1.2 OBJECTIVES The gathering of fall-out data from Mike shot was a logical extension of previous fall-out documentation. The nature of Mike shot, Operation Ivy, made the study of fall-out extremely important. The yield from this shot was expected to exceed by many times that from any previous detonation, and consequently the cloud and associated debris were expected to rise to much greater heights. The additional fact that the shot was to be a surface explosion indicated the possibility of serious fall-out over large areas. The present work (Project 5.4a) was designed to accomplish the following specific ob- jectives:* 1. To measure the amount, distribution, and particle size of radioactive fall-out following Mike shot at Operation Ivy. 2. To determine at a limited numberof close stations the rate of arrival of inert liquid or solid materials and associated radioactive materials. 3. To determine the particle-size fractionation of the radioactive fall-out with time and distance. 4. To analyze the base surge, if formed, for activity and to correlate this information with the fall-out data. 5. To correlate the fall-out pattern obtained with that predicted from a knowledgeof the meteorological conditions and atomic cloud behavior. 6. To calculate from the intensities of radiation from fall-out the radiation field levels which would have been observed if the fall-out had occurred over extended land areas. REFERENCES 1. Los Alamos Scientific Laboratory, “The Effects of Atomic Weapons,” pp. 270-275, U. S. Government Printing Office, Washington, 1950. 2. Charles E. Adams, fall-out Phenomenology, Greenhouse Report, Annex 6.4, WT-4, August 1951. 3. Los AlamosScientific Laboratory, “The Effects of Atomic Weapons,” Appendix F, U. S. Government Printing Office, Washington, 1950. 4. I. G. Poppoff, Fall-out Particle Studies, Jangle Project 2.5a-2 Report, WT-395; also in Particle Studies, WT'-371. *Full attainmentof the objectives of this project was not possible because of operational restrictions imposed at a late date. See Appendix D, Tab A (revised) to Appendix I to Annex V. 10 ee