—— 4 r pertinent question reusinaunsettled is the variation in fallout apart. And .38 d/min/gn from place to place in a given locality. A satisfactory progrim of replication has not been possible up to the present time. Howtver, at iogan, Utah, we did collect replicates from two pastures abouticne mile The total radiostrontium assay of these soils was .22 Retention by Gummed Films of Particulates in Similated Rain An experiment was designed to measure the rention by gam d films of radioactive particulates suspended in raindrops. When we first began to use gummed sampling media in our fallout studies, field that the activity collected by gummed paper was comparable ducible than the reaulta obtained using traye designed for of the rain water. However, reliable controlled data have previously, The following procedure was adopteds tasks danondgrated to,land gore reprotothl coirection motibeen available Normal radioactive debris was simulated by finely divided pilelirradiated iron having a massa median diameter of 3m. To suspend the irom powder, a few milligrams were added to two liters of distilled water aid agitated. Particle size control over the suspended particulates was obtained by elutriation of the original suspension. At a given time, 700 sillizeters at the top of the cylinder was decanted into a sprinkling arrsdgenent (Figure 5) which provides for contimed agitation of the suspegsion until the sample enters a capillary tube from which droplets are pergitted to fall to the gummed file. Under the conditions reported here, of "rainfall" was 1" per hour. fhe rate The retention of the gumed fijn was expressed as the percentage of suspended activity recovered byithe film, A cumulative frequency curve of particle size versus time was dalculated, using Stokes Law (with Cunningham's correction as necessary). curve, and the data on retention at various times, Figure 6 wag [From this developed. The retention of the gummed films in these tests was not as high as was Similar tests at lower rainfall rates are being planned but have not as expected, This may be because of the heavy rate of simulated yet gotten under way. gainfall. Experiments to determine the effect of 2 hours of temperature konditions of the gummed papers are given in Table 3. Conditioning at 5° and at 85°C do not appear to significantly influence the retentivity af the filus. In order to determine if the iron was going into solution, sacples ef Suspensions of various ages were passed through @ Millipore filker. Essentially 100% of the activity was recovered on the filters, indicating that solubility is not a factor in the above procedures. 00131986 018 —_— LOS 704)