214 PERKINS, THOMAS, AND NIELSEN However, the annual precipitation in this area is only about 8 in., and it seems unlikely that local precipitation has a marked effect on air concentrations. Precipitation is not the major mode of fallout deposi- tion during the summer months at our geographical location. Figure 12 shows the fractions of the various airborne radionuclides that were | > oO | | Ww Oo th oO ° | DEPOSITION BY RAIN, % 50 22nic Mn Hr, 88 957 SKIL 106n V24ch, We, Me. RADIONUCLIDE Fig, 12—Percent of radionuclide deposition due to rain from June 11 to Sept. 15, 1964. carried down by rain during the summer of 1964, The total fallout, including both dry deposition and rain, was collected in plastic-lined trays containing about Vy, in. of water and with a surface area of about 80 sq ft. In addition, rain was collected separately in a 90 sq ft dry tray that was lined with a new coat of plastic daily to prevent accumulation of dry fallout in the tray before it rained, The fractions of various radionuclides that were carried down by rain ranged from 16% for '“Sb to 43%for ‘Ru. The reason for this selectivity is not clear, but such selectivity does suggest that the various airborne radio- nuclides are attached to aerosols of different characteristics. The water solubility of the fallout radionuclides is of interestin. the estimation of their availability for uptake in the biosphere, The relative solubility of these radionuclides was determined by filtering both the water in which the dry fallout was collected and rainwater samples through a membranefilter of 0.3 » pore size. The fractions of the various radionuclides that were found to be in solution by this method are shown in Fig. 13. A considerable variation exists in the solubility of the different radionuclides. The solubilities shown for the rain-carried radionuclides are probably more representative of the actual properties of the fallout since the rainwater was collected in a Aon