NAVAL RESEARCH LABORATORY
q
Table 8 gives the results of additional pack-filter measurements made during Operation
TEAPOT. In this case, each sample was measured on the day after collection. Here the
averagerelative activity on the top papers appeared tobe appreciably greater than was found
from measurements made after the samples had decayed, as shown in Table 7. However,
r
the change in relative activity with decay varied widely in individual samples. After five
weeks, the activity of the top paper of the collection of 3/28 to 4/4 increased from 72% to
:
85% to 66% in 3 weeks. Similar variations in the decay rates of the different fractions had
76% of the total, while thatof the top paper of the 4/11 to 4/18 collection decreased from
been found previously during Operation GREENHOUSE.
TABLE 8
Pack-Filter Collections Made During Operation TEAPOT
Date of
Percent of Total Activity
Collection
Top Filter Middle Filter Bottom Filter
3/28
4/4
4/11
4/18
- 4/4/55
-4/11
- 4/18
- 4/25
5/2
5/9
-5/9
-5/16
4/25 - 5/2
Average
.
,
72
60
85
58
11
12
7
14
70
- 70
11
12
19
18
12
20
57
16
68
'
-
17
28
8
28
27
It seems reasonable to expect that a greater proportion of the activity of old fission
products in the air will be in the smaller size ranges, but, from the present data, the
evidence for this effect is not conclusive. It appears that the actual number of particles
in the small size range is comparatively large for both old and new fission debris, since
considerably fewer large particles are required for a given activity. The variability in
decay rates may result from a nonhomogeneity which is common to both large and small
particles.
.
5
CONCLUSIONS
.
‘
'
There appears to be little basis for the correlation of individual daily measurements
of the air concentration of atomic bomb debris andfallout of this material on the ground.
Over extended periods, however, it may be possible to determine experimentally a rate
of fallout which, when applied to the figures for the air concentration, will give a reasonable approximation to the deposition. At Washington, D. C., the fallout in a single 3-day
period from Operation TEAPOT produced approximately 65% of the total deposit over a
_ two-month period. Similar large variations can be anticipated until the clouds of fission
activity become well dispersed, .either through time or distance.
In almost every case, greatly increased fallout accompanied rain. However, these
instances did not always lead to a corresponding increase in the air concentration. This
probably is due to high-level entrainment of activity in the rain droplets. The above
phenomenaindicate the need for additional experimental studies on the efficiency of rainfall for washing out the fission products.
.
.