Table 1f (Continued) Rain, in. Site No. Sampling site March 1956 April 1956 May 1956 June 1956 July 1956 WB WB WB WB WB AF AF AF 51 54 56 Albuquerque, N. Mex. Las Vegas, Nev. Winnemucca, Nev, 0,78 1.76 57 58 59 Spokane, Wash. Boise, Idaho Fresno, Calif. 1.62 1.38 1.51 1,26 0.81 0.69 60 Roanoke, Va. 3.12 1.72 1.58 1,07 61 62 63 64 66 67 Seottsbluff, Nebr. Yakima, Wash. Tatoosh Island, Wash. Grand Rapids, Mich. Stephenville, Newf. Laredo, Texas 1.54 0.95 2.75 0.48 1.07 0.76 0.78 0.89 4.34 3.80 3.62 1.53 9.88 8.39 4.39 1.57 1.62 2,29 0,92 1.16 AF 1.18 0.80 1.26 0.77 1.72 1.46 1,81 6.35 3,96 3.21 1.03 4.58 1.18 2.29 AF 1,49 1.64 1.05 1.03 2.08 1.26 2.08 1.51 Averaged data and ranges for each month are shown in Table2. Table 2—-SUMMARY OF FALLOUT DATA FOR RAIN WATER COLLECTIONS FROM MARCH THROUGH JULY, 1956 Sampling 3 Total 8 activity, ; mc/sq mile/month month Average March 22 April May June July 39 19 20 44 Range Sr? : me/sq mile/month Average Range 5.9—54 1.2 0.25-—2.9 22 7.3—66 3,1—140 4.3-—110 6.1-—78 6.3—170 1.1 1.6 1,0 1.5 0,34—2,9 0.21+-3.4 0.22—3.6 0.24—-3.6 9.7 9,3 7.0 29 0.0—23 0.0—33 0.0—22 0.0—67 Average Range DISCUSSION The data present several possible modes of analysis. Fallout debris in rain water can be dated; its activity can be correlated with the amount of rainfall; and the relationship between total fallout and rain water activity can be established. It is impossible to predict that there will be correlation between activity and amount of rainfall over the entire sampling network because the amount of activity in the atmosphere is not necessarily constant but varies with local conditions. However, it is possible that better correlation might be found by investigating a fraction of the sampling network over which conditions are more likely to be uniform. The age of fallout can be estimated in two ways: one from the sr*/Sr® ratio, which varies as a function of time after burst; and the other from percent contribution of Sr®® to total B activity. The theoretical Sr®®/Sr® ratios used to calculate burst dates were obtained from the Hunter and Ballou yield data for these isotopes and their most recently reported half-life values.® The expected percent Sr*® in total 8 activity as a function of time was obtained in the same way. The approximate burst times have been calculated for all the data, and the av- erage burst months for each month’s samples, as obtained by both methods, are listed in Table 3. From Table 3 it can be seen that the Sr®’ contribution to total 8 activity is high, indicating old debris. At the same time, the Sr®/sr* ratio is large enough for a much later burst date 346 RE Sr? 89 /Sr /,.90 '