CHAPTER 1 INTRODUCTION Surface and sub-surface detonations of nuclear weapons on land produce hazardous gamma-radiation fields over areas far beyond the range of physical damage. Fallout which is responsible for the gammeradiation fields is inherently the least predictable of all weapons effects, Variations in the dispersal and deposition of radioactive debris are affected by meteorological conditions during and subsequent to detonztion as well as by the device yield, the charge depth, and the explosion media, Yet, the exploitation of this anti-personnel capability, end the -apacity to defend against it, are directly dependent upon the ability to predict those target areas which will be involved. The investigation of fallout, and of the factors which influence it, are therefore important to the development of nuclear weapons and to both military end civil defense planning. 1.1 PREVIOUS FALLOUT STUDIES Fallout has been observed and documented in some degree at all previous nuclear test programs. In addition, suw:face and sub-surface high explosive detonations on land and underwater are being studied for their usefulness as models for fallout distribution from nuclear detonations, 1.1.1 Nuclear Tests Out of a total of 43 nuclear test explosions carried out by the United States, four have produced significant residual radiation fields, the Baker shot, Operation CROSSROADS, surface and underground shots, Operation JANGLE, and Mike shot, Operation IVY. Of these four, only the JANGLE series adequately had documented fallout. At JANGLE, the residual gamme fields were recorded in detail; in addition, extensive sampling of the fallout events was carried out 14/ Results of the JANGLE surface test were used to predict fallout from Mike shot, IVY, They also formed a basis for fallout predictions for the CaSTLE series reported here, At IVY, although cnly partial documentation was accomplished, 19