APPENDIX A EXPERIMENTAL PROCEDURE A.1 ANALYSIS OF THE TOTAL-COLLECTOR SAMPLES Since the total collectors were open to the atmosphere before and after the fall-out period, the samples recovered from them were mixed with rain water. Consequently some of the fission product leached from the particulate to the rain water. When each sample was recovered, 1 pt of distilled water was poured through thetotal collectors. This flushing washed most of the particulate from the funnel and tubing into the collecting bottle. The samples were treated as follows: 1. Samples werefiltered with Whatman No. 30 filter paper. 2. The filter paper containing the solid particulate matter was ignited, and the residue was weighed to the nearest 0.1 mg on a Sartorus analytical balance. 3. The weighed portion of the solid sample was mounted on an aluminum holder. This sample was chosen small enough to decrease the effects of self-absorption. The sample was counted with a proportional counter, where the first, second, or fourth shelf was used, depending on the activity of the sample. All values were corrected for the efficiency of the counter; no absorbers were used. Since no corrections for back-scattering, self-absorption, or absorption were made, only relative counts were obtained. 4. The total and specific activities of the solid samples were determined. 5. An aliquot of the filtrate was mounted on an aluminum holder, dried under a heat lamp, and counted as described in 3. 6. The total volume of the filtrate was measured for each sample. 7. The total and specific activities of the liquid were obtained. A.2. ANALYSIS OF THE GUM-PAPER SAMPLES In some cases, upon recovery of the samples, field readings of the gamma doserate were taken. At the laboratory the 12- by 12-in. sheets of gum paper were counted, relative to each other, to determine the time of arrival of the secondary fall-out. This counting was done by folding each sheet into a 4- by 9~in. rectangle which was then mounted on an aluminum plate and counted with a proportional counter which had a 4- by 9-in. window. No compensation was attempted for the counting error introduced by absorption because only the times at which the activity began and ended were desired. A.3 ANALYSIS OF THE DIFFERENTIAL FALL-OUT SAMPLES These samples were collected in lucite compartments and delivered to the laboratory in an undisturbed state. Each collector had 72 compartments, every other one of which contained a 57