CHAPTER 1 INTRODUCTIONS Radiation-fields produced by fallout from ea nuclear detonation oreate debilitating effects far beyond the range of its blast damage. Information on transport and distribution of fallout and knowledge of its physical, chemical, and radiochemical properties are prerequisite to development of countermeasures against its radiation fields. At Operation CASTLE the transport and distribution of fallout was prineipally the concern of Projects 2.5a and 6.43 Project 2.56 stuiled the fallout on islands near the shot point; investigation of fallout prop- erties was the concern of Projects 2.6a and 2.6b. lel OBJECTIVES AND BACKGROUND The purpose of Project 2.6 was to investigate the chemical, physical, and radiochemical properties of the fallout fors a. Deducing the mechanism whereby conteminant is formed, be Assessing radiological situationa, c. Specifying realistic simulents of radiological contaminants for use in contamination and decontamination tests. d. Interpreting the data obtained in proof testing atomic warfare countermeasures for ships, 1.1.1 Mechaniem of Contamination The contamination formed from surface or sub-surface detonation of a nuclear weapon has important TAtaryoppeeanences » at Operations CROSSROADS,5/JANGLE,*+//and It was found IVY¥+</that high levels of surface contamination were produced as a result df surface or sub-surface detonations. Eech of these operations represented a unique condition of detonation, but provided insufficient data to establish bases for predicting radiological effects for a wide range of probable conditions of detonation, An unméerstanding of the mechanism whereby contamination is produced is necessary in saking such predictions. Data obtained in CASTLE are applicable in answering such questions on the mechanics of the event as: To what extent is wet contaminant formed by condensation Phenomena? With what type of particles do the primary particles of 15