472
MAHLMAN
as time progressed (see Table 2). This was done for each month so
that the rate of decay of a given fallout sample could be obtained by
computing the mean half-life from the available data (see Fig, 3). The
measured fallout intensities were then adjusted to an age of 100 days
by taking simple ratios from Fig. 3, thus yielding the age-adjusted
fallout intensities of Fig, 2.
Table 2— PERCENT CONTRIBUTION OF PARTICULAR NUCLIDES
IN TOTAL MONTHLY RADIOACTIVE DEBRIS MEASURED
IN RAINFALL AT WESTWOOD, N. J.
Contribution in 1963, %
Nuclide
Half-life, *
days
Jan.
Feb.
Mar.
Apr.
May
June
80Sy
88Sr
144C@
s7r
137Cs
141Ce
10,120
50.5
285
65.0
11,140
33.1
00.9
26.2
21.5
44,8
01.4
05.2
01.2
23.8
34.2
34.2
01.6
05.0
01.6
18.0
36.8
30.8
02.3
10.5
02.0
15.2
49.7
25.8
02.8
04.5
02.2
11.4
44,8
28.2
03.2
10.2
02.8
10.1
51.6
26.2
04.1
05.2
*Half-life of each nuclide is given in days.’®
A comparison of the index time series with that of the mean ageadjusted monthly fallout was then attempted. This analysis revealed
that no significant relation appeared to exist between these two quantities. Although there were general index breakdowns preceding the
January and April fallout peaks shown in Fig. 2, equally large breakdowns at other times did not produce similar trends in mean fallout
distribution. It thus appears that a simple causal relation cannot be
established between the seasonal changes of the index and the spring
fallout maximum.
On the other hand, a similar comparison between the cyclone index
and the mean five-day age-adjusted fallout was constructed (Fig. 1).
In this case a very interesting relation between the two time series
was noted. The diagram reveals that the shorter period fluctuations
superimposed upon the mean monthly fallout curve appear to be related
to rapid decreases of the cyclone index. It also was noted that the fallout peaks occurred approximately five days after the center date of
the period over which the drop in C took place,
Because a fallout peak did not occur shortly after all the observed
drops in the cyclone index, an attempt was made to determine whether
or not it was possible to differentiate between the fallout-producing
and the non-fallout-producing index decreases, By trial it was empirically determined for the limited sample of data that the parameter
[100(C, — C,)]/At provided a reliable method for separating the fallout-
producing index drops from the nonproductive ones (C, and C, are the