0018933 : CHAPTER 1 INTRODUCTION 1,1 OBJECTIVES The general objective of the project was to estimate, from analytical data on cloud samples, the relative distribution of certain radionuclides between the local and world-wide fallout formed by megaton-range detonations on Jand and water surfaces, with particular emphasis on the distribution of Sr°° and Cs?37 between local and world-wide fatiout. Specific objectives were to: (1) obtain airborne particle and gas samples by rocket and aircraft sampling techniques; (2) determine the distribution of radionuclides between two groups of particles which differed from one another in their falling rates in air and which could be considered representative of local and world wide fallout; (3) attempt to determine an early-time distribution of radionuclides and pzrticles between the upper and lower halves of the cloud and radially cutward from the cloud exis; (4) estimate the extent of seperation of fallout from gaszous fission products by fission determinations on gas end particle cempies collected coircidentclly rear the top of the cloud at vzrious times following the shots, 1,2 BACKGROUND AND THEORY Deta on the geographical distribution of fzllout are particularly necded to assess the global bazards assozizted with the testing of nuclear weapons,