for plutonium. This result is not consistent with results obtained from a one-point detonation where gamma dose rates gave a fair indication of the plutonium present (Reference 3).
Plutonium concentration contours cannot be inferred on the basis of this small amountof
data.
3.9 FALL-RATE MEASUREMENTS
Filters from air samplers located on barges in the lagoon were counted in the same
geometry used for sticky-pan counting. Results are listed in Table 3.4 together with the
mean fall rates that were inferred, where possible, from Equation 1.5. Since the airsampling rate was 50 cfm and the area of a sticky pan was 0.55 ft?, the forms of Equation
1.5 used for the calculations were
Cs
f = 90 — ft/min
Cr
and
r
fF = 1,125 —— ft/min
Cr
Cg = average counting rate at H+3 hours for sticky pans that were
exposed at the air sampler station
Tr
dose rate in mr/hr at H+1 hour from monitor readings
counting rate for the air samplefilter
Cr
"
Where:
Two air samplers were located on the large YCV barge at Station S-6, and results are listed
for both.
For each air sampler, the average of the counting rates for all sticky pans located on
each barge was used for Cg for one calculation, and the dose rate as measured by monitors
was used for the other. For two stations (W-4 and W-8), the filter counting rates were be-
low the mean background counting rate, and for another the “signal” was only about 8 per-
cent of background. For these stations, no calculations were attempted.
The difference shown from two air samplers located at Station S-6 indicates that a much
larger air volume should be :iltered to gain a representative sample. Also, for such low
contamination levels as experienced over the lagoon part of the array, it is doubtful if 8- by
1-inch sticky pans have a reasonable probability of collecting a representative sample.
Probable error in dose rate, determined by a single sticky-pan reading, is certainly higher
when monitor dose-rate readings and sticky-pan readings from the barges are compared.
By use of the average value of f for each of the two closest barge stations and on the
assumption that the collected particles originated from the vertical axis of the visible cloud,
a range of contributing altitudes in the cloud was defined as listed in Table 3.4. This altitude range was determined graphically from Figure 3.4 by constructing lines with slopes
equal to the average values of f through points corresponding to time of arrival at the barge
stations.
The intersection of these lines with Curves h, and h; defined the range of con~
tributing altitudes. A windspeed of 15 knots was used for this determination. A range of
times for the start of free fall by collected particles is also indicated by this procedure.
It was hoped that it would be possible to use these measurements to help indicate the
proper approach to the problem of constructing a dynamic model for close-in fallout computation.
Specifically, it was desired to test the assumption that particles are released
43