hele2 Observat Result. Results of the investigations of the properties of aerosols are summarized in a series of general observations on Shots 1, 2, 4, and 5, by a consideration of the physical state of the activity on the air filters and in measurement of the specific gravity of the settled active aerosols. hele2eld Gene Observation t Millipore filters were examined with the optical microscope by reflected and transmitted light. The general deposit consisted of large friable aggregations white in color, and frequently exhibiting black specks of adherent material. Autoradiographs of thin sections of the larger fallout particles (Section 4.3) show very little correlation be- tween particle size and activity. Two general types of active particles were found; (1) surface-active, with some diffusicn toward interior if the particle was exposed to water, and (2) approximately spherical, with the activity distributed throughout the particle volume, In an effort to determine the physical nature of the radioactive components of these particles, DMT filter samples were leached in water and weak acetic acid, and filtered witb the hydrosol type millipore filter, It was found that after the water leach, 76 per cent of the activity was retained on the filter, whereas after a weak acetic acid leach only 4 per cent was retained. The active particles from the water leach, as disclosed by autoradiograph, were red-brown, red-gray, gray, and black, with some smooth and white (type 2, above). The white particles frequently pre- sented black surface-occluded particles. The active solids surviving the ecetic acid leach were red- orange to black in color, irregular in shape, and generally lumpy in appearance, Small black specks were generally distributed about the surfaces, Other faint autographs were found for which no source could be located under 600X magnification. Figure 4.1 comprises photomicrographs of the original, water leach, and acid leach active particles, while Fig. 4.2 gives their size distributions. All MP filters recovered from Shot 1 were damaged to some ox- tent by blast and large coral fragments tearing through the paper; consequently, the total airflow through the filters is unknown, 4.1.2.2 General Observations, Shot 2 The aerosol from this shot was fundamentally different from Shot 1, the explosicn having taken place over water. Much of the information obtained was derived from VP filter sarples from Project g 4 with additional information sometimes available from ESP film samples/ and DAT filters. The millipore filters exposed topside on the washdown ship YAG 39 were intensely radioactive, The mijor portion of the radioactivity 83