13 B, Test of Rain Collection Method If the collection of precipitation is to be used as a method of follow- ing the deposition of fallout Sr90, it would be highly desirable to increase the collection period to about one month. During a long period of collection, the collector would be alternately dry and wet. Under these circumstances, it may be considered that a significant amount of fallout would be blown out of the collector during dry periods between rains or accumlated in excess when the collector contained water, As a test of these possibilities, a number of collections made at Chicago during March, April and May 1955 included, in addition to the standard open tub, a second tub covered with a plastic sheet with a small center hole and a third tub with the water level maintained at an inch or more by periodically adding water. Results for the "covered" tub and "wet" tub collections have been reported in Chicago Bulletin No. 11 and in this report. In the case of the "wet" tub, the volume reported is that obtained from the collector area and depth of precipitation reported by the Weather Bureau for the University of Chicago station. The total Sr70 activity collected by each of these methods can be direct- ly compared since the collection areas are equal, The data are as follows: 1. Period 1000, March 16, 1955 to 0915, March 21, 1955 _ CL S9-P “— _CL 460—P 2. Open tub Covered tub 29.0 + 2.0 dpm total 31.8+ 2.2 " " Period 1530, March 21, 1955 to 1000, April h, 1955 CL 62 & 66 Open tub Wet" tub CL 77 4S.1 + 4.0 dpm total & 35.24 2.2 " 3. Period 0950, April , 1955 to 1400, April 1h, 1955 CL 551-P CL 552-P Open tub Covered tub 29,0 + 1.9 dpm total 3.3 F 24 9 8