670
THATCHER, PAYNE, AND CAMERON
Such a comparison has been undertaken by using the IAEA tritium
data and the Health and Safety Laboratory (HASL) *’Sr data. It is gener-
ally observed that tritium fallout and Sr fallout give the same general
pattern with time at any given site. Thisis shown for Viennain Fig. 11,
where millicuries of fallout per square kilometer are plotted. The
similarities for tritium and *°Sr are obvious. However, important dif-
ferences exist,
and the
examination of these should give significant
information.
It is found that the ratio of tritium to Sr has varied over the
years. This reflects the variation in proportions of tropospheric and
stratospheric fallout in the air masses. Immediately following a
weapons-test series that involves both kiloton and megaton bursts, the
*°Sr componentis relatively higher because of the contribution of the
kiloton bursts whose products remain in the troposphere. These fall out
quickly, and after a few months the stratospheric fallout predominates.
This contains a higher proportion of tritium from the fusion weapons.
Data for Vienna (IA), which are given in Table 6, clearly show these
effects.
Table 6—— VIENNA FALLOUT, MC/KM?
December 1961 through
February 1963
Month
90S
December
0.07
April
0.69
March
May
June
July
August
September
October
November
December
January
February
Total
HTO
49
March 1963 through
December 1963
Sr
HTO
0.44
186
0,80
435
1.71
0.46
1.00
0.46
199
80
205
74
2.60
2.60
0.86
1.92
1330
850
208
820
45
0.60
342
0.35
0.30
77
a4
10.27
4116
0.24
210
0.35
0.47
0.27
3.20
0.10
83
208
86
160
134
6.16
1424
Ratio HTO /*sr = 232
Ratio HTO/Sr = 406
It is seen from the monthly data that ratios are more variable
shortly following a test series. For example, in the first half of 1963,
the minimum ratio was 50 in January, and the maximum was 1340 in
February. In the last half of 1963, the range had narrowed to 180 for
the minimum in December and to 570 forthe maximum in September.