CHAPTER II FIREBALL DETERMINATION OF TOTAL YIELD 1, Introduction This section describes the theory of hydrodynamic growth and the der ivation of the scaling laws, by means of which the total energy release of a nuclear explosion may be derived from the experimental observations. The observations are recorded by means of high-speed ciné cameras, during the phase of the explosion in which the shock front is luminous and coincident with the edge of the expanding fireball. The details of the experimental plan will be described, the parameters of the experimental equipment, the meas urements that are required and the methods by which they are carried out and checked, the operational program, and finally the analysis equipment and procedures, The methods-and numbers to be used have been developed over a period of thirteen years or more, not only from the published literature but also by detailed observations of all tests detonated by the United States Atomic Energy Commission. The methods employed will provide a figure for the total yield of the Pinon shot that is accurate to approximately + 5 percent; the data on which this figure will be based will be supplied to the United Nations Observers. In addition to this, facilities, equipment, techniques, and assistance will be provided so that the U. N. Observers may check the USAEC data in the field. Since some of the USAEC information--for example the survey data-- has been accumulated over a period of seven years, it is impractical to carry out a field check to the same precision in just a few days. Thus the U. N. checking procedures will carry a greater margin of error than do the USAEC numbers; nevertheless the check should result in a figure for the energy release that is good to about + 15 percent. 2. Hydrodynamic Theory and Scaling Laws Photographic observations of the hydrodynamic growth of fireballs, produced at test explosions of the USAEC, have been studied both empirically and theoretically. The aim has been not only to derive a reliable method for evaluating the total energy release of each explosion, but also to understand some of the factors that perturb the growth pattern from that predicted by simple theoretical considerations. ~-3- Empirical scaling constant