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
'