For the special case of a wind-height structure with no shear in direction or speed,
d = ue?)
(3.2)
Since Fig wind conditions were nearly this, it was assumed that Equation 3.2 was applicable for Fig data.
The value of d was determined for Fig by the length of the instrumentation array (10,500
feet). It was assumedthat all fallout particles originated from the central point of the
rising puff ((h, + hg}/2, as shown in Figure 3.2). For various values of f, release heights
and times were computed graphically (Figure 3.15). The height of the puff midpoint was
plotted as a function of time. The point corresponding to time of arrival at 10,500 feet
was located at 6.9 minutes on the abscissa, and lines with slopes corresponding to various
chosen fall rates were constructed through that point.
Intersections of fall-rate lines with
the puff midpoint line gave the release height and time for each fall rate taken.
With the usual assumption of similar vertical distribution for activity, the corresponding
release heights for Jangle Surface were determined by applying a factor of 2, which was
the ratio of cloud heights for the two shots. With these values of h and t, a downwind distance d, for Jangle Surface corresponding to 10,500 feet, was obtained from Equation 3.1
for each fall rate originally chosen. For a given fall rate, the ratio of this distance to
10,500 feet is a distance scaling factor. Distance scaling factors were computed for a
range of fall rates with the results shown in Figure 3.16. Jangle Surface winds used were
taken from Reference 6 and are listed in Table 3.5. It was assumed that both clouds required the same time to reach a given relative height.
Distance scaling factors range from 1.7 for 40-knotfall rate to 0.8 for 2-knot fall
rate.
However, considering the rate of rise of the (h, + h3)/2 point, it is unlikely that fall
rates smaller than 5 knots made much of a contribution within the Fig instrumentation
array. Thus, a scaling factor of 1.5 to 1.6 is probably a reasonable one to apply for comparison of the percentage of activity deposited. It can be seen from Equation 3.2 that, for
comparison of two events having a cloud-height ratio of 2 to 1 under the same no-shear
wind conditions, the distance scaling factor will approach 2 as fall rate increases and 1
as fall rate decreases. The relatively low wind speeds at low levels and high wind speeds
at high levels for Jangle Surface have practically reversed this behavior.
Thus, if assumptions regarding similarity of activity distribution are valid, it would be
expected that 4 percent of the fission product activity produced by Jangle Surface would be
found within 17,000 to 16,000 feet of ground zero. However, when the Jangle Surface pattern is integrated out to this downwind distance, it is found that 6 percent of the activity is
accounted for. This smal! variance is believed to be indicative of a real difference in relative activity distribution for the two shots, in spite of the fact that measurements were
somewhat iaadequate over the lagoon part of the instrumentation array during Shot Fig.
The primary reason for this conviction is that about 3 percent of Fig activity was accounted for within the 100-r/hr contour, largely over well-instrumented land. For fallout
over the lagoon to account for 3 percent rather than 1 percent, a large consistent error in
many individual measurements would be required.
However, such a difference is not surprising, considering the
difference in
yield for the two shots. Also, the difference is such as to make low-yield fallout less of a
military problem.
The interesting side of this result is whether the same sort of behavior extends farther
up the yield scale. Yields 10® times greater than Fig are to be considered.
Assumptions regarding similarity of vertical space distributions for activity and fall-~
rate distribution of activity might also be questioned on inductive grounds. These two
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