INITIAL INVESTIGATION OF THE HOMOGENEOUS NUCLEATION OF CESIUM VAPOR

Initial measurements of the homogeneous nucleation of supersaturated c esium vapors using an upward thermal diffusion cloud chamber specially designed for use with highly reactive materials are presented. Compar ison of the supersaturations measured at higher temperatures (greater than 455 K) with the supersaturations predicted by Classical nucleatio n theory show for the first time that the nucleation behavior of simpl e normal metals can be described by Classical theory. This agreement i mplies that the description of relatively large clusters of simple met al atoms (more than 25 atoms) as small liquid droplets with bulk metal lic properties is valid. However, as the temperature decreases below 4 55 K, an increasingly larger supersaturation than that predicted by th eory is required. This deviation from theory is so sharp that by 430 K the difference is an order of magnitude, and below 420 K nucleation c annot be observed. The deviation is discussed in the context of loss o f bulk metallic properties with decreasing critical nuclei size. Other possible reasons for a deviation towards larger supersaturations are also considered.