react when dissolved in saturated, hot water vapor. The area of the reaction disk produced, easily measured with a microscope, is proportional to the amount of NaCl present (Reference 33). The values of NaCl mass listed in Table 3.12 were obtained by this method; the values of H,O mass were obtained by constructing a calibration curve relating the volume of water in the particle at the time of impact to the area of its initial impression, usually well defined by the insoluble solids trace (Figure 3.28). Because the water content of slurry fallout varies with atmospheric conditions at the time of deposition, mass is expressed in terms of the amount of NaCl present; the weight of water may be estimated by multiplying the NaCi mass by 1.2, the average observed factor. Conventional X-ray diffraction methods were used for qualitative analysis of the insoluble Solids, stripped from the reagent film by means of an acrylic spray coating, and they were found to consist of calcium iron oxide (2 CaO-Fe,0,), oxides of calcium and iron, and various other compounds (Table 3.13). Some of these were also observed by electron diffraction. Thirteen of the most-active slurry particles Radiochemical Characteristics. removed from the SIC trays in the YAG 40 laboratory during Shot Flathead were combined (Reference 26), and analyzed radiochemically in much the same way as the solid particles described earlier in Section 3.3.1. The sample was assayed in the gamma well counter (WC) and the 4-7 gamma ionization chamber (GIC), then analyzed for Mo®’, Ba'#°-La‘°, sr®®, and Np?"*; total fissions, activity ratios, R-values and the product/fission ratio were computed as before. The results are presented in Table 3.14. It may be seen that the product/fission ratio and R°(89) value are comparable with the values obtained for gross fallout samples (Tables 3.17, 3.18, and 3.21), and that the overall radionuclide composition resembles that of the unaltered solid particles. Slight depletion of both Ba‘°-La'° and Sr®® is indicated. Since the mass of slurry-particle fallout was expressed in Activity Relationships. terms of-NaCl mass, it was decided to attempt to express activity relationships in the same terms. This was accomplished in two steps. First, the H+12-hours well-counter activities measured on the IC trays from the majority of the stations listed in Table 3.12 were summed to arrive at the total amounts of activity deposited per unit area (counts per minute per square foot). These values were then divided by the average specific activity calculated for each sta- tion (counts per minute per microgram NaC)) to obtain the total amount of NaCl mass deposited per unit area (micrograms NaCl per square foot). Results for Shot Flathead are plotted in Figure 3.30, and numerical values for both shots are tabulated in Table B.11; the Navajo results were not plotted because of insufficient data. (Figure 3.30 and Table B.11 have been corrected for recently discovered errors in the tray activity summations reported in Reference 31.) While this curve may be used to estimate the amount of activity associated with a given amount of slurry-fallout mass in outlying areas, it must be remembered that the curve is based on average specific activity. It should also be noted that the unusually high values of NaCl mass obtained for the YFNB 29 during Shot Flathead have not been plotted. A correspondingly high value for the YFNB 13 during Shot Navajo appears in the table. ferences in composition which are not yet well understood. These were felt to reflect dif- A preliminary effort was also made to determine the way in which the activity of slurry particles was divided between the soluble and insoluble phases. As illustrated in Figure 3.31, radioautographs of chloride reaction areas on reagent films from all of the Flathead collections and a few of the Navajo shipboard collections indicated that the majority of the activity was associated with the insoluble solids. This result was apparently confirmed when it was found that 84 percent of the total activity was removable by physical stripping of the insoluble solids; how- ever, more careful later studies (private communication from N.H. Farlow, NRDL) designed to establish the amountof activity in solids that could not be stripped from the film, and the amount of dissolved activity in gelatin removed with the strip coating, decreased this value to 65 percent. It must be noted that the stripping process was applied to a Flathead sample from the YAG 40 only, and that solubility experiments on OCC collections from other locations at Shot Navajo (Reference 32) indicated the partition of soluble-insoluble activity may vary with collector location or time of arrival. The latter experiments, performed in duplicate, yielded 34