larger. b. Urinalysis of individuals and analysis of tissues of animals present during the fall-out support the conclusionthat po harm was done.-* “ vem oe oe is. Tees 5 * oe oe c. The information obtasied trv. chord sam-~ pling in the past provided no hic: of che possibility of such an event as the Dog shot fall-out on inhabited islands of the Atoll. Unless further analysis of the cloud sampling of Operation Greenhouse provides much more information of the kind needed, it will be clear that present techniques are not adequate for this purpose. In any event, the sampling aircraft cover only a limited part of the range of altitudes from which information is needed. d. Some data were obtained that may be useful in predicting the intensity of heavy-particle fallout in the future. Such predictions should be made with a great deal of caution. It appears that the quantity of airborne heavy radioactive particles may depend critically on certain factors about whichlittle is yet known. e. Of the various methods that were tried in an effort to obtain further fall-out information from Easy and George shots, the method of conducting an early low altitude aerial survey and sampling in the predicted fall-out area appears to be by far the most promising method (higher altitude surveys were not tried). 2.6.12 Recommendations a. Unless Greenhouse sampling provides much more information than did former sampling about the radioactive heavy-particle content of clouds, more satisfactory equipment and techniques should be developed. Special attention should be given to the possibilities of aerial surve, and sampling. b. An effort should be made to learn more about factors such as soil stabilization methods and materials which may affect strongly the quantity of radioactive fall-out. 2.6.13 Item Shot Fall-out The following information was obtained subsequent to the preparation of the report on which most of Sec. 2.6 is based. A cascade impactor was operated near the radiological safety building from I+11 hr till 1+13 hr. All the radioactive material collected was isolated in seven particles, each of which was about 100 microns in diameter. 2.7 EXTERNAL RADIATION ... Careful exposure records were kept for all personnel ofJTF-3 who-itwas expected might gee kote eRMeMOF SH