The leveling device (not shown in the schematic) consists of polyethylene tubing extended from the bottom of the column to a Y-tube above the paper pulp in the column. This prevents the column from running dry during the collection period. 3 3.1 PREPARATION AND ANALYSIS OF COLLECTOR Preparation The ion-exchange column is packed with a triple filter consisting of paper pulp, anion exchange resin, and cation exchange resin. The paper pulp is Whatman No. 41 filter paper blended in a Waring blender with distilled water. The anion exchange resin, IRA 400 Amberlite resin, is used throughout this paper. This resin is prepared by an aqueous and nonaqueous extraction of the commercial product followed by conversion to the chloride form and thorough washing with distilled water. Dowex 50 x 16 is used as the cation exchange resin. This resin is treated by an aqueous and nonaqueous extraction, converted to the hydrogen form, and washed with distilled water. A glass wool plug is added to the bottom of each column and cation exchange resin, anion exchange resin, and paper pulp are added in this order. Approximately 3 in. or 50 ml of wet settled resin and 1 in. of paper pulp are packed into an ion-exchange columnfilled with distilled water. Care is taken to prevent the formation of air pockets. 3.2 Care of Collector During dry periods the funnel is rinsed and policed every three days. At the end of the exposure period, any residue on the funnel is washed into the column with water. 3.3 Analysis cm The total activity may be determined by ashing the paper pulp and resin, individual isotopes may be eluted, or the three absorbents may be separated for gamma spectral analysis and later chemical analysis. The data for total beta activity in this report was obtained by ashing the absorbents and counting the residue. The Sr®, Sr®®, and Ba? data were obtained by chemical separation! of these isotopes from the ash. 4 FALLOUT IN NEW YORK CITY (JUNE TO DECEMBER 1957) Table 1 summarizes the Sr®, Sr®®, and Ba™° activities found in fallout in New York City from June to December 1957 by the ion-exchange fallout collection system. The total beta activity level, counted approximately 14 days after the end of each sampling month, decreased from a high of 163 mc/sq miin July to a low of 46.4 mc/sq mi in November. A rise in activity to 81 mc/sq mi occurred in December, probably due to the announced Russiantests in November. 5 EFFICIENCY OF COLLECTION UNIT The efficiency of the ion exchange fallout collection unit was measured by the following methods: 1. Per cent of activity in effluent: The effluent from the collector during the monthly exposure was retained in a covered polyethylene pail. This solution was evaporated and the residue analyzed for total beta activity. In all cases the activity found was less than 5 per cent of the total activity of each unit. No marked discrimination of isotopes was found in the ef- fluent. 2. Collector comparison: During the six month period, duplicate units of the following description were exposed side by side: (1) funnel and column containing the three filtering media, (2) funnel and column containing no filtering medium, and (3) open-potcollectors. Figure 2 gives the total beta activity for each collection device plotted against the counting date. Each point represents the collection from a month. From these data it is evident that the funnel and resin column method of collecting fallout is equivalent to the pot method. Table 2 357