giasa microscope slide covered with a very thin film of silicone grease. The following work was done on these samples: 1. The total activity of each compartment not containing a microscope slide was measured by mounting the fall-out particles in a steel planchet and counting with a proportional counter. Only relative values were obtained by this method. 2. The particulate on the glass slides was analyzed for particle-size determination. Radioautographs were made by using an Eastman NTE nuclear-emulsion overlay. The emulsion was developed in place, and the radioactive particles were located by viewing through the darkened areas on the emulsion. Measurements were made to determine only the presence or absence of particles within certain size ranges. This work was done with an optical microscope having a magnification of 23.25. Similar work was conducted on the secondaryfall-out particles. A.4 CHEMICAL ANALYSIS OF FALL-OUT SAMPLES Certain selected samples of the fall-out particles were subjected to emission spectrographic and X-ray-diffraction analyses to determine their chemical characteristics. Extensive petrographic analysis of the particulate was made, and its results will be publishedlater. A.5 ANALYSIS OF THE LEACHED ACTIVITY The activity that leached into the rain water in the total collectors was analyzed for the relative percentage of ionic or colloidal species. This analysis was accomplished by ultra- filtration at 38 atm through a cellophane dialyzing membrane and by counting the separations. A.6 RADIOCHEMICAL ANALYSIS OF SELECTED SAMPLES Samples with a high order of radioactivity were subjected to a limited radiochemical analysis. This work is currently done by the usual radiochemical techniques. A.7 ION-EXCHANGE-COLLECTOR ANALYSIS A mixed-bed resin (Amberlite MB-1) and a cation exchanger (Dowex-50) were the two types of ion-exchange resins used as collecting agents. Discussion of the ion-exchange-col- lector analysis will be published later. 38