craters themselves have filled with water following the surface bursts
in the Pacific, and thus hold that a true land burst would give higher
crater intensities; others contend that the deposition mechanisms change
with yield, so that the increased scouring effect and higher cloud
rise of large yield weapons would tend to keep the crater and lip dose
rates at H+l hour more or less constant with yield.
A firm resolution
of this uncertainty is not likely until a test detonation of a medium
or large yield weapon is held on a truly representative dry land surface.
The time of arrival of fall-out particles of various sizes from
atomic clouds can be estimated using Figure 3, which gives cloud
heights, in conjunction with Figure 5, which gives the times for par-
ticles of various representative surface burst weapons with yields between 1 KT and 500 KT.
The 1000 micron size is probably representative
of early fall-out arrival, mainly in the area near the burst point;
while the 75 micron size is representative of the fall-out likely to
occur in the downwind extremes of the elliptical patterns.
TABLE 3
Total
Cloud Bot-
Yield tom (ft)
1k
5 kT
10 KT
100 KT
500 KT
4,000
15,000
20,500
39,000
51,000
Cloud
Bottom of Cloud
Top_of Cloud
_Top(ft) 1000» 175» 75 1000 n 175
9,000
24,000
31,000
54,000
70,000
15min 30min
15 "75
20 "90
45 "150
55
"160
90 min
"180 "
"300 "
"480 "
"650
"
15 min
30
ho
50
60
"
“
"
”
75 4p
60 min 150 min
90
120
180
210
"
"
"
*
300
hao
700
&50
"
"
”
"
In evaluating the data presented and the material discussed on the
problem of the areas involved in close-in fall-out, it must be remembered that most of the information has been gathered from controlled
field test operations.
Winds at all altitudes were known to the best
of the ability of the meteorologists and shot days were selected so
that the best conditions existed to minimize the hazard from close-in
fall-out.
Uncertainties in the information presented are due primarily
to the question as to whether the burst conditions wnder which the test
hig