phase consists of those elements in the gas phase when the liquid droplets solidify. The refractory phase consists of those elements in the liquid droplets when they solidify. The volatile/refractory ratio is the ratio of the amounts of volatile phase to refractory phase, denoted by r(A) for mass chain A. Consider for the moment only the material vaporized by the detonation. The condensate is in the form of small spheroids and the refractory nuclides are assumed to be distributed uniformly throughout the volume of the droplet (amount varies as r°). The volatile nuclides are assumed to be distributed uniformly over the surface (amount varies as r’). The volatile/refractory ratio associated with a given particle will vary as rl: the smaller the particle, the larger the proportion of volatile phase. This ideal picture becomes complicated because spheres of debris can attach to each other or to unmelted dust particles which have been entrained by the cloud. irregular particles. The result is a mixing of spherical and This mixing should tend to reduce the strong dependence of the volatile/refractory ratio on the size of -particles collected in the field. The solid particles in the cloud of nuclear debris fall to earth at different velocities and from different altitudes. This process has the effect of separating the debris by particle size along the path of the cloud. Thus, the refractory phase and the volatile phase are